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Pierre J. Ausloos, Director

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory Center for Chemical Physics

Gaithersburg, MD 20899

December 1986

U.S. DEPARTMENT OF COMMERCE. Malcolm Baldrige, Secretary

National Bureau of Standards, Ernest Ambler. Director

INTRODUCTION

This book is a summary of the technical activities of the NBS Center

for Chemical Physics (CCP) for the period October 1, 1985 to September

30, 1986. The Center which is one of four units in the National

Measurement Laboratory consists of four divisions with a total permanent

staff of about one hundred which is augmented by approximately seventy guest

scientists

.

The Center for Chemical Physics (CCP), (1) develops and maintains the

scientific competences and experimental facilities necessary to provide

the nation with measurement methodologies and measurement services in the areas of thermochemistry, chemical kinetics, surface science and molecular

spectroscopy; (2) measures, compiles, critically evaluates, and

disseminates reference data to the industrial, government, and academic

communities nationally and internationally; (3) develops theoretical

methods and concepts, predictive equations and models; (4) develops

standards and techniques of measurement; (5) provides federal, state and

local governments, industry and the academic community with essential

standards and certified standara reference materials needed to maintain

the integrity of the measurement system; (6) provides consultative

services and participates in collaboration efforts with other NBS Centers

and the outside community.

The summary of activities is organized by division: Surface

Science, Chemical Kinetics, Chemical Thermodynamics and Molecular

Spectroscopy. The report of each division is divided into: (1) an introductory discussion of the objectives and programs of the division;

(2) a review of all projects which includes accomplishments and future

plans; (3) lists of outputs and actions which indicate in a quantitative

way the activity and accomplishments of the division.

A detailed table of contents has been provided. It will permit the

reader to find those activities of greatest interest. More information

about particular work may be desired. To obtain this, the reader should

address the individual scientists or their division, c/o Center for

Chemical Physics, Chemistry Building, B-162, National Bureau of Standards,

Gaithersburg , MD 20699.

NOTE: Certain commercial equipment, instruments, or materials are identified in this report in order to adequately specify the experimental

procedure. Such identification does not imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that

the materials or equipment identified are necessarily the best available

for the purpose.

l
Table of Contents

SURFACE SCIENCE - - DIVISION 591

1 . INTRODUCTION ............ \

2. SURFACE STANDARDS PROGRAM 6

Ref erence Data 6

Reference Materials 20

Review Articles and Books 25

Standards-Committee Activities 33

3. SURFACE MEASUREMENT PROGRAM Hi

Reaction Kinetics Over Single Crystal Catalysts Hi

Molecular Structure and Reactivity on Surfaces H 3 Neutron Scattering Studies of Reactions on Catalysts H 7 Surface Characterization Using Synchrotron Radiation 50

Dynamic Effects Associated with Core-Level Ionization 55

Development of Silicon Diode Radiation Detectors 57

Production and Characterization of Uitrasmooth Surfaces 59

Electron Spectroscopy of Surfaces 59

Laser Diagnostics of Surface Dynamics 61

Theory of Dynamical Molecular Processes at Surfaces 6 ^

H. SURFACE COMPETENCE PROGRAM 69

Novel Two-Dimensional Materials 69

State Characterization of Species Ejected from Surfaces 76

5. PUBLICATIONS. 62

6 . TALKS 92

7. SURFACE SCIENCE DIVISION SEMINARS 10C

8 . TECHNICAL AND PROFESSIONAL COMMITTEE PARTICIPATION AND LEADERSHIP 10;

9. PROFESSIONAL INTERACTIONS, CONSULTING, AND ADVISORY SERVICES. . . 106

10. VISITING SCIENTISTS 11;

ii
CHEMICAL KINETICS - - DIVISION 542

1. INTRODUCTION 115

2. DATA CENTERS • 119

Chemical Kinetics Data Center 119

Ion Kinetics and Energetics Data Center 123

3. KINETICS OF NEUTRAL SPECIES 126

Multiphoton Ionization Detection of Reactive Intermediates ... 127

Reactivity of Small Radicals 131

Reactions of Biradicals and Unsaturated Free Radicals 133

Energy Transfer from Vibrationally Excited Molecules 135

MS/MS Tandem Mass Spectroscopy 136

Single Pulse Shock Tube Studies 140

Substituent Effects on Bond Strength 144

Chemical Tneory of Graphite 146

4. ION KINETICS 150

Gas Phase Ion Kinetics 151

Liquid Phase Ion Kinetics 156

5. PUBLICATIONS 163

6. TALKS 171

7. CHEMICAL KINETICS DIVISION SEMINARS 174

6. TECHNICAL AND PROFESSIONAL COMMITTEE PARTICIPATION AND LEADERSHIP 175

9. PROFESSIONAL INTERACTIONS, CONSULTING AND ADVISORY SERVICES ... 176

10. VISITING SCIENTISTS 180
CHEMICAL THERMODYNAMICS DIVISION 5^3

1. INTRODUCTION 1 83

2. BIOTHERMGDYNAMICS 187

Biochemical Thermodynamics 1 87

Differential Scanning Calorimetry 191

3. BIOMOLECULAR STRUCTURE 1 97

Structural Studies of Mutations of Calabolite Gene Activator . . 197

Predicted Structure of Two Domains of a Protein 198

Structural Studies of Anti-tumor Amidohydrolases 198

High Resolution Structures of Bovine Pancreatic Trypsin Inhibitor 199

High Resolution Refinement of Ribonuclease A 200

Structure of the Solvent in Crystalline BPTI 201

Crystallization of Synthetic Fragments of DNA 201

Application of Repulsive Regularities in Water Structures . . . 203

4. CHEMICAL THERMODYNAMIC MEASUREMENTS 20b

Large Sample Combustion Calorimetry 206

Calorimetric Update on SRM Coals 26o2, 2683 , 268A, and 268b. . . 210

Bomb Calorimetric Measurements for Biotechnology 211

Estimation and Calorimetry on Organic Phosphorus Compounds ... 212

Drop Calorimetry of Non-Reacting Systems Below 2600K 21*4

5. CHEMICAL THERMODYNAMIC DATA ACTIVITIES 217

Chemical Thermodynamics Data 218

Electrolyte Data 227

Thermodynamic Properties of Organic Compounds 232

Automating Data Center Procedures 233

6 . PUBLICATIONS 236

7. TALKS 2M2

8 . CHEMICAL THERMODYNAMICS DIVISION SEMINARS 2*6

9. TECHNICAL AND PROFESSIONAL COMMITTEE PARTICIPATION AND LEADERSHIP 2*8

10. PROFESSIONAL INTERACTIONS, CONSULTING AND ADVISORY SERVICES . . . 250

11. VISITING SCIENTISTS 257

iv
MOLECULAR SPECTROSCOPY - - DIVISION 545

1. INTRODUCTION 259

2. HIGH RESOLUTION SPECTROSCOPY 264

Calibration and Data Center Activities 264

Spectroscopy for Environment Studies 268

Spectroscopy of Hydrogen-bonded and van der Waals Complexes. . . 277

Matrix Isolation Spectroscopy 287

General Spectroscopy and Theory 291

3. LASER PHOTOCHEMISTRY 298

Condensed Phase Energy Transfer 298

Laser Diagnostics of Surface Dynamics 306

Dynamics of Van der Waals Molecules 311

Photophysicai Studies of Photosenitizers 315

4. QUANTUM CHEMISTRY 317

Theoretical Calculations on Biomolecules 318

Quantum Chemistry of Small Molecules 325

Scattering in the Presence of Radiation 328

Atomic and Molecular Scattering Theory 331

* 5. PUBLICATIONS 334

6. TALKS 341

7. MOLECULAR SPECTROSCOPY DIVISION SEMINARS 347

8. TECHNICAL AND PROFESSIONAL COMMITTEE PARTICIPATION AND LEADERSHIP 350

9. TECHNICAL INTERACTIONS, CONSULTING AND ADVISORY SERVICES .... 352

10. VISITING SCIENTISTS 357

v

SURFACE SCIENCE DIVISION

C.J. Powell, Chief

SUMMARY OF ACTIVITIES

Fiscal Year 1986

1 . Introduction

A. Background

Over the last ten years, there has been a dramatic growth of surface

science and its applications. This growth and its significance have been

documented in detail in two major reports, the Pimentel report to the

National Academy of Sciences on "Opportunities in Chemistry" (National

Academy Press, Washington, D.C. 1985) and the Brinkman report to the

National Academy of Sciences on "Physics Through the 1990s" (National

Academy Press, Washington, D.C., 1986).

© The Pimentel report identifies chemical catalysis as one of five

research frontiers in chemistry. A major recommendation was that modern

chemical techniques be applied to obtain a molecular-level and coherent

understanding of catalysis that encompasses heterogeneous, homogeneous,

photo-, electron-, and artificial enzyme catalysis. For heterogeneous

catalysis, in particular, surface science methods can be applied to

identify reaction mechanisms and rates important in molecular sieve

synthesis and catalysis and in catalysis by metals and oxides. These

methods also enable evaluations to be made of the direct effects of

catalytic poisons and promoters and can be used to develop new conversion

catalysts, catalytic substitutes for precious metals, and catalysts to

improve the quality of air and water. In addition, chemistry at solid

surfaces is discussed at some length as a prominent example of the

intellectual frontiers associated with the national well-being and surface

science instrumentation is similarly identified as a significant example

of instrumentation needed for modern chemical analysis and research. Other

opportunities identified in the Pimentel report include understanding

molecular dynamics for the control of chemical reactions, understanding

the properties of clusters and of reactions on their surfaces, and the

role of surface chemistry in diverse areas ranging from the synthesis of

novel materials to energy production, reduction of environmental

pollution, increased national security, and improved economic

competitiveness

.

1
The Brinkman report identifies surfaces and interfaces as a key area

of condensed-matter physics in one of the volumes of the report. Specific

topics discussed are the determination of surface-atomic structure,

spectroscopy of elementary excitations at surfaces, interactions of atoms

and molecules with surfaces, characterization of the interfaces between a solid and either a solid, liquid, or gas phase, and surface theory.

Numerous opportunities in these areas were specified including experiments

and theory to define the dynamical processes when atoms and molecules

interact with surfaces, critical phenomena at surfaces, and measurements of

the kinetics of surface processes. Extensive connections of surface

and interface science were identified with information processing, speech

and data communications, energy generation, transportation, space

technology, national security, and medical applications. The significant

role of surface and interface characterization was also identified in

sections of the volume on Scientific Interfaces and Technological

Applications dealing with the physics-chemistry interface, materials

science, and microelectronics. Finally, a number of key questions and

opportunities in the general area of atomic physics, particularly those

dealing with atomic and molecular excitations and dynamics, state-to-state

chemistry, laser spectroscopy, and clusters, were described in the volume

on atomic, molecular, and optical physics; these issues are also important

in surface science and in fully utilizing a number of the surface

spectroscopies

.

In a third recent report "Research Briefings 1986" (National Academy

Press, Washington, D.C., 1986), the science of interfaces and thin films

is one of four areas of science and technology identified as having

"high-leverage research opportunities." Topics discussed in this report

include characterization of "buried" interfaces, the production and

characterization of smooth, defect-free epitaxial films, reactivity and

catalytic activity of ultrathin films, characterization of processes

occurring at biomaterial-tissue interface, mechanical properties of

f iber-reinforced composites, and improvement of thin films for corrosion

prevention, amongst many others. These topics are vital in the

development of improved microelectronic devices, biomaterials, new structural materials, and coatings as well as technologies for new materials and processes.

A large number of techniques are utilized for surface and interface

characterization. A choice of one of more techniques is made typically

on the basis of the property to be measured, the specimen material, and

the specific needs (e.g., spatial resolution, chemical information,

sensitivity, degree of difficulty, and cost). The most common type of

surface measurement is the determination of surface composition. Most

surface analyses now are qualitative but there is a growing demand for

quantitative analyses with improved accuracy. At the present time, there are few standard procedures and limited reference data and reference

materials. A variety of techniques is employed for the determination of

surface atomic structures, surface electronic structure, and for

investigations of surface processes such as reactions, diffusion,

segregation, etc. Theories of the measurement process need to be

developed for the newer techniques. For all techniques, the^e is a ne< for relevant proceaures, tests to establish measurement reliability, ar.d

2
applicable reference data. In most cases, the measurement science needs

to be developed since knowledge of the key concepts and parameters is

often extremely limited.

The techniques utilized in surface science have generally been

applied to characterize surfaces in an ultrahigh vacuum environment. The

solution of many scientific and technical problems often requires removal

of liquid- or gas-phase material prior to surface examination and/or the

removal of solid-phase material to expose a region of interest. While

this approach has often been successful, artifacts of many different types

can arise during the removal of one or more phases. There is therefore a growing need for improved measurement methods that can be used for the in

situ characterization of solid-solid, solid-liquid and solid-gas

interfaces with the sensitivity, elemental specificity, and spatial

resolution comparable to those attained with the current

surface-characterization methods

.

3. Goal, Objectives and Division Program

The goal of the Surface Science Division is to improve the quality of

existing surface-characterization measurements and to extend the present

capability. Specific objectives of the Division are:

(1) Perform experimental and theoretical research in surface science

to provide a scientific base for surface-measurement

methodology;

(2) Develop measurement methods and provide properties data for the

physical and chemical characterization of surfaces and surface

processes to meet identified needs of industry, government, and

other groups;

(3) Develop standard procedures, calibration data, and reference

materials in cooperation with national and international

standards organizations; and

(M) Develop expertise in selected new areas of science in order that

NBS can provide measurement services where needs are anticipated

in the near future.

Objectives (1) through (3) are met organizationally through an N5S

task titled "Surface Science-Standards and Measurements" (program codes

155, 156, and 272). The Division's program for this task is divided into

two principal activities, a Surface Standards Program and a Surface

Measurements Program. Work performed during the year in these two area is

reported in Sections 2 and 3. respectively.

Objective (H) is met through the Surface Competence Program (program

code 261). This task was established in October, 198^ and represents a new focus by the Division in two areas, "Novel Two-Dimensional Materials"

and "State Characterization of Energetic Species Ejected from Surfaces".

A separate report on these activities is given in Section

3
The Division's program is supported financially by other NBS offices

and by other Federal Agencies (in addition to the base support allocated

by NBS, the National Measurement Laboratory and the Center for Chemical

Physics). These arrangements enable the Division to meet NBS objectives

and standards needs and also to contribute its expertise and facilities to

important national programs. During FY86, support was received from the

following offices and agencies:

Office of Standard Reference Data

o Surface Science: Sputtering Yield Data

o Workshop on Quantitative Surface Analysis

Office of Standard Reference Materials

o Characterization of Additional Lots of SRM2135

o Workshop on Quantitative Surface Analysis

NBS Brookhaven Project Coordinator

o Travel to Brookhaven National Synchrotron Light Source

Department of Energy

o Structure and Reactivity of Chemisorbed Species and Reaction

Intermediates

o Structure and Reactivity: Applications of Neutron Inelastic

Scattering and of Negative-Ion ESDIAD

o Laser Studies of Chemical Dynamics at the Gas-Solid Interface

(joint with Molecular Spectroscopy Division)

Air Force Office of Scientific Research

Laser Studies of Chemical Dynamics at the Gas-Solid Interface

(joint with Molecular Spectroscopy Division)

Office of

o Naval ResearchUse of Synchrotron Radiation to Characterize Oxide Surfaces

U.S. -Spain Joint Committee for Scientific and Technological Cooperation

o Structure and Reactivity in Catalysis by Metals and Oxides

C. Technical Output and Professional Interactions

Sections 5 and 6 of this report contain listings of the publications

and talks, respectively, for the past year by Surface Science Division

staff and for projects supported by the Division.

Many members of the Division staff hold leadership positions in

professional societies and groups, as listed in Section 8. These

interactions not only reflect the professional esteem in which these staff

members are held but provide useful mechanisms for both disseminating the

results of NBS work and for learning of significant measurement problems

being faced by those using surf ace-characteri zation equipment.

Interest in surface science and surface characterization at NBS

continues to grow. The Division has had an active Seminar program, as indicated in Section 7, and these seminars have been attended by other NB

4
staff. The Division staff also participates in an informal weekly lunch

meeting, attended by scientists from a number of NBS organizational units,

at which developments in surface science are discussed. Members of the

Division staff are frequently consulted on a wide range of NBS problems.

Much of the Division's work is carried out in collaboration with other

scientists within the Center for Chemical Physics, within NBS, within the

U.S.A., and internationally. The nature of these collaborations is shown

in Section 9. These collaborations are considered important because they

enable a relatively small Division staff to work synergistically with

other experts, they enable us to have access to unique facilities or expertise, and they enable our expertise to be extended to a larger range

of important scientific and technical problems.

The Division has been fortunate in having seventeen visiting

scientists work at NBS for varying periods during the past year, as indicated in Section 10. These scientists enrich our staff and our projects. A further enrichment of our programs comes from Postdoctoral

Research Associates who typically hold two-year appointments; five

Postdoctoral Research Associates worked in the Division during FY 1986.
2 . SURFACE STANDARDS PROGRAM

G. P. Chambers, W. F. Egelhoff, Jr., N. E. Erickson, J. Fine,

Y. Hashiguchi, R. D. Kelley, R. L. Kurtz, T, E. Madey,

D. Marton, C. J. Powell, R. Stockbauer, and S. Tanuma

The term ’’surface standards" is intended to cover a broad range of

activities that are directed to improving the quality of

surface-characterization measurements through: (1) development of needed

reference data and standard reference materials; (2) leadership in

standards-comraittee activities, the development of standard practices, and

other actions to improve the accuracy and reliability of surface-analysis

measurements; and (3) publication of review articles and books that enable

scientists to make surface-characterization measurements of the needed

quality

.

A. Reference Data

We describe here results of projects in which needed reference data

are being generated. Section 2.C includes recent review articles by

Division Staff that summarize and evaluate data required in a number of

surface spectroscopies.

1. Sputtering Yield Data Compilation

(J. Fine and G. P. Chambers)

Sputtering techniques for depch-prof il e analysis are presently

being used in conjunction with a number of surface analytical methods to

analyze compositional changes of materials at surfaces and at interfaces.

Many of these techniques have now progressed to the point of being able to

provide quantitative sputtei—depth-profile information yet the necessary

sputtering yield data is not readily available in easy-to-use, evaluated

form

.

We are preparing a compilation of evaluated sputtering-yield data for

those parameters that will have specific use in surface analysis and depth

profiling. This work is supported by the NBS Office of Standard Reference

Data. Our compilation will be in tabular form for those ion species (Ne,

Ar, Kr, Xe, O

2

, N

2

, Cs) and energies (0.5 to 20 keV) and angles of

incidence used in surface characterization. The compilation will contain

sputtering yields for elemental targets only.

The HP-1000 Data System in the Center for Chemical Physics is being

used for the data compilation. Dr. D. Neumann and members of his group

have provided guidance as well as technical assistance with the software

development

.

Two interactive data-base management programs were previously

developed to handle the specific needs of the data compilation. The

structure developed allows easy data entry into one of these data baser;

information can then be transferred to the second data base for rapii access and searching. Additional software has been written to sori ar..:

6
tabulate the searched data in a format suitable for publication. In this

past year extensive use was made of our on-line abstract searching

capability in order to bring our reference files up to date. Abstract

searching has been completed and checked for completeness by making

selected author searches. Sputtering yield papers have been identified

and compiled, and data has been abstracted and entered into our data base.

Work has begun on abstracting certain experimental parameters which will

be used to evaluate the reliability of the sputtering yield data.

In the coming year, we intend to make an evaluation of the sputtering

yield data available for elemental targets. These data are to be assigned a "quality rating" which will be determined from an evaluation of the

measurement method and the conditions under which the measurements were

made. This evaluation will include an assessment based on the combined

effect of ambient vacuum condition, target reactivity, and rate of

sputtering. We will compile this evaluated data in both tabular and

graphical form for those parameters of interest to the surface-analysis

and sputter-depth-prof il ing community.

2. Reference Data for the Calibration of the Energy Scales of X-Ray

Photoelectron Spectrometers and Auger-Electron Spectrometers

(N. E. Erickson, S. Tanuma, and C. J. Powell)

The energy scales of x-ray photoelectron spectroscopy (XPS) and

Auger-electron spectroscopy (AES) instruments need to be calibrated so that

measurements of core-electron binding energies (BEs) by XPS or electron

kinetic energies (KEs) by AES can be transferred meaningfully from one laboratory to another. The principal motivation of many practical BE and

KE measurements is in the determination of the so-called chemical shifts

in the energies from which chemical-state information can be obtained.

Calibration of the XPS and AES energy scales enables reliable use of the

available BE and KE data (if these have been acquired on calibrated

instruments). The accuracy required in the calibration of the BE scales

in XPS is typically 0.1 eV or better and of the KE scales in AES is

typically 1 eV or better. Round robins conducted by NBS staff members

about eight years ago indicated that the accuracies of BE and KE

measurements then could be appreciably inferior to those required for

valid chemical-state identification.

Several years ago, we made preliminary measurements of the BEs by XPS

for the principal core levels of Cu, Ag , and Au and of the Auger-electron KEs

from the same metals. It was hoped that data of this type would be

convenient and satisfactory for the calibration of individual instruments.

Unfortunately, the electronics on our instrument were not then as stable

as we desired so we have replaced critical power supplies with

high-precision programmable power supplies (PPSs) whose outputs can be

monitored with high-precision digital voltmeters (DVMs). In the meantime,

BE data for Cu, Ag, and Au have been published by the National Physical

Laboratory (NPL) and similar AES KE measurements there have recently been

concluded. While we believe the NPL measurements to be of high quality,

we consider that independent measurements at NBS are important to ensure maximum user confidence, particularly since there are still some discrepancies in some recent high-accuracy measurements.

7
We give below two reports that summarize work over the past year.

First, we have compared the outputs of several high-precision PPSs in our laboratory with several high-precision DVMs. These comparisons indicate

that artifacts can occur in these instruments. Artifacts of the type we have found may in fact make an energy-scale calibration of an XPS or AES

instrument at a limited number of points (such as with reference data for

Cu, Ag, and Au) of doubtful validity since there could be nonlinearities

at intermediate energies. If measurements of high accuracy are required,

it may be necessary for a user to characterize the performance of the PPS

or DVM in more detail. Reference data for Cu, Ag, and Au (and eventually

other materials) will then be useful benchmark values. Second, we have

analyzed algorithms for locating peak maxima in XPS. Our analysis

provides a means for a user to select the conditions for data acquisition

so that peaks can be located with a desired accuracy.

We have recently completed the calibration of one PPS and one DVM in

collaboration with Mr. T. E. Kiess of the NBS Electricity Division. There

were a number of technical problems to be overcome, particularly in

extending the calibration to voltages above 1000 volts. These instruments

have now been calibrated with an uncertainty of better than 10 mV at

voltages close to those to which we will make the BE and KE measurements

for Cu, Ag, and Au. We expect to make these measurements soon.

(a) Investigation of Errors in Programmable Power Supplies and

Digital Voltmeters

The determination of XPS BEs and AES KEs is usually based on the assumption that the analyzer energy has been incremented uniformly

through the energy region selected and that the actual analyzer energy is

a continuous and linear function of the programmed value. We checked this

assumption in the course of making our new BE and KE measurements. A programmable power supply was used to step the analyzer over the spectral

region of interest while a precision digital voltmeter sampled the

voltages to verify that no transmission errors had occurred. In the

course of checking this agreement with a number of different instruments,

a variety of both digital and analog faults were uncovered which are believed to be of a generic nature and hence are likely to be found to

greater or lesser degree in virtually all extant instruments.

Fig. 2.1 shows a plot of the voltage difference between a DVM output

and the input voltage to a PPS observed for a particular pair of

instruments for a sequence of voltages between 10 and 1000 V. Instead of

there being a strictly linear deviation between the instruments, whlc.n is

what might be expected for instruments that had not recently been

calibrated, one sees that there are eight discontinuous regions (octades

with a progressively increasing discrepancy between the programmed and

measured voltages. This particular set of data indicates, via the steps,

that there are bit errors in the resistor decoding network that d-ives the

power supply such that, as one octade is incremented, the supply does not

transfer smoothly over into the next higher octade. The number of such

discontinuous regions depends on the particular sequencing arrangem<".*

that the manufacturer has chosen to use so the number and exact voltages

8
where such discontinuities are apt to occur cannot generally be predicted.

It can be predicted, however, that transition regions will occur. In this

particular example all the major deviations are of the same sign, but the

deviations could be rather variable in both magnitude and sign.

The progressi vely increasing discrepancy with increasing voltage in

Fig. 2.1 is suggestive of a power heating effect in a resistor divider

network such that the resistor value increases with the square of the

applied voltage. This type of problem can be expected in virtually all

high voltage power supplies and can be difficult to detect since many

analyzer power supplies have a high impedance and cannot be checked with

an ordinary voltmeter because the supply will be loaded. Checking the

voltage across the feedback resistor segment of the divider network will,

of course, not reveal this particular problem.

j

cco

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[xlO 3 V]

VOLTAGE

Fig. 2.1 Plot of deviation between a digital voltmeter output and the

input voltage to a programmable power supply for a sequence of

voltages between 10 and 1000 V.

In other comparisons, we have found appreciable deviations (up to 150

mV) that have occurred over a one volt interval, as illustrated in Fig.

2.2. This fault, which was identified as occurring in a particular

voltmeter, is most likely due to a bit decoding error in the circuitry

9
providing communication between an internal counter and the applied

voltage. This type of error is expected to be repeated as the same sequence of low- or medium-order bits is repeated at other voltage levels.

[V]

VOLTAGE

Fig. 2.2 Plot of deviation between a digital voltmeter output and the

input voltage to a programmable power supply over a ^ V range of

output voltage.

These problems can be extremely difficult for the manufacturer or user to locate since more than a million different combinations of values

are possible with high-precision instruments. Fortunately, a modeling and

test-point selection method has recently been developed in the NBS

Electrosystems Division and it is hoped that analyzer manuf acturers will

avail themselves of this methodology as it becomes known. This

methodology greatly decreases the number of test points that have to be

sampled since most logic elements are used in a repetitive fashion as values are incremented. It is also hoped that more complete calibration

procedures will be developed by instrument manufacturers for their

specific equipment. The errors indicated in the two figures would reflect

themselves as shifts in peak positions and possible peak distortions

depending upon the relative position of the peak and the transition

regions

.

(b) Analysis of Peak Location Algorithms

The assertion that a particular electron peak has a certain

binding or kinetic energy implies that it is known how to determine the

location of the peak. The peak location is usually defined as the

position of the peak maximum but a procedure for determining this position

is rarely specified. The practical problem is that most real peaks are

not symmetric about their center and the location of the maximum is

sometimes a matter of subjective evaluation. There are, however, a*, least

10
two procedures that can be found in the literature although neither seems

to have been subjected to any validation checks. The first involves

fitting, via a least-squares procedure, a quadratic equation to the top 5$

of the peak. The problem with this method is that, in order to get a good

fit, one should have a sufficient number of points and good counting

statistics since the curvature close to the maximum is not very large.

Many electron analyzers, especially older ones, can only step with fairly

large energy increments, say 0.05 or even 0.1 eV. With a reasonably

narrow peak one may then have only 5 to 10 points to determine the three

parameters which describe a quadratic equation. This lack of redundancy

in the presence of a small curvature and possibly poor statistics can lead

to a fairly large uncertainty in the peak location.

The second procedure is to locate the centers of a sequence of

fractional peak heights and to extrapolate these to the top of the peak.

The accuracy of this method is limited by the precision with which the

centers of the chords can be located.

To st.udy this problem, we have generated a series of synthetic XPS

spectra using broadened Doniac-Sunjic line shapes of different widths and

with various values of the asymmetry parameter covering the range of

values normally encountered. The exact peak maximum location is known

from the generating function. We have then determined the accuracy and

precision with which least-squares quadratic and quartic fits locate

the peak maximum in the presence of various amounts of generated random

noise and for various fractions of the peak height in the fit.

It is difficult to summarize this multiparameter space succinctly.

In general, a quadratic curve will give good results only if the very top

of the curve, say the top 5$ to 10?, is analyzed. The difficulty is that

noise combined with a small number of data points can make this analysis

very unreliable. A quadratic fit over a larger fraction of the peak

height leads to a systematic position shift if the asymmetry parameter is

substantial. The best solution seems to be to use as small a step size as possible so as to maximize the number of data points, use the top 25$ to

30$ percent of the peak so that the sides are reasonably well defined even

if the data are fairly noisy, and use a fourth order polynomial fit to

account for peak asymmetries.

An additional method is also being investigated. This involves

applying a Savitzky-Golay smooth to the data and then taking the

derivative. Preliminary results indicate that this procedure is

competitive in accuracy to the quartic fit method.

3. Reference Data for X-Ray Photoelectron Spectroscopy and

Auger-Electron Spectroscopy

(C. J. Powell and N. E. Erickson)

A project was initiated in FY 82 with funding by the MBS Office

of Standard Reference Data to prepare compilations and evaluations of

core-electron binding energies and of the kinetic energies of selected

Auger electrons f or a wide range of elements and compounds. In

particular, data are being compiled of the "chemical shifts" that can

11
give useful information on the chemical state of a particular element.

Data of this type are now scattered throughout the scientific literature

but there is a need both for a convenient single source and for evaluation

of the sometimes conflicting data. The reference data are being compiled

by Dr. C. D. Wagner, a contractor to NBS, and the Surface Science Division

is providing technical review.

To date, over 800 references have been examined and more than 11,000

line positions included. The database can be searched for reference,

compound, element, spectral line, and physical state of the compound.

Work will be completed in the next few months. The reference data will be

included in a report for the Journal of Physical and Chemical Reference

Data.

Comparison of L^-Shell Binding Energies in Six 3<3 Metals

Measured by X-Ray Photoelectron Spectroscopy, AppearancePotential Spectroscopy, and Electron Energy-Loss Spectroscopy

(C. J. Powell and N. E. Erickson)

The binding energies (BEs) of core electrons in solids are of

importance in a number of electron-spectroscopic methods of surface or thin-film characterization such as x-ray photoelectron spectroscopy (XPS)

,

Auger-electron spectroscopy (AES), appearance-potential spectroscopy

(APS), and electron energy-loss spectroscopy (EELS). A frequently made

assumption is that BEs measured by one technique are identical to those

measured by another (within the common measurement uncertainties), but

there have been some indications of systematic differences. The extent to

which significant differences occur, however, has been obscured by

uncertainties in BE values associated with the particular measurement

method, with possible errors in voltage measurements, and with possible

specimen impurities.

We have measured L^-shell BEs for Ti, V, Cr, Fe, Co, and Ni by XPS,

APS, and EELS. In order to avoid the more obvious sources of error, we have used the same specimens for each of the three BE measurements and the same reference power supply (whose output is believed accurate to 0.01 V).

Our work also differs from most previous comparisons in the following

three respects. First, the electron energy scales for the XPS and EELS

measurements were calibrated by a method in which electrons from a thermionic source were accelerated to a selected energy, scattered

elastically by the specimen, and detected at an energy close to that of

the XPS or EELS feature or interest. These calibrations were performed

with an uncertainty of about ± 0.1 eV, and the XPS and EELS BEs were determined with a total estimated uncertainty of ± 0.2 eV. Second, we have found that the one-electron model previously used in the analysis of

APS data for the 3d metals is invalid for Ti and V (see section 3-H) and

is only marginally valid for Fe and Cr. An improved model has been

developed that allows us to extract more reliable BEs for these metal 3. The APS BEs have an uncertainty of about ± 0.3 eV except for Cr for which

the uncertainty is estimated to be ± 0.4 eV. Finally, we have made EELS

measurements as a function of incident electron ranging from about 50 eV

above the threshold for core-level excitation (i.e., the L^-ievei BE' to

about 1500 eV. These measurements were made to investigate the extent tc

12
which the EELS spectral data and the derived BEs changed as the excitation

varied from near-adiabatic (as for the APS measurements) to sudden (as for

the XPS measurements).

Our BE results are summarized in Fig. 2.3 where we show BE values as

a function of excess energy in the excitation. APS is a threshold-excitation method so all APS BEs are shown at zero excess

energy. For EELS, the excess energy is the incident energy minus the BE

while for XPS, the excess energy is the photoelectron kinetic energy.

EXCESS ENERGY (eV)

Fig. 2.3 Values of L^-level binding energies for Ti, V, Cr, Fe, Co, and

Ni as determined by three techniques: +, APS; o, EELS; x, XPS.

The BE values are shown as a function of excess energy in the

measurement, as defined in the text.

The BEs measured by the three methods for Ti and V are very similar

although the EELS BEs for both metals appear to be systematically lower

than the APS and XPS BEs. The EELS BE values at high excess energies

agree with the other values but the non-dipole final states excited at low

incident electron energies exhibit lower BEs. For both Co and Ni, the

EELS and APS BEs are in good agreement and are appreciably lower than the

XPS BEs. The difference between the XPS and APS BE values is 0.9 eV for

Ni and 1.1 eV for Co. For Fe, we find a 1.7 eV difference between the XPS

and APS BEs, and EELS BEs that are intermediate. For Cr, it was more

13
difficult to determine an APS BE and two values are shown in Fig. 2.3 that

represent reasonable limits in our analysis. The average difference

between the XPS and APS BEs is then 0.8 eV and the EELS BEs are intermediate between the XPS and APS values, as for Fe

.

Our results clearly show that BEs measured by different methods can have significant differences; for the L^-le^els of the 3d metals, these

differences were up to 1.7 eV. The larger differences occurred to the

right of the series where the XPS BEs of Fe, Co, and Ni exceeded the APS

BEs by 0.9~1. 7 eV. The reasons for the differences are not known in

detail but are believed to be associated with the different relaxation and

screening responses of each metal for each type of spectroscopy. For APS,

a core hole is created adiabatically together with two slow electrons,

while for XPS a core hole is created suddenly with a relatively fast

(400-800 eV) photoelectron in our experiments. In the EELS experiments, a core hole is generated together with an excited electron above the Fermi

level (which may be localized in the presence of the core hole) together

with another electron with energy here of = 50-1000 eV. It is therefore

not considered surprising that BEs determined by spectroscopies with

different excitation mechanisms are different. Only for chromium, however,

do the EELS BEs interpolate approximately between the APS and XPS BEs, the

limits for adiabatic and sudden excitations, as might naively be

expected. Finally, our work clearly indicates that BEs determined by one spectroscopic method should not be used for the energy calibration of

another type of instrument unless the extent of systematic differences is

known.

We plan to explore the origins of the BE differences by making

similar measurements with other materials (e.g., non-transition metals),

alloys, adsorbates, and for implants (e.g., of rare-gas ions) into

different solids.

5. Inelastic Mean Free Paths and Attenuation Lengths of Low-Energy

Electrons in Solids

(W. F. Egelhoff, Jr., R. L. Kurtz, C. J. Powell, and R. Stockbauer

)

Values of inelastic mean free paths (IMFPs) and attenuation

lengths (ALs) of low-energy electrons are required in quantitative surface

analysis by Auger-electron spectroscopy (AES) and x-ray photoelectron

spectroscopy (XPS) for correction of so-called matrix effects. These

parameters also define the surface sensitivity of these and other

electron-spectroscopic methods of surface characterization. The AL is

distinguished from the IMFP by the fact that AL values are usually derived

from overlayer-f ilm experiments on the basis of a model In which elastic

electron scattering has been assumed to be insignificant. The IMFP, on the other hand, is usually obtained from theory.

Accurate values of IMFPs and ALs are urgently required for a rang’ of' materials and for electron energies of practical Interest in AES and XPS.

AL measurements of high accuracy are generally difficult since the value; are typically in the range 3 to 30A and specimen characterization on this

scale (morphology, thickness, homogeneity, uniformity, etc.) is difficult.

14
Calculations of IMFPs are also difficult since approximations,

particularly for electron energies below about 200 eV, may not be valid.

Useful formulas are needed to enable useful predictions to be made of AL

or IMFP values in materials for which no measurements or calculations have

been made. Reliable predictions of this type require knowledge of the

dependence of AL or IMFP on electron energy and on material parameters

(e.g., density, atomic or molecular weight). Finally, knowledge is needed

of the extent to which concepts (and data) developed for polycrystalline

or amorphous materials break down in single- crystal materials.

Our accomplishments of the past year have been in the following three

areas.

(a) Energy Dependence of Electron Inelastic Mean Free Paths

Comparisons of the AL and IMFP data are often made through

plots of AL and/or IMFP values versus electron energy. While these plots

are very useful for assessing the relative magnitudes of AL and IMFP

values and their trends as a function of energy, they are not well suited

to a detailed examination of the energy dependence. A particularly

convenient and appropriate method of examining the dependence of AL or IMFP values on electron energy is the Fano plot. The product of a particular inelastic cross section (which in the simplest cases could be

for a discrete excitation, ionization, or total inelastic scattering in a gas) and electron energy is plotted versus electron energy on a logarithmic scale. At sufficiently high electron energies, this plot is

expected to be linear with a slope that can be derived from appropriate

optical data. Such behavior is expected quite generally from the Bethe

theory for inelastic electron scattering in matter. Since the Bethe

theory is well established, use of the Fano plot is a simple and effective

means for analyzing the internal consistency of experimental cross-section

data with optical adsorption measurements, and for determining the minimum

incident electron energy for which the Bethe theory is valid.

An analysis has been made of the energy dependences of calculated

IMFPs for Al, Cu, Ag, and Au from four recent sources of data. Linear

Fano plots were obtained for each metal using data from the calculations

of Ashley et al. and Powell but the Fano plots with the data of Szajman et

al . had distinct curvature. Fano plots with the data of Penn showed

linearity over two separate energy ranges, typically from 80 to 500 or 1000 eV and from 1000 or 1500 eV to 10000 eV. These variations were attributed to different treatments in the calculations of exchange and

correlation and of the dependence of the differential inelastic scattering

cross section on momentum transfer.

There were significant variations in the slopes of the Fano plots for

each material using the four sources of IMFP calculations. The expected

slope of the Fano plot can be calculated from optical absorption data and

thus can be used as a guide in selecting a preferred data set. Values of

the Fano-plot slopes from three of the data sets generally agreed well

with the optical values but the slope values based on the data of Szajman

et al . exceeded the optical values by 9 to 40$.

15
It was found that the slopes of Fano plots using AL data for Al, Cu,

and Au, were larger than the optical values by 29 to 54$. A similar

result has been obtained in other analyses of inelastic-scattering

cross-section data and is believed due to the electron energies not being

high enough to be in the asymptotic Bethe region. A separate analysis of

the optical data showed that the minimum electron energy for which linear

Fano plots can be expected is about 400 eV for Al and about 1000 eV for

Cu, Ag , and Au. Experimental AL measurements in different types of

materials over a wide electron energy range are required to define more clearly the energies where the Fano plots attain their asymptotic slopes.

Calculations are in progress of IMFPs from experimental optical data

using an algorithm developed recently by Dr. D. R. Penn of the NBS

Electron Physics Group. Since optical data are available over a sufficiently wide photon-energy range for a limited number of materials,

it is of interest to compute IMFPs and to search for possible systematics

in the dependences on electron energy and material parameters.

(b) Measurements of Electron Attenuation Lengths in Condensed

Molecular Solids

During the past year we expanded our efforts to measure

electron attenuation lengths in condensed molecular solids by performing

experiments on the X-24C beam-line (a joint effort of NBS and the Naval

Research Laboratory) at the Brookhaven National Synchrotron Light Source.

The goal of this experiment is to measure electron attenuation lengths

over a wider electron energy range than is possible at the NBS SURF-II

storage ring. Films of molecular solids of variable thickness are condensed on a cooled copper substrate and the Intensity of substrate

valence-band photoemission measured as a function of film thickness. These

experiments were conducted with different photon energies and attenuation

lengths measured for corresponding photoelectron energies. At Brookhaven,

we can make the attenuation-length measurements over the range of about 50

to about 1200 eV which is the range of practical interest for Augerelectron spectroscopy and x-ray photoelectron spectroscopy. Furthermore,

careful attenuation-length measurements over a wide electron energy range

should enable more accurate determination of the energy dependence.

Films of the molecular solids are prepared by the technique of

microcapillary-array dosing, the method we developed in our previous

experiments at SURF-II. The Brookhaven surface science chamber was modified to include an in-si tu photon intensity monitor, the

microcapillary array dosing system (with gas-handling manifold), and an additional cryopumping block for reduced operating pressure. Preliminary

measurements were made with water at an electron kinetic energy of 155 eV

however, several experimental snags developed. These complications,

coupled with erratic machine operations, precluded the completion of these

measurements. Most problematic was that the grating installed in the

extended-range monochromator had been manufactured with an Improper bl aze angle; this mistake resulted in usable photon flux with a maximum photon

energy near 160 eV. This grating is being replaced and beryl crystal

diffracting elements are presently being prepared also. These elements

should be in place for the next run.

16
The electron attenuation-length measurements will continue in the

next available time-slot and will include measurements on condensed films

of water, methanol, and cyclohexane (materials for which

attenuation-length measurements were made earlier in the energy range

18-68 eV)

.

(c) Layer-By-Layer Analysis of the Effects of Forward

Scattering of Electrons in Attenuation Length Measurements

with Single Crystals

Attenuation lengths have been frequently measured from the

characteristic decay of an AES and XPS signal as a film of increasing

thickness is deposited on a substrate. This decay is generally monotonic

for amorphous or polycrystalline samples. For single- crystal samples,

however, a fundamental complication for such measurements is the

enhancement of an AES or XPS peak intensity along crystal axes. These

enhancements along nearest-neighbor directions are due to forward

scattering of the emitted electrons by lattice atoms (see Fig. 2.4(b)).

As part of an effort to characterize and elucidate the influences of

forward scattering on AL measurements, several simple model systems have

been studied. Figure 2.4(a) presents data on such a system. The

substrate consists of a monolayer (ML) of Cu epitaxially grown on Ni(lOO).

The attenuation of the Cu AES signal is measured as epitaxial layers of Ni

are grpwn on the Cu. Extreme departures from monotonic decay are observed. At the angles at which the strongest forward scattering is

expected, 45° and 0°, the Cu AES signal is actually increased by

overlayers and is not reduced to below the clean-Cu levels until more

than 4 ML of Ni has been deposited.

Certain types of electron analyzers (e.g., the cyl indrical-mirror

analyzer) may integrate XPS and AES signals over a wide range of angles

and still recover a monotonic decay. Other types of analyzers (e.g., the

hemispherical analyzer) often select small solid angles and in such cases,

as here, it is clear that the simple concept of exponential electron

attenuation breaks down in single-crystal materials. In such cases,

quantitative surface analysis by XPS and AES will have large uncertainties

unless corrections can be made for the effects of forward scattering.

Data of the type shown in Fig. 2.4(a) can be used to select the polar

angles and solid angles for which the current simple models for

quantitative AES and XPS are more likely to be valid.

Figure 2.4 also provides insight into the layerwise breakdown of the

angular distribution of pure Cu(100). Summing the spectra shown in Fig.

2.4 from 0 to - » ML of Ni (including those not shown) produces a result

essentially identical to the pure Cu(100) angular distribution. This

result is reasonable since Ni overlayers scatter electrons in very nearly

the same manner as Cu overlayers. Thus, Fig. 2.4(a) makes it possible to see the layerwise contributions to the angular distribution of the Cu AES

signal from pure Cu (100)

.

17
Fig. 2.4(a) Changes in the angular distributions of Auger electrons from

an epitaxial Cu monolayer for the indicated number of nickel

overlayers

(b) Illustration of the atomic geometry for these sandwich

structures

6. Algorithm for Fitting Sputtei—Depth Profiles at Interfaces

(J. Fine, G. P. Chambers, and D. Marton)

The determination of interface widths from sputter-depth-prof 1 i er is presently accomplished by means of graphical methods. Since the shaper

of such interface profiles are generally not symmetric and since the^e Is no accepted method of measuring interface widths, accurate width

18
determination as well as intercomparison of results is often difficult to

accomplish. One solution to this problem is to fit numerically the

interface profile shape to an appropriate analytical expression from which

one can obtain a factor proportional to different definitions of the

interface width.

In collaboration with Dr. W. H. Kirchhoff of the NBS Chemical

Thermodynamics Division, a fitting analysis for Auger-electron

sputter-depth profiles has been developed using a logistic function of the

form:

I - CA + a(T-T 0 )]/(i + e_t ) + [B + b(T-T 0

)]/(1 + e

t

)

where I is the peak intensity of the Auger spectrum of the sputtered atom

as a function of the time T. A is the intensity from a totally covered

surface, B is the background intensity from a completely uncovered surface,

and a and b empirical parameters which can account for additional time

dependence or instrumental effects. T

Q is the apparent midpoint of the

transition region and t is a dimensionless, reduced time defined as (T-T 0 )/D. The scaling factor, D, is the characteristic time for

sputtering through the interface region. Asymmetry in the depth profile

can be accommodated by allowing D to vary with time.

A least-squares fitting program has previously been written to fit

measured Auger spectral intensities to the above equation for completely

resolved interfaces (i.e., where component X goes from 100 to 0 % and

component Y goes from 0* to 100?). We showed that this logistic function

could be fitted to Auger data for the NBS multilayered Ni/Cr thin-film

structure SRM2135 to within the experimental error of a few percent.

This past year, extension was made of this fitting using the logistic

function to interfaces which are not fully resolved. This situation

occurs when sputter profiling a very thin layer of material (less than,

say, 5 nm) in between two thick layers of another material. By making use

of the derivative of the above equation, we have shown that remarkably

good fits can be made to high-resolution sputter profiles obtained in our laboratory. The fits were made to depth profiles of a multilayer Ni/Ag

thin-film structure which had thin Ag layers ( = H nm) and thick Ni layers

(= 50 nm) . These fits to the analytical logistic function give functional

parameters from which we have been able to make quantitative

determinations of layer thickness for such very thin films.

A limited distribution has been made during the year of the fitting

program and its documentation. The program has been written in Fortran 77

and can be run on IBM-compatible personal computers. Packages containing

the program on a floppy disc, a program listing, a detailed description of

the program, and examples of its use (with corresponding test data on the

disc) were distributed at the spring meeting of ASTM Committee E-42 on Surface Analysis and at the Applied Surface Analysis Symposium in Dayton.

At the latter meeting, a demonstration was also given of the program. The

purpose of the distribution was to enable further tests and evaluations of

19
the program to be made. We are currently exploring mechanisms for wider

dissemination of the program that will enable a larger number of people to

make use of this software.

7. Adsorbate Surface Coverage Measurements

(T. E. Madey)

An important parameter in surface science measurements is the

coverage (surface density in atoms/unit area) of atoms or molecules which

are adsorbed on a given surface. In many instances, there is a factor of

two or three uncertainty in measurements of coverage. Such large

uncertainties provide major problems in data interpretation, modelling of

surface structures, determination of surface kinetics, etc. During the

last few years, several experimental methods have been developed which

have the potential for providing absolute measures of surface coverage,

with a substantially smaller uncertainty ( - ± 25$). Such methods include

molecular- be am reflection techniques, high-energy ion backscattering

,

radiotracer measurements, and nuclear reactions induced by ion

bombardment. We expect shortly to initiate a comparative study of these

methods with the goal of preparing a critical review of absolute coverage

data and of relevant measurement methods.

B. Reference Materials

1. Developments and Production of Standard Reference Materials for

Sputter-Depth Profiling)

(J. Fine, Y. Hashiguchi , and D. Marton)

The objective of this project is to develop standard reference

materials (SRM's) that will allow convenient determinations of ion-beam

sputter-removal rates in commonly used surface-analysis instrumentation.

Thin-film reference materials of known thickness will be used to calibrate

ion-gun current densities for particular operating conditions. This

information together with sputtering-yield data for a range of materials

will establish depth scales in the measurement of depth profiles.

Prototype thin-film structures were initially fabricated in order to

evaluate their usefulness as depth profiling SRM's and to develop

appropriate characterization techniques. These structures were made by

sputter deposition as part of a joint US/Yugoslavia program between NBS

and Dr. B. Navinsek at the J. Stefan Institute in Ljubljana. Analyses of

these prototype materials at NBS and by members of ASTM Committee on Surface Analysis were done using Auger-electron spectroscopy (AES) , x-ray

fluorescence, secondary-ion mass spectroscopy (SIMS), Rutherford

backscattering spectroscopy, and proton-induced x-ray emission. The

results were satisfactory and a stock of similar thin-film SRM's were fabricated in 1982 using the sputter deposition facility at the J. Stefan

Institute in Ljubljana. Production and characterization of the Ni-Cr

thin-film SRM was supported by the NBS Office of Standard Reference

Materials

.

20
Preliminary analyses obtained on the nickel- chromium multilayered

thin-film structures indicated that this material should be of

considerable benefit as a depth-profiling SRM. It has been characterized

and calibrated in order to determine the uniformity and periodicity of the

thin-film layers, absolute film thicknesses, sputtered interface depth

resolution, and structural stability. The results of these measurements

indicated that this Ni/Cr structure could be accurately calibrated for

depth profile analysis; it was issued as NBS Standard Reference Material

2135 in the fall of 1985.

Sales of the SRM through the NBS Office of Standard Reference

Materials were greater than we anticipated and by the spring of 1986 our initial stock of 80 specimens was sold. An additional stock of 25

specimens, which we had previously calibrated, was issued as NBS SRM 2135a

and these, too, were sold by the summer of 1986.

Two additional batches of Ni/Cu structures (about 200 specimens) were characterized by Auger sputter-depth profiling and by neutron activation

analysis. These should be ready for issue in the fall of 1986 and should

be sufficient to maintain our stock of SRM 2135 for about another year.

We are now making arrangements with Dr. Navinsek for the fabrication of

about 600 Ni/Cr structures.

Future work includes characteri zing and certifying ’’marker" . layer-type sputter-depth-profile SRM which we have recently fabricated in

production quantities. This material also was fabricated in Dr.

Navinsek' s laboratory and consists of eight Cr layers (- 40 nm each)

separated by about 2 monolayers of C^Og. Preliminary experiments have

been carried out to characterize these structures by Auger depth

profiling. This is a difficult test since the C^Og marker layers are very thin and since the oxygen Auger peaks nearly overlap those of

chromium. We have been able to detect the oxygen Auger signal after

developing a special background subtraction program. In some experiments,

we were able to detect all seven oxide layers in a structure (even the one

that was 280 nm deep) after very careful instrumental alignment and with a low-energy (1 keV) argon ion beam. Accurate determination of the position

of the marker could be achieved by fitting a theoretical curve to each of

the seven oxygen peaks in the depth profile. The theoretical curve was

the same as that used to describe the Ag/Ni depth profiles (section 2. A. 6)

and had terms that described surface-roughness development and

radiation-enhanced diffusion occurring during the sputtering of the

specimen. In other experiments, we were unable to detect the deeper oxide

layers, presumably because of the higher interface broadening associated

with roughness development and radiation-enhanced diffusion.

We plan to perform additional characterizations of the Cr/C^Og

structures. We will measure depth profiles for a wider range of

experimental conditions and will calibrate the chromium total film

thickness by neutron activation analysis. It is possible that the

material may not be suitable for routine use in Auger depth profiling

(except perhaps as a stringent test of operating conditions). We expect,

however, that it will be useful as a depth-profile standard in SIMS since

21
this technique is more sensitive than AES and does not suffer from the

problem in AES for Cr and 0 of peak overlap in energy. We anticipate that

this structure can be issued as an SRM next year.

2. Quantitative Sputter Depth Profiling of Interfaces

(J. Fine, D. Marton, Y. Hashiguchi, and G. P. Chambers)

Determination of composi tion-versus-depth at virgin solid/solid

interfaces is at present difficult to achieve with current

sputter—depth-prof iling techniques. This is due, to a large extent, to a lack of understanding of the effects of the various bombardment conditions

(i.e., ion beam energy, species, angle of incidence, current density, and

sputtered depth) on interface resolution. A consistent set of

measurements obtained for various ion beam parameters, all done on the same material, would significantly enhance our ability to assess the

abruptness of interfaces before sputter-prof lie analysis took place and

would be of value in determining optimum sputter-prof ile conditions.

Our development of multilayer thin-filra structures with known layer

thickness and periodicity (as described above) makes it both possible and

practical to examine systematically the dependence of interface resolution

on ion beam parameters. Use of the computer- controlled, sequential-mode

N(E) Auger data system which has been previously developed allows us to

obtain reliable and accurate Auger measurements while the fitting of this

data to particular functions results in quantitative determination of

the interface width and the asymmetry of the interface profile.

Our principal objective in the past year has been to investigate

interface broadening mechanisms if) depth-profile measurements and to

define the limits on the use of layered structures as sputtering-rate

reference materials. Two important processes occurring during sputtering

have been selected for these studies: the development of surface

roughness and radiation-enhanced diffusion. Silver/nickel multilayered

samples, fabricated in the laboratory of Dr. B. Navinsek (Ljubljana,

Yugoslavia) and consisting of five thin (- 4 nm) Ag layers embedded between

six thicker (50 nm) Ni layers and sputter-deposited on Si wafers have been

used as test materials for these measurements.

(a) Surface roughness development during sputter— depth profiling

Both theoretical and experimental studies have been carried

out. A simple statistical model has been developed to explain the

phenomenon of increasing surface topography (roughness) during ion

sputtering of solid targets. The square-root depth dependence of the

surface roughness, which has been observed in some cases, is explained by

assuming that the roughness increase is caused by the differences in

sputtering rates obtained on differently oriented crystallographic

surfaces, and that the distribution of the sputtering rates is fully

random. Deviation from the random distribution of the sputtering rate

leads to different types of depth dependences for the surface roughness.

22
A light-scattering experiment has been set up in conjunction with the

Auger depth-profiling apparatus to measure the surface roughness changes

in-si tu (i.e. without breaking the vacuum). Stylus measurements with a Talystep instrument (in collaboration with Dr. T. Vorburger of the NBS

Precision Engineering Division) have been utilized as calibrations. The

light source used in this experiment is a 5 mW unpolarized 630 nm He-Ne

laser, and the scattered light is collected by an ellipsoidal reflector.

The opening angle of the reflector is about M5° which limits the maximum

surface wavelength that can be measured to about 1.85 ym. This experiment

is far from the ideal arrangement in which the total scattered light

intensity could be measured and thus only relative roughness values can be

measured here. This is, however, the first known experiment to measure

surface roughness changes JLn situ following sputtering.

Preliminary experiments carried out with this set-up at 1 keV argon

ion energy showed that the surface roughness increased from the starting

value for the unsputtered surface of 1 nm to about 6 nm at 50 nm depth and

to about 12 nm at 250 nm depth. These results are consistent with the

assumption of a square-root depth dependence of the roughness increase and

with semi-empirical results obtained from the Auger depth profiles

described below.

(b) Radiation-enhanced diffusion during sputter-depth profiling.

Earlier studies in this laboratory have shown that ion

bombardment of Ag/Ni multilayer thin-film structures similar to those used

in the present experiments lead to a segregation of Ag at* the same

surface. This phenomenon was explained by assuming that radiationenhanced diffusion (RED) was responsible for the Ag transport. This

process has now been investigated in more detail by sputtering

through all Ag and Ni layers and by describing all peaks in the Ag Auger

depth profiles in terms of a distortion of the initially ideal step-like

concentration profile. Such Ag-layer profiles become Gaussian-like as a result of surface roughening and are made asymmetric by the RED. The

equation describing this modified Ag profile is:

c 0 (St-zQ

) 2

c = exp [ ]

( MDt+AZp/2) 1 /2 ^Dt+AZp/2

where c is the Ag concentration, t is the diffusion time, D is the RED

rate, S is the sputtering rate, c Q is a constant depending on the Ag layer

thickness, Az

R is the RMS surface roughness, and z Q is the propagation

range of the sputter-induced defects.

A computer program has been developed for fitting the above equation

to the experimental data. One example of such a fit is shown in Fig. 2.5.

The fit is excellent, and both diffusion rate and roughness data can be

easily obtained. The same approach seems to be useful for the

interpretation of oxygen depth profiles in Cr/Cr2 0^ multilayers (see

section 2. B. 1 )

23
[xlO 3 MIN]

TIME

Fig. 2.5 Plot of the Ag Auger-electron signal as a function of sputtering

time for an Ag/Ni multilayer thin-film structure consisting of

five Ag and six Ni layers on a Si substrate. The points are the

experimental intensity measurements and the line is the fit

based on the equation given in Section 2. B. 2(b).

RED rates have been determined for 1 keV argon Ions as a function of

current density. It was expected that at low current densities of the lor

beam, the sputtering rate would be smaller, the diffusion process would

take longer time, and thus wider interfaces would be obtained. This is

correct, but the RED rates also decrease for smaller current densit.es,

presumably because of the partial recombination (healing) of the

24
radiation-induced defects. This process decreases the number of defects

which then reduces the RED rates. If this process of defect healing is

assumed to be exponential, a lifetime or about 250 minutes is obtained. For

high sputtering rates, D is found to be 4 x 10“17 cm2 /s for 1 keV ions and

around 1 x lO -1 ^ cm^/s for 4 keV ions. These values for the RED rate are

very much larger (by orders of magnitude) than the normal diffusion

coefficients for similar systems. The values are strongly dependent on

ion energy and therefore appear to be related to defects (probably point

defects) caused by the ion bombardment.

These studies of interface layer broadening are to be completed in

the next year by obtaining more detailed information on the dependence of

these phenomena on the energy of the incident ions. Another important

aspect concerns the Ni/Cr standard reference material (see section 2.B.1).

Both roughness effects and RED may be applicable to this system; in '

particular, RED may explain the asymmetry observed in Auger depth profiles

of the Ni/Cr multilayers. A rather extensive set of interface

measurements obtained on Ni/Cr multilayered structures is now being

analyzed to determine the dependence of interface width and asymmetry on

the ion bombardment energy and current density as a function of sputtered

depth.

C. Review Articles and Books

1 . Review Articles

The Division Staff authors many review articles and book

chapters that provide information on measurement methods, relevant

reference data, reference materials, theories of the measurement process

for many surface spectroscopies, and surface standards.

Division staff members have authored 23 review articles recently.

The titles and abstracts of review articles published since 1985 are listed below:

(a) "The Thermal Desorption of Adsorbed Species," J. T. Yates, in

Methods of Experimental Physics , Vol. 22, Solid State Physics : Surfaces , R. L. Park and M. G. Lagally, eds. (Academic Press,

N.Y.), 425 (1985).

The experimental and theoretical basis of thermal desorption

spectroscopy as a tool for surface characterization is described. Methods

of analysis of thermal desorption spectra to obtain kinetic information

(desorption energies, desorption order, coverages of adsorbed species) are included, together with numerous examples of desorption on small molecules

from single^ crystal metal surfaces.

25
(b) "Experimental Methods in Electron and Photon Stimulated

Desorption," T. E. Madey and R. Stockbauer, in Methods of

Experimental Physics , Vol . 22, Solid State Physics : Surfaces , R. L. Park and M. G. Lagally , eds. (Academic Press, N.Y.), 14 65

(1985) .

We review experimental techniques and applications of electron

stimulated desorption (ESD ) and photon stimulated desorption (PSD) of

atomic, molecular, and ionic species from surfaces. The physical

principles of these methods, as well as details of experimental

measurements and data analysis are discussed. We close with a discussion

of beam damage in surface analysis.

(c) "Innershell Ionization Cross Sections," C. J. Powell in

Electron Impact Ionization , T. D. Mark and G. H. Dunn, eds.

(Springer-Verlag, N.Y., 198 (1985).

A review is presented of cross sections for the ionization of

inner-shell electrons by electron impact. Calculations, measurements, and

empirical formulas are described and compared. Recommendations are given

for the selection of cross-section data. Finally, applications of

inner-shell ionization cross-section data to materials and surface

analysis problems are described.

(d) "The Coordinated Development of .Standards for Surface Chemical

Analysis", M. P. Seah and C. J. Powell, NBS Internal Report

NBSIR 85-3120 (March, 1985).

This report is based on a proposal to the Steering Committee of

the Versailles Project on Advanced Materials and Standards (VAMAS) ?or the

coordinated development amongst the VAMAS member states of standards for

surface chemical analysis. VAMAS was established following a meeting of

the Heads of State or government at Versailles, France in 1982 that agreed

on a number of projects relating to technology, growth, and employment.

Specifically, VAMAS was organized to promote international coordination in

the development of standards in a wide range of advanced material sectors.

Surface chemical analysis was approved as a VAMAS Technical Working Area

in June, 1 984

.

The report describes the growth and diversity of surface analysis in

the development of advanced materials in modern technologies and the use

of surface analysis for improved films and coatings. The principal

techniques of surface analysis in common use are Identified and the

technical limitations to accurate surface analyses pointed out. Accurate

surface analyses require: (i) knowledge of the principles of the

measurement method, (ii) knowledge of the behavior of the measuring

instrument and the (iii) correct interpretation and expression of the final

measured result. Standards for the measurement of surface composition

with known accuracy and for the reliable determination of chemical stat*-' require: (a) a base of principles, definitions of terms, and suitable

equations; (b) reference procedures for the measurement of intensities anc spectral features, (c) procedures and data for instrument calibrations, (d

reference data for material parameters such as elemental sensitivity

26
factors, matrix terms, chemical state spectra, ion sputtering rates, etc.;

and (e) standard methods for specifying an analysis. Specific needs are identified for the common methods of surface analysis, Auger-electron

spectroscopy, x-ray photoelectron spectroscopy, and secondary-ion mass spectroscopy together with needs for ion sputtering which is used to

obtain composition versus depth information in films and coatings.

Existing standards activities in the member countries of VAMAS are reviewed

and suggestions are made for additional standards for surface chemical

analysis.

(e) "Surface Harpooning", J. W. Gadzuk, Comments on Atomic and

Molecular Physics, 1_6» 21 9 (1985)

The principles involved in charge transf er/harpooning collisions

between atoms or molecules and surfaces are presented in terms of concepts

drawn from gas-phase atomic and molecular collision theory. As specific

examples, the charge state of atoms and the vibrational excitation or dissociation of molecules which have experienced harpooning while scattering

from a surface are considered.

(f) "The Uses and Limitations of ESDIAD for Determining the

Structure of Surface Molecules", T. E. Madey, in The Structure

of Surfaces , Springer Series in Surface Science 2, M. A. van

Hove and S. Y. Tong, eds. (Springer-Verlag , N.Y.), 264 (1985).

The principles and mechanisms of electron-stimulated desorption

(ESD) and photon-stimulated desorption (PSD), as well as the utility of

the electron stimulated desorption ion angular distributions (ESDIAD)

method as a tool for determining the structure of surface molecules, have

been described in a recent book and several review articles. The present

short paper is intended to provide a guide to the relevant literature, and

to describe briefly some recent work relating to the uses and limitations

of ESDIAD for determining the structure of surface molecules.

(g) "Recent Advances Using ESDIAD: Applications to Surface

Chemistry", T. E. Madey, C. Benndorf, N. D. Shinn, Z. Miskovic,

and J. Vukanic, DIET-II, Desorption Induced by Electronic

Transitions , Springer Series in Surface Science 4, W. Brenig and

D. Menzel, eds. ( Springer-Verlag , N.Y.,), 104 (1985).

Recent applications of ESDIAD (electron stimulated desorption ion

angular distributions) to surface chemistry are described. Examples

include the influence of catalytic promoters and poisons on surface

structure and reactivity, the evidence for a new structural form for

adsorbed H

2 0 (i.e., H

2 0 dimers on Ni(110)), and the characterization of a new bonding mode for CO on Cr(110). Calculations of the perturbing

influence of image force and reneutralization effects in ESDIAD are described

.

27
(h) "Recent Developments in Quantitative Surface Analysis by

Electron Spectroscopy", C. J. Powell, J. Vac. Sci. Tech. A 4,

1532 (1986)

An overview is given of recent developments in quantitative

surface analysis by x-ray photoelectron spectroscopy and Auger-electron

spectroscopy. The two major tasks of an analysis are the identification

of the surface phases that are present and the determination of the

concentrations of particular elements or compounds. Methods for

accomplishing both tasks will be described together with the pitfalls and

problems that remain. Particular attention is given to the following

topics: identification of surface phases and reference data for the

calibration of instrumental energy scales; reference data on inelastic

mean free paths and attenuation lengths; effects of specimen

crystallinity; intensity measurements; measurement of the imaging

properties of electron energy analyzers; and the intensity-energy response

functions of different instruments.

(i) "Surface Chemical Analysis - Report on the VAMAS Project", C. J. Powell and M. P. Seah, Surf. Interface Anal. 9, 79 (1986)

The VAMAS project on surface chemical analysis is a multi-national cooperation for the provision of standards data and

materials for surface chemical analysis measurement and for the provision

of the basic understanding necessary for these activities. This project

is one of a rapidly growing suite of projects initiated as a result of

decisions following the 1982 Versailles Summit Meeting of the Heads of

State or Government of Canada, France, Germany, Italy, Japan, UK, USA and

the Representatives of the Commission of the European Community. During

the past year national representatives to this VAMAS project have been

appointed and national committees established. This article summarizes

the philosophy, scope, and organization of the project and describes

specific activities that have been initiated. Information is given on how

individuals, both within and outside the group of member states, may

participate

(j) "Dynamics of Molecular Processes at Surfaces: Vibrational

Lineshapes and Spectra", J W. Gadzuk, J. Electron Spectroscopy

38 233 ( 1986)

Extremely useful connections exist between the dynamics of

adsorbed molecule vibrations, as revealed in spectroscopic lineshapes, and

the dynamics of molecular processes at surfaces because in both cases, the

constituent atoms of a molecule, solid, or combination of the two execute

multi-dimensional motion over the same potential energy surfaces,

undoubtedly sampling different regions of it.

In this paper, recent insights and advances in surface dynamics will

be applied to the problem of vibrational lineshapes. Classical particle

and semi-classical wavepacket dynamics will be used to address the issue?

of energy decay (T 1 ) vs. pure dephasing (T 2

') overtones, and non-linear

dynamics as they apply to lineshape analysis.

28
(k) "Electron Stimulated Desorption and its Relation to Molecular

Structure at Surfaces", T. E. Madey, J. Vac. Sci. Tech. A M, 257

(1986).

Recent examples of the use of electron stimulated desorption ion

angular distributions ( ESDIAD ) in determining the structures of molecules

on surfaces are discussed. These include the adsorption and decomposition

of NH^ on Fe(100), and the stabilization of H2 O on Ag ( 1 10) by impurity 0

and Br atoms. ESDIAD evidence for "lying down" CO on several surfaces is

presented, and the influence of beam damage in producing new surface

structures for H

2 0 on Ni(100) is discussed. Calculations of the influence

of the surface image potential and reneutralization effects on ion

trajectories are described briefly.

2. Review Articles in Publication

We list below the titles and abstracts of review articles in the

course of publication.

(a) "The Chemisorption of Carbon Monoxide by the Transition Metals",

J. T. Yates, Jr., T. E. Madey, and J. C. Campuszano, The Chemical

Physics of Solid Surfaces and Heterogeneous Catalysis", D. A.

King and D. P. Woodruff, eds. (Elsevier, N.Y.)

A comprehensive review of the adsorption of carbon monoxide by

transition and noble metals is presented. The systematics of CO

adsorption and dissociation are discussed, along with detailed

examinations of the surface structures, electronic and vibrational

spectra, and kinetic behavior of adsorbed CO.

(b) "Final-State Resolved Studies of Molecule-Surface Interactions",

D. S. King and R. R. Cavanagh in New Laser and Optical

Investigations of Chemistry and Structures at Interfaces , (Verlag Chemie)

Quantum state-specific diagnostics as applied to surface

dynamics are discussed. The NO molecule is used as an illustration of the

experimental determination of gas-surface interactions. Topics reviewed

included beam-surface scattering, thermal desorption, vibrational

accommodation, Doppler profiles, and Fourier-transf orm infrared emission

spectroscopy

(c) "Core-Level Binding-Energy Shifts in Solids at Surfaces", W. F. Egelhoff, Jr., Surface Sci. Reports.

This review presents an overview of the theory and of various

successful approaches to the interpretation of core-level binding-energy

shifts observed in photoelectron spectroscopy. The theoretical background

is presented at a level readily accessible to the general reader.

Particular attention is paid to the relative merits of two basically

different conceptual frameworks for interpreting core-level binding-energy

shifts, the initial-state—final-state approach and the equivalent-core

Born-Haber cycle approach.

29
(d) "Excitation Mechanisms in Vibrational Spectroscopy of Molecules

on Surfaces", J. W. Gadzuk, in Vibrational Spectroscopy of

Molecules on Surfaces , J. T. Yates, Jr., and T. E. Madey, eds.,

Vol. 1 of Methods of Surface Characterization (Plenum, N.Y.).

An introduction to the theoretical basis of vibrational

excitation mechanisms and processes relevant to vibrational spectroscopy of

adsorbed molecules is presented.

(e) "Neutron Inelastic Scattering: Vibrational Spectroscopy of

Adsorbed Molecules on Surfaces:, R. R. Cavanagh, J. J. Rush, and

R. D. Kelley, in Vibrational Spectroscopy of Molecules on Surfaces , J. T. Yates, Jr., and T. E. Madey, eds., Vol. 1 of

Methods of Surface Characterization (Plenum, N. Y.).

An introduction to neutron scattering as a probe of adsorbates

at surfaces is presented. Emphasis is placed on experimental aspects of

triple-axis and time-of-flight techniques along with a single-phonon model

for the spectral features. Wilson FG methods for constructing molecular

force fields relevant to the molecular modes of the adsorbate are presented. The applicability of neutron scattering for exploring

rotational diffusion and adsorbate torsions is also examined.

(f) "Field Emission Microscopy - Trends and Perspectives", A. J. Helmed, Chemistry and Physics of Solid Surfaces VI , Springer-Verlag

The author’s view of the role of surface microscopies, in

particular the field emission microscopies, is given. Brief outlines of

the historical development and nature of field-electron emission

microscopy (FEEM) and field-ion microscopy (FIM) are given and selected

examples are presented to illustrate the scope of research in FEEM and

FIM. Research trends are described and some projections for the future

are made,

(g) "Electron and Photon Stimulated Desorption: Probes of Structure

and Bonding at Surfaces", T. E. Madey, Science

Techniques for analyzing the structure and composition of solid

surfaces using electron and photon beams often suffer from difficulties

due to radiation damage. Damage-producing processes compete with

inf ormation-producing events during measurements, and beam damage can be a serious perturbation in quantitative surface analysis. However, there are also substantial benefits of electron and photon stimulated damage

processes for studying molecules adsorbed on surfaces. Direct information

about the geometrical structure of surface molecules can be obtained from

measurements of the angular distributions of ions released by electron- or photon-stimulated desorption. The directions of ion emission are determined by the orientation of the surface bonds which are ruptured by

beam irradiation. Moreover, photon-stimulated desorption studies using

synchrotron radiation are revealing the fundamental eiectroni:

30
excitations which leaa to oona-breaking processes at surfaces. These

measurements are providing new insights into radiation-aamage processes in areas as diverse as x-ray optics and semiconauctor electronics.

(n) "Mechanisms and Applications of Electron Stimulated Desorption

in Surface Science", T. E. Madey, Vacuum (TAiP)

The principles and mechanisms of electron-stimulated desorption

and the utility of the electron-stimulated desorption ion angular

distributions (ESDIAD) method as a tool for determining the structure of

surface molecules have been described in several recent books and review

articles. The present article is intended to provide a guide to the

relevant literature, and to outline briefly some recent work relating to

the uses of ESDIAD for determining the structure of surface molecules.

(i) "The Interaction of Water with Solid Surfaces", P. A. Thiel and

T. T. Madey, Surface Sci. Reports

Tne purpose of this review is to compare and discuss recent

experimental and theoretical results in the field of ^O-solid

interactions. Emphasis is placed upon adsorption studies performed on well-cnaractenzed, single- crystal surfaces of metals, semiconductors and

oxides. We discuss the factors which influence dissociative vs. associative adsorption pathways. When H2O adsorbs moiecuiariy, it tends

to form three-dimensional hydrogen-bonded clusters, even at fractionalmonolayer coverages, because the strength of the attractive interaction

between the two moiecuies is comparable to that of the substrate-^O bond.

The template effect of the substrate is important in determining both the

local and long-range order of H2O molecules in these clusters. The

influence of surface additive atoms (e.g., 0 , Br, Na, K) on the surface

structure and chemistry of H2O is examined in detail. Results on single

crystal substrates are compared with earlier available measurements of H2O

adsorption on high-area materials.

( j ) "Core Levei Spectroscopy: A Dynamics Perspective", J. W.

Gadzuk, Physica Scnpta

Various aspects of the dynamics of time-dependent localized

potentials and interactions in solids and at surfaces, as they might

relate to the fundamental screening and relaxation processes involved in

core-level spectroscopies, are explored.

(k) "Dynamics of Molecular Collisions with Surfaces: Excitation,

Dissociation, and Diffraction", S. Holloway, M. Karikorpi, and

J. W. GaczuK, Nuclear Instruments and Methods B

Aspects of molecular collisions are discussed which are important in the chemically relevant energy range of - 1-10 eV. In

particular, the role of charge transfer, potential-energy-surface

topology, and intra-molecuiar ground- and exc 1 tea- state potential curves

are investigated as they pertain to internal vibrational excitation,

dissociative adsorption or scattering, ana diffractive scattering. The

31
modeling and analysis are based on classical trajectories and

semi-classical wavepacket dynamics, both for intra-molecular and

translational motion.

(1) "Neutron Scattering Studies of Hydrogen in Catalysts", in Hydrogen

in Catalysis: Theoretical and Practical Aspects , Z. Paai and P. Gc Menon, eds. (Marcel Dekker, N.Y.).

Neutron scattering studies of hydrogen in catalysis are reviewed. Techniques applicable to catalysis studies (incoherent

inelastic neutron scattering (IINS), quasielastic neutron scattering

(QNS), and powder neutron diffraction) are introduced. Selected examples

are presented with an emphasis on illustrating the utility of these

neutron scattering techniques for probing the vibrational, diffusive,

chemical, and structural behavior of hydrogen on catalyst surfaces.

3. Books

(S. M. Girvin, C. J. Powell, and T. E. Madey)

Division staff have been active on two book projects during the

past year.

(a) The Quantum Hail Effect

Tne quantum Hall effect is among the most important discoveries

in condensed-matter physics in recent years. There has been a great deal

of experimental and theoretical activity in the area since its discovery

in 1980 by Klaus von Klitzing. Professor von Klitzing received the 1985

Nobel Prize in Pnysics in recognition of the importance of this

phenomenon. While the original experimental discoveries of the integer

ana fractional effects were quite surprising ana unexpectea, recent

theoretical progress has led to a fairly weil-establ ished standara

picture of the physical basis of the effects ana the field has reacnec at

least tne preliminary stages of maturity. However to date, there have not

appearea any extensive review articles on the subject. To remedy this, S.

M. Girvin in collaboration with Prof. R. E. Prange of the University of

Maryiana organized a ten-part lecture series on tne quantum Hall effect.

The lectures were held at the University of Maryland during the 1985 Fall

semester. The attenaance was extremely gratifying, averaging 70-75

people for the introductory portions ana 35 for the last few advanced

lectures. In adaition to students and faculty members from the University

of Maryland, the audience contained people from other local universities

and from area industrial and government laboraton es . After extensive

editing of the notes, we are publishing a book based on these lectures

through bpringer-Verlag , New York. This will be the first major review of

the field to be published and we anticipate that it will be well received.

We have already received a request for permission to translate the book

into Russian for publication through Mir, Moscow.

32
(b) Methods of Surface Characterization

While there are many books and review articles on different

aspects of' surface science ana its applications, there is a dearth of

information on how to make reliable surface-characterization measurements.

There is, in essence, a large information gap between review articles in

which the latest scientific advances are discussed and manufacturers’

handbooks in which tne operation of commonly used surface-characterization

equipment is described. Arrangements have been made with a commercial

publisher to proauce a series of books, "Methods of Surface

Characterization which will address this need. Two Division staff

members (Powell and Madey) and three other scientists (A. W. Czanderna at

the Solar Energy Research Institute; D. M. Hercules and J. T. Yates, Jr.,

at the University of Pittsburgh) constitute an editorial board 'that will

oversee the production. A series of four volumes is currently planned

which will describe the principles, techniques, and methods considered

important for surface characterization. It is intended to describe how

important surf ace-characterization measurements are made and how to ensure

that the measurements and interpretations are satisfactory (to the

greatest extent possible). The approach of the series will be peaagogicai

or tutorial.

Two volumes of the book series will describe the techniques and

methods for electron spectroscopy and ion spectroscopy, respectively,

which are in widespreaa use for surface analysis. These volumes will be

concerned largely with techniques for which commercial instrumentation is

available. Writing for both volumes is close to completion.

A third volume will describe techniques for specimen handling and

depth profiling. For specimen nandling and treatment, this volume wiii

provide a compilation of methods that have been proven useful. This

volume will also adaress the common artifacts and problems associated with

the bombardment of solid surfaces by electrons and ions. Finally, a description will be given of methods for depth profiling. It is hoped

that writing for this volume will be completed in 1987.

A fourth volume brings together a description of methods for

vibrational spectroscopy of molecules on surfaces. Most of the techniques

are currently under active development; commercial instrumentation is

available for some techniques but this situation could change in the next

few years. Writing of this volume has been completed and manuscripts sent

to the publisher.

D. Standards-Commi ttee Activities

Three staff members of tne Division hold offices on two ASTM

Committees, the E-42 Committee on Surface Analysis and the D-32 Committee

on Catalysts, and on the recently established Surface Chemical Analysis

Working Party organized under the auspices of the Versailles Project on Aavanced Materials and Stanaards. Participation in the activities of

these groups provides an opportunity for leadership, for dissemination of

NbS expertise, and to learn of significant measurement problems in

relevant areas.

33
1. ASTM Committee E-42 on Surface Analysis

(C. J. Powell, J. Fine, and N. E. Erickson)

The ASTM Committee E-42 on Surface Analysis, founaed in 1976, now has some 120 members; in addition, a larger number of non-members,

both within the U.S. and throughout the world, participate in Committee

activities, The purpose of the Committee is to advance the field of

surface analysis and the quality of surface analyses through the

development of appropriate standards, standard practices, reference data,

reference materials, round robins, symposia, workshops, and publications.

During the past year, we have drafted a proposed Standard Practice

for Determination of the Specimen Area Contributing to the Detected Signal

in Photoelectron Spectroscopy and Auger-Electron Spectroscopy for

consideration by the ASTM E-42 Committee. This practice describes methods

for determining the active specimen area for different conditions of

instrument operation, for verifying adequate specimen alignment, and for

characterizing the imaging properties of the electron energy analyzer.

The practice is restricted to instruments in which the specimen is excited

by x-ray or electron beams with widths at the specimen much larger tnan

the specimen dimensions viewed by the analyzer. This draft standard is

based in part on recent work at NBS in which extensive measurements were

made of the imaging properties of a double-pass cyi indncai-mirror

analyzer for various operating conditions. The XPS and Auger

Subcommittees of the E-4a Committee are currently ballotting the proposed

standard

Committee activities of the past year have included development of

the following documentary standards (which are at varying stages of review

ana approval):

Additional definitions of terms for AES, XPS, SIMS, ano Energetic Ion Analysis

Guide to Deptn Profiling in Auger Electron Spectroscopy

Practice for Reporting Spectra in XPS

Method for Calculating Data-Gathenng Speed in XPs

Guide to Steady-State Charge-Referencing Techniques in XPS

Practice for Reporting Sputter Depth Profile Data in SIMS

(secondary-ion mass spectroscopy)

Guide for Specification of Ion Beams for Use in Surface Analysis

- Procedure for Sample Positioning with Cylindrical Mirror

Analyzers in ISS (ion-scattering spectroscopy)

Procedure for Approximate Energy Scale Calibration with

Cylindrical Mirror Analyzers Used in ISS

Proposed Guide for Data Reporting in ISS

Proposed Guide for the Measurement of X-ray Flux in XPS

Instruments

Proposed Guide for Establ isnment of Data Bases in Surface

Spectroscopies

34
An E-42 round robin to compare depth-profile measurements of 1

1

B in Si

by secondary-ion mass spectroscopy is being concluded. The study was designed to allow participants to compare the accuracy of analysis,

background signal levels, detection limits, and artifacts of their

instruments and metnods. Eacn participant received three implanted

specimens, a standard implanted to a peak concentration of 2.0x102 0

atoms/ cm3 and two other specimens implanted with different, but

unreportea, concentrations of •B. Each participant was asked to

determine the concentration of 1

1

B in the two unknown specimens. The

results determined by 12 participants using 6 different instrument types

showed very good agreement. One specimen implanted to 5. 0x102 °atoms/cm3

was determined to have a peak concentration of 4.9x102° ± 0.3*102 ° atoms/ cm3; ana the other specimen implanted to 3.0x10^ atoms/ cm3 was determined to have 3. 4x10^ ± 0.6x10'

9

atoms/ cm3. These and other results

including values for the dynamic range, detection limit, and sputtering

yield of Si for each instrument type will be tabulated in a paper being

prepared for publication.

The Committee has prepared a booklet of E-42 surface analysis

standards which is about to be published by ASTM. It is believed that

many users of surface-analysis equipment will find the booklet to be a convenient compilation of terminology, guides, and recommended practices.

Tne booklet will be updated roughly every two years and should be an effective means of disseminating E-42 standards. Arrangements have also

been concluded during the year by which E-4^ standards will be repubxished

in the journal "Surface and Interface Analysis" on a timely basis.

The Committee arranges a half-day symposium at the annual Pittsburgh

Conference on Analytical Chemistry and Applied Spectroscopy in the spring.

The Committee had also been active througn 1985 in arranging sessions at

the National Symposium of the American Vacuum Society in the fall but this

responsibii lty will now be taken by the newly formed Applied Surface

Science Division of the AVS. The E-42 Committee arranges evening

workshops at these meetings to discuss common measurement problems. The

topic at the 1985 AVS Symposium was "Analysis of Buried Solid-Solid

Interf aces"

.

2. Surface Chemical Analysis forking Party of the Versailles

Project on Advanced Materials and Standards (VAMAS)

(C. J. Powell)

The "Versailles Agreement" arose from a meeting of the Heads of

State or Government (Economic Summit) of industrialized nations at

Versailles in 1982. The participants represented Canada, the Federal

Republic of Germany, France, Italy, Japan, the United Kingdom, the United

States of America, and the Commission of the European Communities (CEC). A

Summit Working Group on Technology, Growth, and Employment was established

consisting of government science advisers. This group established

international committees in eighteen areas such as photovoltaic solar energy,

f ooa technology, advanced robotics, biotechnology, high speed trains,

remote sensing from space, and advanced materials and standards.

35
The Versailles Project on Advanced Materials and Standards (VAMAS)

consists of a Steering Committee with representatives from the seven nations above and the CEC. VAMAS supports international trade through

projects aimed at providing the technical basis for drafting Codes of

Practice and Specifications in Advanced Materials. The scope of the

collaboration embraces all agreed aspects of enabling science and

technology— data bases, test methods, design methods, materials

technology—which are required as a precursor to the drafting of standards

in advanced materials. VAMAS activity emphasizes collaboration on prestandards measurement research, intercomparison of test results, and

consolidation of existing views on priorities for standardization action.

Through this activity, VAMAS fosters the develpment of internationally

acceptable standards for advanced materials by the various existing

standards agencies.

The overview of VAMAS and the otner international committees was concluded recently at the Tokyo meeting of Heads of State. VAMAS will,

however, continue as an independent international collaboration tnrougn a VAMAS Memorandum of Understanding now being signed by the founding

governments

The Surface Chemical Analysis (SCA; Working Party of VAMAS is one of

twelve such groups that have been approved to date. The main objective of

the SCA working party is to produce, by coordinated effort, tne reference

procedures, data, and materials necessary to estaolish standards for

surface chemical analysis. This effort is expected to lead to the

international coordination of standards-related activities before national

standards are adopted and to the development of standards on an international level.

The SCA Working Party was approved by the VAMAS Steering Committee in

June, 1 96-4 . National representatives to the SCA Working Party nave Deen

appointed with C. J. Powell as Chairman for a three-year period. Tne most

urgent needs for surface analysis pertain to the use of Auger^-electron

spectroscopy (AES), x-ray photoelectron spectroscopy (XPS; , secondary- ion mass spectroscopy (SIMS) and sputter-depth profiling (SDP). As projects

in these areas become estabiisned and as other techniques come into

greater use, it is expected that the project will broaden. The general

requirements are as follows:

o an agreed based of principles, definitions of terms, and

equations to relate the techniques and procedures to the

measurement;

o reference procedures specifying how to measure intensities and

spectral features;

o reference procedures, reference data, and reference materials

for calibrating instruments, determining instruments functions,

ano inter-relating instruments of different designs;

36
0 reference data of elemental sensitivity factors, matrix terms,

information depths, libraries of chemical-state spectra,

information on ion- sputtering rates, radiation damage, etc.;

and

o standard methods of specifying an analysis.

Details of standard needs for AES, XPS, SIMS, and SDP have been

identified.

Suitable inf restructures have been developed in most VAMAS states for

the SCA project. In the U.S., the ASTM Committee E-42 on Surface Analysis

has agreed to participate ana cooperate in VAMAS SCA projects. Standards

already developed by the E-M2 Committee will be disseminated to the other

VAMAS states; standards developed later in the other states will be

considered for adoption by the E-42 Committee. Suitable projects at KBS

and other U.S. laboratories also contribute to the VAMAS SCA activity.

The first meeting of the SCA working Party national representatives

tooK place in October, 19db during a conference in The Netherlands. Three

international projects were approved at that time and tneir current status

is as follows:

o Development of thin oxide films as reference materials. Work is

nearing completion between laboratories in the UK, France,

Canada, and Belgium to define the accuracies of different

methods for determining the atomic thickness of a tantalum

pentoxida on tantalum material developed earlier in the UK. The

material is available with two oxiae thicknesses ana will be

useful as standards for calibrating ion-beam fiuxes in

sputtering experiments and in high-energy ion-beam reaction and

scattering experiments.

o Development of calibration data for the energy scales of

Auger-electron spectrometers. Traceable calibrations have been

established in the UK for Cu, Ag, and Au Auger peaks with an accuracy of ± 0.02 eV. Similar but independent measurements are nearing completion in the USA (at NBS)

.

o Procedures for quantitative x-ray photoelectron spectroscopy.

Test materials prepared in Canada and Germany have been

identified as candidates for a proposed round robin to give

information on measurements of film thickness and film

stoichiometry. A round robin will be designed following test

measurements in the USA.

A number of additional international projects have recently been

proposed and are currently under review by the national representatives.

These projects are listed below together with the countries expected to be

interested in participation.

o Correction Methods for Backscattenng in Auger-Electron

Spectroscopy (FRG, France, Italy, Japan, UK, USA)

37
0 Measurement of Spatial Resolution in Auger-Electron Spectroscopy

(Canada, France, UK, USA)

0 Tests of Algorithms ana Software for Data Processing (Canada,

FRG, France, Italy, Japan, UK, USA, CEC)

0 Tests of Channeling Effects in Auger-Electron Spectroscopy

(Canada, FRG, France, UK, USA, CEC)

0 Reference Data for Electron Attenuation Lengths and Inelastic

Mean Free Paths (UK, USA)

0 Development of Reference Materials Prepared by Ion Implantation

(FRG, Italy, UK); this project could be carried out in

collaboration with IUPAC Working Group on Surface Analysis

0 Development of Reference Materials for the Measurement of Depth

Resolution in Depth-Prof ixe Analysis (Canaaa , FRG, UK, USA)

0 Development of Methods for Instrument Alignment and Calibration

(Canada, France, Italy, Japan, UK, USA)

0 Development of Reference Materials for the Surface Analysis of

Polymers (Italy, USA)

0 Reference Data for Ion Sputtering Rates in Oxides (FRG, UK,

USA)

0 Intercomparison to Assess the Reproducibility of Preferential

Sputtering in Surface Analysis (UK, CEC)

0 Intercomparison to Assess tne ReproduciDii ity of Auger-Electron

Energy and Intensity Measurements (UK, CEC)

0 Multi technique Characterization of Vacancies in Alumina

(France

0 Evaluation of Sensitivity Factors for Seconaary-I on Mass

Spectroscopy (Canada, UK, USA)

It is expected that some of these topics will be initiated following

discussion at a meeting of the national representatives scheduled for

London on November 17, 1986.

The organization of the SCA Working Party has stimulated the

initiation of new national activities related to and supportive of the

Working Party objectives. Information on these activities is exchanged

twice a year and it is anticipated that a number of these will lead

naturally to new multilateral activities. Some examples of projects of

tms type are:

38
o Development of a standard data transfer format. Initial work

has been done in the UK and a draft should be ready for Working

Party consideration shortly.

o Calibration of the intensity scale of Auger-electron

spectrometers. Methodology is under development in the UK (with

CEC support) and it is expected that interlaboratory tests will

be conducted in member states next year.

o Development of reference materials by ion implantation. Some

research materials have been prepared in the UK and there is

interest in calibrating these and other implanted materials in

FRG and other countries.

The VAMAS SCA Working Party has aroused a considerable amount of

interest and enthusiasm in many of the VAMAS states. Many scientists

believe that VAMAS has already provided and will continue to provide a considerable stimulus to the development of standards for surface chemical

analysis in each state. Furthermore, through cooperation via VAMAS,

national standards will be developed more efficiently and, it is hoped,

without conflicts. The specific areas where international cooperation

through VAMAS will be most effective are believed to be: (1) the

development of data banks and preferred data formats; (2) the development

of reference materials; (3) the development of documentary standards for

instrument operation and calibration; ana (4) tne development of

recommended procedures for data acquisition, data reduction, and

expression of final results.

3. Workshops on Quantitative Surface Analysis

(C.J. Powell)

Two Workshops on Quantitative Surface Analysis will be held in

tne autumn of 1966. Tne first Workshop will be held at NBS on October 24

and is co-sponSored by the ASTM Committee E-4a on Surface Analysis, the

Surface Chemical Analysis (SCA) Working Party of the Versailles Project on Advanced Materials and Standards' (VAMAS), the Appliea Surface Science

Division of the American Vacuum Society, and NBS (Surface Science

Division, Office of Stanaara Reference Data, and Office of Standard

Reference Materials). The second workshop will be held at the National

Pnysical Laboratory (NPL) in London on November 17 and is co-sponsored by

NPL and the VAMAS SCA Working Party. Each workshop will precede a major

international meeting and wiil have discussions on reference data,

reference materials, reference procedures, and instrument calibration in

surface analysis. In a workshop format with ample time for auaience

participation, it is hoped that recent advances in these areas will become

better known, important problem areas ana possible solutions will be

identified, and opportunities for new national and international (VAMAS)

projects will become apparent.

39
ASTM Committee D-32 on Catalysts

(R. A. Haines and R. D. Kelley)

Tne activities of tne ASTM Committee D-32 on Catalysts are concerned with the physical ana chemical properties of commercial

catalysts and with developing suitable proceaures for catalytic activity

measurements. The membership of the Committee numbers approximately 130

representatives of the major producers and users of catalysts including a significant international component. The technical activities are carried

out in four sub-committees: Physical/Chemical Properties which has 6 task

groups; Physical/Mechanical Properties - 6 task groups; Chemical Analysis

- 2 task groups; Catalytic Properties - 5 task groups. In general, the

work of the Committee has moved into areas that involve complex and often

controversial measurements. Examples of these are the measurement of

catalyst acidity, of the sensitivity of cracking catalysts to metallic

impurities, ana of multi-element chemical analysis by atomic absorption.

The Subcommittee on Chemical Analysis is chaired by R. D. Kelley.

The precious metals task group continues to be involved with the Standard

Test Method for platinum in reforming catalysts which has been submitted

for a Main Committee baliot—tne final seep in establishing a stanoara.

This platinum standard has involved eleven draft proceaures, many

round-robin analyses and about ten years of effort. An analytical metnod

for palladium—Standard Test Method for Palladium in Molecular Sieve

Catalysts—nas also been submitted for Main Committee ballot. Tne

palladium procedure is interesting in that it has involved two negative

votes on the suocommittee level and at least, one on the Main Committee

ballot. All of these negative votes are concerned with the fact that

commercial contracts call for greater accuracy tnan nas been possible in

the several round-robin tests conducted with the participation of a large

number of companies. This issue wiii continue to enliven future task

group meetings. The base metals task group is proceding with the

development of a satisfactory test method for determining several base

metals by optical atomic spectroscopy.

The Office of Standard Reference Materials (OSRM) is finalizing an agreement witn ASTM Committee D -32 to distribute catalyst reference

materials. R. A. Haines serves as a liaison between the two groups. Tne

Committee has preservea the catalysts, catalyst carriers and feed stocks

used in their rouna robins. The iyoo-iy87 SRM catalog already lists three

high-surface-area powders for which the Committee has extensive round

robin data using a static BET technique. Material is at NBS awaiting

packaging which has been characterized for particle-size distribution and

reactivity via gas-oil conversion microactivity tests. A series of

zeolites is also available for which diffraction intensity, unit cell

dimensions and zeoxite areas have been determined. Otner materials tor

which the Committee has data include supported metal catalysts (metal

content) and formea catalysts (crush strength). Demand for these

materials, once available, will be used as a guide for NBS catalyst

standards work.

AO
3. SURFACE MEASUREMENTS PROGRAM

D. R. Burgess, Jr., R. R. Cavanagn, H.-H. Chen, N. E. Erickson,

J.W. Gadzuk, T. J. Jach, A. L. Johnson, R. D. Kelley, R. L. Kurtz,

' C. V. S. Larsson, T. E. Madey, J. M. Nicol, C. J. Powell,

D. E. Ramaker, N. D. Shinn, R. Stockbauer and P. D. Szuromi

A. Reaction Kinetics at High Pressures over Single-Crystal Catalysts

(P.D. Szuromi, R. D. Kelley, and T. E. Madey)

The overall objective of this research has been to provide a molecular understanding of heterogeneous catalytic chemistry on well-characterized single-crystal surfaces. Among the areas studied are

the catalytic synthesis of hydrocarbons from carbon monoxide and hydrogen

on metal surfaces, the mechanism of catalytic poisoning and promotion, and

the reforming of alkanes over model supported Pt catalysts. The apparatus

employed for these studies contains high-pressure reactors contiguous to

ultrahigh vacuum surface analysis chambers. This work is supportea, in

part, by the Office of Basic Energy Sciences of the Department of Energy.

Progress during the last year included studies of the hydrogenation

activity of single-crystal W catalysts, as well as the poisoning effect of

adsorbed sulfur and oxygen on the W substrates. A surprising result

involved the poisoning of W by S. In contrast to the poisoning of Ni by

S, where a long-range interaction was observed, there is an apparent short

range effect of S on W(110). Details are given below.

1. Sulfur Inhibition of Methanation Over W ( 1 1 0

)

Sulfur inhibition of methanation (CO + 3H2

-* CH4 + H2O) over an active W(110) catalyst has been studied. Reaction rates were measured for

realistic conditions (P = 100 Torr, H

2 /C0 = 100, 600-750K), while sulfur

coverages (fa s

) ana carbon and oxygen coverages on the working catalyst

were determined by Auger-electron spectroscopy (AES). This work

demonstrated that: (1) E

a is not changed by sulfur; (2) For 6 S a 0.22

(approximately saturation of the S p(ax2) structure), the rate decreases

fourfola, and at higher 6 S decreases slowly by site blocking; (3) Sulfur

has almost no effect on postreaction carbon (a 0.3 ML), but oxygen

coverages decrease from a 0.4 ML at b s

= 0 to a 0.0b ML at b s« 0.4; (4)

Below 6 S a 0.07 inhibition is strong (a 40J at 6 S

= 0.05) and the effect

appears long-range, but at higher t> s it is weaker and the effect appears

short-range. In contrast, earlier work in this laboratory showed that

long-range effects dominate for all 0 £ for methanation over Ni. Model

thermal desorption studies of the decrease in saturation coverages of g-CO

and H

2 at 90 K due to sulfur show good agreement with decreases in the

methanation rate for e s

> 0.22, but below this 8 S the coverages drop

linearly, as for a short-range effect. However, addition of coadsorbed

oxygen (0.05-0.10 ML, the average oxygen coverage in excess of carbon for

the working catalyst at these values of 6„) causea 0-CO and H^ coverages

to decrease in the same way as the methanation rate, i.e., negative

deviations from linearity. Long-range effects of sulfur* are seen when

41
oxygen disrupts sulfur clustering. Thus deactivation of methanation by

sulfur over W(110) is interpreted in terms of oxygen-induced changes in

sulfur cluster formation.

2. Effect of Oxygen on Methanation Over Tungsten

Experiments were performed in which oxygen was added

delioerately to the H

2 +CO reactant mixture in trace quantities (10“^ to

10 -1 Torr at total pressures of 100 Torr). Addition of 1CT2 Torr of

oxygen caused the disappearance of methanation activity even at 700 K.

Auger analysis after reaction demonstrated that surface oxidation had

taken place. This resembles the inactvity of classical tungsten catalysts

toward methanation, which is due to difficulties in fully reducing the

tungsten. The inactivity of the oxidized surface in these studies also

shows that the reactor has a low blank activity.

3. Modifications to the Experimental System

Modifications to the sample manipulator used for the

near-ambient pressure studies have been completed that will allow

low-energy electron diffraction and thermal desorption spectrometry to be

used in conjunction with existing capabilities for Auger and ultraviolet

photoemission spectroscopies. This manipulator is currently being

installed and tested. Also, an x-ray source has become available for our use that will add the capability for x-ray photoelectron spectroscopy

(XPS)

During next year, we will expand the scope of our program to

different types of reactions (aehydrogenation and partial oxidation) and

catalysts (transition metal oxides grown over metals). Sucn reactions and

catalysts are of interest currently for synthesis of important chemical

intermediates. Our overall goal remains the same - to understand more clearly fundamental processes in heterogeneous catalysis by: (1)

preparing catalysts with well-definea surfaces; (2) studying reaction

kinetics under realistic conditions of pressure and temperature; ana (3)

employing ultra-high vacuum surface science techniques for in situ

characterization of working catalysts.

Initially, the studies will focus on reactions over copper-based

catalysts, for several reasons. Several classes of reactions are catalyzed by copper-based catalysts, so a number of avenues are possible,

including rections over metallic copper, copper oxides, and mixed-metal

oxide catalysts (examples include methanol synthesis from syngas over copper-zinc oxide catalysts and from methane over copper-molybdenum

oxide). In addition, many surface science studies have been conaucted for

the adsorption of organic molecules on copper surfaces. This body of work

will be employed in interpreting our results.

These studies will proceed in two phases. The initial work (during

the next year) will focus on the dehydrogenation of methanol to methyl

formate over copper. The second phase will concentrate on partial oxidation reactions over cuprous oxide, in this case acrolein synthesis from

propylene. Methyl formate syntnesis occurs cataly ticaliy over copper

42
2 CH

3 OH -> CHjO-C^jj + 2 H2

.

Methyl formate has the potential of becoming an important chemical

intermediate based on C-j methanol. Metallic copper is unique in producing

both methyl formate and valuable hydrogen using only methanol as a feed.

(The other heterogeneous route to methyl formate from methanol involves

oxidation and produces water rather than hydrogen as the byproduct.) The

Arrhenius and pressure dependence of this reaction over copper will be

determined over as wide a range of conditions as possible. The effect of

surface geometry on the reaction will be determined by using a Cu(100)

crystal in both its well-annealed (cubic close-packed) and sputtered

(amorphous) forms, and, for comparison, polycrystalline samples. In

addition, the effects of promoters, such as alkali metal oxides, and of

inhibitors, which include acidic oxides such as those of Mo and W, will be

investigated. The availability of AES and XPS allows the correlation of

changes in kinetics with the coverages of such surface modifiers.

Finally, as time and resources permit, other avenues will be

explores , including hydrdogenation and hyarogenolysis reactions over model

thin-film catalysts (fractional monolayers of metal deposited on crystalline metal or oxide substrates).

B. Molecular Structure and Reactivity on Surfaces as Studied Using

ESDIAD AND HREELS

(T. E. Madey, A. L. Johnson, N. D. Shiqn, and C. U. S. Larsson)

A continuing challenge in surface science is to determine the

structures of molecules on surfaces, particularly in the absence of longrange order. The goals of this project are to provide a direct

determination of the structures of adsorbed molecules using the Electron

Stimulated Desorption Ion Angular Distribution (ESDIAD) method, and to

characterize the structures and reactivity of surface species using HighResolution Electron Energy Loss Spectroscopy (HREELS). These techniques,

both singly and in combination, are powerful tools for surface structural

characterization.

The thrusts of this project during the last year were (a) to

determine the influence of surface additives (e.g., catalyst promoters and

poisons) on the local structure and reactivity of small molecules (CO,

NH

3

, H2 0) on surfaces, (b) to determine the structures of those molecules

on initially-clean surfaces, particularly in controversial cases, and (c)

to develop a digital imaging ESDIAD system to improve the measurements of

surface molecular structure. This work has been supported, in part, by

the Office of Basic Energy Sciences of the Department of Energy.

During the last year, progress has been made in the following areas:

1. Structure of CO on Surfaces of Catalytic Interest: Is it Standing

Up, Lying Down, or Inclined?

We nave useci ESDIAD in combination with HREELS ana other surface

spectroscopies to study the adsorption of CO on three transition-metal

43
surfaces. In each case, tnere were indications from our own measurements

(as well as from measurements made in other laboratories ) that the CO may

be strongly inclined or "lying down", rather than the more widely-reported

"standing up" configuration. In three cases, CO on Cr (110), CO on Fe(100)

and CO on K-dosed Ru(001 ) , it has been found using HREELS that the CO

stretching frequencies are abnormally low, in the frequency range 1150 to

1460 cm" 1

; these stretches are strongly down-shifted from the typical

frequency range (- 1800-2050 cm"

1 )- for CC adsorbed in a standing-up

fashion, bonded via the C atom. It has been proposed that the low CO

stretching modes are associated with strongly- inclined or lying-down

species coordinated to the substrate via both C and 0 atoms. We performed

ESD and ESDIAD studies in all three cases, and confirm that there is

little or no 0

+ or C0+ ion emission at any desorption angle from the CO

characterized by the low-frequency stretching modes. For CO on the clean

Cr (110) and Fed 00) surfaces, this is the expected result for strongly

inclined or lying-down CO, and confirms the structural assignments. For

CO + K on Ru(001), the influence of reneutralization effects on ion yields

is highly probable due to the CO-K interaction, and the configuration of

CO (standing up or lying down) remains controversial.

2. Evidence for Molecular 02(ads): Chemisorption of Oxygen on

Cr ( 1 1 0)

In most studies of oxygen interacting with transition metals, it

is reported that oxygen dissociates rapidly to form a monolayer of atomic

oxygen; subsequently, an oxide layer forms. We have found a strikingly

different behavior for the adsorption of oxygen on Cr(110) at 120 K. At

low coverages, dissociative oxygen adsorption dominates, while at higher

coverages, HREELS and ESDIAD data provide evidence for a co-existing

minority molecular Q0 state . An 02(ads) vibrational frequency of 1020 cm

-1 and a six-beam ESDIAD pattern are suggestive of super-oxo 0

2 (ads)

bonding at local sites, each with the 0-0 molecular axis tilted away from

the surface normal . Molecular 0

2 (ads) has been seen previously on less

reactive surfaces (Ag, Cu, Pt, Pd), but this is the first time that

02 (ads) has been reported on such a reactive surface having a high heat of

oxygen adsorption.

3. New Digital ESDIAD System

Up to the present time, all of our ESDIAD data have been

obtained by photographing the two-dimensional patterns displayed on a fluorescent screen. In order to permit more quantitative determination of

ion angular distributions, desorption angles (and, by inference, surface

bond angles), we have constructed a new digital imaging system based on a high-sensitivity video camera for detecting the ESDIAD images on the

fluorescent screen.

The digital imaging system is composed of a laboratory computer with

a hard disk, a color monitor, a video camera and hardware boards for vide<j

data acquisition and arithmetic processing. The hardware allows the

44
acquisition of live images or the digitization of photographs, the

formation of histograms and contour plots, digital image manipulation

(such as background subtraction, smoothing, and feature recognition/

enhancement/removal) , and plotting. We have demonstrated the ability to

do single-ion counting as well as image integration to form ESDj.AD

patterns. These abilities are crucial for allowing the ESD1AD pattern to

be quantified, and for when angle and time-resolved spectra (i.e.,

negative ion spectra) are acquired. Several digitized ESDIAD patterns

obtained using this system art shown in Fig. 3.1; these are described in

the following paragraphs.

H+ ESDIAD from OH on Si(100)

(a) 300 K A>) 140 K

• H Oo

o si

Fig. 3*1 H

+ ESDIAD and schematic model illustrating the bonding of OH to

a Si(100) surface. The data were obtained using the new digital

ESDIAD system. Column (a): H

+ ESDIAD (perspective and contour

plots) for T = 300K; column (b): H

+ ESDIAD at 140K. A

schematic bonding model in which H and OH are bound to both ends

of a Si(100) dimmer is shown below. The four H

+ beams resolved

in column (b) are due to ESD from degenerate dimer

configurations. The decrease in resolution of ESDIAD at 300K is

due to increased vibrational motion of the OH.

45
4 . Structure of H^O Adsorption on Planar and Stepped Surfaces of

Silicon

Despite the extensive interest in the surface chemistry of H

2

O,

there have been relatively few structural studies of H

2 o on surfaces

having high heats of M-0 bond formation where dissociation is likely to occur. We have recently applied the new digital imaging ESDIAD system to

the stuay of H

2 0 on surfaces of Si; this is the first ESDIAD study ever reported for adsorption on a semiconductor surface!'

The adsorption of water on the reconstructed planar (100)2x1 and

single domain-stepped (100) 2x1 (cut 5° towards (011)) surfaces of silicon

was studied using LEED and digital- imaging ESDIAD as a function of

temperature (160-650 K) and coverage. Water has been shown by Chabal and

Christman to chemisorb dissociatively to form surface OH groups. At 300K,

the H

+ ESDIAD pattern for the planar surface is a nearly symmetric halo

(see Fig. 3.1). indicating that OH is oriented with its bond vector

inclined away from the surface normal, while at low temperature (£200K) a four-lobed pattern preserving substrate symmetry is observed. This

reversible temperature dependence is related to librations and rotations

of the OH complexes. ESDIAD from the stepped surface exhibits two-fold

symmetry, with enhanced emission towards the steps, consistent witn

bonding of OH to single-domain terrace sites. An interpretation based on the dimer model of tne Si(1G0) reconstruction has been formulated.

Plans for next year are centered on three areas. First, a major new thrust is to develop the technology for measuring ESDIAD of negative 10ns , and to apply the new methodology to challenging problems in surface

chemistry of adsorbed molecules. There are several reasons for these

proposed experiments. First, ESDIAD of positive ions has proven so useful

in surface chemistry that we anticipate new structural information about

adsorbed molecules whose ion fragments include negative ions. Certain

classes of molecules (e.g. halogen-containing species) generate high

yields of atomic negative ions (F~, Cv,“) under electron bombardment.

Other candidates include H

- ano 0- from H

2 0, CU, etc. Second, these

studies will provide new insights into the basic mechanisms of ion

fragmentation ano the influence of surface parameters on ion traj ecton es , etc. In a few special cases, we expect to compare directly negative- and

positive-ion ESDIAD from the same surface species (e.g. H

+ and H from

NHo, H

2 0). Third, this is a new scientific and technical challenge. Such

measurements have never been made before, and there may be unanticipated

benefits; e.g., the tecnnology necessary for negative ion detection will

permit the first mass-resolved, two-dimensional ESDIAD measurements.

Test molecules for ESDIAD of negative ions include HF, F

2 , PF^ , the

completely fiuorinated analogue of acetone KCF^JgCQj, di ( tnfiuoromethyl

)

ether [ ( CF ^ )

2

» and fluorine-substituted pyridine. In all cases, we will combine kinetic measurements with measurements of local structure.

Strong repulsive interactions between the electron-rich

fluorine-containing portions of the adsoroed molecules may well lead to a

46
rich assortment of local structures. Of particular interest will be the

search for adsorbate/ substrate systems where ESDIAD of both positive and

negative ions can provide complementary structural information.

Second, we will continue our studies of the structure of small

molecules on clean metal surfaces, and the influence of surface additives

(such as catalyst promoters and poisons) on the structure and chemistry of

adsorbed molecules. Examples will include several controversial cases,

e.g., the structure of acetylene on Cu(100), and the effect of impurity 0

and Br on the structure and chemistry of H

2 O on Cu(110).

Finally, we will expand our effort in the surface chemistry of

electronic materials by applying ESDIAD to the study of semiconductor

surfaces, in particular, to characterize the surface structures formed on

Si surfaces during adsorption and reaction of small molecules. Despite

the technological importance of semiconductors in catalysis and

electronics, there have been no published studies of adsorbate structures

on semiconductors using ESDIAD.

We intend to cnaracterize the surface chemistry of atomically

stepped ana planar Si surfaces interacting with small moiecuxes (H2

o, H

2 02 , CH3 OH, NP13 , CH3 OH, HF, F2 ) of importance in semiconductor device

processing (wet oxidation, plasma etching, reactive ion etching, etc.).

A promising new area is the adsorption and decomposition of transition

metal carbonyls (Fe(CO)^, Cr(CO)£, etc.) on Si. A study of thermal

desorption, electron beam-induced desorption, ESDIAD and HREELS of

adsorbea carbonyls will provide valuable insights into the physics and

chemistry of metal deposition and silicide formation on Si surfaces.

C. Neutron Scattering Studies of Catalysts

(J. M. Nicol, R. R. Cavanagh, and R. D. Kelley)

Neutron scattering techniques applied to adsorbate systems on high-area catalytic surfaces are providing new insights into catalytic

science. NBS has played a lead role in this effort having a unique

combination of neutron physicists and surface chemists with an interest in

catalysis. During tne past year, work has focused on inelastic incoherent

neutron scattering (IINS) studies of the interaction of hydrogen with

palladium ana quasielastic scattering (QNS) studies of the ammonium ion in

zeolite rho. This work has been carried out at the NBS research reactor

with support, in part, from the Chemical Sciences Division of the Office

of Basic Energy Sciences, Department of Energy.

1. Adsorbate Dynamics in Zeolites

Quasieleastic neutron scattering has been used to characterize

the diffusive motions of NH^ in zeolite rho. This work reflects a collaborataive effort between the Surface Science Division (R. R. Cavanagh

and J. M. Nicol) and the Reactor Radiation Division (T. J. Udovic and J.

J. Rush) at NBS, and E. I. DuPont de Nemours (D. R. Corbin), W. R. Grace

(M. J. Wax), ana the University of California at Santa Barbara (G. D.

47
Stucky). By measuring the influence of neutron momentum transfer on the

elastic incoherent structure factor (EISF), it has been possible to

determine the reorientational motions of the ammonium. We have been able

to demonstrate that the NH^* groups undergo essentially three-fold

reorientational motions. However, the fourth (and "anchoring") proton

periodically changes roles with one of the rotating protons. Figure 3.2

Momentum Transfer (A-1

)

Fig. 3.2 Elastic incoherent structure factor as a function of neutron

momentum transfer (Q) between 1 ana 4 A

-1

. The points

correspond to data taken at the NBS reactor on NHi4

+ in zeolite

rho. Three models of the reorientational motion are indicated:

Fixed three-fold (120° rotations about a single fixed 3 _ fold

axis), random three- fold (120° rotations at random about all

four 3~fold axes), and 90° (90° rotation about a two-fold axis

with each proton sampling four different positions).

shows the data recorded at the NBS reactor along with the predictions of

three different reorientational models (120° rotation about a single fixed

3~fold axis, 120° rotations at random about all four 3-fold axes, and

rotation about a two-fold axis). Two points should be made regarding

these data. Tne value of Q where the minimum in the EISF is observed

provides a measure of the applicability of any model to the observed

data. * Clearly, one of tne models preaicts a Qmin value (-3 A-1

) wmch is

inconsistent with the aata (2.3 A

-1

). The seconc point is related to tht

48
depth of the modulation in the EISF. Since deammoniation of the NH^/rho

generates the protonated form of the zeolite (H-rho), there will be a non-zero contribution to the EISF at all Q from the H-rho in the specimen.

Thus, the observation of a deeper minimum in the EISF than predicted by an anchorea 3-fold rotor (despite the intensity contributed from H-rho)

clearly establishes the random 120° model as the best model for the

reorientational motion.

The activation energy for this mode has also been estimated from the

temperature dependence of the Lorentzian component of the quasielastic

scattering signal. An exceptionally low activation energy (-20 meV) is

obtained. This barrier is comparable to the lowest observed activation

energies for NH^ + in molecular solids, and represents the first direct

measurement of such dynamics in zeolites.

Futher work is in progress to examine the reammoniation of zeolite

H-rho, starting with an ammonia loading equivalent to one NH^ + ion per unit

cell. In addition to characterizing the diffusive motions of the NH^ + ions by quasi-elastic scattering, vibrational spectroscopy of the ammonium

modes in the 5 to 20 meV range is being investigated by inelastic neutron

scattering. By collecting data over the temperature range 4 to 300 K, a more

detailed picture of site geometries and bonding interactions wili be

obtained

2. Interaction of Hydrogen with Palladium

IINS is being used to characterize the adsorption and absorption

of hydrogen by small particles of palladium (Pd black), with particular

emphasis on the identification of subsurface hydrogen. This work is a collaborative effort between the Surface Science Division (J. M. Nicoi,

R. D. Kelley, and T. E. Madey) and the Reactor Radiation Division (J. J.

Rush). The data indicate that bulk tf-hydride forms readily following high

doses of hydrogen at temperatures as low as 77 K. At lower hydrogen

doses, spectral features have been associated with vibrational modes of

both surface and subsurface hydrogen. The subsurface species appears to

be associated with a vibrational mode at ca. 56 meV, consistent with

hydrogen bonded in octahedral sites in the Pd lattice. Evidence for the

subsurface hyardogen is the broad lineshape which is quite distinct from

the more narrow linewidth of the S-hydride, and the reactivity with

chemisorbed oxygen (measured in oxygen-titration experiments).

Experiments are underway to generate and characterize a hydrogen-free Pd sample and to examine the dynamics of the

surface-subsurface equilibrium. Force-constant calculations and other

experimental work is being undertaken to try to establish site geometries

for the H-Pd system.

In the next year, in addition to the continuing work with zeolites

and with palladium black, we will prepare a Raney nickel sample using

u Ni. The low incoherent cross-section of this isotope makes the

substrate nearly invisible and provides an unusual opportunity to study

the structure ana dynamics of an adsorbed hydrogeneous species in great

detail

49
D. Surface Characterization Using Synchrotron Radiation

(R. Stockbauer, R. L. Kurtz, N. D. Shinn, H.-H. Chen,

D. E. Ramaker , ana T. E. Madey)

Major goals of this effort are (a) to determine the electronic

structure of surfaces and adsorbates using variable-wavelength synchrotron

radiation and ultraviolet photoelectron spectroscopy (UPS), and (b) to

identify the electronic excitations which result in the photon-stimulated

desorption (PSD) of ions form molecules adsorbed on surfaces as well as from condensed molecular films. When possible, PSD ion yields are correlated with UPS of both valence states and core-electronic states of

the surface species. These measurements provide tests of recent

theoretical models of electron- and photon-stimulated desorption, and

provide new insights into the bond-breaking processes induced by ionizing

radiation incident on surfaces. The work has been supported in part by

the Office of Naval Research.

Accompli snments during the past year were in six areas: (1)

electron- and photon-stimulated desorption on ions from oxide surfaces;

(2) electronic structure of molecules adsorbed on surfaces; (3)

instrumentation of a new beamline at the NBS synchrotron radiation

facility SURF -I I; (4) construction of a new display analyzer; (5) progress

at the Brookhaven National Synchrotron Light Source (NSLS); and (6) theory

of stimulated desorption.

1. Electron ana Photon-Stimulated Desorption of Ions from Oxide

Surfaces

Recent efforts in our laboratory to understand the mechanisms

involved in stimulated desorption have forced a re-evaluation of the

factors that influence surface stability under ionizing raoiation. Our

experimental results in desorption from different surfaces of Ti02 have

shown that the local surface atomic arrangements can be as important, in

determining ion desorption probability as the electronic structure. To

expand our efforts in further elucidating the fundamental processes

involved in aesorption induced by electronic transitions (DIET), we have

begun to study different materials and (using synchrotron radiation) to

probe deeper core levels.

During the past year, we pursued these two efforts on BL-l of the NBS

SURF-II synchrotron storage ring as well as at the Deutsches Electronen

Synchrotronen (DESY) in Hamburg by studying DIET from single-crystai

surfaces of MgO. At DESY we used the wiggler beam-line coupled to the

Flipper monochromator to measure ion emission from MgO with photon

energies spanning all of the electronic energy levels. Excitations

spanning the 0 Is level produced striking results.

These measurements are the first observation of a f undamentally new excitation producing desorption: core-exciton production whose

subsequent decay induces the desorption of 0 and H

+

. The H signa.

originates from surface contamination on the MgO from the ambient vacuum. We

found evidence for the contribution of several exci tonic states to the

50
desorption of Q

+ and the data show that these states are different from

those giving rise to H

+ desorption. Electron yield data from partially

oxidized Mg imply that these excitations are localized in the near-surface

region.

Core excitons consist of a bound conduction-electron/ core-hole pair

and, with a deep core-hole such as the 0 Is, are localized on a single

atomic site. The obvious signature of an excitonic state is the

observation of excitations that result from photon absorption at energies

below the binding energy. In the case of an insulator such as MgO, this

corresponds to absorption of a photon that places the photo-excited

electron at an energy in the bulk band-gap.

In Fig. 3-3 the 0

+ and H

+ ion yield curves are shown near the onset

in 0 Is excitation. The onset in 0 Is core excitation to unoccupied

Photon Energy (eV)

Fig. 3*3 0

+ and H

+ ion yields from MgO(IOO) versus incident photon

energy. The spectra are decomposed into the excitonic

desorption contribution given by the Gaussian peaks. When the

Gaussians, given by the dashed curves, are subtracted from the

spectrum, the dotted curve is obtained.

51
conduction band states in the bulk is indicated by the shaded bar.

Clearly, the excitation producing 0

+ desorption at 531.0 eV involves

photon energies that place the photoelectron in the 7.8 eV bulk band-gap,

an excitonic state. When the ion yield curves are compared with

fluorescence and electron energy-loss (ELS) measurements, one finds

structure essentially identical to that for photon energies above 535 eV

in Fig. 3 . 3 * Using the usual dipole-selection rules, we therefore

identify the two Gaussian peaks in the Q

+ desorption as 1s^2s^2p^3p^ and

1s 1 2s 2 2p 6 4p 1 excitons and the feature in the H

+ desorption at 532.9 eV as due to a 1s 1 2s 2 2p^3p 1 exciton of 0H“. The observation of H

+ desorption at

the 0 Is level is not surprising since hydrogen is stable on MgO surfaces

in the form of QH“ radicals.

In the decay of these excitonic excitations, the excited electron is

less likely to be a participant (which would result in a 1h final state)

than it is to remain as a spectator to the decay. A 2hle state will

result from the 1s 1 2s 2 2p 6 3p 1

1 s

2 2s 2 2p 4 3p 1 decay. Since the radial

extent of the 3p wavefunction is large, incomplete screening of the 0 core

by the 3p electron will produce a state that is nonbonding and will

influence the stability of the 0 on the surface. Should the 3p electron

escape (and this is assisted by the loss of the exciton binding energy

after the Auger decay), the 0

+ will clearly be in a repulsive surface

Madelung potential.

We plan to continue these studies of ion desorption by expanding our recent work on MgO and T i02 to include studies of other isostructural

oxide surfaces with varying electronic configurations. An example of

such a comparison would be that of Ti02 (001) and Ti^OodO^). We will

also begin work on partially-oxidized transition-metal surfaces. These

surfaces will allow the application of standard synchrotron radiation

techniques tnat are often unsuccessful when applied to insulating oxides.

2. Electronic Structure of Molecules Adsorbed on Surfaces:

Relation to Geometric Structure

Synchrotron ultraviolet photoemission studies of carbon monoxide

chemisorption on Cr(llO) at 90 K confirm the sequential population of two

structurally different molecular binding states. The first state (a-,C0)

consists of molecules with both the carbon and oxygen atoms coordinated to

the chromium surface; a previously proposed model locates these molecules

in the two-fold symmetric surface hollow sites with the intramolecular

axis aligned roughly along the LlTO] direction. The measured photon

energy dependence and limited angular dependence of the ct-| CO photoemission

peak intensities strongly support this model and are consistent with the

proposed local binding site. Only after this binding mode saturates at

1/4 monolayer does the ot2 CO binding state appear. For this latter state,

the CO molecules are terminally bound to the surface with the C-0 axis

aligned approximately along the [110] surface normal. A comparison ot spectral differences for a-j CO and c^CO reveals previously unseen

binding-mode-dependent effects in the adsorbed CO electronic structure,

52
highlighted by an increase in the CO 4 a orbital binding energy for the

lying-down state. These data have been related to previously reported

vibrational and stimulated desorption results for Cr(110)/C0.

In parallel experiments in our SURF -II apparatus, electron-stimulated

desorption (ESD) experiments using a time-of-flight pulse-counting method

were performed for molecular CO chemisorbed on the Cr (110) surface at 80

K. Consistent with previous qualitative observati ons ,' negligible C0+ and

0

+ desorption signals were measured from the o-|CO overlayer which

saturates at 1/4 monolayer. For 6 C0 > 0.25, a terminally-bonded (c^CO)

binding mode is populated in addition to the existing a.|C0 binding mode

and the ion yield sharply increases. For a2C0, both 0

+ -and C0+ ions are observed; the C0+ ions desorb with characteristically lower kinetic

energies than 0

+ ions. Near saturation coverages of CO (ads), an observed

decrease in the 0

+ yield is attributed to adsorbate-adsorbate interactions

which reduce the ion desorption probability, as seen in ESD studies of

terminaiiy-bondea CO on other metals. These results have been considered

in the context of two possible models proposed for the u-j CO binding state,

and related ESD observations for CO chemisorbed on potassium-promoted

Ru(001 ) and Fe(001 )

3. New Laminar Grating Installed at SURF

A laminar-profile toroidal-grating monochromator has been

installed on our dedicated beamline at the NBS SURF-11 synchrotron storage

ring. This grating is expected to reduce significantly the vexing problem

of higher-oraer contributions to the diffracted light and yet result in

good transmission over the 20-100 eV range. Instead of the usual

ruled-grating profile, the grooves in this grating have been ion-etched to

produce a square-wave profile. The groove-depth has been produced so that

destructive interference occurs between the top and bottom faces for all

the even orders. Measurements of the relative contributions of all orders

through 4th order is presently underway; however preliminary results show

significant attenuation of 2nd and 4th order light.

PSD data as well as total secondary-electron emission to which the

PSD data are compared are adversely affected by this higher-order

radiation. In both experiments, the signals from the dif f erent-order

radiation are indistinguishable which necessitates removal of the

higher-order contribution. By reducing the higher-order radiation from

the monochromator , these corrections become smaller allowing us to examine

weaker PSD signals and to determine thresholds more accurately.

4. Construction of Angle-Resolving Display Analyzer

A new ellipsoidal-mirror angle- resolving electron- and

ion-energy analyzer has been assembled and is undergoing initial testing.

This outstanding instrument was designed and constructed at NBS (based on

an instrument constructed at IBM by D. Eastman). It is ideally suited for

angle-resolved PSD, and will be the on.i.y such analyzer in North America

used for these measurements. Details and scientific plans are given in

section 4.B.3.

53
5. Resonant Photoemission from Cu Measured at Brookhaven NSLS

During our run this spring at the Brookhaven National

Synchrotron Lignt Source, we were able to make measurements of resonant

photoemission from sputtered Cu(100) over the photon energy range spanning

the Cu 3p excitation onsets. Photoemission measurements reveal two

distinct 3d shake-up satellites at 12 to 14.6 eV apparent binding energy.

Interference between these satellites and the Auger decay channels that

open up when the photon energy exceeds the 3p excitation onset produce

resonances in the satellite intensity. There are two resonant energies

(75.5 and 78.5 eV) that correpond to resonances with excitations from

3p-|/2 and 3 P 3/2 states. The two distinct satellites are believed to arise

from the multi pi et splitting of the Cu 3d 8 configuration. These

experiments demonstrate the versatility of the NBS-NRL X24C beam-line with

the extended energy range and good resolution of the grating/ crystal

monochromator

We also attempted during this run to measure electron attenuation

lengths in condensed molecular solids. This work is described in section

2. A. 5(b)

6. Theory of Stimulated Desorption

Our work during the last year has addressed an important issue

related to the pnoton-stimulated desorption (PSD) of ions from surfaces.

What are the relative roles of direct photoexcitation and indirect

excitation via secondary electrons in PSD ion yields? The question of the

magnitude of indirect, secondary-electron processes in PSD is an extremely important one. If the ion yield is dominated by such indirect

effects, the utility of PSD for the determination of surface structure is

severely limited.

Recent reports on the magnitude of secondary-electron contributions

in electron/ photon-stimulated desorption (ESD/PSD) appear to be

contradictory, it has been reported that secondary electrons provide the

dominant contnoution to the H

+ yield from NH^/Ni at energies above the N Is core excitation and this process is called X-ray-induced ESD (XESD).

Others nave concluded that the XESD process is the dominant mechanism in

the PSD of N

+ and 0

+ ions from mixed condensed gases such as N

2 and 02 and

in the PSD of H

+ ions from OH/YbO-Sm. On the other hand, large

differences are often found between the secondary-electron yield and the

PSD ion yield (e.g., 0

+ from O/Cr and 0/W, H

+ from OH/Ti and Cr, and H*

from H/diamond) providing strong evidence for the dominance of a direct

photon-excitation mechanism. The total absence of ion yield contributions

at certain core levels (e.g., the 0

+ yields from NG/Pt(110) and

CQ/Ru(0001) reveal no structure at the N, Ru , or Pt core levels) also

indicates that the XESD process is not dominant. Finalxy, a semi quantitative determination of the secondary-electron contribution to

the ESD OH yield from 0H/Ti02, where large contributions are expected,

indicates that backscattered electrons are responsible for only about 3C*

of the OH desorption.

54
In this work, we have re-examined the three systems mentioned above,

in which dominant XESD effects have been postulated. ESD ion angular

distribution (ESDIAD) data on the NH^/Ni system and a detailed

determination of the mechanisms involved in H

+ desorption indicated that

all of the features attributed to the XESD effect may, in effect, arise

from direct core-level processes. A re-examination of the PSD N

+ and 0+ yields from condensed N

2 and O2 reveals that the indirect XESD mechanism

contributes just one-third of the N

+ yield, but dominates the 0

+ yield.

This arises because the direct Auger-stimulated desorption (ASD) process

following core-hole excitation is inactive for 0

+ desorption, but remains

active for the N

+

. This differences is believed to arise because of 2ir*

electron transfer in condensed 0

2 (i.e., electron hopping between

neighboring 0

2 molecules); the 2tt* band is, of course, empty in condensed

N

2 . Finally, a detailed interpretation of H

+ desorption from OH/Ti and

Cr, and comparison with the system OH/YbO-Sm indicate that the direct ASD

process is also inactive in the latter 'case. Thus we snow for these three

systems that either alternate interpretations of the data are possible,

indicating that the XESD effect is small, or that the XESD process

dominates only because the direct mechanism is suppressed. This makes the

results on these three systems consistent with the significantly larger

number of papers which indicate that the XESD effect is generally not a major problem.

Plans for the next year include an examination of recent PSD data for

MgO (section 3 • D . 1 ) . The G

+ and H+ ion yields spectra reveal large

exci tonic-like features which are not completely understood. Detailed

interpretation of these data may also provide information about the role

of secondary electrons and the XESD effect in ionic insulators. The

extent of these effects in the alkali halides, e.g., LiF and NaCl, has

been somewhat controversial. The MgO system is an excellent model system

for such studies, since it is more suable than the alkali halides and the

electronic processes appear to be simpler. A theoretical examination of

the PSD ion yields from condensed and chemisorbed hydrocarbons , ano an examination of hydrogen bonding effects, may also be attempted as the data

become available.

E. Dynamical Effects Associated with Core-Levei Ionization

(T. J. Jach)

The NBS Quantum Metrology Group under the direction of Dr. R. D. Deslattes has developed a program to study the electronic effects

associated with core-level ionization in atoms, molecules and at surfaces.

Specific effects which are being studied include dynamical effects in

inner-shell vacancy production, relaxation of the extra-atomic

environment, and production of multiple vacancies, with or without

ionization. One member of the Surface Science Division Staff has been

working half-time on this project.

For the past four years, this team has designed and built the X-24A

Beamline at the National Synchrotron Light Source (Brookhaven National

Laboratory). During 1966, the beamline, wnich is optimized for soft x-ray

production in the energy range 800-2000 eV, finished its first full year

55
of operation. The X-24A soft x-ray beamline at Brookhaven has been

functioning extremely well, producing the highest flux in the world

O4X10 11 photons/ sec) with an energy resolution of 0.4 eV.

The first round of experiments has been on gas targets, both

monatomic and polyatomic; the model systems we are studying will shed

light on solids we intend to study in the future. Argon is the "hydrogen

atom" of multi-electron atoms since its one-electron excited states are the

easiest to calculate using Hartree-Fock-type procedures. Theorists are therefore actively interested in experiments at this level.

An experimental chamber has been built in which the gas is confined

to a cell with thin beryllium windows transparent to x-rays entering at

the energy range of current interest (about 3 keV) as well as to

fluorescent x-rays produced by radiative decays. The emitted x-rays are analyzed by a highly efficient spectrometer consisting of a crystal bent

along a Rowland circle and a position-sensitive proportional counter.

This state-of-the-art combination allows whole line spectra to be taken

simul taneously

.

The NSLS x-ray ring is due to shut down for 6-8 months starting in

December, 1986 for extensive modifications. As a result, we have

concentrated on taking tne maximum amount of data, witn next year to be

devoted to interpretation of the results and preparation of reports. The

following experiments have been performed during the past year.

1 . X-ray Raman Threshold Behavior Near the A r K-edge

It is possible to induce fluorescence from the Ar Ku (2p-1s) and

KB ( 3 P~ Is) transitions at incident energies which are too low to excite

the Is electron into the lowest empty bound state. This is accomplisned

by a Raman process in which an electron is promoted from a virtual state near the Is state which is then filled by radiative decay of a 2p or 3p

state. Using a high- intensity monochromatic x-ray beam ana a high-resolution crystal spectrometer, we have been able to directly excite

such transitions and measure the amplitudes for fluorescent decay from

these states. Theoretical calculations have existed for some time for

these amplitudes, but the difficulty in observing the effect wi tn

statistically significant count rates has made them difficult to evaluate.

We have already obtained data of sufficient quality to allow us to

separate out resonant and non-resonant Raman contributions

2. Energy Dependence of Shake-up Satellites in the Ar Ka and Kt* Lines

The adsorption spectrum of argon (and of more complicated

molecules) contains a number of features only resolvable with a higniy

monochromatic beam above the threshold K-edge. These features are attributed to excitations of one core and one or more valence electrons

which are excited by a shakeup process. Similarly, there are satellite

lines observed at energies above the fluorescent emission of Ku or Kr radiation which show an energy dependence near threshold. Because of tne

high resolution of our monocnromator and spectrometer , we havt beer. id.

56
to obtain extensive data on the threshold at which these satellites turn

on and relate them to specific features in the absorption spectrum. This

was possible because of the excellent energy stability of our monochromator over long periods of time. The data allow us to

discriminate between various theoretical assignments which nave been made

for the quantum numbers of the absorption and satellite features.

3. Relative Coherent Elastic and Resonant Elastic X-ray Cross

Sections at the Ar K-edge

We have measured the x-rays elastically scattered from argon

atoms at energies all through the K-edge, with sensitivity to their

polarization. This allows us to separate out the resonant and coherent

components and determine cross-sections for each. We hope that this work

will be accurate enough to produce absolute cross sections.

4. The Chlorine Fluorescence Spectrum as a Function of Bonding in

Multi-atomic (Freon) Molecules

As a start on more complicated molecular spectra, we have

observed the K fluorescence lines from chlorine atoms in freon. The

chlorine atom is only one electron removed from argon, and can be present

as one, two, or three neighboring atoms in freon. This system is

therefore appropriate to study the effects of bonding.

5. Photoemission Spectrum of Ar Near the K Edge

In addition to studying the x-ray fluorescence spectra of gases

and soiids, we need to examine their non-raoiative decays and their

photoemission spectra. This is important in studies such as of covalent

bonding and of post-col± isional interactions of the outgoing particles.

We are extending the work we have done with gas targets in cells to

windowiess gas-jet targets. As a step in this direction, we have taken

preliminary data with a differentially pumped gas cell connected to a hemispherical electron analyzer. We have measured the photoemission

spectrum from argon and hope to extend these measurements in the coming

year

.

The above experiments were performed in collaboration with Drs. P. Cowan, S. Brennan, and R. LaVilla of the NBS Quantum Metrology Group. Tne

chlorine fluorescence experiment was a collaboration with Dr. Perera of

Lawrence Berkeley Laboratory and the photoemission experiment was a collaboration with Dr. S. Banna of Vanderbilt University.

F. Development of Silicon Diode Radiation Detectors for Synchrotron

Radiation Research

(T. Jach)

Scientists using x-rays from synchrotron radiation light sources

have been traditionally conservative in selecting detection schemes such

as gas ion enambers, scintillation counters, film, or Si (Li) detectors.

We have developed a new technology over the past four years in which

silicon PIN photodiodes, both as-is and with special modifications, have

57
been employed as radiation detectors in experiments. These diodes are manufactured as detectors of radiation, but in fact they are excellent

detectors of x-rays over an energy range of 500 eV to 20 keV. Their

efficiencies exceed those of ion chambers by an order of magnitude and

they offer additional advantages of small size, compatability with

ultra-high vacuum systems, and lack of a need for power supplies.

Two experiments were performed during the past year on the Naval

Research Laboratory Beamline X-23B. These experiments are part of a continuing (and unique) effort to provide data for synchrotron users on the characteristics of silicon PIN diodes in the x-ray region. As a result of our previous publications, three of the beamlines which use double- crystal monochromators at NSLS now use diode feedback loops which

offer much- improved performance. The following measurements have been made

recently

1. Spectral and Spatial Response of Various PIN Photodiodes from

2-7 keV

We have improved upon our earlier measurements by determining

the spectral sensitivity and spatial resolution of several commercially

available PIN diodes. These measurements were made at the output of a beamline using x-ray mirror optics and a double-crystal x-ray

monochromator . The system offerea a wider energy range than the tube

source used in the previous measurements and allowed us to eliminate

corrections for the harmonic and fluorescence contributions which were potential sources of error.

2. Harmonic Rejection in Feedback Loops for Double-crystal

Monochromators

Diffraction and EXAFS (extended x-ray absorption fine structure)

measurements, among others, are subject to errors due to the fact that

crystal monochromators reflect x-rays not only at the fundamentax Bragg

condition but at higher-order harmonics. One way of eliminating this

error is to overlap the rocking curves of the two crystals in the

monochromator in such a way as to pass the radiation of the first-order

Bragg reflection but not higher orders. This scheme has never been

successfully incorporated into the AC feedback loop circuitry which is the

best way of electromechanicaliy maintaining the two crystals at the Bragg

condition while the energy is scanned. Using PIN diode detectors of

differing sensitivity, we have demonstrated a means of solving this

problem in a most satisfactory manner. It permits the AC feedback loop to

be maintained on the side of the rocking curve in a way which

discriminates against the harmonic component to any degree that is

arbitrarily selected. The method allows scanning the monochromator

through an energy range of 1 keV or more and should prove superior to the

DC method which has been used up to this time.

This work was performed in collaboration with Dr, J. Kirkland of NHL

and Dr. P. Wolf of Virginia Polytechnic Institute and State University.

58
G. Production and Characterization of Ultrasmooth Surfaces

(T. J. Jach)

Previous surface science experiments have indicated a neea for

surfaces which are extremely flat and smooth on an atomic scale. An

example of this need is the desire to study photoemission from a metallic

thin film at grazing incidence to obtain maximum surface sensitivity.

There are also obvious reasons for wanting to make smooth detect-free

substrates and thin film such as in the semiconductor industry where

device widths of 100 A are being approached. We have initiated an effort

to (a) characterize substrates and thin films for roughness down to a scale of 3 A; and (b) push the limit of surface smoothness attainable to

1 0 A or better for a variety of materials.

Studies are progressing on interpreting gold thin-film deposition on amorphous glass surfaces, as observed by scanning reflection electron

microscopy. A wide body of previously unconnected data on the

reflectivity, surface roughness, resistivity, etc. of thin films of gold

(and other metals) appears to be related to surface growth of

microcrystals during deposition. We have observed new whisker growth

modes which occur because diffusion kinetics are limited to certain

crystal faces by substrate temperature. These results, based on electron

microscopy data taken last year, are presently being prepared for

publication. This work is being done in collaboration with Dr. L.

Holdeman of Comsat and Dr. G. Hembree of the NBS Precision Engineering

Division

H. Electron Spectroscopy of Surfaces

(C. J. Powell, N. E. Erickson and D. E. Ramaker)

A number of electron- spectroscopic techniques are in widespread use for the determination of surface composition, surface vibrational modes,

ana surface electronic structure. Techniques such as Auger-electron

spectroscopy, x-ray pnotoelectron spectroscopy, and electron energy-loss

spectroscopy are useful but the observed spectral lineshapes are often

complex. These lineshapes reflect the many processes often involved when

electron beams interact with surfaces and wnen electronic excitations

occur. The factors influencing observed lineshapes need to be understood

in order that the spectroscopic techniques can be fully utilized and, in

particular, so that quantitative intensity measurements can be made (e.g.,

for quantitative surface analysis).

As part of a project to measure the L^-shell binding energies of 3d

transition metals by different spectroscopic techniques (see section

2. A. 4), we have made a detailed examination of the appearance-potential

spectra (APS) of six 3d metals. We measured the so-called Auger-electron

APS in which electrons of variable energy bombard the target material and

a measurement is made of the derivative of the target current as a function of electron energy in the vicinity of the core-level BEs. Our

APS data for Ti, V, Cr, Fe, Co, and Ni are similar to those reported

previously but we have established our electron energy scare with greater

accuracy and made a more extensive analysis of the data.

59
In order to determine an APS BE, it is necessary to compare a measured spectrum with one calculated from a model. In the past, APS data

have been interpreted in terms of a simple one-electron model in which

both the excited core electron and the incident electron have final states

near the Fermi level of the target. According to this model, a self-convolution is made of the empty density of states (DOS), obtained

from published calculations, and this is convolved with a Lorentizian

function to represent core-hole lifetime broadening. A derivative is then

taken for comparison with experiment. While this model has long been

known to be oversimplified, it has been employed successfully for a number

of materials including some 3d metals. We found that this approach gave

satisfactory results for the APS data of Co and Ni but there were significant inconsistencies for Ti and V and inconsistencies of a lesser

degree for Cr and Fe.

We have interpreted the inconsistencies between measured and

calculated APS data in terms of a new Initial-State, Final-State rule in

which intensities reflect the initial state, lineshapes reflect the final

one-electron DOS in the presence of the core hole, and multiplets reflect

electron coupling for tne lighter elements of the transition series ana hole coupling for the heavier elements. The DOS in the presence of the core hole has been modelled using an expression due to Cini which has been

found useful in analogous studies of Auger-electron lineshapes. The

modified DOS is given by:

N(E)

UiUU ' " ^ Cl-UI(E)]2 + [UttN(E)]2

wnere N(E) is the DOS from the literature for each metal, 1(E) is the

Hilbert transform of N(E), and U is the effective core-hole,

valence-electron attractive energy. Figure 3-^ shows our AP spectrum for

vanadium at the bottom and a series of calculated spectra based on

N m0d( E ) for various values of U . As U is increased, the calculated curves become closer in agreement with experiment; although the measured

spectrum does not show two clear peaks, there is a weak shoulder at 515

eV. Similar results have been obtained for Ti. Better agreement between

experiment and calculation could be obtained by adding more broadening in

the calculated spectra (which could be ascribed to the lifetime of the

excited two-electron state).

In addition to obtaining better agreement between measured and

calculated AP spectra, the initial-state, final-state rule enables

satisfactory resolution of apparently contradictory results obtained in

the analysis of APS, x-ray absorption spectra (XAS) , and electron

energy-loss spectra (EELS). Briefly, small values of U are appropriate

for the dipole excitations in XAS and in EELS at high incident electron

energies, but larger values of U are appropriate for the non-dipole fina^

states excited in APS and in EELS at near- threshold incident electron

energies

60
ENERGY (eV)

Fig. 3*^ Comparison of measured (bottom) and calculated Lo-shell

appearance-potential spectra for vanadium. The top curve (U=0) was calculated with the empty density of states and the other

curves with modifications to the density of states due to the

core hole. The parameter U is the effective core-hole,

valence-electron attractive energy. The calculated spectra were plottea using an Lo-shell binding energy measured by x-ray

photoelectron spectroscopy.

We plan to test our model further by examining APS and EELS data of

other' types of metals.

I. Laser Diagnostics of Surface Dynamics

(D. R. Burgess, Jr. and R. R. Cavanagh)

The pathways and rates of energy transfer at surfaces remain the key

unresolved issues for understanding chemical reactions at interfaces.

Such information has eluded experiments which rely on conventional

surface-characterization technique. A variety of laser-based techniques,

however , have recently demonstrated their utility in probing such

molecular dynamics in both the gaseous and liquid states. This program

utilizes both the temporal and spectra characteri sties available in

61
state-of-the-art lasers. Strong collaborations with Drs. M. P. Casassa, E.

J. Heilweil, D. S. King and J. C. Stephenson of the NBS Molecular

Spectroscopy Division play a vital role in these efforts.

1. Laser-Excited Fluorescence as a Probe of Adsorbate Interactions

During Thermal Desorption

Characterization of the mechanisms involved in energy transfer

between an adsorbate and a substrate stands as the primary objective of

this work. Measurements are made of the translational, rotational and

vibrational energy content of desorbed molecules. These population

distributions provide an indication of the interaction potentials which are involved in different desorption processes. By measuring the

state-specific populations which result from elementary surface processes,

it is anticipated that the fundamental steps which influence a variety of

surface reactions can be examined.

We have recently completed a series of measurements of co-adsorDed NO

ana NHg thermally desorbed from Pt(111). The co-adsorption system was known to exhibit a strong NO-NH^ interaction from earlier EELS and TPD

measur ements . The formation of an NO-NH^ complex had been suggested by the

previous studies. Our measurements of the rotational-state distributions

by laser-excited fluorescence (LEF) of the thermally desorbed NO indicate

that, aespite the concerted desorption of both NH^ and NO, strong

adsorbate interactions are not manifested in the rotational-state

distribution. The desorbed NO was found to exhibit a Boltzmann

distribution with a rotational temperature 95* of the surface temperature.

2. Laser-Induced Desorption

The nature of tne surface processes which can be inauced by

laser heating has been the subject of recent experiments on a polycrystail ine platinum foil. In these experiments, NO was adsorbed on the substrate at 200 K and a laser (532 nm, 3 ns FWHM) was used to inauce

a temperature jump of 100 K. The NO liberatea by this heating processes

was aetected by a second laser using LEF. Approximately 10“ monolayers

were desorbed within the illuminated region of the sample on every heating

pulse. By varying the time delay between the heating pulse and tne

probing (LEF) pulse, a time-of- flight distribution could be measured for

individual rovibronic levels. Tuning the wavelength of the LEF probe

laser then provided a measure of the population in different rotational

states of the desorbed NO.

These measurements have revealed several unexpected results. TOF

distributions observed for two experiments, where the only variable is the

rotational state probed by the LEF laser, illustrate the observed trends.

The TOF data for NO with J = 19.5 are characterized by a prompt signal for

a time delay between the heating ana probe pulses of 0.5 us. This result

is in contrast to the TOF data for NO with J = 3*5 where the peak position

is shiftea to a time delay of about 8 ms. The data have been fitted to

the sum of two (non-Maxwell-Boltzraann ) velocity distributions. Our

results inaicate:

62
o For all rotational states, there is a slow component with a mean

kinetic energy of 300 K.

o The rotational temperature for these slow species is = 170 K.

o The mean kinetic energy of the fast component is a function of

rotational state, ranging between 1400 K for J =3-5 and 2650 K

for J = 19.5.

o The population in v = 1 is dominated by fast NO molecules, and

corresponds to a vibrational temperature of = 900 K and a rotational

temperature of approximately 155 K.

These results indicate that it may not be possible to account for the

molecular processes induced by = 5 nsec laser-heating pulses by simple

thermal heating models. Atom-atom recombination , precursors, transient

electron-hole pairs, and exit-channel effects are all consistent with our present data. Still, it should be possible to clarify the source of the

two velocity components in future experiments. For instance, in the

coming year we anticipate exploring the influence of the laser-heating

pulse duration, the sensitivity to surface structure, the influence of

co-adsorbates, the role of the heating laser wavelength, and the extent of

correlation with surface cleanliness. Initial experiments on P t ( 1 1 1 ) are

currently in progress as well as work using a laser wavelength of 1.06 yin

to heat the platinum foil. In addition, further work is anticipated which

will permit direct measurement of the peak temperature jump inducea by the

heating pulse. This work is supported in part by the Department of

Energy

3. Time-Resoived Measurements of Vibrational Energy Transfer

Direct characterization of the time scales and mechanisms for

relaxation and dephasing of vibrational excitation in adsorbed layers is

the aim of this work. Such measurements can provide a quantitative

understanding of a substrate’s ability to quench the energy released upon

chemisorption, reaction, or irradiation.

Two new picosecond sources have been developed for probing

vibrational relaxation at surface. Both sources are capable of generating

picosecond infrared pulses in the frequency range between 1700 and = 4000

cm" 1

. One system produces pulses of 30 psec duration with energies near

20 yJ . The second system produces shorter pulses (3 ps) , but with reduced

energy (3 yJ) . The extension to ionger wavelengths offered by these

systems opens the opportunity to study a range of new surface-related

problems

Planned experiments will use pump-probe techniques to generate

excited-state populations at surfaces and follow the subsequent time

evolution of the excited species. Transmission measurements (on

high-surface-area model catalyst systems) and reflection measurements (on

single- crystal substrates) are anticipated. However, the reduced energy

available in tnis spectra range (compared to the 300 yJ available at 3 ym) , requires a more sensitive detection method tnan hao been employee

63
previously. Not only is the total energy per laser shot reduced, but the

transmission (or reflection) transient induced by the laser is expected to

be diminished. The first point has required the development of ratiometer

techniques based on photoconductive and photovoltaic detectors. The

second factor dictated that we improve our ability to measure

reflectivities of individual laser shots to better than 1$. This

performance must be achieved under conditions where the total energy in

sequential shots can fluctuate by a factor of two. We are new able to

reproducibly measure changes in transmitted light at the level of 3 parts

in 1C)3 S and anticipate that we will shortly acquire the ability to measure

such reflectivities to a few parts in 10^.

Preliminary measurements have now been made on model compounds

[Cr(C0)^ f Rh(C0)H(triphenyphosphine)3, and Rh(C0)Cl(triphenyphosphine)2]

in preparation for probing the vibrational relaxation rate of CO bound to

supported metal particles. The relaxation of the CO (v = 1 ) stretch mode

was characterized using 5 pJ pulses with InSb detectors to monitor the

relative sample transmission. These preliminary results indicate that the

CO (v = 1 ) relaxation time in the hexacarbonyl is significantly longer

than that found for 0H/Si02. In the monocarbonyls, however, the

relaxation times are significantly shorter. The applicability of these

techniques for adsorbates on supported metal particles will be explored in

the coming year. This work is supported in part by the Air Force Office

of Scientific Research.

J. Theory of Dynamical Molecular Processes at Surfaces

(J. W. Gadzuk)

This project is part of a continuing effort directed to understanding

both the static and dynamic behavior of atoms, molecules, solids,

surfaces, radiation and their mutual interactions. This understanding

comes from consideration of the microscopic atomic-scale properties of

individual entities as well as from largei—scale statistical properties of

ensembles. Based upon our studies, phenomenological model theories are constructed which relate to the chemical physics and statistical

mechanical behavior and to the intrinsic properties of relevant

physico-chemical systems. In addition, a significant effort is invested

in the study of the role of an actual measurement process in determining

observed quantities in different surface spectroscopies. Ways in which

measurement-process-specific quantities such as line shapes, satellite

structures, etc. provide additional information on system dynamics are of

considerable interest.

Work has remained focused on the role of excited electronic states

and intra-molecular vibrational degrees of freedom in reactive surface

dynamics. In these situations, energy must be directed in order to break

bonds or be extracted to stabilize highly vibrationally excited species

formed for instance at curve crossings where electronic rearrangement

takes place. There has been significant progress in several different

directions in the application of an analytic model describing the dynaar :s of a diatomic molecular beam incident upon a surface and in which

charge-transf er/curve-crossing events takes place. This has been carried

64
out in parallel with numerical trajectory studies over realistic

potential-energy surfaces (PES) in order to assess the reliability of the

easily-used analytic models.

An extensive study has been carried out on the vibrational

excitation/dissociacive adsorption/dissociative scattering of heavy

diatomic molecules such as I 2 incident upon metal surfaces. Classical

trajectories for the molecule-surface collision have been calculated as a function of incident energy and for various values of the parameters

characterizing the PES. A series of examples illustrating the various

outcomes are shown in Fig. 3*5 for incident I 2 oriented parallel to the

surface. Here z is the molecule-surface separation and p is the

intra-molecular stretch coordinate. The low-energy events shown in Figs.

3.5(a) and (b), result in dissociative adsorption. Increasing the energy,

as in Fig. 3.5(c) leads to resonance-assisted vibrational excitation.

Finally, for energies > 1 eV, simple in-out scattering with substantial

translational to vibrational (T-*V) conversion occurs. Calculated values

of the energy transfer from translation to vibration versus incident

energy, treating the desorption energy parametrically, are shown in Fig.

3.6(a). Results obtained from our analytic modelling are shown in Fig.

3.6(b). It is apparent that for energies greater than - 1 eV where in-out

trajectories occur, the analytic models provide reasonable representations

of reality. This is encouraging and has provided stimulus for new

modeling of more complex phenomena in surface chemical dynamics.

One such example is our recent theory on controlling chemical

selectivity of reactivity in polyatomic molecule-surface collisions

involving the formation of temporary negative-molecular ions due to

molecule-surface charge transfer. As a final example, we have considered

selectivity in the scattering of a prototypical polyatomic, say ABC, from

a surface in which several outgoing channels are possible.

Selectivity is possible if an excited electronic state (negative molecular

ion) is used to assist chemistry on the ground electronic state. Creation

of a temporary negative ion whose geometry differs from the ground-state

neutral permits molecular-ion distortion into configurations which favor

one or the other of the outgoing channels when the ion is neutralized.

Over the past two years, we have developed theory which shows how the

lifetime of such temporary negative ions formed in surface collisions can

be easily controlled. Selectivity is achieved by chosing an ion lifetime

commensurate with the intermediate-state distortion which leads to the

desired outgoing channel (reaction products). Thin exciting prospect has

been demonstrated within the context of classical trajectory modeling.

AB + C

A + B + C

(ABC

)

65
-O.S 0.0 O.S 1.0 l.S 2.0 2.S 3.0 RHO (ANGSTROMS)

(®)

o

RHO (ANGSTROMS)

(C)

"O.S 0.0 O.S 1.0 l.S 2.0 2.5 3.0 RHO (ANGSTROMS)

Cb)

-0.5 0.0 O.S 1.0 1.5 2.0 2.5 3.0 RHO (ANGSTROMS)

<d)

Fig . 3*5 Potential energy surface contours for an iodine molecule

incident upon a physical surface in which dissociative adsorption

is possible. The z axis is the molecule-surface separation and

the p-axis is the intra-molecular stretch coordinate. A progression of trajectories for increasing incident translations!

energy is shown. Figures 3.5(a) and 3.5(b) show dissociative

adsorption, Fig. 3.5(c) shows resonance-assisted T -V conversion,

and Fig. 3.5(d) the basic in-out benavior leading to substantiaT-»-V conversion.

66
0.0 2.0 4.0 6-0

INCIDENT ENERGY (EV)

Ca)

a

(b)

Fig. 3*6 (a) T+V conversion vs. incident I 2 translational energy,

obtained from trajectory calculations, treating desorption

energy parametrically , as labeled, (b) Ratio of AtT

_> v to

(T r,o V efficiency) versus incident I 2 energy,

obtained from the analytic modeling of Fig. 3*5.

67
Theory has been worked out for a number of other new molecular-beam

experiments, which will be carried out in laboratories, other than NBS,

which have beam facilities. Amongst the proposals include scattering of

oriented atoms or molecules in which the orientation is achieved by

initial preparation of electronically excited states. These experiments

should be very useful in providing new information on charge-transfer

dynamics. Another proposal has been put forth for the design of neutral

molecular beams with kinetic energies possibly up to 1 keV. This

development may permit a totally new class of beam scattering experiments

outside the extremely limited domain of beams prepared by the current

supersonic nozzle-expansion method.

Finally, vibrational lineshapes and spectra of adsorbed molecules have

been studied in terms of the quasi-periodic trajectories over a multi-dimensional PES. This is a prudent way to include the anharmonic

effects which lead to dynamically interesting lineshapes because one can "see" what the oscillator is doing to acquire the lineshape. The

lineshape or vibrational spectrum of an excited oscillator is

Km) = ^

im

—r <lj^T eiu>t dt i 2>

2 tt T-* 00 2T 0

where y(t) is the oscillator displacement as a function of time after

initial excitation. A particularly interesting situation exists when the

adsorbed molecule can migrate between inequivalent adsorption sites, as

in the bridge-3“fold site conversion seen for CO/P t (111). Questions arise

as to how the site conversion affects vibrational lineshapes, or turned

around, how one extracts information on site conversion and/or surface

diffusion from lineshapes. We have investigated this phenomenen in detail

by calculating spectroscopic trajectories and from them, lineshapes.

Relationships between the time scales for vibration, anharmonic "damping",

and site conversion have been established which enable one to use experimental information such as line widths and shapes to gain additional

insights on the surface PES.

We plan to continue work in the area of surface reaction dynamics

with near-term emphasis on the determination of self-consistent reaction

trajectories , realistic electron-hole pair coupling constants,

determination of energy-redistribution patterns amongst translational,

vibrational, rotational, and electronic degrees of freedom of "reactant"

molecules and electron and phonon modes of surfaces. Analyses are made

for controllable dynamic and reactive conditions with synthesis of the

various components of the elementary reaction theories into theories of

experimentally realizable processes. Special emphasis will be placed on the phenomenon of dissociative surface processes and on the role of

non-linear dynamics.

In addition, analysis will be made, whenever possible, of novel

experimental results. Current interest includes lasei

assisted surface

processes and state-to-state analysis, high-resolution surface vibrational

spectroscopy, and other experimental probes of non-adiabatic effects.

68
4. SURFACE COMPETENCE PROGRAM

W. F. Egelhoff, Jr., J. Fine, S. M. Girvin, M. J. DeWeert,

T. E. Madey, A. J. Melmed, D. A. Steigerwald, and R. Stockbauer

The Surface Competence Program is a part of the NBS "Competence

Program." The NBS program was introduced to provide long-term support of

the establishment and maintenance of areas of excellence in science and

technology contributing to the NBS mission and the projected needs of the

NBS clientele.

The Surface Competence Program was established October, 1984 with two

principal components, "Novel Two-Dimensional Materials" and "State

Characterization of Energetic Species Ejected from Surfaces". The

initiation of this program represents a new focus on these topics. The

principal objectives of each program component are described in the

following two main sections together with reports of individual projects.

A. Novel Two-Dimensional Materials

In recent years an increasing awareness has developed of the

important modifications in physical properties which occur in materials as they approach the ultra-thin two-dimensional limit. Some examples of

unusual behavior discovered in such systems include the enhanced catalytic

properties of a gold surface with two monolayers of platinum compared to

bulk platinum, superconductivity of a silver monolayer on germanium, the

quantum Hall effect, the enhanced magnetism in alternating monolayers of

iron and cobalt, the electrical properties of metal-semiconductor junctions

(Schottky barriers), and multiple quantum-well systems for optical logic

devices. These examples suggest a whole new range of scientifically and

technically important chemical and physical properties waiting to be

explored in the two-dimensional regime. Concepts and methods developed in

surface and interface science have been particularly valuable in many

areas of application, and it is believed that these concepts and methods

can be further developed and extended to two-dimensional systems with

component thicknesses from one to one hundred atomic layers.

There exist major gaps in current understanding of the fundamental

principles which govern the chemical and physical properties of layered

structures in the two-dimensional limit. In this component of the program,

it is planned to synthesize and determine the fundamental chemical and

physical properties of ultrathin layered materials with layers so thin

(a few atoms thickness) that they exhibit two-dimensional behavior.

Knowledge of the factors influencing the growth and properties of

ultrathin layered systems is expected to allow optimization of desired

chemical and physical characteristics and will thus benefit a number of

scientific fields ranging from catalysis to novel semiconductor devices.

We are performing work in three project areas. First, we are planning to develop tne techniques neeaed to synthesize, by alternating

monolayer deposition, a new class of materials: non-equilbnum ordered

alloys. The structural properties of these materials as grown ana during

69
thermal processing will be investigated by x-ray and electron diffraction.

The chemical reactivity, catalytic activities, and magnetic properties of

these materials will also be investigated. Second, we plan to determine

the microstructure and microcomposition of candidate layered structures by

atom-probe and field-ion microscopy methods with emphasis on the interface

region. These techniques provide composition and structure data with

near-atomic spatial resolution. Finally, we are applying modern many-body

theoretical techniques to the study of the quantum Hall effect, magnetism

and other electronic properties of layered structures and thin films.

1. Surface and Interface Chemical Physics of Ultrathin Films

(W. F. Egelhoff, Jr., and D. A. Steigerwald)

Interest in ultrathin metal films (down to the two-dimensional

limit of one atomic layer) on the part of the surface-science community

has greatly increased in the past several years as it has become clear

than an understanding of such structures will contribute to solving a wide

range of problems in surface science. Among these are an understanding of

the differences between surface and bulk electronic structure, the changes

of surface electronic structure associated with chemisorption, the basis

of surface magnetism, the modification of surface-layer properties by the

substrate, the relationship between electronic structure and epitaxial

growth, and the surface properties of alloys. The experimental program

presently underway is using an integrated approach to study single-crystal

surfaces, alloys and ultrathin films to contribute to an understanding of

all of the above problems.

We have recently developed and applied a technique termed the

’'searchlight effect" in which enhanced electron intensities in x-ray

photoelectron spectroscopy (XPS) and Auger-electron spectroscopy (AES) occur along nearest-neighbor and next-nearest-neighbor axes of single

crystals. The searchlight effect is a powerful probe of the short-range

order in the near-surface region and is well suited to studies of

epitaxial growth, surface segregation, and interdiffusion.

During the past year, the searchlight effect has been applied to the

investigation of various surface morphological phenomena as wexl as studied in its own right to determine how it can be applied with maximum

benefit. Progress has been made in the following areas.

o Epitaxial films and sandwich structures of Au and Ag on Ni(100)

were studied and found to have cubic short-range order by XPS but

hexagonal long-range order by low-energy electron diffraction

(LEED). This combination of results implies a very unusual

surface reconstruction.

o The rate of Cu surface segregation in Ni-Cu-Ni sandwich structure! was investigated as a function of depth of the copper layer. One

such structure is illustrated in Fig. 2.4. It was found that

different segregation mechanisms operate at different depths of

the Cu monolayer.

70
o The effect of surface contamination on epitaxy was investigated.

It was found that, for up to 0.5 monolayers (ML) of carbon or oxygen contamination on Ni(100), the epitaxy of Cu or Ni at 300 K was hardly inhibited. While the top atomic layer was quite

disordered (LEED data), the searchlight effect indicated that the

deeper layers were well ordered. The carbon and oxygen diffuse

rapidly to remain at the growing surface. Even at substrate

temperatures of 100 K, many layers of overgrowth (>>10 ML) are required to, in effect, bury the carbon and oxygen.

'

o A search was made for a theoretically predicted surface-melting

phase transition using the searchlight effect [in this case on

Hg (111)] but none was found to occur.

o The temperature dependence of the diffusion of a Ni monolayer into

a Cu(1 00) substrate was investigated. This interdiffusion begins

around 350 K and is essentially completed by 450 K.

o The effects of multiple scattering on the searchlight effect have

been examined. It was found, as predicted theoretically by Tong

et £1., that the first two or three scattering events enhance the

intensity along interatomic axes but that further scattering

events break up the searchlignt beams. Figure 2.4(a) shows that

the peak at 45° is strong for a 4 ML Ni over layer but vanishes for

a 10 ML Ni overlayer. The peak at 0° shows a lesser weakening

effect at 10 ML Ni since there are fewer Ni atoms along this axis,

as shown in Fig. 2.4(b)

o It was found that multiple scattering events tend to sharpen the

searchlight-effect peaks. The peak at 45° in Fig. 2.4(a) is

considerably narrower for a 4 ML Ni overlayer than for a 1 ML Ni

overlayer

Much of the experimental work of the past year has been conducted to

develop the techniques needed for the next major effort to be undertaken.

This will be the synthesis of a new class of materials, non-equilibrium

ordered alloys, by epitaxial growth of alternating metal monolayers. This

work has the potential for opening up a new area of materials science.

The XPS searchlight effect is a near-perfect tool for diagnosing, in real

time, any growth processes that interfere with the desired synthesis and

should thus aid greatly in recognizing and overcoming barriers. We

anticipate the capability of producing novel material properties by

tailor-making the lattice structure. Later, we expect to characterize the

materials with x-ray diffraction and electron microscopy and to study

their chemical reactivity, catalytic activity, and magnetic properties.

During the past year, much effort has gone into upgrading the

instrumentation in preparation for the synthesis of the ordered alloys.

Changes have been made in the electron optics and in the computer control

of the XPS system to improve its operating characteristics. Conversion of

the detector system from a single channeltron to a position-sensitive

detector is in progress. These changes will permit an increase in the

diagnostic power of the searchlight effect.

71
Another major effort of the past year has been the design,

construction, and testing of molecular-beam epitaxy ovens. These ovens

produce the stable metal flux that will be required for synthesis of

high-quality ordered alloys. The ovens are presently in the final testing

stages

The first alloys to be synthesized will be of the Cu-Fe system. No

ordered alloys of Cu and Fe have been produced by conventional metallurgy.

However, we believe that our approach of epitaxial growth combined with

the XPS searchlight effect (to guide our understanding of how growth

parameters affect morphology) will enable us to produce a variety of novel

structures. Among these are alternating monolayers of Fe and Cu,

monolayers of Fe separated by thicker Cu layers, and alternating bilayers,

trilayers, etc. We have a collaboration planned with a group at Simon

Frasier University in Canada to study the magnetic properties of these

novel materials and we expect to set up other collaborative investigations

of other physical properties in the near future.

2. Microcomposition and Microstructure of Thin Films

(A. J. Melmed)

This effort is directed to the measurement of microcoraposi Lion

in relation to microstructure of thin layers on well-characterized solid

substrates and the determination of interfacial diffusion. The methods of

investigation for these purposes are field-ion microscopy (FIM), capable

of qualitative atomic structural determination, and atom-probe analysis

for compositional depth-probing on an atomic scale. Both _in situ and ex situ specimen preparation will be used in order to vary widely the

layer-formation process parameters.

Further progress was made towards understanding the atomic structure

of the recently discovered icosahedral phase of rapidly solidified Al^Mn,

produced in thin ribbon form. Extensive analysis of FIM images obtained

last year indicated the presence of a hierachy of cluster or grain sizes

from about 1.3 to at least 8 nm in width, and two sizes of discrete

pentagonal arrays, each of five atoms. These features agree qualitatively

with recently proposed models which describe the structure in terms of an aggregation of small icosahedra (see Fig. 4.1). Furthermore, the

unusually irregular appearance of the FIM micrographs is explainable on the basis of such cluster models. Computer simulations of selected areas

of the FIM images, based on a cluster model and perf ormed by Dr. H. A. Fowler of the NBS Center for Applied Mathematics, exhibited good

qualitative agreement with the experimental images. Additional support

for the cluster type of structural model comes from some new transmission-electron-microscopy (TEM) results obtained in collaboration

with Dr. M. J. Kaufmann of the NBS Metallurgy Division. We have shown

that selected-area electron-diffraction patterns from the icosahedral

structure contain diffusely scattered intensity, as well as the weix-knowi.

sharp diffraction features; we have attributed this diffuse intensity to

scattering from atoms filling in the necessary small gaps between

72
clusters. Further low- temperature FIM is underway in an attempt to

provide a complete description of the atomic structure of the icosahedral

phase.

The composition of the icosahedral phase (i-phase) of rapidly

solidified Al^Mn was determined by our general-purpose atom probe FIM in

connection with the FIM structural investigation of this new material.

The composition of the i-phase was found to be approximately Al^Mn, in

agreement with recently published analytical TEM results.

*

Fig. 4.1 Two proposed cluster models of the icosahedral phase of Al^Mn.

Top: exploded views of the two icosahedral clusters. Middle:

top view of one coupling scheme for two icosahedra. ' Bottom:

another coupling scheme. Asterisks indicate Mn atoms and the

other symbols indicate A1 atoms.

73
In addition to microcomposi tional analyses of novel alloys, future

efforts will include depth-probing of various layered structures. These

will consist of thin film/ substrate combinations of metal/metal,'

metal/semiconductor and metal/glass. The aim will be to determine

composition profiles in the films, the interfaces and into the

substrates, using the unique analytic capabilities of the atom probe FIM.

Initially, specimen preparation for such studies will be done by vapor

deposition under well-characterized amoient conditions.

Epitaxial crystal growth of Cr on W and Cr on Re is being studied by

field-electron emission microscopy. In’ both systems, the nucleation and

growth, at temperatures sufficiently high to enable rapid surface

diffusion of Cr, proceeds as expected, with nucleation occurring at

surface steps after about a monolayer of Cr coverage (Stranski-Krastanov

growth mode). However, the lateral growth of Cr crystals is inhibited by

certain substrate geometries; crystal growth does not extend into (001)

planes of W, for example. In addition, a lower— temperature epitaxial

growth is found to occur on (001) W, where small 3“D crystals nucleate

directly on the clean surface ( Volmer—Weber growth mode).

Metal layer deposition on Si is being studied in collaboration with

Dr. W. A. Schmidt and Prof. J. H. Block at the Fritz Haber Institut, W.

Berlin. Thusfar, we have demonstrated that for thin layers ( ( 3

—J^ nm) of

Au, the method of field-ion appearance spectroscopy can be used to

determine the Schottky barrier height for Au/Si. We studied the field ion

energy distributions of inert gases (Kr and Ar) for Au-covered n- and

p-type S i ( 1 1 1 ) specimens. Thin layers of Au were vapor-deposi tea , with

the substrate at 78 K, such that diodes were formed and subsequent

electrical charging occurred through the bulk Si. The measured field

dependence of the ion distribution onset potential was used to calculate a barrier height of about 0.3 eV for the p-type Si, in good agreement with

the literature value of 0.34 eV. Similar measurements for n-type Si are presently being completed and the work is being extended to other metals.

The method is being considered as a possible route to f urther

understanding of the controversial nature of metai/semiconductor Fermilevel pinning.

The NBS Electrodeposi tion Group has been producing layered material

by controlled alternate deposition of Ni and Cu in layers intended to be

uniformly some 10-20 nm thick. There are several questions concerning the

resulting material which we have begun to address using FIM and atom-probe

methods. These are: (1) uniformity of the layer thickness, (2)

composition of the two types of layers, (3) defect densities in the layers,

and (4) coherence of layer interfaces. Thusfar, we have developed

specimen preparation techniques, done initial FIM studies to address

qualitatively points (1) and (4) above, and established feasibility of

doing atom probe analysis.

74
3. Theory of Novel Two-Dimensional Materials

(S. M. Girvin and M. J. DeWeert)

Recent progress in the fabrication of novel two-dimensional

materials has generated intense theoretical and experimental activity in

several areas of condensed matter physics. The present project is

addressing theoretical issues in three of these areas: artificial

semiconductor superlattices, thin metallic films, and a new field now

being referred to as ’meso-scale' physics. Each of these will be

discussed in turn below.

The quantum Hall effect is one of the most remarkable phenomena

discovered in recent years. It occurs in the two-dimensional electron gas

(inversion layer) which can be formed in artificially layered

semiconductor systems. One finds at high magnetic fields and low

temperatures that electron transport in the inversion layer becomes nearly

dissipationless and that the Hall conductance takes on universal quantized

values e

2 i/h where e is the fundamental charge, h is the PiancK constant:

and i is an integral or rational fractional quantum number. This

discovery has had profound implications for both fundamental physics and

electrical resistance metrology.

The theory project has in the recent past focused strongly on the

quantum Hall effect. In addition to providing support for the

experimental effort in the NBS Electricity Division, recent

accomplishments include development of a rather complete and quantitative

theory of the collective excitations in the fractional regime (done in

collaboration with Dr. A. H. MacDonald, National Research Council, Ottawa

and Dr. P. M. Platzman of AT&T Bell Laboratories , Murray Hill) and the

editing of a book giving the first major review of the field (done in

collaboration with Prof. R. E. Prange of the University of Maryland). The

latter is based on a ten-part lecture series which enjoyed a large

attendance from academic, governmental and industrial organizations in the

greater Washington area (see section 2. c. 3(a)).

Theoretical developments in the area of the fractional Hall effect

have proceeded rapidly and a general picture of how the effect arises from

Coulomb correlations is now in hand. The one remaining area which has

been poorly explored is that of the statistical mechanics at finite

temperatures and the question of whether the fractional state is reached

via a phase transition (and hence whether or not there is an order

parameter in the problem). Our work on the collective-excitation spectrum

showed that there exists a deep analogy between the fractional Hall effect

and superfluidity in helium films. This analogy has been pursued further

to develop a phenomenological Landau-Ginsburg theory describing the

statistical mechanics and which exhibits, in a natural way,

fractionally-charged quantized vortices. In collaboration with Dr. R. B.

Laughlin of Stanford University, this phenomenological theory is now being

given a microscopic justification.

Until the next generation of experiments arrives to bring new challenges to theorists, it is probably safe to say that theoretical

developments in the fractional Hall effect have reached at least a

75
preliminary stage of maturity and it will prove useful to begin exploring

other aspects of novel two-dimensional materials. Some new directions

which are now getting under way are discussed below.

There has been considerable interest in recent years in the

electronic- transport properties of thin metallic films, particularly in

connection with weak Anderson localization and the interplay between

superconductivity and localization. A reiatea problem is superfluidity in

layers of helium adsorbed on a disordered substrate. A fascinating

experimental result which has not yet been fully understood has been

obtained recently by Goldman _et al. at the University of Minnesota. They

find in partially-oxidized tin films that if the high-temperature sheet

resistance of the film exceeds a critical value R

c of order h/(2e) 2

, the

system becomes insulating at low temperatures. However, if the

high-temperature sheet resistance is less than R

c , the system becomes

superconducting at low temperatures. This remarkable result is believed

to be due to macroscopic quantum tunneling effects in the superconducting

grains in the presence of dissipation. These questions are being further

explored. A useful spin-off of studies of tunneling in the presence of

dissipation will be a greater understanding of how to treat problems such

as hydrogen and muon diffusion in metals and at the surface of metals.

A newly developed field known as ’meso-scale physics' is generating

intense experimental and theoretical activity. Modern lithographic

techniques allow one to produce small one- and two-dimensional structures

which are smaller than the inelastic mean free path at low temperatures.

This leads to a variety of interesting coherence effects even though the

elastic mean free path may be small on the scale of the system size. This

is because phase information is scrambled but not destroyed by elastic

scattering. One of the most, interesting effects is the existence of

universal conductance fluctuations in which any small perturbation

(displacing a single impurity, adding one quantum of magnetic flux to the

sample, etc.) causes a change of order e

2 /h in the conductance, independent

of the sample size and dimensionality. As an alternative to the usual

diagrammatic techniques, this problem will be investigated using replica

field theory methods. Another problem of particular interest in

one-dimensi onal structures (quantum well wires) is the nature of Coulomb

correlations at low temperatures. This is being investigated in

collaboration with Dr. A. H. MacDonald using variational wave functions

analogous to those developed for the quantum Hall effect.

B. State Characterization of Energetic Species Ejected from Surfaces

Specific state characterization of desorbed and ejected species from

surfaces, whether induced by sputtering or by electron and photon

bombardment, is still rare. It is now possible to address such dynamical

surface interactions using laser techniques to determine the energy state,

velocity, and angular distributions of all the ejected species—especially

the neutrals which are the most abundant. Such studies can provide

detailed microscopic information concerning energy transfer in these

excitation/interaction processes

76
The objective in this component of the program is to understand the

excitation dynamics by which atoms and molecules are desorbed from

surfaces in ion- sputtering processes as well as in electron- and

photon-stimulated processes. Detailed characterization of the internal

energy, kinetic energy, and desorption thresholds of desorbed species will

provide a microscopic understanding of the nature of the electronic

excitations leading to desorption due to collisions with electrons,

photons, and ions. Angular distributions will provide direct structural

information concerning the surface geometry, as well as information

concerning energy transfer during the collisional interaction.

We are combining ultrahigh-vacuum surface-science techniques with

state-of-the-art spectroscopy in several experiments involving

electron-stimulated desorption (ESD), phot on- stimulated desorption (PSD),

and ion sputtering. Specifically, we propose to use multiphoton

ionization and other laser-spectroscopic techniques to detect and analyze

neutral species released from crystalline surfaces by electron, photon,

and ion bombardment. These measurements will provide unique insights into

the mechanisms of desorption induced by both electronic transitions and by

direct momentum transfer. Measurements of neutral angular distributions

will be compared directly with ion angular distributions using a new

two-dimensional display analyzer, thus providing a detailed description of

competing desorption pathways.

We are performing work in three project areas. First, we are

designing an experiment in which laser-spectroscopic techniques will be

used to determine the energy states of neutral atoms and molecules

sputtered from surfaces by ion bombardment. Second, we are collaborating

with scientists at Vanderbilt University on a similar experiment in which

neutral species desorbed from surfaces by electron or photon excitation

will be detected and cnaracterized. This experiment may lead later to

similar work at NBS. Finally, we are constructing a new type of display

analyzer to measure angular and energy distributions of charged species

desorbed from surfaces by electrons or photons to obtain surface-geometry

information and to test theories of ejection mechanisms. Close contact is

made with the related experimental and theoretical projects in the

Division described in Sections 3-B, 3*D, 3.1 and 3.J.

1. Energy States of Neutral Species Sputtered from Surfaces

(J. Fine)

Energetic ion-surface collisions generate extensive near-surface

collision cascades in a solid. The energy transfer and atomic excitations

that take place as a result of such collisions are not well understood in

part because, until rather recently, the primary method for monitoring

these collision phenomena was to measure macroscopic effects such as the

total sputtering yield. The collision cascade causes the ejection of

atoms, ions, electrons, and photons from the surface but it has only been

in the past few years that measurements of the ejected particles or radiation have been utilized to obtain detailed information on specific

atomic collisions that take place in condensed materials.

77
In recent experiments in which aluminum or silicon targets were bombarded by argon ions, we have shown that the Auger decay of

coll isionally excited A1 or Si atoms can take place outside the solid

depending on the distance from the surface (within the material) at which

the excitation occurred, the atom’s velocity, and the lifetime of the

atomic excitation. As a result of our Monte-Carlo calculation to analyze

these experiments, we expect that such sputtered atoms will have rather

high kinetic energies - extending up to hundreds of electron volts.

Collisions capable of transferring this much energy and creating

inner-shell (2p) excitation can generate sputtered atoms (ions) which are

in highly excited states. Such energy- transfer and excitation mechanisms

are basic to our enhanced understanding of collisional processes in

condensed materials. Information is required of those atomic processes

which lead to electron promotion, excitation and ionization, and particle

ejection. It is now possible to obtain this type of information by: (1)

probing specific ejected (sputtered) atoms via resonant, multiphoton laser

techniques; (2) monitoring the Auger-electron de-excitation of ejected

atoms as well as those which decay inside the solid; (3) analyzing the

emitted secondary-electron energy distributions. Progress made during the

first year of this project in each of these areas is described below.

(a) Laser Spectroscopy of Sputtered Atoms ana Ions

In collaboration with Drs. J. D. Fassett (NBS Inorganic

Analytical Research Division) and Dr. J. Boulmer (NBS Inorganic Analytical

Research Division and Universite Pans, France), a new series of

experiments has been designed to determine the kinetic energy distributions

of specific sputtered atoms (ions) and their states of excitation.

Measurements have been planned of: (1) the kinetic energy distributions

of all the sputtered ions as a function of charge state, (2) the kinetic

energy distributions of emitted electrons, (3) the collisional excitation

of Rydberg states, (4) excited-state decay by photon emission, and (5) the

kinetic energy distributions of sputtered atoms in specific excited sates.

Resonance multiphoton laser-ionization schemes have been developed to

detect sputtered atoms in specific excited states.

Construction began on a new instrument this past year. A stainless

steel ultrahigh vacuum (uhv) chamber was constructed at NBS to contain a sample manipulator, pulsed ion gun, pulsed time-of-fl ight (TOF) extraction

optics and detector, Auger-electron spectrometer , and windows for the two

ultraviolet laser beams. Some of this instrumentation is described below.

The UHV sample manipulator incorporates the usual XYZ translations

and rotation about the Z axis, as well as a special sample holder which

permits rotating the sample about an axis in the plane of the surface (the

laser beams are parallel to this axis). This sample rotation, in

conjunction with the two ion gun ports directed at different angles with

respect to the target surface, will allow us to vary the ion beam angle

from near-grazing to near-normal incidence.

78
The ion gun used can produce a 1 mm wide beam with about 0.5 uA

current in the 1-5 keV energy range.' We have designed and built an additional high-speed beam swi tcher 'that can turn the bean on and off in

about 50 ns (rise time). The complete pulsed ion gun can be mechanically

aligned with the target.

The TOF analyzer, which we designed and built, was optimized for

maximum collection efficiency; it is short (about 5 inches long) and has

apertures 1.2 inches in diameter. The extraction and collection grids

are spherical and operate as a modified Pierce lens in order to increase

the collection of sputtered ions which are ejected with a cosine-type

distribution from the surface. Pulsed fields are applied to these

spherical grids to accelerate ' those sputtered ions produced by the

incident pulse of ions from the gun. Electrons also can be measured with

this TOF analyzer using reversed fields. Both ions and electrons, as well

as x-rays, are detected by a microchannel plate TOF detector.

Data acquisition of TOF spectra is accomplished with a transient

digitizer oscilloscope with internal signal averaging that permits spectra

with high time resolution (10 ns) to be acquired over periods of many

microseconds

The completed system as described above was put into operation in

early July, 1986. Using a polycrystalline magnesium target with pulsed

ion beam and' TOF extraction, we have observed the three Mg ion isotopes,

Mg0+

, virtually no Mg++

, and ejected electrons. The system seems to work

very well with high sensitivity and good time resolution; calculated

flight times are in good agreement with those measured. Work is in

progress to characterize and understand the details of the spectra

observed

(b) Auger-Electron De-Excitation of Sputtered Atoms

In collaboration with Drs. C. Le Gressus and J. P. Duraud

(Centre d'Etudes Nucieaires de Saclay, France), a series of measurements

were begun to investigate the Auger-electron emission from ion-bombarded

single- crystal aluminum surfaces. Aluminum (100) and (111) surfaces were

bombarded with argon ions and the dependence of atomic-like and band-like

Auger-electron emission was monitored as the crystals were rotated about

an axis normal to the surface. Preliminary results indicate a very marked

change in the total Auger-electron emission intensity as a function of

azimuthal angle. Intensity minima correspond to geometrical conditions

where the incident ion beam is aligned with a string of atoms (i.e., there

is a shadowing of underlying atoms by the outermost surface atom of a given string).

An example of our results is shown in Fig. 4.2 where we show the

total Auger yield and the ratio of the atomic-like and band-like

Auger-electron emission as a function of azimuthal angle. Both the total

signal and the ratio show minima at the same angles. This result strongly

suggests that most of the coliisional inner-shell excitation, for an ion

beam aligned with an atom string, occurs deep below the surface so that

the probability of an atom being sputtered before it can deexcite is low.

79
Measurements of this phenomena are still in progress in Saclay; we anticipate extending this investigation of collisional excitation

processes in single- crystal solids at NBS.

Fig. 4.2 Plot of the total Auger yield and the ratio of atomic-like and

band-like Auger-electron emission from an A1(100) surface

bombarded by 4 keV argon ions as a function of the angle of

rotation of the sample about its normal

80
(c) Secondary-Electron Energy Distributions Due to Ion

Bombardment

In collaboration with Dr. I. Terzic (Boris Kidric Institute

Belgrade, Yugoslavia), an experiment has been designed to study the

secondary-electron energy distributions that result from Ga+ ~Ga collision

at ion energies from 20 to 60 keV. Previous measurements at NBS indicate

that collisional excitation may account for the high energy (> 100 eV)

emitted electrons observed. An apparatus is presently under construction

in Belgrade which will enable us to examine inner-shell excitation

thresholds in this system.

2. Electron- and Photon-Stimulated Desorption of Neutral Species

Using Laser Detection Techniques

(T. E. Madey)

In a collaborative effort with Prof. N. Tolk at Vanderbilt

University, we have initiated measurements to characterize the mechanisms

by which neutral species are excited and desorbed from surfaces using

electron- and photon-stimulated desorption (ESD/PSD).

The majority of species removed from surfaces via ESD and PSD are neutral atoms and molecules. However, virtually all measurements of the

energy and angular distributions of desorbing species have been of the

more-easily-detected minority ionic species; only recently have laser

techniques been applied to the detection of neutral species. Most

measurements made to data have concentrated on radiation-induced

decomposition of bulk solids (e.g., alkali halides).

Our experiments are designed to search for and characterize the ESD

of both ground-state and excited Li and Na atoms desorbed from

fractional-monolayer films of Li and Na adsorbed on both clean and

oxygen-covered W(100) surfaces. We will employ laser-induced fluorescence

to detect the ground-state neutrals, and light emission following

metastable deexcitation to detect excited neutral species. Depending on

signal levels, a later stage of the measurements involve the use of

synchrotron radiation to determine the threshold energies for desorption

via photon-stimulated desorption. The choice of experimental systems for

these first studies (Na, Li on 0/W(100)) is based on previous related

experiments involving ion desorption and the theoretical interest in these

condi tions

3. Angular and Energy Distributions of Desorbed Ionic Species

(R. Stockbauer and T. E. Madey)

We have designed a special analyzer to measure simultaneously

the angular, energy, and mass distributions of ions desorbed from surfaces

The analyzer will in addition be used for angle-resolved photoemission.

81
The construction and assembly of a new angle-resolving, display-type

ion and electron energy analyzer is completed. This instrument is based

on the IBM design of Dr. D. Eastman. The analyzer is undergoing initial

testing in the laboratory using an electron impact source. The video

processing software which will display the two-dimensional data in an appropriate form is also being developed during this initial testing.

Similar software is being used to process two-dimensional data from a video display system installed for our ESD1AD project (section 3.B).

The initial test experiments using the new analyzer will be a series

of quantitative ESDIAD (Electron Stimulated Desorption Ion Angular

Distributions) studies of small molecules adsorbed on metal surfaces. The

test systems will include NH^ and H2 0 on Ni(1 11), as well as the

coadsorption of each of these molecules with electronegative (0, S, Br

and electropositive (K, Na) additives. Some of these systems have been

studied previously but a number of longstanding and important fundamental

questions remain for which the new analyzer can provide quantitative

answers. Experiments are planned to address the following questions.

o What are the angular profiles of the ion beams?

o Is there quantitative structural information in individual

ESDIAD beam shapes?

o How do the angular profiles of individual ion beams vary with

adsorption coverage and the presence of coadsorbates?

o How do the ESDIAD patterns vary as a function of electron

excitation energy?

o Are the ion energy distributions a function of desorption angle?

o How do measured ion trajectories compare with theory?

In later experiments at the NBS synchrotron radiation source SURF-II,

the analyzer will be used in angle-resolved photon-stimulated desorption

studies of clean and adsorbate-covered oxide surface. Desorption

thresholds and energy dependences will be correlated with angle-resolved

electron spectroscopic measurements (ultrviolet photoelectron

spectroscopy, constant-initial-state, constant-final-state measurements).

These measurements will be the first detailed, angle-resolved mechanistic

studies of photon-induced bond-streaking processes at surfaces.

82
5. PUBLICATIONS

(a) Publications of Past Year

Anton, A. B. , Avery, N. E. , Madey, T. E. and Weinberg, W. H. , ’’The

Coadsorption of Nitrogen with Carbon Monoxide and Oxygen on the Ru(001)

Surface: Local Chemical Interactions in Mixed Layers,” J. Chem. Phys. 85_,

507 (1 986). ' •

Bange , K., Madey, T. E. and Sass, J. K., ”The Structure of the Surface

Hydration Shell of Bromide on Ag(110),” Surf. Sci. 1 62 , 252 (1985).

Brennan, S., Cowan, P. L., Jach, T., LaVilla, R., Perera, R. C. C. and

Winick, H. , "Optical and Spectral Characteristics of an Insertion Device

Used Both as a Wiggler and an Undulator,” Nucl. Inst. & Meth. A 246 , 37

(1986).

Burgess, Jr., D. R. , Mantell, D. A., Cavanagh , R. R. and King, D. S.

"Dynamics of the Laser-Induced Thermal Desorption of Nitric Oxide from a Platinum Foil," J. Chem. Phys. 85_, 3123 (1986).

Casassa, M. P., Heilweil, E. J., Stephenson, J. C. and Cavanagh, R. R.,

"Time Resolved Measurements of Vibrational Relaxation at Surfaces," J.

Elect. Spec. 38, 257 (1986).

Cowan, P. L. , Brennan, S. , Deslattes, R. D., Henins, A., Jach, T. and

Kessler, E. G., "A High Energy Resolution X-Ray Spectroscopy Synchrotron

Radiation Beamline for the Energy Range 800-5000 eV," Nucl. Inst. & Meth.

A 246, 154 (1986) .

Cox, D. F. , Semancik, S. ana Szuromi, P. D., "Summary Abstract:

Structural and Electron Properties of Clean and Water-Dosed Sn02 (110),"

J. Vac. Sci. Tech. A 4, 627 (1986).

Egelhoff, Jr., W. F., "The XPS Searchlight Effect: A New Analytical Tool

for Layered Structures, Epitaxy, and Interfaces," Mat. Res. Soc . Symp.

Proc. 37, 443 (1985).

Egelhoff, Jr., W. F. , "Summary Abstract: X-Ray Photoelectron and Auger

Electron Forward Scattering: A Structural Probe for Studying Ultra-Thin

Epitaxial Films and Interfaces," J. Vac. Sci. Tech. A 4_, 758 (1986)

Erickson, N. E. and Powell, C. J., "Imaging Properties and Energy

Aberrations of a Double-Pass Cylindrical-Mirror Electron Energy Analyzer,"

J. Vac. Sci. Tech. A 4, 1551 (1986).

Erickson, N. E. and Powell, C. J., "Characterization of the Imaging

Properties of a Double-Pass Cyl indrical-Mirror Analyzer, " Surf. & Inter.

Anal . 9, 111 ( 1986) .

83
Gadzuk, J. W. and Holloway, S. , "Charge Transfer and Vibrational

Excitation in Molecule-Surface Collisions: Trajectorized Quantum Theory,"

Physica Scripta 32., 413 (1985).

Gadzuk, J. W., "Dynamics of Molecular Processes at Surfaces: Vibrational

Lineshapes and Spectra," J. Elec. Spect. 3&_, 233 (1 98b).

Gadzuk, J, W. and Holloway, S. f "Collision Induced Dissociation of

Diatomic Molecules on Surfaces: A Charge Transfer Mechanism," J. Chem.

Phys. 84, 3502 (1986).

Gadzuk, J. W. and Holloway, S., "Comments on the Observation of

Vibrational Excitation in Gas-Surface Collisions," Phys. Rev. B. 33, 4298

(1986).

Girvin, S. M., MacDonald, A. H. and Platzman, P. M., "Magneto-Roton Theory

of Collective Excitations in the Fractional Quantum Hall Effect,"

Phys. Rev. B. 33, 2481 (1986).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R. and Stephenson, J. C.,

"Time-Resolved Vibrational Energy Relaxation of Surface Adsorbates," J.

Vac. Sci. Tech. B 3, 1471 (1985).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R. and Stephenson, J. C.,

"Vibrational Energy Relaxation of Adsorbates on Surfaces," in

Ultrashort Pulse Spectroscopy and Applications , M. J. Soileau, ed.,

International Society for Optical Engineering 533 , 15 (1985).

Karikorpi, M., Holloway, S. and Gadzuk, J. W., "A Classical Trajectory

Surface Hopping Approach to Non-Adiabatic Processes Occurring During

Diatom-Surface Scattering," J. Elect. Spect. 39_, 223 (1986).

Kirchhoff, W. H., Chambers, G. P. and Fine, J., "An Analytical Expression

for Describing Auger Sputter Depth Profile Shapes of Interfaces," J. Vac.

Sci. & Tech. A 3, 1666 (198o).

Kurtz, R. L. , "The Influence of Surface Structure on Ion Emission From

Ti02

," J. Vac. Sci. Tech. A 4, 1248 (198b).

Kurtz, R. L., Stockbauer, R. and Madey, T. E. , "Angular Distributions of

Ions Desorbing from Ti02

," Nucl. Instr. & Meth. B J_3 , 518 ( 1986).

Kurtz, R. L., Usuki, N., Stockbauer, R. and Madey, T. E., "Measurements of

Electron Attenuation Lengths in Condensed Molecular Solids," J. Elect.

Spect. & Rel . Phenom. 40_, 35 ( 1986).

MacDonald, A. H. and Girvin, S. M., "Collective Excitations of Fractional

Hall States in Higher Lanaau Levels," Phys. Rev. B. 33 > 4009 (198b).

MacDonald, A. H. and Girvin, S. M., "Quasi-Particle States and the

Fractional Quantum Hall Effect," Phys. Rev. B (Rapid Commun) 53_,

441 4 (1 986).

84
MacDonald, A. H. , Liu, K. L. and Girvin, S. M. f ’’Disorder and the

Fractional Quantum Hall Effect: Activation Energies and the Collapse of

the Gap,” Phys. Rev. 3. 33, 401 -4 (1986).

MacDonald, A. H., Oji, H. C. A. and Girvin, S. M., "Magnetoplasmon

Excitations from Partially Filled Landau Levels in Two Dimensions,” Phys.

Rev. Lett. 55, 22G3 (1985).

Madey, T. E. , "Electron Stimulated Desorption and its Relation to

Molecular Structure at Surfaces,” J. Vac. Sci. Tech. A J*, 257 (1986).

Madey, T. E. and Benndorf, C., "Evidence for Molecular Orientations in

Coadsorption of CO and K on Ru(001)," Surf. Sci. 1 64 , 602 (1985).

Madey, T. E. and Benndorf, C., "Interactions of CO+K on Ru(001):

Structure and Bonding," Surf. Sci. 1 64 , 602 (1985).

Mantell, D. A., Cavanagh, R. R. and King, D. S., "Internal State

Distributions of NO Thermally Desorbed from Pt(111): Dependence on Coverage and Co-adsorbed CO," J. Chem. Phys. 84, 5131 (1986).

Melmed, A. J. and Klein, R., "Icosahedral Symmetry in a Metallic Phase

Observed by Field Ion Microscopy," Phys. Rev. Lett. 56., 1478 ( 1986).

Melmed, A. J. and Klein, R. , "Long-Range Icosahedral Symmetry in a Metallic Phase Observed by Field Ion Microscopy," Journal de Physique C 2,

287 (1 986) .

Miskovic, J., Vukanic, and Madey, T. E. , "Calculations of

Reneutralization Effects in ESDIAD,” Surf. Sci. 1 69 , 405 (1986).

Penn, D. R., Apell, S. P. and Girvin, S. M., "Theory of Spin Polarized

Secondary Electrons in Transition Metals," Phys. Rev. Lett. 55., 518

(1 985).

Platzman, P. M., Girvin, S. M. and MacDonald, A. H. , "Conductivity in the

Fractionally Quantized Hall Effect," Phys. Rev. B (Rapid Commun) 3£, 8458

(1985).

Powell, C. J. , editor, "Technical Activities 1985 - Surface Science Division,"

NBSIR 86-3304 (1985)

.

Powell, C. J., "The Energy Dependence of Electron Attenuation Lengths,"

Surf. Inter. Anal. 7, 256 (1985).

Powell, C. J., "Calculations of Electron Inelastic Mean Free Paths from

Experimental Optical Data," Surf. Inter. Anal. 7, 263 (1985).

Powell, C. J., ’’Recent Developments in Quantitative Surface Analysis by

Electron Spectroscopy," J. Vac. Sci. Tech. A 4, 1532 (1986).

Powell, C. J. and Seah, M. P., "Surface Chemical Analysis: Report on the

VAMAS Project," Surf. Inter. Anal. 9, 79 (1986).

85
Rush, J. J., Cavanagh, R. R. , Kelley, R. D. and Rowe, J. M., "Interaction

of Vibrating H Atoms on the Surface of Platinum Particles by Isotope

Dilution Neutron Spectroscopy," J. Chem. Phys. 83_, 533y ( 1985).

Schmidt-May, J., Senf, F. , Voss, J. , Kunz, C., Flodstrom, A., Nyholm, R. and Stockbauer, R., "Resonant Electron and Ion Emission and Desorption

Mechanisms in Rare Earth Oxides/' Surf. Sci. 1 63 , 303 ( 1985).

Shinn, N. D., "Synchrotron Photoemission Evidence for ’Lying-Down’ CO on

Cr ( 1 1 0 )

, " J. Vac. Sci. Tech. A 4, 1351 (1986).

Shinn, N. D. and Madey, T. E., "CO Chemisorption on Cr(110): Evidence for

a Precursor to Dissociation," J. Chem. Phys. 83., 5928 (1985).

Shinn, N. D. and Madey, T. E. , "Chemisorption and Dissociation of 0

2 on

Cr (1 1 0) : An EELS/ESDIAD Study," Nucl. Instr. & Meth. B 1_3, 537 ( 1986).

Shinn, N. D. and Madey, T. E., "Electronic Structure Changes for

’rr-bonded’ CO Chemisorbed on Cr(110)," Phys. Rev. B 33., 1 46h ( 1986).

Stockbauer, R., Kurtz, R. L., Usuki, N. and Madey, T. E., "The Use of

Synchrotron Radiation to Measure Electron Attenuation Lengths in Condensed

Molecular Solids," Nucl. Instr. & Meth. A 246 , 820 (1986).

Wang, F. W., Lowry, R. E. and Cavanagh, R. R., "Picosecond Excimer

Fluorescence Spectroscopy: Applications to Local Motions of Polymers and

Polymerization Monitoring," Polymer 26, 1657 (1985).

Wax, M. J., Cavanagh, R. R. and Rush, J. R., "A Neutron Scattering Study

of Zeolite Rho," J. Phys. Chem. 90, 532 (1986).

Wax, M. J., Kelley, R. D. and Madey, T. E., "Ethane Hydrogenolysis

Catalyzed by W(100)," J. Catalysis 98, 487 (1986).

86
(b) Publications in Progress

Bange, K., Madey, T. E. and Stuve, E. M., "Summary Abstract: Coadsorpuion

of Water and Oxygen on Ag (110): A Study of the Interactions Among

H

2

O, OH, and 0," J. Vac. Sci. Techn. (submitted).

Bange, K., Stuve, E. M., Madey, T. E. and Sass, J. K., "The Adsorption of

Water and Oxygen on Ag(110): A Study of the Interactions Among Water

Molecules, Hydroxyl Groups, and Oxygen Atoms," Surf. Sci. (in press).

Burgess, Jr., D. R. , Cavanagh, R. R. and King, D. S. , "Accommodation of

Rotational Energy in the Coadsorbed System Ammonia/Nitric Oxide on Pt(111)," J. Vac. Sci. Tech. A (submitted).

Burgess, Jr., D. R., Cavanagh, R. R. and King, D. S., "Kinetics and

Dynamics of the Ammonia/Nitric Oxide Coadsorbate System on Pt(111),"

Surf. Sci. (submitted).

Cavanagh, R. R. , Casassa, M. P. , Heilweii, E. J. and Stephenson, J. C.,

"Vibrational Relaxation of Adsorbed Molecules: Comparison with Model

Compounds," J. Vac. Sci. Tech. A (submitted).

Cavanagh, R. R., Rush, J. J. and Kelley, R. D., "Neutron Inelastic

Scattering: Vibrational Spectroscopy of Adsorbed Molecules on Surfaces," in Vibrational Spectroscopy of Molecules on Surfaces

edited by J. T. Yates, Jr. and T. E. Madey, Vol. 1 of Methods of Surface

Characterization , Plenum Press Publishing Co., New York, (in press).

Cowan, P. L., Brennan, S., Jach, Terrence, Bedzyk, M. J. and Materlik, G.,

"Observations of the Diffraction of Evanescent X-Rays at a Crystal

Surface," Phys. Rev. Lett, (submitted).

Egelhoff, Jr., W. F. , "Core-Level Binding-Energy Shifts in Solids and at

Surfaces," Surf. Sci. Repts. (submitted).

Egelhoff, Jr., W. F. , "XPS and Auger Forward Scattering in Epitaxial

Films," Physics News Section of Physics Today (in press).

Egelhoff, Jr., W. F. , "A Born-Haber Cycle Analysis of Core-Level Shifts

for Atomic C, N, and 0 on Ni(100)," J. Vac. Sci. Tech. A (submitted).

Egelhoff, Jr., W. F. , "The Relative Importance of the Major Factors

Contributing to the Angular Variation of Intensities in XPS and AES of

Crystals," J. Vac. Sci. Tech A (submitted).

Erickson, N. E., "Modified Structural Proposal for the Si ( 1 1 1 )-( 7x7)

Reconstruction Based on an Analysis of Chemisorption Data," Phys.

Rev. B. (submitted).

87
Erickson, N. E. , Powell, C. J. and Ramaker, D. E. , "New Correlation

Effects Observed for Inner-Shell Excitations in Titanium and

Vanadium," Phys. Rev. Letters (submitted).

Gadzuk, J. W., "Excitation Mechanisms in Vibrational Spectroscopy of

Molecules on Surfaces," in Vibrational Spectroscopy of Molecules on Surfaces" edited by J. T. Yates, Jr. and T. E. Madey, Vol. 1 of Methods of

Surface Characterization , Plenum Press Publishing Co., New York (in

press).

Gadzuk, J. W., "Anisotopic Charge Transfer Rates in the Scattering of

Oriented Atoms or Molecules from Surfaces," Surf. Sci. (in press).

Gadzuk, J. W., "Vibrational Excitation in Molecule-Surface Collisions:

Analytical Modeling vs. Classical Trajectories," J. Chem. Phys.

(submitted)

.

Gadzuk, J. W., "Core Level Spectroscopy : A Dynamics Perspective," Physica

Scripts (in press).

Gadzuk, J. W., "Role of Site Conversion in Vibrational Spectroscopy of

Adsorbed Molecules," J. Opt. Soc. Am. (in press).

Gadzuk, J. VI. and S. Holloway, "Dynamics of Molecular Collisions with Surfaces:

Excitation, Dissociation, and Diffraction," Nucl. Instr. & Meth. B. (submitted)

.

Gadzuk, J. W., "Dynamics of Dissociative Adsorption ana Vibrational

Excitation in Molecule-Surface Collisions," J. Vac. Sci. Tech. A (submitted)

.

Gadzuk, J. W., "Selectivity of Elementary Molecular Processes in

Molecule-Surface Collisions," Phys. Rev. Letters (submitted).

Gadzuk, J. W., "Intramolecular Dynamics in Molecule-Surface Collisions:

Excitation, Dissociation, and Selectivity of Reactivity," Surf. Sci.

(submitted)

.

Heilweil, E. J. , Casassa, M. P. , Cavanagn, R. R. and Stephenson, J. C.,

"Population Lifetimes of 0H(v=1 ) and OD(v-l) Stretching Vibrations of

Alcohols and Silanols in Dilute Solution," J. Chem. Phys. (in press).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R. and Stephenon, J. C.,

"Vibrational Energy Decay of Surface Adsorbates," Proceedings of tne 198b

Conference on Time-Resolved Vibrational Spectroscopy, Springer-Verlag (in

press )

.

Holloway, S. , Karikorpi, M. and Gadzuk, J. W., "Dynamics of Molecular

Collisions with Surfaces: Excitation, Dissociation, and

Diffraction," Nucl. Instr. & Meth. (submitted).

Jach, T., Kirkland, J. P., Wolf, P. and Neiser, R., "A Harmonic Rejection

Scheme for X-Ray Monochromators , " Nucl. Instr. & Meth. (submitt-a .

88
Jones, T. S., Holloway, S. and Gadzuk, J. W., ’’Theoretical Study of the

Vibrational Lineshape for C0/Pt(111),” Surf. Sci. (submitted).

Kaufman, M. J. and Melmed, A. J., "Evidence for Structural Disorder in the

Icosahedral Phase, ” The Philosophical Magazine (submitted).

King, D. S. and Cavanagh, R. R., "Final-State Resolved Studies of

Molecule-Surface interactions, Chemistry and Structure at Interfaces," New

Laser and Optical Techniques, Verlag Chemie, Deerfield Beach, FL,

1 986 ( in press)

Kurtz, R. L, , "Stimulated Desorption Studies of Defect Structure on Ti02

,"

Surf. Sci. (in press).

Kurtz, R. L. and Henrich, V. E. , "Surface Electronic Structure and

Chemisorption on Corundum Transition Metal Oxides: aFe2 03 ," Phys. Rev. B. (submitted).

Kurtz, R. L. , Stockbauer, R. , Nyholm, R. , Flodstrbm, A. and Senf, F.

"Photon Stimulated Desorption Induced by Core Exciton States in MgO,"

J. Vac. Sci. & Tech. A (submitted).

Kurtz, R. L. , Stockbauer, R. , Nyholm, R. , Flodstrbm, A. and Senf, F.

"Core Exciton Induced Desorption from MgO," Physical Review Letters

(submitted)

Kurtz, R. L. , Stockbauer, R. and Madey, T. E. , "Site Specificity in

Stimulated Desorption from Ti02 ,» j. Vac. Sci. Tech, (in press).

Larsson, C. U. S. , Johnson, A. L. , FlodstrCm, A. and Madey, T. E.

"Structure of H

2 o Adsorption on Planar and Stepped Si(100)2x1 ," J. Vac.

Sci. Tech, (submitted).

Madey, T. E. , "Mechanisms and Applications of Electron Stimulated

Desorption in Surface Science," Vacuum TAIP (in press).

Madey, T. E. , "Electron and Photon Stimulated Desorption: Probes of

Structure and Bonding at Surfaces," Science (in press).

Melmed, A. J., "Field Emission Microscopy - Trends and Perspectives,"

Chemistry and Physics of Solid Surfaces , Springer-Verlag (in press).

Melmed, A. J., "Progress in Understanding Atomic Structure of the

' Icosahedral Phase," Journal de Physique (in press).

Melmed, A. J., Schmidt, W. A., Block, J. H., Naschitzki, M. and Lovisa,

M., "Effects of a Gold Shank-Overlayer on the Field Ion Imaging of

Silicon," Journal de Physique (in press).

Oji, H. C. A., MacDonald, A. H. and Girvin, S. M., "Superlautice

Magnetoroton Bands," Phys. Rev. B (submitted).

89
Powell , C. J., "The Energy Dependence of Electron Inelastic Mean Free

Paths," Surf. Interface Anal, (submitted).

Powell, C. J. and Erickson, N. E. , "Comparison of L^-Shell Binding

Energies in Six 3d Metals Measured by X-Ray Photoelectron Spectroscopy,

Appearance-Potential Spectroscopy, and Electron Energy-Loss Spectroscopy

Phys. Rev. B (submitted).

Schmidt, W. A., Melmed, A. J., Naschitzki, M. and Lovisa, M. F. , "Field

Ion Appearance Spectroscopy of Gold Overlayers on Silicon," Journal de

Physique (in press).

Semancik, S. , Doering, D. L. and Madey, T. E. , "Coadsorption of Water and

Lithium on the Ru(001) Surface," Surf. Sci. (in press).

Shinn, N. D. and Madey, T. E., "Stimulated Desorption from CO Chemisorbed

onCr(IIO)," Surf. Sci. (submitted).

Shinn, N. D. and Madey, T. E. , "Oxygen Chemisorption on Cr(110): I. Dissociative Adsorption,” Surf. Sci. (in press).

Shinn, N. D. and Madey, T. E. , "Oxygen Chemisorption on Cr(110): II.

Evidence for Molecular 0

2 (ads)," Surf. Sci. (in press).

Shinn, N. D. and Szuromi, P. D., "Alkali Interactions over Cu(311)»"

J. Vac. Sci. Tech. A (submitted).

Szuromi, P. D., Kelley, R. D. and Madey, T. E., "The Influence of Sulfur

on Methanation on W ( 1 10) , " J. Phys. Chem. (submitted).

Szuromi, P. D., Kelley, R. D. and Madey, T. E. , "The Effect of Sulfur on

the Methanation of CO over W(110)," J. Phys. Chem. (in press).

Udovic, T. J., Cavanagh, R. R., Rush, J. J., Stucky, G. D., Jones, D.,

Corbin, D. R. and Wax, M. J. , "Neutron Scattering as a Probe of Adsorbate

Dynamics: Ammmonia in Zeolite Rho," J. Phys. Chem. (submitted).

Udovic, T. J. and Kelley, R. D., "Neutron Scattering Studies of Hydrogen

in Catalysts," to appear in Hydrogen in Catalysis: Theoretical and

Practical Aspects , Z. Paal and P. G. Menon, eds., Marcel Dekker, Inc., New

York, New York, 1986, (submitted).

Yates, Jr., J. T. , Madey, T. E. and Campuszano, J. C., "The Chemisorption

of Carbon Monoxide by the Transition Metals," The Chemical Physics of

Solid Surfaces and Heterogeneous Catalysis , D. A. King and D. P. Woodruff,

eds., Elsevier (in press).

90
c) Recent Publications of New Staff Members Resulting From Previous

Positions (Burgess, DeWeert, Johnson and Steigerwald)

Burgess, Jr., D. R. , Stair, P. C. and Wei tz, E. , "Calculations of the

Surface Temperature Rise and Desorption Temperature in Laser-Induced

Thermal Desorption," J. Vac. Sci. Technol .' A _4 , 1362 (1986).

DeWeert, M. J. and Arnold, G. B., "Superconducting-Quasi Particle

Interface States," Phys. Rev. Lett. 55_, 1522 (1985).

Hitchcock, A. P. , Newbury, D. C., Ishii, I., Stbhr , J., Horsely, J. A.,

Redwing, R. D., Johnson, A. L., and Sette, F., "Carbon K-Shell Excitation

of Gaseous and Condensed Cyclic Hydrocarbons: C^Hg, C^Hg, CgHg, CgHiQi

C^h-iq* CgH-]2» ana CgHg," J. Chem. Phys. (in press).

Horsley, J. A., Stbhr, J. , Hitchcock, A. P., Johnson, A. L. and Sette,

F., "Resonances in the K Shell Excitation Spectra of Benzene and Pyridine

Gas Phase, Solid and Chemisorbed States," J. Chem. Phys. 83, 6099 (1985).

Johnson, A. L. , Muetterties, E. L. , Sette, F. and Stdhr, J.

,

"Chemisorption Geometry of Pyridine on P t ( 1 1 1 ) by NEXAFS," J. Phys. Chem.

89, 4071 (1985).

Sette, F., Stohr, J. , Koliin, E. B. , Dwyer, D. J. , Gland, J. L.

,

Robbins, J. L. and Johnson, A. L., "Na Induced Bonding and Bond Length

Changes for CO on P t ( 1 1 1 ) : A Near Edge X-Ray Absorption Fine Structure

Study," Phys. Rev. Lett. 54_, 935 (1985).

Steigerwald, D. A., Miller, S. J. and Wynbiatt, P., "Anisotropy of Surface

Composition in a Ni-Au Alloy," Surf. Sci. 1 55 , 79 (1985).

Wynbiatt, P. and Steigerwald, D. A., "Equilibrium Segregation to Terraces

and Steps," Surf. Sci. 150, 289 (1985).

91
6 . TALKS

Burgess, Jr., D. R. F., "Calculations of the Surface Temperature Rise and

Desorption Temperature in Laser-Induced Thermal Desorption," American

Vacuum Society Meeting, Houston, TX, November 20, 1985.

Burgess, Jr., D. R. F., "Laser-Excited Fluorescence Measurements of

Rotational and Translational Energy Distributions of NO Desorbed from

Platinum by Laser-Induced Thermal Desorption," American Vacuum

Society Meeting, Houston, TX, November 21, 1985.

Burgess, Jr., D. R. F. , "Laser—Exci ted Fluorescence Measurements of

Rotational and Translational Energy Distributions of NO Desorbed from

Platinum by Laser-Induced Thermal Desorption," American Physical

Society Meeting, Las Vegas, NV, April 2, 1986.

Burgess, Jr., D. R. F. , "Dynamical Interactions of Molecules with

Surfaces," Applied Physics Division Seminar, U.S. Army Harry Diamond

Laboratories, April 22, 1986.

Burgess, Jr., D. R. F., "Dynamical Interactions of Molecules with

Surfaces," Materials Science Group Seminar, Johns Hopkins University

Applied Physics Laboratory, May 1, 1986.

Burgess, Jr., D. R. F. , "Dynamical Interactions of Molecules with

Surfaces," Laser Group Seminar, National Bureau of Standards,

Gaithersburg, MD , May 12, 1986.

Burgess, Jr., D. R. F. , "Dynamics of the Laser-Induced Thermal Desorption

of Nitric Oxide from Platinum," 46th Annual Conference on Physical

Electronics, University of Texas, Austin, TX, June 16, 1986.

Burgess, Jr., D. R. F., "Dynamical Interactions of Molecules with

Surfaces," Chemistry Division Seminar, Naval Research Laboratory, July

31, 1986.

Burgess, D. R. F. , "Laser— Induced Thermal Desorption: Characterization of

Rotational, Virbrational , and Translational Energy," 192nd American

Chemical Society, Anaheim Convention Center, Anaheim, CA, September

10, 1986.

Cavanagh, R. R. , "Time-Resolved Measurements of Vibrational Energy

Transfer on Surfaces," Davison Division, W.R. Grace & Co., Columbia, MD

November 20, 1985.

Cavanagh, R. R. , "Time-Resolved Measurements of Vibrational Relaxation on Surfaces," University of Chicago, Chicago, IL, February 11, 1986.

Cavanagh, R. R. , "Neutron Scattering as a Probe of Surfaces: Aasorbat*-

Bonding and Dynamics," National Measurement Laboratory Review Panel,

Gaithersburg, MD , March 6, 1986.

92
Cavanagh, R. R. , "Energy Transfer to Chemical Bonds on Surfaces," Gordon

Research Conference on Chemistry of Electronic Materials, Concord,

NH, August 20, 1986.

Chambers, G. P., "An Analytical Expression for Auger Sputter Depth

Profiles," American Vacuum Society Meeting, Houston, TX, November 21,

198b.

DeWeert, M., "Magnetic Field Dependence of Superconducting Quasi Particle

Interface States," American Physical Society Meeting, Las Vegas, NV,

April 1, 1986.

DeWeert, M., "Theory of Magnetically-Induced Quasiparticle Bound States at

Super Conductor-Ferromagnet Interfaces," Washington Area Statistical

Physics Symposium, Gaithersburg, MD May 6, 1986.

Egelhoff, Jr., W. F., "Photoelectron Forward Scattering," American Vacuum

Society Meeting, Houston, TX, November- 21, 198b.

Egelhoff, Jr., W. F., "Auger and XPS Forward Scattering," American

Physical Society Meeting, Las Vegas, NV, March 31, 1986.

Egelhoff, Jr., W. F., "Forward Scattering in XPS as a Tool for Studying

Surface Segregation and Interdiffusion in Thin Films," Eastern Electron

Spectroscopy Society, W.R. Grace & Company, Columbia, MD, May 8, 1986.

Erickson, N. E. , "Study of the Performance Characteristics of Programmable

Power Supplies & DVMs: Possible Relevance to Electron Energy

Measurements," Eastern Electron Spectroscopy Society, W. R. Grace & Co., Columbia, MD, May 8, 1986.

Erickson, N. E. , "Effects of Operational Faults of Programmable Power

Supplies and DVMs on Measured Line Positions," Physical Electronics Users'

Meeting, Hagerstown, MD , September 23, 1986.

Fine, J., "Characteristics of NBS Standard Reference Material 2135 for

Sputter Depth Profile Analysis," European Conference on Applications of

Surface and Interface Analysis, Veldhoven, The Netherlands, October

15, 198b.

Fine, J., "Collisionaliy Excited Auger Electron Emission from Al(100):

Dependence on Azimuthal Orientation," Thirteenth Symposium on the Physics

of Ionized Gases," Sibenik, Yugoslavia, September 1, 1986.

Gadzuk, J. W., "Common Ground in Surface Science and Electrochemistry,"

Summary talk at "Fourth Electrochemical Study Group,

Fritz-Haber-Institute, Berlin, W. Germany, September 27, 1985.

Gadzuk, J. W., "Dynamics of Molecular Processes at Surfaces: Vibrational

Excitation and Dissociation," Solid State Physics Seminar, Institut

fUr Festkdrperf orschung der KFA Julich, Julicn, West Germany,

January 22, 1986.

93
Gadzuk, J. W., "Molecular Dynamics at Surfaces: Harpooning, Vibrational

Excitation, and Dissociative Adsorption," Chemistry Department,

University of Toronto, Toronto, Canada, February 13, 1966.

Gadzuk, J. W., "Molecular Dynamics at Surfaces: Harpooning, Vibrational

Excitation, and Dissociative Adsorption," Physics Department Colloquium,

University of Waterloo, Waterloo, Canada, February 14, 1986.

Gadzuk, J. W., "Exciting Vibrations: Scattering and Spectroscopy at

Surfaces," Rutgers University, Piscataway, NJ, February 26, 1986.

Gadzuk, J. W., "Dynamics of Molecular Processes at Surfaces: Vibrational

Lineshapes and Spectra," American Physical Society Meeting, Las

Vegas, NV, March 31. 1986.

Gadzuk, J.W., "Site Conversion, Chaos, and Vibrational Lineshapes of

Adsorbed Molecules," Institute of Theoretical Physics Seminar, Chalmers

University, Goteborg, Sweden, April 22, 1986.

Gadzuk, J.W., "Exciting Vibrations: Scattering, Spectroscopy, and

Wavepackets at Surfaces," Physics Department Colloquium, Rice University,

Houston, TX, May 19, 1986.

Gadzuk, J.W., "Exciting Vibrations: Spectroscopy and Scattering at

Surfaces," Solid State Seminar, Georgia Institute of Technology, Atlanta,

GA, May 21 , 1986.

Gadzuk, J. W., "Core Level Spectroscopy: A Dynamics Perspective,"

Adriatico Research Conference, "Dynamical Screening and Spectroscopy

of Surfaces," International Centre for Theoretical Physics, Trieste,

Italy, June 25, 1986.

Gadzuk, J. W., "Theoretical Aspects of Electronic, Vibrational, and

Rotational Energy Flows in Molecular-Surface Interactions," Sixth

International Workshop on Inelastic Ion-Surface Collisions, Argonne

National Laboratories , Chicago, IL, August 27, 1986.

Girvin, S, M., "Introduction to the Quantum Hall Effect," University of

British Columbia, Vancouver, B.C., Canada, October 17, 1985.

Girvin, S. M., "Wave Functions for the Fractional Quantum Hall Effect,"

Department of Physics, University of Maryland, College Park, MD, October

28, 1985.

Girvin, S. M., "The Quantum Hall Effect," Physics Department, University

of Maryland, College Park, MD, October 29, 1985.

Girvin, S. M., "Collective Excitations in the Fractional Quantum Hall

Effect," Physics Department, University of Maryland, College Park , ML,

November 11, 1 985

.

94
Girvin, S. M., ’’Unsolved Problems in the Quantum Hall Effect,” Physics

Department, University of Maryland, College Park, MD, November 18, 1985.

Girvin, S. M., "Collective Excitations in the Fractional Quantum Hall

Effect,” Institute of Theoretical Physics, Chalmers University, Gothenburg,

Sweden, December 4, 1985.

Girvin, S. M., "The Fractional Quantum Hall Effect: Superfluidity, Rotons

and Fractionally Charged Vortices", Physics Department, University of

Virginia, Charlottesville, VA, February 28, 1986.

Girvin, S. M., "Collective Excitations in the Fractional Quantum Hall

Effect: Superfluidity, Phonons, Rotons, and Fractionally Charged

Vortices," American Physical Society Meeting, Las Vegas, NV,

March 31 , 1986.

Girvin, S. M., "The Fractional Quantum Hall Effect: Superfluidity,

Phonons, Rotons and Fractionally Charged Vortices," Department of

Physics, Massachusetts Institute of Technology, Cambridge, MA, June 3,

1986.

Girvin, S.M., "Collective Excitations in the Fractional Quantum Hall

Effect," Fourth Summer Institute of Theoretical Physics, Queen's

University, Kingston, Ontario, Canada, July 15, 1986.

Girvin, S.M., "Collective Excitations in the Fractional Quantum Hall

Effect," NORDITA Conference on Fundamental Effects in Semiconductors

Copenhagen, Denmark, August 7, 1986.

Girvin, S. M., "Collective Excitations in the Fractional Quantum Hall

Effect," Physics Department, University of Notre Dame, IA, September 17,

1 986.

Jach, T. , "Dynamical Diffraction of X-rays from Crystal Surfaces at

Grazing Incidence", Eidigenossiche Technische Hochschule, Zurich,

Switzerland, October 15, 1985.

Jach, T. , "Dynamical Diffraction of X-rays from Crystal Surfaces,"

Laboratoire pour 1 ' Utilisation du Rayonnement Electromagnetique

Universite Pans-Sud, Orsay, France, November 4, 1 985.

Jach, T. , "Dynamical Diffraction of X-rays from Crystal Surfaces and

Its Use in Surface Science", University of California at Berkeley,

Physics Department, Berkeley, CA, November 13, 1985.

Jach, T., "Dynamical Diffraction of X-rays form Crystal Surfaces and

Its Use in Surface Science", Applied Physics Department, Stanford

University, Stanford, CA, November 14, 1985.

Jach, T. , "Dynamical Surface X-ray Diffraction and its Requirements of a High Brightness Source", Advance Light Source Workshop, Lawrence Berkeley

Laboratory, Berkeley, CA, November 15, 1985

95
Jach, T., "Determination of Dispersion Surfaces by Surface Dynamical

Diffraction at Grazing Incidence," American Physical Society Meeting,

Las Vegas, NV, April 1, 1986.

Jach, T. , "Energy-Dependent Intensities of the KB Fluorescent Line and its

Satellites in Ar Gas," American Physical Society Meeting, Washington,

DC, April 30, 1986.

Jacn, T., "PIN Diodes as Detectors of X-Ray Reflectivity from Optical

Surfaces," Brookhaven Workshop on X-Ray Optics, Brookhaven National

Laboratory, Upton, NY, June 2, 1986

Jach, T., "PIN Diodes as X-Ray Detectors for Synchrotron Experiments,"

National Synchrotron Light Source Annual User's Meeting, Brookhaven

National Laboratory, Upton, NY, June 5, 1986.

Jach, T. , "Dynamical Diffraction of X-Rays from Crystal Surfaces at

Glancing Incidence—A New Surface Science Technique," AT&T Bell

Laboratories, Murray Hill, NJ, July 21, 1986.

Johnson, A. J., "Small Particles Chemisorbed on Si(100) Studied by ESDIAD:

Water," Gordon Research Conference on Chemistry of Electronic Materials,"

Concord, NH, August 18, 1986.

Johnson, A. J. , "Small Molecules Chemisorbed on Si(100) Studied by ESDIAD:

Water," Chemistry Department, Harvard University, Cambridge, MA,

August 22, 1986.

Kelley, R. D., "Surface Science and Catalysis," Chemical Engineering

Department, Auburn University, Auburn, AL, May 22, 198b.

Kelley, R. D. , "Oxygen Atom-Olefin Reactions in Low Temperature Films:

Relation to Catalytic Epoxidation of Ethylene," Gordon Research

Conference on Catalysis, New London, NH, June 2b, 198b.

Kurtz, R. L., "The Influence of Surface Structure on Ion Emission from

TiO^," American Vacuum Society Meeting, Houston, TX, November ^0, 1985.

Kurtz, R.L., "Structural Dependence in Stimulated Desorption from Ti0 2

,"

American Chemical Society Meeting, New York, NY, April 17, 1986.

Kurtz, R. L. , "Measurements of Electron Attenuation Lengths on Condensed

Molecular Solids," Georgia Institute of Technology, Atlanta, GA,

May 9, 1986.

Madey, T. E. , "Mechanism of Applications of Electron Stimulated Desorption

in Surface Science," Joint Vacuum Congress of Hungarian, Yugoslavian and

Austrian Vacuum Societies, House of Debrecen Committee of the Hungarian

Academy of Science, Debrecen, Hungary, October 7, 1985.

Madey, T. E. , "The Influence of Surface Additives on the Structure and

Chemistry of NH^ and H2 0 on Metal Surfaces," Josef Atilla University,

Dept, of Chemistry, Szeged, Hungary, October 10, 1985.

96
Madey, T. E. , "Recent Advances in Electron and Photon Stimulated

Desorption," American Vacuum Society Meeting, Houston, TX., November

21, 1965.

Madey, T. E. , "Recent Applications of Electron Stimulated Desorption in

Surface Structure Determination," Physics Department Colloquium, Cornell

University, Ithaca, NY, December 4, 1985.

Madey, T. E., "The Surface Chemistry of Water," Gordon Research Conference

on Electrochemistry, Santa Barbara, CA, January 20, 1986.

Madey, T. E., "Uses of Electron Stimulated Desorption in Surface Science,"

Materials Research Division, University of California at Berkeley,

Berkeley, CA, January 23, 1986.

Madey, T. E. , "Mechanisms and Applications of Electron and Photon

Stimulated Desorption," Joint Institute for Laboratory Astrophysic

,

NBS, Boulder, CO, January 28, 1986.

Madey, T. E., "Mechanisms and Applications of Electron and Photon

Stimulated Desorption," Physics Department, University of

Pennsylvania, Philadelphia, PA, February 5, 1986.

Madey, T. E. , "Early Applications of Vacuum Science and Technology,"

American Vacuum Society Symposium on Ion Beam Technology and Applications,

Anaheim, CA, March 18, 198b.

Madey, T. E. , "The Structure and Chemistry of H

2 0 on Surfaces," Beijing

Laboratory of Vacuum Physics, Beijing, China, April 9, 1986.

Madey, T. E. , "Advances in Electron and Photon Stimulated Desorption,"

Beijing Laboratory of Vacuum Physics, Beijing, China, April 9, 1986.

Madey, T. E. , "History of Vacuum Science and Technology," Beijing

Laboratory of Vacuum Physics, Beijing, China, April 10, 1986.

Madey, T. E. , "The Use of Electron Stimulated Desorption to Determine the

Structures of Surface Molecules," Fudan University, Shanghai, China,

April 17, 1986.

Madey, T. E. , "Secondary Electron Effects in Photon Stimulated

Desorption," Sixth International Workshop on Inelastic Ion-Surface

Collisions, Argonne, IL, August 16, 1986.

Madey, T. E., "Influence of Electronic and Geometrical Structure on Desorption Kinetics of Isoelectronic Polar Molecules: NHo and H2 O,"

Joint Workshop on Interface Phenomena, ’Kinetics of Interface Reactions,'

Campobello International Park, ME, September 26, 1986.

Melmed, A. J., "Field Ion Appearance Spectroscopy of Gold Overlayers on Silicon," 33rG International Field Emission Symposium, W. Berlin, Germany,

July 10, 1986.

97
Melraed, A. J., "Effects of a Gold Shank-Overlayer on the Field Ion Imaging

of Silicon," 33rd International Field Emission Symposium, w. Berlin,

Germany, July 10, 1986.

Melmed, A. J. , "Progress in Understanding Atomic Structure of the

Icosahedral Phase," 33rd International Field Emission Symposium,

W. Berlin, Germany, July 11, 1985.

Melmed, A. J., "Atomic Structure of the Icosahedral Phase in AIMn,"

University of Erlangen-Nurnberg , Erlangen, W. Germany,

July 111, 1 986.

Powell, C. J. "Overview of Surface Analysis Techniques," New England

Section of the Society for Applied Spectroscopy, Newton, MA,

October 9, 1985.

Powell, C. J. "Surface Chemical Analysis - Report on the VAMAS Project,"

European Conference on Applications of Surface and Interface Analysis,

Veldhoven, The Netherlands, October 17, 1985.

Powell, C. J. "Characterization of the Imaging Properties of a Double-Pass

Cyl indncal-Mirror Analyzer," European Conference on Applications of

Surface and Interface Analysis, Veldhoven, The Netherlands, October

17, 1985.

Powell, C. J. "Lo-Level Binding Energies and Excitation Spectra of 3d

Transition Metals by Different Techniques," Physical Chemistry Department,

University of Nijmegen, Nijmegen, The Netherlands, October 18, 1985.

Powell, C. J., "Recent Developments in Quantitative Surface Analysis by

Electron Spectroscopy," American Vacuum Society Meeting, Houston, TX,

November 19, 1985.

Powell, C. J. , "Imaging Properties and Energy Aberrations of a Double-Pass

Cylindrical-Mirror Electron Energy Analyzer," American Vacuum Society

National Symposium, November 19, 1986.

Powell, C. J., "Lectures on Surface Science and Surface Analysis," Short

Course of the Mexican Vacuum Society, Mexico City, Mexico, March 17-18,

1986.

Powell, C. J., "Auger Electron Spectroscopy," Short Course on Microanalytical techniques in Materials Science, Washington Chapter of the

American Society for Metals, NBS, Gaithersburg, MD , April c2, 1986.

Powell, C.J., "Comparison of L^-Shell Binding Energies in 3d Metals by XPS,

APS, and EELS," IBM Almaden Research Center, San Jose, CA, May 20,

1 986 .

Powell, C.J., "Comparison of Measured and Calculated Appearance-Potent : ai

Spectra of 3d Metals," Physical Electronics Conference, University of

Texas at Austin, Austin, Texas, June 1 6 , 198o.

98

j
Powell, C.J., "Comparison of Measured and Calculated Appearance-Potential

Spectra of 3d Metals," Gordon Research Conference on Electron

Spectroscopy, Wolfeboro, NH, July 14, 1986.

Powell, C.J., "Energy Dependence of Electron Inelastic Mean Free Paths,"

Physical Electronics Users’ Meeting, Hagerstown, MD, September 23, 1986.

Shinn, N. D., "Dossier of a Molecular Precursor to Dissociation: The

Cr(110/C0) Case," Department of Chemistry, University of Texas, Austin,

TX, November 19, 1985.

Shinn, N. D., "Synchrotron Photoemission Evidence for Lying-Down CO on Cr(110)," American Vacuum Society Meeting, Houston, TX, November 19, 1985.

Shinn, N. D., "Synchrotron Photoemission Study of ir-Bonded CO on Cr(110),"

American Chemical Society Meeting, New York, NY, April 16, 1986.

Shinn, N. D., "Alkali Overlayer Ordering on the Atomically Corrugated

Cu (311) Surface," American Chemical Society Meeting, New York, NY, April

17, 1986.

Stockbauer, R. L. , "Photon and Electron Stimulated Desorption of Ions from

Surfaces," Department of Physics, Lehigh University, Bethlehem, PA,

October 17, 1985.

Stockbauer, R.L., "Use of Synchrotron Radiation in Studies of Adsorbed

H

2

0: Surface Chemistry and Radiation Damage," American Chemical

Society Meeting, New York, NY, April 16, 1986.

© Szuromi , P. D., "Sulfur Poisoning of CO Hydrogenation over a Tungsten

Catalyst," Chemistry Department, George Washington University,

Washington, DC, February 7, 1986.

Szuromi, P. D., "Inhibition by Sulphur of Catalytic CO Hydrogenation over Tungsten," Inorganic Materials Division Seminar, National Bureau of

Standards, Gaithersburg, MD , March 25, 1986.

Szuromi, P. D., "Inhibition by Sulfur of Catalytic CO Hydrogenation over Tungsten," Surface Chemistry Branch, Naval Research Laboratory,

Washington, DC, April 7, 1986.

Szuromi, P. D., "Effect of Sulfur and Oxygen on the Hydrogenation of CO

over W(110)," American Chemical Society Meeting, New York, NY,

April 17, 1986.

Szuromi, P.D. "Effects of Metallic Surface Structure on Molecular

Dissociation," Physics Department, Stevens Institute of Technology,

Hoboken, NJ , April 28, 1986.

Szuromi, P. D., "Sulfur Inhibition of Methanation over W ( 1 10) ,Gordon

Research Conference on Catalysis, New London, NH, June 24, 1986.

99
7. SURFACE SCIENCE DIVISION SEMINARS

Adelman, S. A., Purdue University, West Lafayette, IN, "Some Concepts in

Condensed Phase Chemical Kinetics," October 30, 1985.

Behm, R. J., University of Munich, Munich, W. Germany, "Local Surface

Processes Detected by Scanning Tunneling Microscopy," Joint Seminar with

Electron Physics Group, December 2, 1985.

Bono, J., Pennsylvania State University, University Park, PA,

"Free-Electron Theory of Scanning Tunneling Microscopy," November 13,

1 985.

Bonzel , H. P. , KFA, Jtilich, Germany, "Morphological Changes of Periodic

Surface Profiles on Pt(1 10) : Surface Self Diffusion, Anisotropy of

Surface Energy, and Surface Reconstruction," June 26, 1986.

Burgess, Jr., D. R. F., "Laser-Induced Thermal Desorption as a Probe of

Surface Processes," Surface Science Division Seminar, Gaithersburg,

MD, October 23, 1985.

Ceyer, S. T. , Massachusetts Institute of Tecnnology, Cambridge, MA, "Dynamics

of Molecular Chemisorption, Site Conversion and Activated

Dissociative Adsorption on Ni(111)," May 29, 1986.

Chabal, Y., AT&T Bell Laboratori es , Murray Hill, NJ , "Structure and

Dynamics of Hydrogen on Si(100) and W ( 1 00 ) - An Infrared Study," January

6, 1986.

Chambers, G. P. , Nuclear Engineering Dept., Univ. of Maryland, and Guest

Worker, Surface Science Division "Design of an Interactive Sputtering

Yields Database Using Commerical and In-House Software", October 25,

1985.

Davenport, J. , Brookhaven National Laboratory, Upton, NY, "Surface

Relaxation in Gold (110)," September 11, 1986.

Demmin, R. A., University of Pennsylvania, Philadelpnia , PA, "Methanation

Reaction Kinetics over Model Pt Catalysts," September 5, 1986.

Eesley, G., General Motors Research Laboratories, Warren, MI., "Energy

Relaxation in Metals on the Picosecond Timescale", October 1 8, 1 985.

Einstein, T. L. , University of Maryland, College Park, MD , "Informal

Lecture Series on Phase Transitions at Surfaces: I. General

Introduction to Concepts in Critical Phenomena," April 8, 1986.

Einstein, T. L., University of Maryland, College Park, MD , "Informal

Lecture Series on Phase Transitions at Surfaces: II. Application to

Surfaces," April 9, 1986.

100
Einstein, T. L. , University of Maryland, College Park, MD , '’Informal

Lecture Series on Phase Transitions at Surfaces: III. Chemisorbed

Systems and Universality Classes," April 10, 1986.

Einstein, T. L., University of Maryland, College Park, MD, "Informal

Lecture Series on Phase Transitions at Surfaces: IV. Transfer Matrix

and Monte Carlo Methods," May 28, 1986.

Einstein, T. L. , University of Maryland, College Park, MD, "Informal

Lecture Series on Phase Transitions at Surfaces: V. Aspects of

Roughening on Surfaces, How to Measure It, and How It Relates to

Other Models" , June 5, 1986.

Gallagher, A., Joint Institute for Laboratory Astrophysics, NBS,

Boulder, CO, "Issues Concerning Hydrogenated Amorphous Silicon Surfaces",

June 6, 1986.

Glaus, U. W., University of Maryland, College Park, MD , "Adsorbed Phases

with Impurities and the Random Field Ising Model," June 11, 1986.

Heller, E. , University of Washington, Seattle, WA, "Chaos, Quantum

Mechanics, and the Mexico City Earthquake," February 18, 1986.

Holloway, S. , Liverpool University, Liverpool, England, "Surface Dynamics:

The Liverpool Perspective," January 15, 1986.

Hall, R. , EXXON Research & Engineering Co., Annandale, NJ, "Surface

Chemistry Induced by Pulsed Lasers—Competition Between Desorption and

Reaction", May 16, 1986.

& MacDonald, A. H. , National Research Council of Canada, Ottawa, Canada, "In

Defense of Normalcy: Why Potassium Ought Not to Have a Charge-DensityWave Ground State," April 14, 1986.

Marton, D., Technical University of Budapest, Budapest, Hungary and Guest

Scientist, Surface Science Division, "Depth Resolution in Sputter

Depth Profiling," January 15, 1986.

Mitchell, G. E. , University of Texas, Austin, TX, "The Surface Chemistry

of Ketene on Pt(111)," September 9, 1986.

Netzer, F. , University of Innsbruck, Innsbruck, Austria, "Angle Resolved

Photoemission of Aromatic Molecules Adsorbed on Transition Metals,"

Joint Seminar with Photon Physics Group, July 11, 1986.

Nicol, J. M., "Infrared Studies of Zeolite—Adsorption Complexes," Surface

Science Division Seminar, Gaithersburg, MD , January 30, 1986.

Nordlander, P., Chalmers University , Goteborg, Sweden, "Potential Energy

Surfaces for Atoms and Molecules Near Metal Surfaces," March 21, 1986.

101
Pfluger, P., BBC Brown, Boveri & Company, Ltd., Baden, Switzerland,

"Electronic Processes in Organic Dielectrics Under High Electrical

Fields", October 18, 1985.

Sanche, L. , Universite de Sherbrooke, Sherbrooke (Quebec), Canada,

"Electron Spectroscopy of Molecular Solids Condensed on Metal Surfaces",

February 14, 1986.

Sarma, S. D., Physics Department, University of Maryland, College Park,

MD, "Molecular Statics and Dynamics Studies of Epitaxy", June 10, 1 986.

Sass, J. K . , Fri tz-Habei—I ns ti tute , Berlin, Germany, "Tuneable Laser

Radiation and Surface Plasmon-Polariton Excitation in Infrared Spectroscopy

at the Metal-Electrolyte Interface", October 21, 1985.

Schuetzle, D., Ford Motor Company Research Laboratories, Dearborn, MI,

"Recent Advances in ESCA and SIMS: Applications to Materials

Science," Joint Seminar with Center for Analytical Chemistry, May

15 , 1986 .

Snowdon, K., Vanderbilt University, Nashville, TN and University of Osnabruck.

Osnabruck, Germany, "Surface Neutralization of Low Energy Atomic and

Molecular Ions", June 9, 1986

Stiles, M., Cornell University, Ithaca, NY, "Inelastic Molecular Hydrogen

Surface Scattering," February 21, 1986.

Tobin, R. , University of California, Berkeley, CA, "Infrared Spectroscopy

of Molecules Adsorbed on Metal Surfaces," March 17, 1986.

Umbach, E. , Technical University of Munich, Munich, W. Germany,

"Photoemission and Auger Spectroscopy as Probes for the Investigation

of Adsorbate Systems," April 24, 198b.

102
8. TECHNICAL AND PROFESSIONAL COMMITTEE

PARTICIPATION AND LEADERSHIP

Cavanagh, R. R. Surface Science Division Safety Officer (through 1/86)

Treasurer, General Committee of the Physical Electronics Conference

Erickson, N. E.

Member, ASTM Committee E-42 on Surface Analysis

Fine, J.

Chairman, Subcommittee E-42. 09 on Standard Reference Materials of

ASTM Committee E-42 on Surface Analysis

Gadzuk, J. W.

Member, Editorial Advisory Board, "Progress in Surface Science"

Member, International Steering Committee, 5th International Conference

on Vibrations at Surfaces, Garmisch-Partenkirchen , FRG, September,

1987

Girvin, S. M.

Member, Program Committee, 7th International Conference on

the Electronic Properties of Two-Dimensional Materials (Sante Fe,

July 1987)

J a ch , T . © Invited participant, Workshop on an Advanced Soft X-Ray and

Ultra-violet Synchrotron Source, Berkeley, CA, Nov. 13-15, 1985

Participant, Workshop on X-Ray Optics, Brookhaven National

Laboratory, June 2-4, 1986

Kelley, R. D.

Chairman, Subcommittee D-3^.03 on Chemical Analysis of ASTM Committee

D-32 on Catalysts

Kurtz, R. L. Member, Local Arrangements Committee, 10th International Vacuum

Congress, 6th International Conference on Solid Surfaces, 33rd

National Symposium of the American Vacuum Society, Baltimore, MD

October, 1986

Madey, T. E. Member, American Institute of Physics Subcommittee on Electronic

Publishing

Program Chairman, 10th International Vacuum Congress/6th International

Congress on Solids Surfaces/33r’d National Symposium of the American

Vacuum Society, Baltimore, MD , October, 1986

103
U.S. Representative to Surface Science Division of the International

Union of Vacuum Science, Technique and Applications (IUVSTA) and

Secretary of Committee

Member, Program Advisory Committee for the Synchrotron Radiation

Center of the University of Wisconsin, Madison, Wisconsin

Member, International Advisory Committee, Beijing Laboratory of Vacuum

Physics, Peoples Republic of China

Member, Advisory Committee for Laboratory of Surface Science and

Technology at the University of Maine, Orono, ME

Chairman, Committee for Foreign Interactions, American Vacuum Society

Member, International Advisory Committee, Second International

Conference on the Structure of Surfaces, Amsterdam, The Netherlands,

June, 1987

Member, International Advisory Committee, Workshop on Desorption

Induced by Electronic Transitions, DIET-III, Long Island, NY, May,

1987

Member, ASTM Committee E-42 on Surface Analysis

Member, Editorial Board, "Methods of Surface Characterization";

co-editor of two volumes in series

Melmed, A. J.

President (from 7/86) and Secretary, International Field Emission

Society

Division Safety Officer (from 2/86)

Powell, C. J.

Chairman, ASTM Committee E-42 on Surface Analysis (through 12/85) and

International Liaison (from 1/86)

Chairman, Surface Chemical Analysis Working Party, Versailles Project on Advanced Materials and Standards

Chairman, Board of Trustees, Gordon Research Conferences

Chairman, American Vacuum Society Applied Surface Science Division

Chairman, American Vacuum Society Scholarships and Awards Committee

Member, Ad Hoc Committee on Topical Conferences, American Vacuum

Society

Chairman, Applied Surface Science Division Steering Committee,

International Union of Vacuum Science, Technique, and Applications

104
Member, Board of Visitors, Research Advisory Board, Physics Program,

Office of Naval Research

National Representative, Commission 1.6 on Colloid and Surface

Chemistry including Catalysis, International Union of Pure and

Applied Chemistry

Member, Editorial Board, "Applications of Surface Science”

Member, Editorial Board, "Surface and Interface Analysis"

Member, Editorial Board, "Methods of Surface Characterization”;

ccr-editor of one volume in series

Stockbauer, R. Assistant Program Chairman, 10th International Vacuum Congress/6th

International Conference on Solid Surface/33rd National Symposium of

the American Vacuum Society, Baltimore, MD , October, 198o

Member, Office Automation Committee, American Vacuum Society

105
9. PROFESSIONAL INTERACTIONS, CONSULTING

AND ADVISORY SERVICES

Cavanagh, R. R. Collaborating with Dr. D. S. King of the NBS Molecular Spectrostopy

Division on state-specific diagnostics of molecular desorption

processes

Collaborating with Drs. M. P. Casassa, E. J. Heiweil and J. C.

Stephenson of the NBS Molecular Spectroscopy Division on real time

measurements of vibrational relaxation processes at surfaces

Collaborating with Drs. T. J. Udovic and J. J. Rush of the NBS

Reactor Radiation Division on neutron inelastic scattering studies of

adsorbates on high-surface- area transition metals

Collaborating with Dr. J. J. Rush of the NBS Reactor Radiation

Division, Dr. G. D. Stucky of the University of California at Santa

Barbara, and Dr. M. J. Wax of W. R. Grace Co. on vibration and

diffusion properties of hydrogen and ammonia in zeolite H-rho

Collaborating with Drs. T. J. Udovic and J. J. Rush of the NBS

Reactor Radiation Division and Dr. B. J. Tatarchuck of Auburn

University on neutron inelastic scattering measurements from

adsorbates on dispersed ruthenium catalysts

Egelhoff, Jr., W. F. Collaborating with Dr. J. E. Rowe of AT&T Bell Laboratories in

studies of semiconductor surface reconstructions by the technique of

X-ray photoelectron forward scattering

Collaborating with Dr. B. Henrich of Simon Frasier University

(Canada) on the synthesis and characteri zation of metallic

superlattices

Erickson, N. E. Collaborated with Mr. T. E. Kiess of the NBS Electricity Division on

the calibration of a high-precision digital voltmeter and a high-precision programmable power supply.

Fine, J.

Collaborated with Prof. B. Navinsek of the J. Stefan Institute,

Ljubljana, Yugoslavia on the effect of surface topography on measurements of sputtering yields, on depth resolution at interfaces,

and on the fabrication and characterization of standard reference

materials for surface analysis. This collaboration is conducted

under the auspices of the U. S. -Yugoslavia Agreement for Cooperation

in Science and Technology

106
Collaborating with Dr. I. Terzic of the Boris Kidric Institute,

Belgrade, Yugoslavia on electronic excitation and electron emission

for ion-bombarded surfaces. This collaboration is conducted under

the auspices of the U. S. -Yugoslavia Agreement for Cooperation in

Science and Technolgoy.

Colloborating with Drs. L. and N. Tanovic of the University of

Sarajevo, Yugoslavia on characterizing surface topography changes

that result from ion bombardment. This collaboration is conducted

under the auspices of the U. S. -Yugoslavia Agreement for Cooperation

in Science and Technology.

Collaborating with Dr. T. Nenadovic of the Boris Kidric Institute,

Belgrade, Yugoslavia on the surface topography effect of both

particle and laser-beam interactions with thin solid films. This

collaboration is conducted under the auspices of the U.S. -Yugoslavia

Agreement for Cooperation in Science and Technology.

Collaborating with Dr. J. D. Fassett of the NBS Inorganic Analytical

Research Division and Dr. J. Boulmer of the Universite Paris, France

and guest scientist in the NBS Inorganic Analytical Research Division

on the use of laser multiphoton ionization techniques to identify

sputtered atoms and to determine their kinetic energies.

Collaborating with Dr. W. Kirchhoff of the NBS Chemical

Thermodynamics Division on a data analysis procedure for

sputter-depth-profile interface characterization.

Collaborating with Dr. R. F. Fleming of the NBS Inorganic Analytical

Research Division on thin-film thickness measurements of standard

reference materials for surface analysis.

Collaborating with Drs. C. Le Gressus and J. P. Duraud of the Centre

d'Etudes Nucleaires de Saclay, France on the colloisional excitation

and electron decay of atoms at single- crystal surfaces.

Gadzuk, J. W.

Collaborating with Prof. M. Sunjic of the Rudnor Boskovic Institute

and the University of Zagreb, Yugoslavia on theories of electron

spectroscopies and dynamics of molecular processes at surfaces. This

collaboration is conducted under the auspices of the U. S. -Yugoslavia

Agreement for Cooperation in Science and Technology.

Collaborating with Dr. S. Holloway, University of Liverpool, England

on classical trajectory theories of molecular processes at surfaces.

This collaboration is assisted by a grant from the NATO Scientific

Affairs Division.

Collaborating with Dr. E. Hood, Montana State University on a theory

of high-energy neutral-molecular beams.

107
Collaborating with Dr. N. Satyamurthy, Indian Institute of

Technology, Kanpur, India, and serving as monitor for a project

"Chemical Dynamics and Laser Spectroscopy", under the auspices of the

India-U.S. Materials Science Program funded via the provisions of

PL-480

Consulted with Dr. J. K. Sass, Fritz Haber Institute, W. Berlin on problems of spectroscopy at electro-chemical interfaces (Nov. 25“30,

1985 )

Consulted with Dr. J. Harris and other members of the Solid State

Theory Group, KFA (Nuclear Research Organization) Julich, W. Germany

on problems associated with molecular dynamics at surfaces.

Consulted with Professors S. Andersson and B. Lundqvist of the

Chalmers University of Technology, Gothenburg, Sweden on molecular

dynamics at surfaces.

Invited lecturer ana participant at Adriatico Research Conference,

"Dynamical Screening and Spectroscopy of Surfaces", International

Centre for Theoretical Physics, Trieste, Italy (June 23 _27, 1986).

Invited lecturer and participant at Sixth International Workshop on Inelastic Ion-Surface Collisions, Argonne National Laboratory (August

25~29, 1986).

Invited discussion leader at Gordon Research Conference on Electron

Spectroscopy, Wolfeboro, NH (July 14-1 8, 1 986).

Girvin, S. M.

Collaborated with Drs. A. H. MacDonald, (National Research Council,

Ottawa) and P. M. Platzman (AT&T Bell Laboratories, Murray Hill) on

the study of collective excitations in the fractional quantum Hall

effect

Completed a collaboration with Drs. D. R. Penn and S. P. Apen of the

NBS Electron Physics Group on a theory of spin-polarized secondary

electron cascades in f erromagnets

Collaborated with Prof. R. E. Prange (University of Maryland) in

organizing a ten-part lecture series on the quantum Hall effect and

in editing the lecture notes for publication.

Jach, T. J. Collaborating with Drs. P. Cowan, S. Brennan, and R. Lavilla of the

NBS Quantum Metrology Group on gas-phase x-ray fluorescence

experiments at the Brookhaven National Synchrotron Light Source.

Collaborating with Dr. R. Perera, Lawrence Berekely Laboratory on gas- phase x-ray fluorescence experiments at tne Brookhaven Nation.).

Synchrotron Light Source.

108
Collaborating with Dr. S. Banna, Vanderbilt University on gas-phase

x-ray photoemission experiments at the Brookhaven National

Syncnrotron Light Source.

Collaborating with Dr. J. Kirkland, Bachs Freeman Associates on measurements of silicon photodiode yields at x-ray energies at the

Brookhaven National Synchrotron Light Source.

Collaborating with Dr. J. Kirkland and P. Wolf, Virginia

Polytechnical Institute and State University on harmonic detection

and elimination in double-crystal monochromators at the Brookhaven

National Synchrotron Light Source.

Collaborating with Dr. L. Hoi deman. Cansat Corp. , and Dr. G. Hembree,

MBS Precision Engineering Division on measurement at the surface

morphology of thin films.

Advised Mr. C. E. Bouldin of the NBS Semiconductor Electronics Division

on the use of silicon photodioides for the measurement of extended

x-ray absorption fine structure in a beamline to be set up at the

Brookhaven National Light Source.

S&Ley, R. D.

Collaborating (with J. M. Nicol) with Drs. T. J. Uaovic and J. J.

Rush of the NBS Reactor Division on neutron inelastic scattering

measurements of adsorbates on high- surface- area transition metals.

Working on detail as a Program Manager with the Department of Energy,

Office of Energy Research, Division of Chemical Sciences. This

detail is on a 80? part-time basis f or a two-year period that began

June, 1985.

2arcs, R. L.

Collaborating with Prof. V. E. Henri eh and members of his group at

Yale University in studies of the electronic structure and the

influence of adsorbates on transition-metal oxide surfaces.

Collaborating (with R. Stockbauer) with Dr. V. Bermudez of the Naval

Research Laboratory in a study of the influence of adsorbates in

promoting phase transitions in the surface conductivity of oxides.

Collaborating (with R. Stockbauer) with Dr. A. Flodstrdm of the

Royal Institute of Technology, Stockholm, Sweden in studies of the

mechanisms involved in stimulated desorption of ions and in studies

of the influence of surface structure on ion angular distributions.

109
Collaborating (witn T. E. Madey and R. Stockbauer) with Drs. W. R. Hunter, J. Rife, and M. Kabler of the Naval Research Laboratory and

Dr. R. Williams of Wake Forest University in experiments at the

x-ray ring of the Brookhaven National Light Source. This work

includes the instrumentation of the double- grating monochromator

designed by the NRL group and implementation of a surface science

chamber that will be used for studies of the mechanisms of stimulated

desorption of ions as well as extended-energy measurements of

electron attenuation lengths in condensed molecular solids.

Collaborating (with T. E. Madey and R. Stockbauer) with Dr. J. L.

Pena of the National Polytechnic Institute, Mexico City in studies of

molecular chemisorption and ion desorption from Ti02 surfaces.

Collaborating (with T. E. Madey and R. Stockbauer) with Prof. J. L.

de Segovia of the Instituto de Fisica de Material es, in Madrid, Spain

in studies of the structure and reactivity in catalysis by metals and

oxides. This work is conducted under the auspices of the U.S. -Spain

Joint Committee for Technical Cooperation.

Madey, T. E. Collaborating with Drs. I. Terzic, J. Vukanid and Z. Milkovic of the Boris Kidric Institute, Belgrade, under the

auspices of the U.S. -Yugoslav Agreement for Cooperation in Science

and Technology, on theoretical and experimental studies of

electron-stimulated desorption and scattering of alkali ions from

surf aces

Collaborating (with R. L. Kurtz and R. Stockbauer) wi tn Drs. W. R. Hunter, J. Rife and M. Kabler of the Naval Research Laboratory and

with Dr. R. Williams of Wake Forest University on the design and

instrumentation for a beamline and chamber at the Brookhaven National

Synchrotron Light Source to study chemisorbed molecules on clean

metal surfaces, mechanisms of photon-stimulated desorption of ions,

and electron attenuation lengths in condensed molecular solids.

Collaborating with Dr. N. Tolk of Vanderbilt University on studies of

electron-stimulated desorption of exci ted-alkal 1 neutral atoms from

surfaces

Collaborating with Dr. C. Benndorf of the University of Hamburg,

under the auspices of a NATO grant, on studies of the influence of

surface additives on local molecular structure.

Collaborating with Prof. P. A. Thiel of Iowa State University in

writing a comprehensive review article on the interaction of water

with solid surfaces.

Collaborating with Dr. J. L. de Segovia of tne Instituto de Fiscia de

Materiales, in Madrid, Spain, under the auspices of the U.S. -Spain

Joint Committee for Technical Cooperation on experimental studies of

adsorption on metals and oxides using electron-stimulated desorption

and synchrotron radiation methods.

110
Collaborating (with R. Kurtz and R. Stockbauer) with Prof. J. L. Pena

of the National Polytechnic Institute, Mexico City in synchrotron

studies of oxide surfaces.

Melmed, A. J.

Collaborating with Dr. W. A. Schmidt and Prof. J. H. Block of the

Fritz Haber Institute, Berlin on properties of semiconductors in

electric fields and effects due to metallic overlayers.

Collaborating with Dr. R. D. Arollia of the General Electric Company

and Prof. H. Fraser of the University of Illinois to investigate

atomic structure and chemical microcoraposi tion for a series of

nickel-based superalloys.

Collaborating with Mr. J. Smith and Prof. H. Fraser of the University

of Illinois on studies of three related nickel-based superalloys

using field ion microscopy, transmission electron microscopy, and

atom-probe analysis.

Collaborating with Dr. M. J. Kaufman of the NBS Metallurgy Division

on comparative studies with atom-probe field-ion microscopy and

transmission electron microscopy of nickel-based superalloys and a series of Al-Li-Cu alloys.

Collaborating with Dr. N. Shinn of the Sandia National Laboratories

on the growth of chromium crystal layers by expitaxy from the vapor

phase.

Powell, C. J.

Collaborating (with S. Tanuma) with Dr. D. R. Penn of the NBS

Electron Physics Group on calculations of inelastic mean free paths

of low-energy electrons in solids.

Collaborating with Dr. M. P. Seah of the National Physical

Laboratory, London on the development of plans and programs for the

Surface Chemical Analysis Working Party of the Versailles Project on Advanced Materials and Standards.

Adjudicator for the Science Prize of the UK ESCA and Auger Users Group

Stockbauer, R.

Collaborating (with R. L. Kurtz) with Drs. C. Kunz and F. Senf of the

German Synchrotron Laboratory DESY, Hamburg and Drs. R. Nyholm and A.

Flodstrdm of the Royal Institute of Technology, Stockholm, Sweden

in studies of the mechanisms of the photon-stimulated desorption of

ions from surfaces.

Collaborating (with R. L. Kurtz) with Dr. A. Flodstrbm of the Royal

Institute of Technology, Stockholm, Sweden on experiments at the NBS

Synchrotron Radiation Facility SURF-II to investigate (1) mechanisms

of photon-stimulated desorption of ions from a non-maximal- valent

oxide and (2) ions desorbing from adsorbates on semiconductors.

Ill
Collaborating (with R. L. Kurtz) with Dr. V. Bermudez of the Naval

Research Laboratory on studies at the NBS SURF-II facility of the

influence of adsorbates in promoting phase transitions in the surface

conductivity of oxides.

Collaborating (with R. L. Kurtz and T. E. Madey) with Drs. W. R. Hunter, J. Rife, and M. Kabler of the Naval Research Laboratory and

with Dr. R. Williams of Wake Forest University on the design and

instrumentation for a beamline and chamber at the Brookhaven

Synchrotron Light Source to study chemisorbed molecules' on clean

metal surfaces, mechanisms of photon-stimulated desorption of ions,

and electron attenuation lengths in condensed molecular solids.

Collaborating (with T. E. Madey and R. L. Kurtz) with Dr. J. L. Pena

of the National Polytechnic Institute, Mexico City in studies of

molecular chemisorption and ion desorption from T i02 surfaces.

Collaborating (with T. E. Madey and R. L. Kurtz) with Prof. J. L. de

Segovia of the Institute de Fisica de Materiales, in Madrid, Spain in

studies of the structure and reactivity in catalysis by metals and

oxides. This work is conducted under the auspices of the U.S. -Spain

Joint Committee for Technical Cooperation.

Collaborating with Dr. A. C. Parr of the NBS Radiation Physics

Division and with Dr. D. Holland of Daresbury Laboratory, England on measurements of the fragmentation of molecules using

photoelectron-photoion coincidence techniques.

Interacting with Drs. A. C. Parr, J. Hardis, and D. L. Ederer of the

NBS Radiation Physics Division, Dr. J. L. Dehmer of Argonne National

Laboratory, and Drs. J. B. West and D. Holland of Daresbury

Laboratory, England on measurements of photoelectron angular

distributions as a function of photon energy in gas-phase molecules.

112
10. VISITING SCIENTISTS

The Surface Science Division has been host during the past year to a number of scientists who have worked with the Division staff on problems

of mutual interest.

Barak, D., Head of the Electronic Design Department of the Israeli Nuclear

Research Center-Negev , worked at NBS for one year beginning August

1985. He interfaced an x-ray photoeiectron spectrometer to a computer system and developed new software for this instrument and

for a new digital ESDIAD system.

Bermudez, V. M., of the Naval Research Laboratory worked one month at NBS

in early 1986 performing photoemission experiments on vanadium oxide

surfaces at the SURF-II synchrotron radiation facility.

Chambers, G. P., a graduate student at the University of Maryland, has

worked at NBS this past year under a cooperative agreement. He has

been involved in the development of a data base system for the

compilation of evaluated sputtering yield data and in quantitative

sputter-depth-profiling of interfaces.

Chen, H.-H., of the National Science Council in Taiwan is spending a year

at NBS, beginning in July 1986, working on applications of

synchrotron radiation to the characterization of surfaces.

Clinton, W. L. , of Georgetown University spent eight months at NBS on an intermittent basis performing theoretical studies related to

electron- and photon-stimulated desorption of ions and neutrals from

surfaces

Einstein, T. L. , of the University of Maryland worked at NBS for about

five months on an Intergovernmental Personnel Assignment on studies

of surface critical phenomena.

Hashiguchi, Y., of the Nippon Steel Corporation, Japan worked at NBS since

March 1 985 on a one-year assignment involving measurements of

sputter-depth profiles of multilayer thin-film reference materials.

Holloway, S., of the University of Liverpool, visited NBS for two weeks

during the winter of 1985-86 and one week during the summer of 1986

to work on theoretical modeling of reactive molecular processes at

surfaces

Hylden, J. L. , of the Naval Research Laboratory spent one month at NBS in

early 1986 performing photoemission experiments on vanadium

oxide surface at the SURF-II synchrotron radiation facility.

113
Jansen, W. R. , a graduate student of the Twente University of Enschede, The

Netherlands worked at NBS for three months in the fall of 1 985. He

extended software for automated x-ray photoelectron spectroscopy

measurements in a timesharing mode and for data reduction.

Larsson, C. U. S. , of the University of Lund, Sweden, is spending about 4 months per year at NBS, starting December 1985, performing ESD1AD

studies of the surface chemistry of silicon.

Marton, D „ , of the Technical University of Budapest, Hungary , is a Ful bright Scholar who is spending sixteen months at NBS, beginning

September, 1985, on studies of the surface topography of

ion-bombarded surfaces and characterizing multilayer thin-fiim

structures

.

Nicol, J. M., of the University of Maryland is spending two years at NBS,

beginning November 1985, using neutron scattering methods to

characterize adsorption on surfaces of high-area metallic and zeolite

catalysts.

Polak, M., of the Ben Gurion University of the Negev, Isarel, is spending one

year at NBS beginning August 1986, performing studies of molecular

structure on semiconductor and metal surfaces using high-resolution

EELS and ESDIAD

.

Shinn, N. D., of Sandia National Laboratory, spent four months at NBS

during the fall of 1985 performing synchrotron radiation studies of

small molecules adsorbed on single- crystal chromium surfaces.

Tanuma, S., of the Nippon Mining Company is working at NBS on a two-year

assignment that began in August 1985. He is participating in

measurements of core-level binding energies by different

electron-spectroscopic methods, in calculations of electron

inelastic mean free paths in solids, and in analyses of algorithms

for x-ray photoelectron spectroscopy.

Wei, J., a graduate student at the University of Maryland from the

People's Republic of China, spent two months at NBS during the summer

of 1986 performing studies of catalysis over well-characterized

copper surfaces.

114
CHEMICAL KINETICS DIVISION

S. E. Stein, Chief

SUMMARY OF ACTIVITIES

Fiscal Year 1986

1 . INTRODUCTION

A. Background

The goal of chemical kinetics is to understand the critical factors

controlling chemical change and reactivity. To achieve this goal chemical

change is interpreted in terms of individual molecular events and

quantitative theoretical models are devised for these events. The

societal importance and exciting scientific opportunities in this area are documented in the Pimentel Report to the National Academy of Sciences

on "Opportunities in Chemistry" (National Academy Press, Washington, D.C.,

1985). In this report chemical kinetics is listed as the first of seven

"Intellectual Frontiers in Chemistry" where the greatest opportunities for

major advances lie. Understanding chemical reactivity is given as the

first of five priority areas where continued growth can "provide the basis

for U.S. competitive advantage in development of new processes, new

substances, and* new materials". Moreover, chemical kinetics is an important part of each of the other four priority areas, especially

"Chemistry Around Us" and "Chemical Behavior Under Extreme Conditions".

The breadth and vitality of this area were also evident in the

proceedings of the first International Conference on Chemical Kinetics,

recently published as an issue of the Journal of Physical Chemistry and

spanning a wide range of chemical reaction systems and experimental

methods. A sampling of areas represented were, _a priori calculations of

potential energy surfaces, rate measurements of organic and organometallic

species in solution, state-to-state energy transfer determinations and

ion-molecule rate measurements. Underlying this striking diversity was a common concern for transition states and for the basic molecular

properties determining reactivity.

Exciting experimental breakthroughs and theoretical developments have

been made over the last few years that have dramatically expanded the

breadth and depth of the discipline. Experimentally, largely as a result

of advances in laser and computer technology, a new array of instrumentation has been developed with improved precision and sensitivity which is now yielding increasingly varied and detailed kinetic information. Spurred

on by practical concerns such as combustion, these new instruments,

alongside more established techniques, have brought certain areas of

115
kinetics to a high degree of development where practitioners are on the

verge of devising reliable theories with broad predictive power. The

development of these theoretical tools is of critical importance to the

field, since they provide frameworks for interpreting as well as generalizing results of individual experiments.

While the number and diversity of reactions investigated by

kineticists are increasing at a rapid pace, the area has actually become mere cohesive as interrelations between formerly divergent areas become

increasingly clear. For instance, concepts developed from the study of

unimolecular reactions are being widely used to explain critical features

of gas-phase ion-molecule chemistry. In a similar manner, results of

gas-phase ion chemistry are beginning to provide a solid conceptual

foundation for solution ion chemistry, a poorly understood area of immense

practical importance.

B. Scope

Over the past several years the scope of research within the Chemical

Kinetics Division has expanded significantly. Five years ago its primary

emphasis was on gas-phase reactions of neutral species. Through recent

additions of staff and changes in research direction, it is now roughly

equally divided into groups studying ion and neutral reactions and on studies in the gas and condensed phases. In addition, the data centers

(ion and neutral) are broadening their efforts in kinetic and

thermochemistry data evaluation. Since predictive theories are required

by both experimentalists and "data evaluators", advancement of these

theories provides a key unifying factor for the diverse activities in the

division. In fact, it is expected that the Division will ultimately be

able to offer not only NBS evaluated data but also NBS "calibrated"

predictive models for data not currently available.

C. Activities

Most activities within the Chemical Kinetics Division fall within one

of two distinct, but closely interacting areas, kinetic measurement and

data evaluation. In the former area we both develop new measurement

techniques and determine rates and mechanisms of selected chemical

processes. These new techniques either allow monitoring reaction

intermediates not observable by existing techniques (two new techniques

are multiphoton ionization and modular MS/MS spectrometry) or enable

kinetic measurements to be made in unique, hard-to-study chemical environments (examples are studies of large species at high temperatures using

heated shock tube, flow reactor and novel laser heating techniques). We

measure rates, determine products and develop reaction mechanisms for

selected simple processes needed for the interpretation of complex,

practical processes. Special attention is given to those cases where a small number of measurements can yield a broad advance in predictive

theory. A wide range of programs of this nature are underway including

reactions of ions and neutral molecules in both the gas and condensed

phases

116
Other programs are devoted to the theoretical analysis of important

reacting systems too difficult to fully analyze by experimental means. An

example is our development of a chemical theory of graphite and very large

polycyclic aromatic molecules.

Data center activities and associated theoretical studies are

at the heart of the division’s efforts. This work not only organizes a wide spectrum of kinetic data and thermodynamic properties of reactive

intermediates, but also utilizes this data to extract general reactivity

patterns and develop improved predictive theories. Major areas of

uncertainty revealed in the course of evaluations often prompt studies in one of our experimental programs. Moreover, the considerable breadth of

ongoing experimental work in the division ensures that insight needed for

thorough data evaluation is available.

Several significant improvements in our instrumentation have been made

over the past year. A state-of-the-art, optical multichannel analyzer has

been purchased and optimized for real time detection of vacuum UV

irradiation. This replaces detection by photographic plates, a much more

laborious and less flexible procedure. A new heated shock tube has been

constructed, enabling the study of even larger molecules. Construction of

a unique, very high temperature (up to 2500 K) graphite flow reactor is near completion. This will enable the study of reactions at organic

molecules at temperatures well above those normally employed in flow

reactors

.

This has been a highly productive year. Both the total number of

research publications (60 published, 42 in press or submitted) and the

number per research staff member (4.3, 3*0) are at an all-time high for our division. Viewed in another way, the net cost per published paper was $41,000, comparable to that for productive academic institutions and well

below that for research institutes. Moreover, the cost per publication in

terms of total NBS support was only $20,000. A major reason for this

increased productivity was the very large number of guest workers

attracted to our division (21 individuals, see Section 10). Another

reason was the maturation of two programs begun several years as competence-development initiatives

.

D. Services to Other Bureau Programs and Other Agencies

The Chemical Kinetics Division serves as a technical resource for a wide range of external programs. This activity is an integral part of our mission, and a key means of applying our scientific expertise to

industrial, defense, and environmental problems. Moreover, these projects

are directly related to, and strongly supportive of, the basic long-range

scientific objectives of the division. In FY 86 we participated in the

following NBS and other agency programs:

117
Office of Standard Reference Data

• The Chemical Kinetic Data Centers (ion and neutral) for data

compilation and evaluation.

Department of Energy

• Compilation and evaluation of combustion chemistry data

• Chemistry of nazardous waste incineration

• Pulse radiolysis studies of electron transfer in solution

• High pressure mass spectrometric studies of ion kinetics and

thermodynamics

.

Department of Defense

• Chemical theory of carbon

• Kinetics of the decomposition of nitroaromatics

• Multiphoton ionization processes

• Tandem mass spectrometric studies

• Ion-cyclotron resonance studies of ion-molecule condensation

processes in hydrocarbons

.

National Aeronautics and Space Administration

• Elementary kinetic studies of stratospheric reactions

• Chemical kinetics of planetary atmospheres

• Evaluation of stratospheric chemical kinetic data

Environmental Protection Agency

£

• Acid rain chemistry

118
2 . DATA CENTERS

R. F. Hampson, Jr., J. T. Herron, R. D. Levin,

S. G. Lias, W. G. Mallard, W. Tsang, and G. W. Zumwalt

R. J. Cvetanovic, F. Westly

Evaluated kinetic and thermochemical data are the most important

output of the Chemical Kinetics Division. It is a responsibility of every

member of the division. The focus for the data evaluation activities is

in the two data centers within the division: the Chemical Kinetics Data

Center (led by J. T. Herron) and the Ion Kinetics and Energetics Data

Center (led by S. G. Lias). On an operational basis the two data centers

work together closely through a sharing of operating procedures, data

bases, and personnel.

A. Chemical Kinetics Data Center

( R. F. Hampson, Jr., John T. Herron, R. Levin, W. Tsang,

G. W. Zumwalt, R. J. Cvetanovic and F. Westley,)

The goal of the Chemical Kinetics Data Center is to serve as the

nation's primary source for evaluated chemical kinetic data. The emphasis

is on gas phase processes for which there is a demonstrated need.

The approach is to compile all data on gas phase chemical kinetics,

and to evaluate specific sub-sets of this general database. This allows us to concentrate our efforts on those areas of greatest practical interest,

while maintaining the ability to move rapidly into new evaluation

activities as the need arises. The evaluated and unevaluated databases are also available to outside users.

Evaluated chemical kinetic data is most needed in those areas of

science and technology in which computer simulation studies are being used

to predict the behavior of large scale, complex chemical systems. Thus, the

focus of our evaluation program is in the area of the oxidation of organic

compounds, particularly as related to combustion and atmospheric chemistry.

This also constitutes the largest active area in experimental chemical

kinetics

1 . Accomplishments

The most important accomplishments of the past year have been in

redefining and setting new goals for the data center and in making major

changes in the daily operations of the center in order to achieve these new goals. The coverage of the data center has been expanded to include the

whole of gas kinetics. The entire backlog of evaluated data on combustion

chemistry has been edited and reformatted, and will be published or submitted for publication by the end of 1986. The same is true for the

backlog of unevaluated data. New projects have been initiated and new approaches to database management and dissemination explored.

119
Over the past year we completed the task of establishing an evaluated

chemical kinetic database for combustion chemistry. This was a monumental

undertaking that has been in preparation for almost five years. It is

unique in providing complete coverage of all possible reactions of all

possible species involved in the combustion of the Cl to C5 hydrocarbons.

The evaluations were based on published experimental data, or where no data

existed, on the basis of theory. In almost all cases the evaluation involved

the extrapolation of data into pressure and temperature regions beyond the

range of the experimental measurements. This work is a particularly good

example of the application and power of predictive techniques in data

evaluation. We fully expect that extension of the data base to alkanes

greater in size than C5 will be accomplished through the use of predictive

techniques based on the existing evaluated database.

The combustion database contains data on 563 elementary chemical

reactions, and will be published in four parts:

"Chemical Kinetic Data Base for Combustion Chemistry. Part 1. Methane

and Related Compounds", W. Tsang and R. F. Hampson, J. Phys. Chem.

Ref. Data, 15, 1087 (1986)

"Chemical Kinetic Data Base for Combustion Chemistry. Part 2.

Methanol", W. Tsang, submitted to J. Phys. Chem. Ref. Data

"Chemical Kinetic Data for Combustion Chemisty. Part 3- Propane,

n-Propyl , and i-Propyl", W. Tsang, to be submitted to J. Phys. Chem.

Ref. Data

"Chemical Kinetic Data for Combustion Chemistry . Part 4. t-Butyl,

i-Butyl and i-Butane" , W. Tsang, to be submitted to J. Phys. Chem.

Ref. Data

In addition, two related papers concerned with the thermochemical and

kinetic properties of free radicals have been published:

"The Stabilty of Alkyl Radicals", W. Tsang, J. Am. Chem. Soc . , 107,

2872 (1985)

"Thermodynamic and Kinetic Properties of the Cyclohexadienyl

Radical", W. Tsang, J. Phys. Chem., 90, 1152 (1986)

Work is in progress on the evaluation of data on the reactions of

atomic oxygen. This will be published in three parts. The first part,

"Evaluated Chemical Kinetic Data for the Reactions of Atomic Oxygen 0(3P)

with Unsaturated Hydrocarbons", by R. J. Cvetanovic, has been submitted to

J. Phys. Chem. Ref. Data. Parts 2 and 3, "Evaluated Chemical Kinetic Data

for the Reactions of Atomic Oxygen 0( 3 P) with Sulfur Containing

Compounds", by R. J. Cvetanovic and D. Singleton, and "Evaluated Chemical

Kinetic Data for the Reactions of Atomic Oxygen 0(^P) with Saturated

Organic Compounds", by J. T. Herron, are in preparation.

120
The compilation of chemical kinetic data for combustion chemistry,

which consisted of several distinct data sets set up at different times,

has been put into a common format. This compilation of unevaluated data

is a much larger database than the comparable evaluated database, listing

data on upwards of 1984 elementary reactions. This is the core database

that will be used for development of a general database containing data on all gas phase chemical reactions. This task involved the entry of data

published between 1977 and 1982, and the reformatting and further

annotation of data previously abstracted and published as NBSIR 81-2254

( 1981 ), which covered the literature published between 1971 and 1977.

The center continues to provide support to the NASA stratospheric

chemistry program. Robert Hampson was one of the authors of the recently

released NASA report to Congress; "Present state of knowledge of the upper

atmosphere. An assessment report. Processes that control ozone and other

climatically important trace gases", which warned of the consequences of a global warming trend. The role of trace gases in promoting the greenhouse

effect means that trace atmospheric constituent chemistry is of great

importance. For that reason we are initiating a new program with NASA

support to re-consider the existing database. This is described in more

detail below.

In addition, evaluation activities in the area of halogen chemistry

have continued including participation on the NASA Panel for Data

Evaluation.

Plasma cnemistry is of great practical importance in the fabrication

of microelectronic components, the surface coatings industry and in the

transmission ana switching of electric power. There are, however

remarkably few data available to carry out computer simulation studies of

what are very complex chemically reactive systems. A part of that problem

has been successfully treated through evaluation of both the thermochemical and kinetic databases for the species involved in the dielectric

breakdown of sulfur hexafluoride, which is widely used in the power

industry. By accompanying the data evaluation activities with computer

simulation, the potential for hazards resulting from the formation of

toxic breakdown products has been demonstrated.

Three papers have resulted from this work:

"Thermochemical Data on the Gas Phase Compounds of Sulfur, Fluorine

and Oxygen Related to Pyrolysis and Oxidation of Sulfur

Hexafluoride," J. T. Herron, J. Phys. Chem. Ref. Data, submitted.

"A Critical Review of the Chemical Kinetics of SF^, SF5

, and S 2

F-|q in

the Gas Phase," Int. J. Chem. Kinetics," J. T. Herron, accepted for

publication

"£> 2^10 Formation in Computer Simulation Studies of the Breakdown of

SF5

," j. T. Herron, IEEE Transactions on Electrical Insulation,

accepted for publication

121
A major undertaking of the data center was the organization and

running of the International Conference on Chemical Kinetics which was held at the NBS Gaithersburg site. It was supported by OSRD and by AFOSR,

GRI, NASA, and NSF. Our goal in holding this meeting was to strengthen the

connections between theory and experiment. We see an increasing reliance

on theoretical methods in data evaluation and want to encourage their

development. The meeting program was designed to do this. The meeting

proceedings were published as a special issue of the Journal of Physical

Chemistry (Volume 90, #3, January, 1986).

The design of the database management system for the HP-1000 computer

is complete. Work on providing unique descriptors for all chemical species

in the system will be finished this year, at which point the kinetics data

base can be loaded. In summary, the design of the system is complete, and our goals have shifted from design to implementation.

Work started this year on developing a stronger capability in the

area of modeling complex reaction systems. A prototype modeling program

has been prepared and tested. An associated graphics program has also

been written. Walter Braun is responsible for developing these programs

in collaboration with David Kahaner of the Scientific Computing Division.

2. Plans

(a) Compilation of Gas Phase Chemical Kinetic Data.

We will continue to identify, abstract, and enter chemical

kinetic data for all types of gas phase reactions into the existing data

base. This will be the starting point for future data evaluation projects

both within the Data Center and by outside workers.

(b) Combustion Chemistry Database.

The expansion of this data base will continue to be a high

priority activity of the Data Center. We will do this by including new classes of fuel type species such as the alkenes or alkynes, or reactive

species such as oxygen atoms or alkyl peroxy radicals. The objective will be

to evaluate the existing body of data and to use the evaluations as a basis

for developing estimation methods for reactions for which there are no data.

A start was made last year on the evaluation of data on oxygen atom

reactions with unsaturated organic species. That will be extended this year

to include reactions of oxygen atoms with organic sulfur compounds, and

reactions with saturated organic species.

(c) Stratospheric Chemistry Database.

Our existing programs in support of the NASA Upper Atmosphere

Research Program will continue. The Data Center will retain responsibility

for the evaluation of stratospheric halogen chemistry. We will actively

participate in the activities of the NASA Data Evaluation Panel and of the

122
re-established CODATA Task Group on Gas Phase Chemical Kinetics. These

activities will be augmented through a new program involving a re-evaluation

of the chemical kinetic data base recommended for use in modeling

stratospheric chemistry. The goal of this program will be to provide

documentation for including or rejecting each of the possible reactions of

the reactive species included in current models. It will involve the

development and use of techniques for estimating thermochemical and chemical

kinetic parameters.

(d) Plasma Chemistry Database.

This activity will continue at a modest level. The earlier

work on the properties of S-F compounds will be extended to some of the

organic analogues, the sulfoxides and the sulfones. The thermochemistry of

these compounds will be reviewed and new group values derived for the S-0

type groups.

(e) Database Management System.

With the loading of the chemical kinetics database onto the

HP-1000 computer, the emphasis will shift to the development of database

management systems for desktop computer systems. Wherever possible

commercially available systems will be used. The goal is to make the

various databases available to outside users through easily transportable

disk or tape media. As an added service to users, we will continue to

develop auxiliary program packages to assist in the use and extension of the

databases

(f) Data Evaluation and Application Programs.

The activity started this year on the development of a set of

programs for modeling complex chemical reaction systems and graphically

displaying the results will be pursued in collaboration with Walter Braun of

this Division and David Kahaner of the Scientific Computer Division. The

possibility of devising a sensitivity analysis for the modeling program will

be explored. Other program packages under consideration include RRKM

programs, BEBO and BSBL programs, and various associated programs for

obtaining thermochemical properties.

B. Ion Kinetics and Energetics Data Center

(S. G. Lias and R. D. Levin)

The goals of this Data Center are to collect and maintain an up-to-date file of experimental data pertaining to the thermochemistry of

ions (ionization energies, appearance potentials, and equilibrium

constants as well as the heats of formation of positive and negative ions

in the gas phase) and the kinetics of ion/molecule reactions, to make

compilations of these data and to publish evaluations of the collected

data for use by the scientific and technological communities.

123
The Data Center is closely associated with both the Ion Kinetics Group,

from which it derives scientific support, and the Chemical Kinetics Data

Center, with which facilities and expertise are shared.

1 . Accomplishments

During the past year, efforts were concentrated on completing the

comprehensive compilation of evaluated ionization energies and heats of

formation of positive and negative ions in preparation for submission to the

Journal of Physical and Chemical Reference Data. Accomplishments on this

task included: (a) abstracting data for approximately 1400 additional

species, which appeared in the literature in the years 1981-1986, and adding

these data to the data base; (b) locating or estimating heats of formation

for the newly-added compounds; (c) identification of compounds within this

group for which structural drawings need to be made for the publication,

preparation of rough drawings, and arranging for the preparation of the

final ink drawings; (d) writing of a review of the field to be included as introductory textual material; (e) writing of software to sort the data

base; (f) downloading the associated bibliographic data base from a microcomputer to the HP-1000; and (g) coordinating efforts of NBS and non- NBS collaborators in reviewing the evaluations and the textual material.

At this writing, the sort software is being de-bugged, the contributions

of non-NBS authors to the textual material are being incorporated, and the

task of evaluating the need for drawings is being completed. It is anticipated that the publication will be submitted to the Journal of Physical

and Chemical Reference Data on or before January 1, 1987, as "Gaseous Ion

and Neutral Thermochemistry" (GIANT) by J. E. Bartmess (University of

Tennessee), J. L. Holmes (University of Ottawa), R. D. Levin, S. G. Lias,

J. F. Liebman (University of Maryland, Baltimore County Campus), and

S. E. Stein.

The data base for the 1984 Data Center publication of 780 evaluated gas

basicities/proton affinities of neutral molecules was brought up to date by

the addition of all the data which had appeared in the literature since the

cut-off date of the original publication (1984). New data for 234 species were added, and some of the values of proton affinities were re-evaluated as

a result of the appearance of better experimental or theoretical data. Work

on this up-date continues.

With the collaboration of S. Stein, the entire ion energetics data

base (containing heats of formation of more than 5000 neutral and ionic

species) has been stored on disks for a microcomputer , where it is

searchable using commercial software. This accomplishment represents a feasibility study by S. Stein for the possible future use of such systems

for routine Data Center tasks.

2. Plans

During the first months of the coming year, top priority will be

given to completing the major publication which is in progress, as described

above

124
As mentioned above, an up-date was prepared during the past year

concerned with the data base of evaluated gas phase basicities and proton

affinities of molecules. Since the data represent an extensive

thermochemical ladder, maximum utility is obtained when they are presented

in a sorted version according to proton affinity; it is anticipated that

the data included in the original publication will be merged with the newer information and a publication will be prepared during the coming

year. This small data base is ideal for distribution on disk for use with

microcomputers; exploratory work on accomplishing this is beginning.

R. E. Huie and P. Neta, in collaboration with the Radiation Chemistry

Data Center, Notre Dame University, are preparing an evaluated compilation

of rate constants of inorganic radical reactions with organic and

inorganic compounds in aqueous solutions. A publication will be prepared

to be submitted to the Journal of Physical and Chemical Reference Data.

Discussions have begun with Drs. Vincent Anicich (Jet Propulsion

Laboratory), Albert Viggiano (Air Force Geophysics Laboratory) and Jean

Gallagher (JILA) on the possibility of collaborating on an comprehensive

compilation and evaluation of ion/molecule rate constant data.

125
3 . KINETICS OF NEUTRAL SPECIES

W. Braun, R. L. Brown, J. W. Hudgens, M. J. Kurylo, R. I. Martinez,

S. E. Stein and W. Tsang

R. Chen, J. P. Cui, S. Dheandhanoo, A. Fahr, Y. Z. He,

R. D. Johnson, III, S. Kafafi, A. H. Laufer, G. R. Long, H. Okabe,

M. D. Scheer, V. Senthilnathan, M. Suryan, T. Wallington, J. A. Walker,

A. Overview

The focus of the activities of this group is the study of the

chemical kinetics of neutral species, with special emphasis on free

radicals and excited state molecules. Our goals are to develop methods for

the detection and quantification of transient reaction intermediates, to

measure rate constants for processes involving these species and their

precusors, and to determine the mechanisms of reactions in which these

species are reactants or products. Individuals in this group interact

strongly with our data evaluation program by providing key measurments,

theoretical concepts and through direct involvement in evaluation

activities. The past year has been an exceedingly succesful one for this

group. By all the usual measures, productivity is at an all time high.

Even more important, the ground work has been laid for increasingly

significant contributions in future years.

The fundamental quantities of interest to this group remain

elementary rate constants. They are a measure of the rate of change of the

chemical constituents in a system where the molecules have a Boltzmann

distribution. We regard this as the key interface between more detailed

scientific information at the state-to-state level and the technological

marketplace where kinetic information is used in predictive models. These

measurements are also direct inputs into our data center. Furthermore,

from these numbers one can derive data on molecular properties such as bond energies, enthalpies and entropies of formation, and transition state

structures and energetics, that are necessary for our data evaluation

activities in that they lead to algorithms for prediction and define the

boundaries for the evaluation of existing data.

The range of problems under study by this group is very broad. They

range from studies of reactions of atoms and small radicals and biradicals

in the gas phase to the chemistry of large polynuclear aromatic

hydrocarbons. In the following, the activities of the group are given very

roughly in the order of the complexity of the molecular system under

study. This ordering illustrates the fact that progress in studying

complex chemistry depends on data on the kinetics of simpler systems. That

is, although new factors are introduced with molecular complexity, the

chemistry of atoms and small radicals is always an essential component for

the understanding of the total system. Thus our background in the

chemistry of atomic and small radical chemistry has been a major factor in

the developement of our newer programs on the transformation of complex

126
organic compounds. Indeed, at the present time much of the quantitative

work at a fundamental level on the stability and reactivity of aromatic

systems at high temperatures is coming from our laboratories.

B. Multiphoton Ionization Detection of Reactive Intermediates

(J. W. Hudgens, G. R. Long, and R. D. Johnson, III)

Resonance enhanced multiphoton ionization (REMPI) spectroscopy has

become a popular optical technique because it can sensitively detect

reactive intermediates not suitably detected using laser induced

fluorescence (LIF), Raman, or CARS spectroscopies. REMPI selection rules

also allow investigation of molecular states that are forbidden in

conventional one photon experiments. The objective of this project is to

develop and use REMPI to explore the spectroscopy and reaction dynamics of

reactive intermediates.

In a REMPI experiment an intense laser beam irradiates molecules with

laser light. When the frequency of the laser light becomes equal to either

one-half or to one-third of the energy separation between two electronic

molecular states and selection rules permit, the molecules absorb photons

until they ionize. A mass spectrometer analyzes the ions.

Major improvements of the laboratory facilities which have benefitted

the research program occurred during the year. Laboratory space was remodeled to suppy improved power and utility services for lasers, and a crane was installed to handle heavy vacuum components. In February, lasers

and vacuum equipment were moved into this space. The new laboratory has

provided a safer and more advantageous layout of equipment.

During FY85 significant effort was invested to design and procure

components for a new mass spectrometer system designed specif ifcally for the

needs of REMPI experiments. During the past year these components arrived

and we assembled the apparatus and optimized its performance for

experiments that involve molecular beams, effusive ovens and flow reactors.

The new multiphoton ionization apparatus is built with the vacuum

system integrated into an optical table. This design allows precise and

stable laser beam alignment. The vacuum system consists of a large

chamber where molecular beams and laser beams interact, two sidearms where

pulsed molecular beams of radicals are generated, and a chamber which

houses a Reflectron time-of-flight mass spectrometer. The system has

demonstrated excellent sensitivity and ion throughput efficiency.

127
315 320 325

LASER WAVELENGTH (nm)

Fig 3*1 • The m/z 23^ REMPI spectrum observed from the perdenterated

methoxy radical produced by the reaction F+CD^OD.

In the inaugural study employing this new apparatus, we discovered the

first REMPI band systems of methoxy radicals. During a second study which

involved the development of an oxygen atom source, we observed the first

REMPI bands of transient 0

2 ('a) molecules. We believe that this REMPI

detection method for 0

2 ('a) molecules exceeds the sensitivity of any other

optical technique. In addition, these experiments revealed previously

unreported electronic states of 0

2 molecules which reside between

67 , 000- 73,000 cm

-1

.

1 . Spectroscopy of methoxy and hydroxymethyl radicals during the

reaction of fluorine atoms with methanol.

Methoxy radicals, CH^O, and hydroxymethyl radicals, CH 2 OH,

play important roles in a wide variety of chemical systems including the

atmosphere, flames, interstellar space, and catalytic surfaces. During our REMPI studies these radicals were generated in a flow reactor by reacting

fluorine atoms with methanol and isotopically substituted methanols, e.g.

CH

3 0D + F > HF + CH3

O (m/z 3D (la)

> HF + CH 2 0D (m/z 32) (1b)

Methoxy radical REMPI spectra (Fig. 3»D appeared as bands of dense

rotational lines between 3 1 3~ 328 nm. Mass spectra of each isotopic analog

showed that the molecular ions do not fragment. An isotopic substitution

study proved that the chemical structure of the laser ionized species was that of methoxy radical.

128
The fact that methoxy ions do not fragment is significant. The ground

state of the methoxy cation is unstable, but its lowest triplet state is

bound. Thus, to produce unfragmented molecular ions, REMPI ionization must

specifically prepare the triplet a 3 a state methoxy cation. Additional

work is underway to resolve the REMPI mechanism and the identity of the

resonant electronic state which generates the spectrum.

Besides methoxy radicals reaction (1) also generates hydroxymethyl

radicals, CH 2 0H. Currently, REMPI spectroscopy is the only laser method

that can detect the CH 2 OH radical. This year we published an extensive

analysis of REMPI spectra observed from four isotopically substituted

hydroxymethyl radicals. The electronic bands observed between 420-495 nm

(Fig. 3.2) were shown to originate from a 3p Rydberg state.

Fig. 3*2. Multiphoton ionization spectrum of the CD 2 0H radical.

A normal mode analysis of the REMPI spectra enabled assignments of six

active vibrational modes in the excited state. As a result 85? of the 1 30

vibrational bands observed between 420-495 nm were assigned. The normal

mode assignments enabled a comparative analysis of electronic structure and

bonding of the ground and Rydberg state hydroxymethyl radicals. Among other

points this analysis showed that the hydroxymethyl ion is more strongly

bound than the ground state radical. The methoxy to hydroxymethyl

radical isomerization rate was directly measured and found to be slower than

2.9 sec

-1 at 300K.

We note that as a result of these studies REMPI spectroscopy can now optically measure each transient species (F, CH^O, and CH 2 0H) produced and

consumed in reaction (1). No other optical spectroscopy can accomplish such

measurements

129
2 . REMPI studies of the F + Ketene reaction.

We have also applied REMPI spectroscopy successfully to the

previously uncharacterized reaction of fluorine atoms with ketene and

ketene-d2. The exothermic allowed channels are:

F + CH 2co ——> HF + HCCO AH = -27 kcal/mol (2a)

> CO + CH 2 f AH = ~35 kcal/mol (2b) ——> H + FHCCO AH = -11 kcal/mol (2b)

The reaction was conducted in a flow reactor and mass resolved REMPI

spectroscopy characterized the reaction products.

REMPI signals from fluoromethyl radicals, CH 2 f and CD 2 F, were observed

between laser wavelengths of 270-380 nm. Besides showing the activity of

reaction (2b) for the first time, these spectra are also the first spectra

of any excited electronic state of the fluoromethyl radical. The REMPI

spectra originate from two photon resonances with 3p and Up Rydberg states.

Absorption of a third photon ionizes the radicals. The spectra show

vibrational progressions of the CF and CH 2 'scissors modes.

During the study unexpected signals from CH and CF appeared. At

-311 nm a 2+1 REMPI band from CH radicals was observed. We determined that

the CH radical was generated by the two-step photolysis of ketene:

CH2C0 + hv > CH2 + CO (3)

CH2 + hv > CH + H (4)

CF radical m/z 31 REMPI bands were observed at 3^5 and 356 nm. Although

we did not directly determine that HFCCO was produced by reaction (2), CF

radicals are probably symptomatic of this reaction product. In this view CF

radicals would originate via two-step photolysis of HFCCO:

FHCCO + hv ——> CFH + CO

CFH + hv ——> CF + H

Halocarbenes are known to have predissociati ve states over the study

wavelength

3. Future Work

During the next year we will be continuing our search for free

radicals of importance to combustion, photochemistry, and catalysis. Some

of the targeted radicals are the phenyl, phenoxy, vinoxy, H02

, ethynal

propargyl, and vinyl radicals. We will conduct experiments that determine

REMPI excitation mechanisms and state identities of the new detection

schemes we discover.

The new multiphoton ionization apparatus enables us to generate react i ve specie by laser photolysis in molecular beams. Because molecular beams

enhances the control of experimental conditions during studies, we expect

130
that a significant fraction of our future work will feature this synthetic

approach. The new apparatus has facilities to support two molecular beams.

During the next year and after initial studies which use molecular beam

radical generation, we plan to try some crossed beam bimolecular reactive

studies and probe for the nascent products with REMPI mass spectrometry.

C. Reactivity of Small Radicals

(M. J. Kurylo, P. A. Ouellette, and T. J. Wallington)

In this research program, spectroscopic measurement techniques are applied to the detection and chemical kinetic characterization of small

gas phase free radicals in a controlled reactive environment. A major goal

is to provide a quantitative data base for developing of theory of

association reactions. Such studies also have direct applicability in the

understanding of tropospheric acid rain formation, stratospheric ozone

depletion and other important technological areas. In the area of

chemistry we have seen on impressive application of fundamental chemical

kinetic information for the solution of societal problems. Increasing

emphasis is being placed on high accuracy rate measurements. The Chemical

Kinetics Division has long been a participant in this program, with our data center playing a key role. One of us (MJK) is a member of the NASA

Stratospheric Kinetics Data Panel. Our choice of problems is thus

influenced by the needs of this community. However, these high accuracy

measurments also provide important information with regard to fundamental

energy exchange effects in unimolecular decompositions.

1 . H02 Chemistry

as a function of pressure. This work, supported by the NASA Upper

Atmospheric Research Program, utilized the technique of flash photolysis

kinetic absorption spectroscopy. Reaction (1) is the primary source of

pernitric acid in the atmosphere and plays an important role in the

catalytic reaction cycles describing stratospheric ozone depletion. The

temperature dependence work is a follow-up to our earlier room temperature

investigations from which we were able to calculate the fall-off parameters

which relate the pressure dependence of the reaction rate constant. The

data from the present work were fit to this same fall-off equation

During the past year, detailed measurements have been completed

which describe the temperature dependence of the reaction

ho 2

+ N02+ n2 ho2 no2+ n2

( 1 )

k([M] z T) = a and N = 0.75 - 1 .271og(F^‘)‘

with the temperature dependence of the fall-off parameters given by

and

k o M

(t) = k o M

( 3°°K H T/ 300}~n

{< (T) = k ( 300K) { T/300}

m

(II)

(III)

131
The room temperature (300K) values of the fall-off parameters could be

determined from the equation (I) analysis of our earlier results. For data

evaluation purposes, our results have been fitted jointly with the one other

existing temperature study reported in the literature to give (in molecular

units)

and

k o,N2 (300K) = 1 .8 x 10_31

k o ' 02 (300K) = 1.5 x 10-31

k inf (300K) = 4 . 7 x 10-12

n = 3*2 q m = 1.4 q These results support current recommendations which have been based on a limited data set coupled with theoretical computations. A manuscript giving

full details of the measurements and data reduction has been prepared for

submission to the Journal of Physical Chemistry.

2 . OH Reactivity

In addition to the hydroperoxy radical studies, we have initiated a series of experiments directed at the determination of the rate parameters

for the reaction of OH radicals with a series of halogen-substituted

benzenes. The kinetic parameters derived from this work will lend

themselves to mechanistic interpretations and will yield important

information about substituent effects in aromatic oxidation reactions

thereby assisting our understanding of more complex transformations. This

work is nearing completion and a manuscript will be prepared for submission

to the International Journal of Chemical Kinetics.

3. Plans

Next year, the HO2 kinetic studies will be extended to the

investigation of reaction ( 2 ).

H0 2

+ CH

3 O 2 "> CH

3 OOH + 02 (2)

This reaction is important in the atmospheric oxidation of methane and other

hydrocarbons as well as in low temperature combustion systems. Laboratory

experiments designed for the study of reaction ( 2 ) do not lend themselves to

standard first or second order kinetic analyses due to complications caused

by the self reaction of the two radicals. Instead, the experimental radical

concentration vs. time profiles must be compared to concentration profiles

produced via computer modeling over a range of experimental conditions for

determination of the rate constants. During the previous year we completed

work on the computer analysis routines which will be employed in the data

reduction and conducted modeling experiments to indicate the experimental

conditions which will be most sensitive to the determination of the rate

constant

.

132
Future OH studies will be extended to include other substituents (for

the aromatic systems) and/or reactions with various reduced sulfur

compounds. The former systems will extend the data base for the

development of predictive models, while the latter have more direct

applicability to atmospheric oxidation and should yield important

information regarding the role of Coulombic effects in free radical

reactions

.

Over the next several months, we also plan to initiate the design and

construction of an apparatus suitable for studying reactions of the NO^

radical. Although this species plays a major role in the chemistry of the

troposphere and stratosphere, considerable rate constant and mechanistic

data are still needed. A few kinetic studies can be performed for NO^

using flash photolytic generation. These, however, are limited due to

reaction interference of the precursors. For this reason we plan to

utilize discharge flow technology coupled with detection via absorption

spectroscopy to investigate a series of oxidation reactions involving this

important free radical.

D. Reactions of Biradicals and Unsaturated Free Radicals

(W. Braun, A.Fahr and A. Laufer)

The objectives of this program are to produce and chemically

characterize biradicals and unsaturated free radicals through flash

photolysis using vacuum ultraviolet kinetic spectroscopy to follow species

concentrations. Gas chromatography is used for end-product analysis.

Isotopic substitution is used to clarify mechanistic processes.

Our recent efforts, supported by the NASA Planetary Atmospheres

Program, are directed towards understanding the mechanism of formation and

the chemistry of the vinylidene biradical. This species, the smallest of a large class of unsaturated biradicals, was initially identified by us on

the basis of its characteristic absorption in the vacuum ultraviolet. We

have determined that the particular state of vinylidene under observation

is the lowest lying excited triplet, about 40 kcal/mol above the ground

singlet state. The particular excited state is metastable with respect to

the ground singlet as there is a 45 kcal/mol barrier to its isomerization

to acetylene. The intermediate is quite stable requiring about 104

collisions to quench.

Triplet vinylidene has been identified as an important intermediate

in several photochemical and reactive processes. Although directly

observed from the vacuum ultraviolet photolysis of C2H4 and C

2 H2, a more

convenient source has proven to be the be flash photolysis of vinyl

chloride, C2H3CI. The photodecomposition has been previously studied and

may be described as follows,

C2H3CI -> H 2 C=CH 2

+ HC1

-> C0H0 + HC1

(1)

( 2 )

( 3 )

133
Aside from C

2Ho radicals all the decomposition products could readily be

monitored by their VUV absorptions. Channel (1) is the primary process and

the initial temporal profiles of H

2 c=C and HC1 are identical. They are thus formed in the same reaction. HC1 is a non-transient whose

concentration could be directly deduced from its absorption. At times

short compared to the collisionally induced isomerizaton of the triplet

vinylidene , the concentration of H

2c=c and HC1 are equal. This leads to an extinction coefficient for the former of 694 cm-1 atm-1 at 137 nm. This

permits a direct determination of the quantum yield of triplet vinylidene

in the photolysis of other systems.

In an earlier study it was shown that He quenched the deuterated

vinylidene (D2 c=C) about 5.5 times slower than the protonated moiety. The

observation has been utilized to examine the quenching of vinylidene by a series of non-reactive molecules; Ar , N

2 , h 2 , CO, and CHij. To improve the

accuracy of the experiments, the study was carried out with deuterated

vinylidene rather than protonated which allows for longer time profiles.

The rate constants are the sum of all removal processes, including

chemical reaction. In the two cases where reaction were possible, H

2 and

CHty, there was no evidence of chemical reaction. The observation agrees

with our earlier bond strength-bond length theoretical prediction of slow

abstraction rate parameters for the triplet vinylidene radical. The rate

constants were of the order of 1

0

—

1

^—1

0

—

1

^ cm^ molec -1 s

-1

. We were able to

measure quenching parameters for only a limited number of molecules of

interest. To provide an approximation scheme for estimation of physical

quenching rate parameters for other species we fit our data to a model

using the potential well-depth that has proven to be remarkably useful.

This past year we were able to obtain the first definitive measurement

of a chemical process involving triplet vinylidene, i.e., the reaction with

molecular oxygen. The reaction, written as

D

2 C = C +0 2 ~> D 2 CO + CO (4)

was found to proceed through a cyclic intermediate comparable to that

found in the reaction of several other unsaturated radicals such as C

2 H,

C

2H

3

, C^H^, and in the present work D 2 CC, with 0 2

. The striking feature of

the reaction was the 1:1 correspondence between the formation of the two

products, D

2 CO and CO. Nevertheless it was difficult to determine the

kinetic parameters in the presence of competing CO producing reactions

such as reaction of 0(3P) with product acetylene or with C

2H

3 C1 reactant

remaining following photolysis. All the competing processes were con- sidered and the rate constant for (4), 1.5 x 10~ 3 cm3 molecule ^ , was obtained from a model.

We have obtained a commercial array detector with which preliminary

experiments are in progress to optimize the vacuum ultraviolet response.

The commercial device is designed to maximize the output over a wavelength

region from the ultraviolet through to the infra-red. Our requirement,

however, is limited to the up-conversion from the vacuum ultraviolet to a wavelength observable by the photosensitive device. Initial efforts to

improve the response are underway. A factor of 2-3 improvement in

134
fyM-l-t

sensitivity seems feasible. A critical factor is maintenance of

instrumental resolution as it is planned to join the detector to the exit

plane of the 2-m Eagle vacuum spectrograph in a configuration that will

permit simple conversion from array detection to vacuum ultraviolet

sensitive plates which have certain advantages. Our interest is to record a large number of spectral elements, the unique advantage of plate technology,

with photomultiplier sensitivity and speed without loss of spectral

resolution.

E. Energy Transfer from Vibrationally Excited Molecules

(W. Braun and M. D. Scheer)

We have developed a new method for determining rapidly changing

translational temperatures in a gas that has been heated by such transient

phenomena as the passage of a shock wave or the absorption of submicrosecond pulses of radiation from an infrared laser. The method depends

upon the use of trace amounts of Hg vapor and its absorption of radiation in

the neighborhood of the 253.7 nm isotopic and hyperfine multiplet. As the

Hg atoms sense changes in the translational temperature of the host gas, the

absorption of 253.7 nm radiation also changes by virtue of the Doppler and

Lorentz broadening of the multiplet lines. Emission spectra of a Hg

discharge light source in the neighborhood of 253.7 nm were shown to be

readily simulated by a two zone computer model even at large optical

densities. The same lamp parameters that were used in these calculations

could also be used to simulate the experimental pressure and temperature

dependence of the total integrated absorption. This provided a means for

obtaining the temperature calibration curves needed to monitor the changing

translational temperature of a gas undergoing rapid heating or cooling.

This detection method has been directly applied to the measurement of

v-r,t energy transfer of vibrationally excited gases. Use was made of a C0 2 TEA laser tuned to P

2 0 (10.6um) lines to excite SFg into some initial

distribution of vibrational states. The degree of excitation was systematically varied by attenuating the laser beam with partially absorbing CaF2

windows. The relaxation was measured by monitoring the time resolved

absorption of a 25^nm beam by a 500:1 SFg-Hg mixture. The final temperature, Teq, (i.e. the T after complete equipartit ion of the excitation

energy but before the beginning of significant cooling by thermal

conduction) was obtained from the above mentioned Hg absorption vs. temperature calibration.

The experimental results were analyzed as follows: The Hg absorption

data (A absorption vs time) were converted to AT or AE vs time curves

and the relaxation time constants (t) were determined from the initial

slopes. To obtain the average energy transferred per collision, <AE>, it

is necessary to calculate the energy change during the relaxation process,

which is equal to the energy per model of SFg required to bring its

translational and rotational degrees of freedom from 298K to Teq. It

follows then that <AE>=( x)/(Z)

,

where X is the SF^ collision frequency and

<AE> is the average vibration energy transferred to rotation and translation per collision between two vibrationallly excited SF^ molecules. A

135
decadic plot of log <AE> versus log <E> (where <E> is the energy required

to bring the SF^ from 298K to Teq). Shows that <AE> increases as the

square of the excitation energy <E>.

In a second series of experiments, a trace of toluene (instead of Hg) was added to SF^ and its absorption of the Cd 228nm resonance line

monitored the vibrational energy transfer from the SFg* into the internal

degrees of freedom of the toluene. The time constants obtained with

toluene (for v-v transfer) were almost identical to those obtained with Hg

as the tracer (for v-v, t transfer) suggesting that toluene may acquire

internal energy via the route SFg(v)-SF6(r f t)-toluene(v,r,t)

.

We plan to apply the Hg tracer technique in future experiments to

molecules that are larger and more complex than SFg and to study how the

rates of energy transfer are affected by the structure of the colliding

molecule and whether it is a net donor or net acceptor of energy in the

relaxation process.

F. MS/MS Tandem Mass Spectrometry

(R. I. Martinez and S. Dheandhanoo)

1 . Goals

The focus of this study is the use of MS/MS tandem mass spectrometry to monitor in real time reactive polyatomic species in

complex reacting mixtures. The time dependence of the concentrations of

all reactants and products provides unique insights into the mechanisms of

complex physicochemical systems. Our instrument has been operational

since the beginning of the year and we have successfully developed a generic transferable target thickness standard for the common target gases

Ar and N2. This goes a long way towards eliminating one of the major

impediments blocking the measurement of standardized MS/MS spectra for

characteriza-tion of unknown species. There is a pressing need for

quality assurance in this area and the work is supported by the Air Force.

2. Instrumental Approach

Tandem mass spectrometry (MS/MS) exploits the ion fragmentation

patterns which are characteristic of the structure of a compound. Thus the

ion-fragmentation mapping obtained in the MS/MS by collision-induced

dissociation (CID) of ions allows one to uniquely identify any component

in a complex mixture. These characteristic profiles ["breakdown curves"]

of ion abundance vs. target density (or collision energy) correspond

uniquely to the sequence:

(granddaughter )i < — ( daughter )j <-- ( parent )k

thus allowing the "genealogical tree" of CID fragmentation to be

reconstructed , and the structure of an unknown species to be assigned.

136
3. Critical Parameters

To permit the characterization of unknown compounds in complex reacting

mixtures, it is essential to analyze their CID "breakdown curves". There

are several critical parameters which can significantly alter the observed

CID spectra. However, one of the most important is the effective gas

target thickness. The effective target thickness of the CID gas is

defined as: (actual path length traversed by the ion through the CID gas

target) x (effective number density of the CID target gas). A recent

international round robin test indicated that the effective target

thickness of a CID gas was in error by estimated factors of 2-4. More

importantly, there has been no direct way to measure the effective target

thickness actually perceived by the ions undergoing CID in either

molecular beam target or collision chamber instruments. Because of the

complex oscillatory trajectories of ions within a quadrupole mass filter,

the actual path length traversed by the ion through the CID gas can be

significantly longer than the nominal gas target length. Hence, our first

task was to develop an absolute target thickness standard. In this we have

succeeded.

Knowledge of effective target thicknesses is also essential for the

development of CID spectral libraries generated in different types of

instruments. On the order of 150 commercial triple quadrupole MS/MS

instruments are in operation worldwide, being used as analytical tools for

rapid, direct speciation of complex multicomponent mixtures (gas, liquid,

or solid). Nonetheless, effective utilization is hindered by instrumental

artefacts which have prevented the use of reference spectral libraries.

The generation and interchange of reference libraries of CID spectra

necessitates standardized operating conditions for the various designs of

these instruments.

4. Accomplishments

We have developed a new measurement method which permits in situ

calibration of effective target thickness. It involves determination of

the cross-section o(E) versus energy (E) curve of the simplest of

ion-molecule charge transfer reactions A+ + B -> B+ + A under pseudo-first

order conditions. Since,

Ln Y = oE Leff [B]= 8 PB,

where Y*[ A+]0/[ A+] , oE is the reaction cross-section at a collision energy

E, Leff= effective path length traversed by projectile ion through CID

target gas, Leff [ B] = effective target thickness for A+ in B, B=

proportionality constant, and PB= pressure of target gas B corresponding

to [B], measurement of Ln Y provides in-situ calibration of the effective

target thickness if oE is known. Moreover, if we monitor B+, from the

relation

Ln W = oE Leff [B] = 8 PB

137
where W» [B+]/{ [B+] - [B+] } = [A+]0/{ [A+]0 - [B+] }, obtaining the same results from Ln Y and Ln W measurements provides strong assurance that the

instrument is well, behaved.

We have thus obtained the o(E) vs. E relation for the symmetric

(resonant) charge transfer reaction 22^je +(20Ne ,22^e )20Ne +

. This reaction

was selected to validate instrument performance because the theory of

resonant charge transfer is reasonably well established, and because the

natural abundance of 22Ne (9.22$) is sufficient to permit the measurement

(with good signal-to-noise ratios) of the projectile ion decay (Ln Y

measurements) and product ion growth (Ln W measurements). Figure 1 shows

our o(E) for collision energies from ca. 5-60 eV (LAB) and summarizes the

experimental and theoretical results reported for this reaction by several

investigators. Prior to our work, it was not clear from the limited

number of experimental studies which theoretical model one could or should

use to obtain reliable estimates of o(E) for use in target thickness

calibrations. Our results from Ln Y and Ln W measurements provide new o(E)

which are in excellent agreement with the Rapp-Francis theory as corrected

by Dewangan (see Fig. 3.3 - solid line labelled D). Moreover, our review of

work in the field of charge transfer reactions, as summarized in Figs. 1 and 2, indicates quite a disparity among different workers. Similarly,

Figure 3.4 shows our results for Ar+( Ar , Ar ) Ar+, showing equally good

agreement with the Dewangan theoretical line for this reaction (labelled D in Fig. 3.4). Hence, since our instrument is kinetically well behaved, it

should be possible to readily determine for polyatomic CID gases the

branching ratios a(E) for different reactive channels i. This work has

been submitted for publication.

Fig. 3.3. Plot of o1/2 (reaction cross-section)1 /2 vs. projectile ion

velocity v. Ne+(Ne,Ne)Ne+ Comparison of our results with

other workers and with theoretical models. 0,0 - our projectile decay experiments; the two symbols correspond to

two different sets of experiments. - our product growth

experiments

if. e

1 10 100

v, 10 5 cm/s

138
E

o

CD

Io

iad

O

Fig. 3.4. Plot of o1/2 (reaction cross-section)1 /2 vs. projectile ion

velocity v. Ar+( Ar , Ar ) Ar+ Comparison of our results with other

workers and with theoretical models, o - our projectile decay

experiments o - our product growth experiment

Other workers can now perform in-situ target thickness calibrations

in their instruments by using our measurement protocol with our o(E) vs. E

results for the appropriate CID target gas. Since Ar and N

2 are commonly

used as CID target gases, our measurements of o(E) for Ar+(N2 , Ar )N2

+ and

Ar + ( Ar , Ar )Ar+ allow one to calibrate in-situ the target thickness of N

2 or

Ar gas targets.

5. Plans

Interlaboratory round-robin testing of our kinetic method in

various types of instruments is essential to confirm its reliability as a generic target thickness standard. Consequently, we will soon initiate

collaborative round-robin experiments with academic, industrial, and

government laboratories. Several investigators have agreed to participate to

establish the degree of variability one encounters when using a standardized

protocol with different operators on the same and/or different instruments

of several types. We will also be measuring o(E) for CH ^ targets. Then

we will use our kinetic protocol to correct for mass discrimination within

the MS/MS between the parent and fragement masses. This is essential to

standardize the CID spectra independent of instrument parameters. We will

then measure absolute breakdown curves for selected compound classes.

139
G. Single Pulse Shock Tube Studies on Thermal and Chemical Stability of

Aromatic Compounds

(W. Tsang., W. G. Mallard, J. A. Walker, Y. Z. He, and J. P. Cui)

The focus of our work continues to be the behavior of aromatic

systems under extreme conditions. This has been a neglected area in

chemical kinetics as evidenced by the lack of quantitative data. Our

approach has been to study the fundamental aspects of the reactivity of

aromatic structures and thereby establish quantatively the scientific basis

for future advances. During the past year we have concentrated on defining and resolving a number of uncertainties in the decomposition of

nitrotoluene compounds and in exploiting our technique for studying the

mechanisms and rates of hydrogen atom attack on substituted aromatic

compounds where there is the possibility of multiple reaction channels.

The heated single pulse shock tube has worked extremely well and has in

fact been in continuous use for the entire year. We are in the process of

putting together another instrument. Details of our experiments are given

in the following sections. We are particularly interested in extending

our data base for the transformation of aliphatic hydrocarbons to cover aromatic systems. This will then permit the full use of the powerful

techniques of chemical kinetics modeling for the understanding and

optimization of the full range of processes in which aromatic compounds

are of key importance.

1. Nitroaromatic Decomposition

Nitroaromatic compounds are important industrial chemicals. Their

most important use is as explosives. The stability of such compounds is

of great importance for safety as well as a determinant for ignition

behavior. As a result there has been much past interest and controversy on the rates and mechanisms of the initial decomposition process. In our report last year we discussed some unexpected results in the decomposition

of o-nitrotoluene. We noted that toluene and cresol, the expected

products, amount to less than one-half of the total o-nitrotoluene that

disappeared. We have now resolved this problem and discovered a remarkable new mechanism for its decomposition. Specifically, it involves

the formation and disappearance of anthranil as a key reaction

intermediate. The conversion of o-nitrotoluene to anthranilic acid in

strong base was first reported by Preuss in 1900. Subsequent isotopic

labeling work has established that the reaction proceeds through the

initial formation of anthranil. In our shock tube, reactions can only

occur in the gas phase and there is no possiblility of base catalysis. It

appears that at sufficiently high temperatures a reaction channel has been

opened which leads to the same product as the base catalyzed reaction.

Our conclusions are based on detection of trace quantities of anthranil in

steady state concentration, the determination of its rate of formation and

decomposition and the identification of a common product of anthranil and

o-nitrotoluene decompositon (which we believe to be cyanocyclopentadiene )

Fig. 3*5 is a plot of the larger stable products found during

o-nitrotoluene decomposition. Fig. 3.6 shows the effect on the mass

140
balance when anthranil formation and decomposition is taken into account.

It is clear that we have accounted for all the decomposition channels of

o-nitrotoluene

.

The rate expressions that we have found for anthranil formation and

destruction are

k(o-CH

3 c 6H4N02 => anthranil ) = 1 . 2x1 0, _Exp( -26020/T) /s

k( anthranil =*> products ) = 4.0x1 0,^Exp(-25300/T)/s

lb

These rate expressions are compatible with the mechanisms as outlined in

Fig. 3.7 and 3*8* A paper on these findings has been submitted to the

Journal of the American Chemical Society.

N 0 0 HO 0 \/

0% H y°\ *0%

\ /

°\

CM H «

• H. OH

/°N

CH

H«0

* CO

Fig. 3-5. Reaction Products from Fig. 3.6. Mass Balance for

o-Nitrotoluene Decomposition as a o-Nitrotoluene Decomposition

function of C-N02 bond cleavage

rate constants

0

- • -H- + + + ++ H-+

— 1 O-NITROTOLUENE

+ 1 m i -2 r . • +

m O-CRESO^

-3

TOLUENE «• < ,!*» 4

! t *

-4

-5 _ A

0

v CYANOCYCLOPENTAOIENE 1 -6 *

* »

*

00

. s • *

* * j ANTHRANIL -7 _ 0

• i

a

1.5 2.5 U

log k(0-nitrotoluene = > N02 + o-methylphenyl)

Fig. 3.7. Mechanism for

Anthranil Formation from

o-Nitrotoluene Decomposition

Fig. 3.8. Mechanism for

Anthranil Decomposition

141
We have completed and published in the Journal of Physical Chemistry

a paper dealing with C-N02 bond cleavage in the decomposition of

nitroaromatic compounds. This is the main decomposition channel for all

except the compounds with a methyl grouping ortho to the the nitro group.

The rate expressions are,

K(C

6h 5N0 2 -> C(SH 5

+ N02 ) - 1 .9x10 15 Exp(-33026/T)/s

k(o“CH

3 c 6

Hj4 N02 -> 0-^

305

^ + N02 ) - 6 . 4x1 0 ^ ]|Exp( ~30888/T)/s

k(p-CH

3 c 6H 4N02 => P-CH3 C5H 4 + N02 ) = 7.7x1 0 1 4 Exp(- 32305/T)/s

In addition, we estimate that the rate expression for the isomerization of

the nitro compounds to the nitrite is approximately 1

1 3 Exp( -27600/T) /s.

The general trend of these rate expressions is in accord with

thermokinetic expectations. It can be seen that the A-f actors for C-N0 2

bond breaking are very close to each other. Thus, transition state

structures for similar processes do not vary greatly. In conjunction with

the thermochemistry we obtain a combination rate between phenyl type

radicals and N0 2 of approximately IO 9 1/mol-s. This is somewhat lower

than combination rates involving organic radicals and is due to the

possibility of nitrite formation as an alternative reaction channel. The

relative rate constants for C-N02 bond breaking are of the order of

2.4:1 :.

for o-nitrotoluene: nitrobenzene: p-nitrotoluene at the reaction

temperature of approximately 1050K. Thus the effect of methyl

substitution is seen to be relatively small under our conditions. The

degradation of o-nitrotoluene ultimately to form anthranil is

characterized by a relatively small pre-exponential factor. This is

expected on the basis of a concerted process similar to the retroene

reactions that we are familiar with in hydrocarbon chemistry. In the

course of conversion to anthranil either OH and H atom or H

2 o is formed.

From the yields of the light hydrocarbons which are the result of the

induced decomposition of cyclopentane by active radicals we conclude that

both channels must make some contribution. The relatively large A-factor

for anthranil decomposition is in line with the large entropy of

activation to be expected with the breaking of the five membered ring.

Finally, the formation of cyanocyclopentadiene suggests the presence of

nitrene as an intermediate.

Methyl substitution ortho to the nitro moiety leads to the opening of

a new preferred reaction channel. This pathway releases radicals into the

system. At temperatures lower than that utilized here, where ignition of

nitroaromatic explosives occurs, this will be strongly preferred in

comparison to simple C-N0 2 bond cleavage or N02 isomerization. Note that

the rate expressions given here provide to minimum values of the rate

constants since in the condensed phase catalysis can occur. These results

are in accord with the detection of substantial quantities of

dinitroanthranil in TNT decomposition in the condensed phase. Our results

are in quantitative disagreement with recent work on the same systems

using laser pyrolysis. We attribute this difference to the uncertainty in

142
the reaction conditions in laser pyrolysis. A comparison of the two set of

results leads us to suspect that the temperatures may be much higher than

claimed. This work has been supported by the Army Research Office.

The results of this study are indicative of the interesting new reaction channels that become available as one goes to more complicated

molecules. At the present time we have no basis for predicting how and when

such processes will occur. Nevertheless organic chemists have for many years

used high temperature pyrolysis as a preparative tool. We believe that we

have now the means of systematically examining the details of such processes

and placing the kinetics for decomposition into a quantitative frameworks.

2. Hydrogen Atom Attack on Substituted Aromatics:

We continue to exploit the technique discussed last year for the

determination of the mechanisms and rates of hydrogen attack on substituted aromatic compounds. These processes are characterized by a multiplicity of reaction channels and at the present time there are no other methods that are capable of determining the kinetic characteristics

of these very interesting processes. These include the effect of

resonance energy on hydrogen atom abstraction reactions and the

controlling factors affecting displacement processes. A paper on hydrogen

atom reaction with toluene has recently been published. We have now completed work on the reactions with phenol, aniline and several

chlorinated toluenes. Phenol is a key intermediate in the oxidation of

aromatic structures, while chlorinated aromatics represent the most

pressing issue in the incineration of hazardous wastes.

For the phenol study we have also determined the rate constants for OH

attack on phenol and H-atom combination with phenoxy radical. A paper has

been submitted for publication in the Journal of Physical Chemistry. In the

following we summarize briefly the salient points in this work.

The experiments involve decomposing hexamethylethane in the presence of ' sufficiently large excesses of phenol. Hydrogen atoms, formed through the

reaction

C

8 H 18 => 2 t-C 4H

9 => CijH 8

+ H

react with phenol via abstraction of the phenolic hydrogen and displacement

of OH. From the isobutene and benzene that is formed we find,

k(H+C

6H

5 0H=>C 6H

5 0+H2 )/k(H+C 6H

5 0H=>C 6H

6 +0H)= 1 6xExp( -3366/T)

over the temperature range 950-1 100K and between 2.5 to 5 atms. In the

presence of added methane, the benzene yield is depressed due to the

reaction of hydrogen atoms with methane. Using a rate expression of

k(H+CH 4 =>CH

3

+H 2 )=2.4x10 1

Exp( -7000/T) 1/mol-s , we find

143
k(H+C

6H

5 0H=>H2 +C 6H

5 0) = 1 . 1 5x1

1

exp(~3289/T) 1/mol-s

k(H+C6H 5OH=>C 6H 6 +OH) = 1.8X10 11 exp(-6655/T) 1/mol-s

The substitution of large quantities of carbon monoxide in place of methane

leads to increased yields of benzene. This is due to the conversion of the

displaced hydroxide radicals to hydrogen atoms and its reaction with phenol.

On the basis of k(0H+C0->C0 2 +H)=7 x 10 7 exp (.00092T) 1 /mol-s, we find

k(OH+C 6H 5 0H=>C 6H5 O+H 2 O)= 6 x109 1/mol-s

at 1032K. From the equilibrium constant the rate expression for the

displacement of a hydrogen atom by hydroxyl radical is

k(OH+C

6H 6 =>H+C 6H 5 OH) = 6.5x10g exp( -M30/T)l/mol-s

Comparison with OH disppearance rates in high temperature benzenes systems

indicates that the primary process is the abstraction of a ring hydrogen.

Finally, from results of experiments which lead to high yields of phenoxy

radicals, we find

k(H+C

6H

5 0 -> C 6H 5 OH) = 2 x 10 n 1 /mol-s

Through detailed balance this leads to

k(C

6H

5 OH -> C 6H5 0 + H) = 4 x 10 15 exp( -86000/RT) /s

The results of these and earlier study demonstrate that we have now a

. unique methodology for studying the reactions of hydrogen atoms with

molecules where there are multiple reaction pathways. We plan to systematically exploit the possibilities and therebye build up an internally

consistent set of rate constants for all high temperature reactions

involving hydrogen atoms and organic substrates.

Ho Substituent Effects on Bond Strengths

(S. E. Stein and M. Suryan)

In the simplest terms, rates of elementary chemical reactions in gases

and non-polar environments depend on properties of the reaction center

(atoms directly involved in bond making and breaking) and on effects of

substituents. The nature of the reaction center defines the type of

reaction and is generally the dominant factor. However, substituents can be

very important and have long been of interest as a means of perturbing

chemical reactions in a controlled and variable manner. One way in which

substituents influence reactions is through their effects on bond strengths.

However, remarkably little information of this nature is available.

Moreover, most of the available data does not provide accurate differences

in bond strengths because of the divergent experimental techniques used and

the different treatments of the data. We have therefore undertaken a program for measuring accurate relative bond strengths for a variety of

substituents of general chemical interest.

144
Our focus has been on substituents attached to methyl, benzyl and

phenoxyl groups. We have measured rates of bond breaking for a large number

of 2-substituted ethylbenzenes, anisoles (methoxybenzenes ) and ringsubstituted ethylbenzenes (reactions 1-3) using our very low pressure flow

reactor. Differences in decomposition rates of substituted compounds yield

differences in bond strengths.

PhCH2-CH2 X - PhCH2

* + CH 2X

( X«CH

3

, COCH3 , OH , CN , CHO , NH2

, NHCH3 ,

C

2H ,

C

2H

3

, Ph

)

(X-CH

3

, COCH3, OH , Offl 3, CN , CHO , NH2 , N02 , C2H

3

, F , Cl , Ph # C^Hij

)

( 1 )

( 2 )

(3)

Studies of reaction 1 led to the determination of accurate relative

bond strengths for bonds of wide chemical interest (those forming

substituted methyl radicals upon dissociation). While bond strengths of the

majority of these bonds have been reported in the literature, accurate

relative values are not available because of the wide variety of precursor

molecules and experimental systems used. Preliminary values for lowering of

Gibbs dissociation energies (in kcal/mol relative to ethylbenzene at 1000K)

by X in PhCH2 -CH2X are, X=CH

3

, 3; COCH3 , 3; OH, 4; CN, 5; CHO, 5; NH2 , 6;

NHCH

3

, 7; C2 H, 9; C2H

3

, 11; Ph, 11.

Effects of substituents on the second reaction type were surprisingly

large for electron "donating” groups (X« NH2 , CH3, OH, and OCH3) and

strongly dependent on the position of substitution. For such groups bonds

were weakened by ortho- and para-substitution and slightly strengthened by

meta-substitution. To illustrate, relative to the unsubstituted compound

(X*H, anisole), for X=OCH

3

rates were 10, 1.7, and 7 (at 1000 K) in the

ortho, II meta and para position. A particularly large effect was found

for substitution at the ortho position for X=0H and NH 2

. In these cases rates for ortho, meta, para substitution (again, relative to anisole) were

40, 0.7, 12 (X=0H) and 50, 0.7, 11 (X*=NH 2

). The origin of this ortho

effect is unclear and is under further study. Polar electron withdrawing

groups (X=CN , C0CH

3

, CHO and N0 2

) have effects on bond strengths opposite

those of donating groups, although the magnitudes of their effects are much smaller. Phenyl, benzo- and vinyl-groups significantly weakened

145
bonds. Fluorine and chlorine substitution had a smaller effect. Relative

rates closely parallel published electron spin densities in substituted

phenoxyl radicals (W. T. Dixon et al. J. Chem. Soc., Faraday Trans I, 1713

( 1 974 ) and roughly follow available substitutent constants for

electrophilic reactions in solution (the Hammett sigma+ constant). The

large effect observed for electron donating groups is apparently due to

the combined effect of destabilization of the anisole molecule by the

substituent and stabilization in the product phenoxyl radical. Electron

withdrawing groups presumably stabilize both tne molecule and the radical

and therefore have less effect. These ideas are being tested by theory.

The effects of substituents in the ring-substituted ethylbenzenes

(reaction 3) were far smaller (a factor of ca. 5 less) than for substituted

anisoles and both electron donating and withdrawing groups weakened the

benzylic C-C bond. This again is in agreement with trends observed in ESR

experiments. Along with the above results, these findings enable the

parameterization of ESR data for the quantitative prediction of bond

strengths not readily measured in a direct manner.

Over the next year we will examine these reactions using both ab initio

and semi -empirical theory to gain further insight into the origin of these

substituent effects. We will also use these values to separate so-called

polar and thermodynamic effects on available rate constants for reactions

involving these substituents. We will then turn our attention to the

measurement of bimolecular rate constants at high temperatures using both

our conventional low pressure flow reactor and a new, very high temperature

graphite Knudsen cell reactor now under construction. Specifically, we will

attempt to measure rates of reaction of vinyl radicals with unsaturated

molecules. No data of this nature are available despite the widespread use of these reactions in combustion models. The possibility that these

reactions may involve chemically activated isomerization steps make these

reactions very interesting at a fundamental level.

I. Chemical Theory of Graphite

(S. E. Stein, R. L. Brown and S. A. Kafafi)

Graphite and many carbonaceous substances consist primarily of large

polyaromatic molecules of varying size, shape, and edge composition. An

understanding of the chemistry of graphite is hampered by the inability to

isolate these large molecules for individual study. As a result, the

chemistry of graphite is often treated phenomenologically. Reactivity is

thought to involve edges, defects and other "active" sites, although the

chemical nature of these is a matter of speculation.

To develop this understanding we have been engaged in a program which

focusses on the fundamental chemical properties of very large polyaromatic

structures. Graphite and nearly all carbonized organic materials are composed primarily of these structures. Early in this program we discovered that the atomic orientation at the edges of these structures

146
and their overall size were critically important factors in determining

the reactivity of these structures. Our work has therefore concentrated

on separating and examining individually these two variables.

Our major recent finding has been that a modified version of

classical Huckel theory is both qualitatively reliable and quantitatively

accurate when applied to large polyaromatic species. In addition, we found that both the simpler theories (PMO, structure-resonance theory and

other perturbation methods) and the more computationally involved

SCF-methods make serious errors in their extension to very large

molecules. We now have a predictive theory that we feel is not prone to

major errors. Fortunately, this theory is sufficiently simple to allow

calculations for molecules as large as we wish (up to several thousand

carbon atoms). One important result of this application is that attack of

interior carbon atoms in graphitic sheets results in a significant loss of

resonance energy and is thus not likely to be an important process in

graphitic systems. Another finding is that large differences in

reactivity between different edge sites remains even in the limit of an arbitrarily large graphite structure. Simpler theories incorrectly

predicted that all sites become equally reactive in the limit of very

large cluster size. More sophisticated theories incorrectly predict a finite, edge- dependent band gap in very large clusters as well as an unrea sonable bond alteration. We have also discovered that this modified

Huckel method accurately predicts heats of formation of pi-radicals. This

technique has not previously been thoroughly applied to these species, so that this observed accuracy strongly supports the reliability of this

theoretical approach.

In general terms, edge carbon atoms behave very much, like those of

normal polynuclear aromatic molecules, with properties depending strongly

on the local structure. Phenanthrene-like edges are rather unreactive and

thermodynamically stable. They are as susceptible to free radical and

electrophilic attack as are structurally related positions in naphthalene

and phenanthrene. Anthracene-like edges are thermodynanamically unstable

and highly reactive, with properties comparable to those of the linear

polyacenes. Regardless of edge structure, interior carbon atoms situated

only several bond lengths from an edge have properties (bond orders, free

valence) not far from those of the in terior carbon atoms in catacondensed polyaromatic molecules like coronene. A significant general

finding for the molecules studied is that there is only a weak relation

between the posi tion of the highest occupied molecular orbital and the

reactivity of the most reactive position. For instance, while very large

Series 3 molecules (phenanthrene-like edges, see Fig. 3«9) will have higher

HOMO energies than small Series 1 molecules (anthracene- like edges, see

Fig 3*9), they will be far less reactive (cf., Figs. 3.10 and 3.11). This HMO

method predicts that thermodynamic stability is strongly influenced by

edge type. In contrast, because they utilize local properties only, group

additivity methods do not predict significant edge effects.

147
Fig. 3 .

Fig. 3.1

9. Homologous series of hexagonally symmetric molecules.

0. 58 “

0

C

:2

°* 5:

a

Of i

3

§

48 —

a 4i

-H+H-++ +

' O O

cud o a a

^9999999? *

a

A, 1 l 1 J I I L 1 1 J—I I L

a os o. jo o. js o. 20

1/ (mo] ecu1 ar diameter)

000

00

o

0 . Maximum free valence for each molecule in the four

homologous series as a function of molecular size.

148
N~lyz

Fig. 3.11. Energy of highest occupied molecular orbital (HOMO) as a function of molecular size. The reciprocal of the square

root of the number N of Pi-electrons in the molecule was used for the abscissa. This was done to expand the scale

near the origin (i.e., where N goes to infinity). Energy

is in units of g.

Wave functions, whicn describe overall molecular properties, separate

into two distinct classes for molecules with reactive edges. Those of a more stable variety are qualitatively similar to those of an infinite

plane and of the molecules with stable edges. Those of a less stable

variety correspond to orbitals whose electron density are located

primarily at the edges. The latter variety lead to a near zero band gap,

and the associated spectroscopic and electronic properties, for molecules

of relatively small size. For example, a molecule with reactive edges

containing 60 carbon atoms has the same band-gap as a molecule of the

stable variety containing between 2000 and 2500 carbon atoms.

149
4. ION KINETICS

R. E. Huie, R. D. Levin, S. G. Lias, M. Mautner, P. Neta, L. W. Sleek,

N. Altstein, A. Harriman, and S. Mosseri

A. Overview

Research of the Ion Kinetics Group is concerned with the mechanisms and

rates of chemical reactions of charged species in the gas and condensed

phases. The group was originally associated with the competence-building

program, "Kinetic Studies of the Effects of Ionizing Radiation" which

investigated the chemical effects of ionizing radiation on matter. While

this highly successful initiative expires in October, 1986, an important

part of the research of the group remains in the field of radiation

chemistry. The radiation chemistry studies primarily address the kinetics

and mechanisms of reactive intermediates generated in the liquid phase by

high energy pulses of electrons. Related studies in the gas phase examine

the bimolecular chemical reactions and thermochemistry of positive and

negative ions using kinetic mass spectrometry as a research tool.

The broad interest of the program is illustrated by the diversity of

Other Agency support granted to members of the group. The liquid phase

radiation chemical studies of electron transfer processes are supported by

the Chemical Sciences Division, Department of Energy, because of

applications of the results to solar energy conversion. A grant from the

Environmental Protection Agency has been given for the studies of the

chemistry of aqueous inorganic solutions for understanding the mechanism of

formation of acid rain. Some aspects of the gas phase ion chemistry program

are supported by the Department of Energy, which is* interested in

developmental work on the analytical technique known as chemical ionization

mass spectrometry. The Air Force Office of Scientific Research also gives

support to the kinetic mass spectrometry work because an understanding of

the reactions and photochemistry of small hydrocarbon ions is of concern for

spacecraft survivability.

The group also has been historically affiliated with the Ion Kinetics

and Energetics Data Center, with members of the scientific staff

collaborating on compilations and evaluations of data necessary for the

understanding of the chemistry of ions and the effects of ionizing radiation

on matter. The activities of the Data Center are described in Section 2.

The individual tasks included in the program of the Ion Kinetics group are summarized as follows:

Kinetics of the Interactions between Ions and Molecules

Fundamental investigations of the chemistry of ions, including

determination of reaction rates, mechanisms and thermochemistry.

150
Energetics of Solvation and the Chemistry of Solvated Ions

Studies of the link between the kinetics and thermochemistry of

ions in the gas phase and in the liquid phase; the prediction of

liquid phase thermochemical parameters from the results of gas

phase mass spectrometric studies.

Radiation Chemistry of Organic and Biochemical Solutions

Pulse radiolysis investigations into energy transfer and

radiation damage mechanisms in biologically important

substances

Kinetics and Radiation Chemistry of Aqueous Inorganic Solutions

The study of electron transfer reactions in aqueous solutions of

inorganic salts, with particular emphasis on the kinetics of

reactions involving S03~» S05“, and HS05-.

Ion Kinetics and Energetics Data Center

The maintenance of an up-to-date evaluated data base on the

thermochemistry of ionization processes and the kinetics of

ionic reactions, and the publication of related compilations.

B. Gas Phase Ion Kinetics

The program aims at achieving a fundamental understanding of

unimolecular and bimolecular reactions of positive and negative ions in the

gas phase, and further, at examining the kinetics and thermochemistry of

ion/molecule clustering, i.e. of solvation. Experimental work is carried

out using two kinetic mass spectrometers, a pulsed ion cyclotron resonance

spectrometer (ICR), ideal for establishing reaction mechanisms and for

accurate rate constant determinations, and a unique pulsed high pressure

mass spectrometer which is particularly adapted for studies of the

thermochemistry of ion/molecule clustering processes.

1. Kinetics of Ion/Molecule Reactions: Thermochemical Kinetics of

Ions (S. G. Lias, M. Mautner , and L. W. Sieck in collaboration

with P. J. Ausloos, 540, and T. J. Buckley, 543)

This task involves the elucidation of the bimolecular chemistry of

ions generated in the gas phase, including an examination of reaction

mechanisms and measurements of rate and equilibrium constants as a function of temperature. The latter experiments lead to quantitative

information about the thermochemistry of proton transfer, charge transfer,

and other ionic reactions. The scientific emphasis of the work ties in

directly with the data evaluation efforts of the Ion Kinetics and

Energetics Data Center. Accomplishments of the past year are discussed

below.

151
(a) Rate Constants of SFg- Reactions

A collaborative study is in progress with R. J. Van Brunt

of the Electrosystems Division (NBS) and I. Sauers (ORNL). This project

involves measurements of the rate constants for reactions involving

SFg-and various neutral species such as SOF4, SOF2, SO2F2, SO2, SiFjj,

etc., which are known to be major long-lived stable by-products of the

decomposition of SFg in the presence of trace oxygen and water vapor. The

temperature dependences of the various rate constants are under

investigation here, while the ORNL measurements involve the dependence of

k on electric field strength (E/N). Some of the reactions, including SFg-

+ SOFjj -> SOF5” and SFg- + SO2 -> products, are found to exhibit rate

constants which show strong negative temperature coefficients (see

Fig. 4.1). The information derived from these studies is being used to

generate a computer model which predicts the behavior of oxy-fluoride

production during corona discharge in high pressure SFg, which in turn

will provide new insight on the processes occurring in vapor-insulated

high voltage systems and during plasma etching, both of which incorporate

SFg as the gaseous dielectric.

InT(K)

Fig. H.l.

152
(b) Proton Affinities of Hydrazines

In spite of the wealth of data which exists concerning the

gas phase basicities and proton affinities of organic compounds, no information is available for relatively complex alkyl-substituted

hydrazines. This class of molecules is of special interest due to its

biological importance, and because of the large geometry changes which

occur upon ionization. The individual proton affinities of 16 cyclic and

acyclic hydrazines were measured relative to monoamine standards. As

expected, the values were found to be quite high, ranging from 224.4

kcal/mol for tetramethyl- to 231.6 kcal/mol for bis-piperidine and

2,

-diaza-2,

_dimethylbicyclo[2.2.2]octane. Variable temperature

equilibrium constant measurements verified that entropies of protonation

are smaller than 1 cal/deg-mol. The proton affinities were combined with

adiabatic ionization energies (also measured in this laboratory) to give

the (N+-H) bond dissociation energies, which can then be used to

quantitate the stabilization conferred on a hydrazine cation radical by . its 3 electron pi bond. The accumulated data indicate approximately 20

kcal/mol stabilization in the tetraalkylhydrazines . These studies were

collaborative efforts with the laboratory of Professor Steve Nelsen,

University of Wisconsin.

(c) Structures and Kinetics of CgH^+ Ions

A comprehensive examination of the structures and reaction

kinetics of CgH^+ ions has been carried out on the NBS ion cyclotron

resonance spectrometer (ICR). It was found, in agreement with previous

work, that ions generated as fragment ions in aromatic compounds,

from dissociative proton transfer to halobenzenes, or as products of

ion/molecule condensation reactions such as:

C 4 H

3

+ + C2H 2 “) C 5H

5 +

dsplay two or more structures. Ions which unambiguously have the phenyl

structure were formed by irradiating C

6H

5 C 1 + ions with an argon ion laser;

dissociation of the molecular ion results in the formation of phenyl ions

in a two-photon process. An examination of the bimolecular reactions (and

rate constants for these reactions) of the phenyl ions and the various

C^H^+ isomers formed in different systems, revealed that structural

assignments made in collision-induced dissociation studies in the

literature had were erroneous. The isomerization mechanisms were mapped

as a function of energy. These results were used in the Ion Kinetics and

Energetics Data Center evaluation of the thermochemistry of CgH^* species.

153
(d) Comparison Standard for Acidity Scale: The Acidity of

Methanol

An existing scale of gas phase acidities of molecules,

which had been established by ion/molecule equilibrium constant

determinations in ICR instruments in a number of laboratories, suffered

from the fact that absolute values assigned to acidities at the high end

of the scale were unreliable, particularly for aliphatic alcohols,

acetylene derivatives, and aromatic compounds. This unreliability was linked to the acidity of a key compound, methanol, which could not be

directly determined by ICR spectroscopy relative to a reference standard

such as HgO for which an absolute acidity value is available; because of

the large difference in their respective acidities the proton transfer

equilibrium constant for the reaction:

OH- + CH

3OH <-> CH 3 O- + H 20

is too large to be determined by ICR. However, -the equilibrium constant

associated with this process was readily accessible to measurement by the

pulsed high pressure mass spectrometer because that instrument has a much

greater dynamic range than ICR. Taking advantage of the variable

temperature capability of the instrument, the equilibrium constant was determined as a function of temperature, leading to reliable enthalpy and

entropy changes for the equilibrium. From these results, it was determined

that the acidity of methanol is 381.6+-0.7 kcal/mol. Experimental re- evaluation of acidities of compounds in the range 370-410 kcal/mol is in

progress.

2. Solvation Thermodynamics and the Kinetics of Solvated Ions

(M. Mautner and L. W. Sieck)

Ionic species such as those generated in acidic or basic

environments or by radiation are ubiquitous intermediates in biochemical and

organic reactions. The stabilities and reactivities of ionic intermediates

are affected by their intrinsic molecular properties (studied in the gas

phase as described above), and by interactions with the condensed phase

environment. This task utilizes the high pressure mass spectrometer to

bridge the gap between the understanding of ionic chemistry attained in the

gas phase studies and that required for understanding and predicting

processes occurring in irradiated liquids, acid catalyzed reactions, and

enzyme catalyzed processes. In the high pressure mass spectrometer, it is

possible to generate a given ion in the presence of a solvent molecule (such

as H

2 0, for example) to determine the thermochemistry of solvation by an examination of equilibria such as:

A+ + M -> [A+.M]

[A+M] + M -> [A+.M2

]

134
and to study the kinetics and mechanisms of reactions of the solvated ions.

These data can then be used to interpret liquid phase data on ionic

processes in terms of intrinsic molecular properties.

In the fall of 1985, a comprehensive study of the kinetics and

thermochemistry of clustering reactions initiated by anions of the type

RO-and RCO2- (where R is an alkyl group or H) was initiated. The goal of

this project is: (1) to provide the first-ever information concerning the

thermochemistry (stabilities) of association ions incorporating organic

ligands where the bonding is of the type R0-...H-0- and RC02-. . .H-0-; and

(2) to use the information derived from model systems to generate

predictive schemes (correlation lines) which define the relationship

between the dissociation energy of the cluster ion and the gas phase

acidity of the ligand. Related work involving determinations of the

acidities of organic compounds has been described above. This is an ongoing project which continues as of this writing. Work has been carried

out during the past year on the following problems:

(a) Dissociation Energies of R0-...H-0- and RC0 2 -...H-0 Bonds

Dissociation energies of RO-HOR, RC00-H0R, and RC00-H00CR

complexes were measured and found to range from 1 4 to 29 kcal/mol. High

values (28.8 and 29.3 kcal/mol) were found for the symmetric dimers

CH^O-HOCHo and CH3COO-.HOOCCH3. The binding energy was found to decrease

as the difference between the acidities of the components increase. For 13

dimers, it was found that the relationship between the differences in gas

phase acidity of the complexed molecules and the binding energy of the

complex could be expressed as a linear correlation. However, data for some

dimers were found to deviate substantially from the correlation,

suggesting structural effects. For example, the large binding energy value

of 36.8 kcal/mol found for HCOO-HOOCH suggests double hydrogen bonding

involving a CH...0- type bond. On the other hand, the data indicate that

only one hydrogen bond is formed in RC00-.H 2 0 association ions. Comparison

between anionic and cationic hydrogen bonded systems shows that the

bonding energies are similar for RO-B and R0H2 +.B complexes involving the same ligand, B, suggesting primarily electrostatic interactions in both,

while RCOO-.B is weaker by 4 - 6 kcal/mol than RC00H 2 +.b, possibly due to

charge delocalization in RC00-. The weakening of 0-...H0 hydrogen bonds to

charge delocalized anions was also observed in CH 2 =CHO- .H 2 0 , where the

binding energy is 15.3 kcal/mol. Additional measurements involving a variety of delocalized anions are currently in progress.

(b) Thermochemistry of Mixed Water-Methanol Cationic and

Anionic Clusters

The thermochemistry of mixed water-methanol cationic

clusters, (H 2 0)n(CH30H)mH+, and anionic clusters, [ (H 20)n(CH^0H)m

-H]-(i.e. clusters containing OH- or CH^O-) was measured. It was found

that the total hydrogen-bonded network in as given positive cluster was more stable by 3 ~ 6 kcal/mol than that in the corresponding negative

cluster. The variations of the stabilities of the cationic and anionic

155
clusters with number of components (n + m) show remarkable similarities.

For example, both HoO+.r^O and OH-.nl^O exhibit effects of solvent shell

filling at n = 3° The neat methanol clusters were found to be more stable

than neat water clusters, and the difference varied only slightly with n. This was found to be true for both the anionic and cationic systems. The

thermochemistry suggests that the favored topology in mixed water-methanol

clusters is one which places the methanol molecules near the charge center

and water molecules at the periphery.

(c) Structures of Ionic Clusters

Another study involved evaluation of attachment energies for

successive solvation of cations in order to determine at which step a distinct solvent shell is filled. Thermochemical criteria were developed

and applied to data on clustering about metal ions and onium ions.

Satisfactory evidence for the distinct filling of shells was found in 14

systems, and tentative evidence was found in another 15 out of the 59

systems evaluated.

(d) Heats of Hydration of Protonated Oxygen and Nitrogen Bases

In a related project, gas phase clustering data were used

to predict heats of hydration of protonated oxygen and nitrogen bases.

Using simple empirical relations, the ionic heats of hydration were found

to be predictable within -+2 kcal/mol on the basis of just one parameter,

the gas phase proton affinity of the base. The model which was developed

demonstrates the use of gas phase data in analyzing the factors which

influence ion solvation in solution.

C. Liquid Phase Ion Kinetics

The program aims at achieving a fundamental understanding of the

chemistry of reactive intermediate species generated in liquids by pulses of

high energy electrons. Experimental work is carried out using two electron

accelerators, a Febetron and a pulsed Van de Graaff, coupled with optical

detection techniques. The scientific emphasis of the work also leads to

data evaluation efforts, described under the write-up for the Kinetics Data

Center. Accomplishments of the past year are discussed below.

1. Radiation Chemistry of Organic and Biochemical Solutions

(P. Neta, A. Harriman, M. Mautner, and S. Mosserl)

Pulse radiolytic techniques are used to characterize the

chemical properties of short-lived species in irradiated solutions.

Particular attention is given to the chemistry of reactive transients

which have been implicated as intermediates in a variety of chemical and

biological systems. An important aspect of this program is the study of

inter- and intramolecular electron transfer processes aimed at

understanding similar phenomena in biological systems, as well as in

photochemical systems of interest for possible use in solar energy

conversion; this aspect of the work is supported by the Department cf

156
Energy. By studying the kinetics and mechanisms of the various transient

species and by understanding the parameters that control them, one can hope to be able to predict the behavior of these species in more complex

systems.

(a) Photogeneration of Oxygen or Hydrogen from Water:

Laboratory Studies of Solar Energy Storage

Photogeneration of oxygen from water is an integral part of

green plant photosynthesis and many laboratory models aimed at the storage

of solar energy have tried to mimic this natural process. In this problem

area, an experimental examination of the catalytic oxidation of water to

oxygen by metalloporphyrin pi-radical cations has been carried out. In the

ideal case, a metalloporphyrin (synthetic .analogue of chlorophyll) absorbs

light and forms an excited state which then donates an electron to another

compound in the system. The electron acceptor then reacts with a catalyst

to form hydrogen from water. The metalloporphyrin radical cation (formed

after donating an electron) should react with another catalyst that will

produce oxygen. Thus the overall process is the decomposition of water by

sunlight to hydrogen and oxygen with no net change in the other components

of the system. For this purpose, it is necessary to find the proper

catalyst, the best metalloporphyrin, and the optimal experimental

conditions. This was done using pulse radiolysis and monitoring the rate

of reaction of various porphyrins and catalysts to determine the factors

that influence these rates.

Previous work in this laboratory, which was concentrated on zinc

porphyrins, examined the effects of variations in porphyrin structure and

solution conditions on the oxidation of water to oxygen by the porphyrin

radical cation, catalyzed by Ru02

. During the past year, the effect of

variations in the metal center was examined, with attention given to Mg,

which is also the metal center of chlorophyll. Comparing Mg to Zn and other

metals (Pb, Cd, Pd, Cu, Fe, In) correlations between the electronegativity

of the metal, the oxidation potential of the porphyrin, and the lifetime of

the metalloporphyrin radical cation are found. Increased electronegativity

pulls electrons from the porphyrin ligand to the metal center, raising the

oxidation potential and making water oxidation more thermodynamically

favorable. On the other hand, increased electronegativity promotes

hydroxylation of the radical cation which results in shorter lifetime and

thus a lower probability of reaction with the Ru0 2 catalyst. Thus, the

electronegativity of the metal exerts two opposing effects on the processes

leading to oxygen products and necessitates optimization of conditions.

In examining variations in the metal center, attention has also been

given to metalloporphyrins in which the metal is oxidized, rather than the

ligand. Certain Mn(III) porphyrins were found to undergo oxidation to the

Mn(IV) state, which is unstable in neutral solutions. The Mn(IV) is reduced

back to Mn(III) but without oxidizing water to oxygen. The Ru0 2 catalyst

has a pronounced effect on the decay kinetics and some oxygen is evolved in

the process, but the yield is very poor. Therefore, studies have been

initiated on other transition metal porphyrins that may form higher

157
oxidation states. Preliminary examination of ruthenium and osmium

porphyrins indicates that the former produce radical cations while the

latter are oxidized at the metal center.

Related work is aimed at improving the properties of the Ru02

catalyst. Preparations have been attempted using radiolytic reduction of

RuOjj- without the polymer. (The usual procedure involves chemical reduction

of RuOjj- with H 2

C> 2 » followed by stabilization with a short water-soluble

polymer). The product formed appears to have smaller size particles and to

be more stable over long periods. Its exact structure and its efficiency in

oxygen production are under study.

Some attention was also given during the past year to hydrogen

production through the photodecomposition of water. Preliminary studies on Au(III) porphyrins indicate formation of stable radical anions which react

on the surface of colloidal platinum catalyst to reduce water to hydrogen.

The kinetics of reaction of Pt catalyst with several reducing radicals is

under study.

(b) Study of the Reactions of Peroxy Radicals

The toxicity of halogenated alkanes (such as carbon

tetrachloride and the anaesthetic agent halothane, CP^CHClBr) Is believed

to originate from cytochrome-Pii^Q-mediated generation of peroxyl radicals

with subsequent attack on biological targets, especially unsaturated

lipids. The feasibility of this proposed mechanism was demonstrated in this

laboratory in a pulse radiolytic study of the reactions of peroxyl radicals

with iron porphyrins and with fatty acids.

During the past year, the rate constants for oxidation of zinctetraphenylporphyrin by CCI

3 O2 radicals were determined. They are found to

be strongly solvent -dependent (two orders of magnitude). This dependence

was found to be due to complexation of certain organic solvents at the

axial position of the zinc porphyrin, which affects the redox potential to

a certain extent but has a dramatic effect on the rate of reaction of

CCI 0 O 2 in hydrogen abstraction reactions is being studied with cyclohexane,

cyclohexene, and hexamethylbenzene. The rate constants for these reactions

can not be followed directly by kinetic spectrophotometry and are,

therefore, determined by competition kinetics.

Because CF^Br is widely used as a fire extinguisher and a refrigerant,

experiments were carried out which were designed to examine its possible

toxicity by determining the reactivity of the peroxyl radical that may be

produced from it, the CF^0 2 radical. This radical is more reactive than

CC1^02 by a factor of approximately 10 in oxidation reactions. The peroxyl

radical formed from CBr^ has also been studied; surprisingly, this radical

displays a higher reactivity than CCl-^O^ This discrepancy is under

investigation. The probability of formation of these damaging radicals in

biological systems is being examined by a collaborator (Brault) using mode,

systems.

158
The common peroxyl radicals produced in biological systems are less

reactive than the halogenated analogues and can be best represented by

CH

3 O 2 , the simPles t organic peroxyl radical. The reactivity of this radical

as a one-electron oxidant was determined with several molecules and found

to be generally about 100 times less than the rate constants for CCl^c^.

The redox potential for CH

3 o 2 was estimated to be in the range 0.6-0. 7 V.

(c) Temperature Dependence of Rates and Equilibria of Electron

Transfer Processes

In order to determine the enthalpy and entropy changes that

contribute to the electron affinities of organic and biological molecules

in aqueous solution, the temperature dependences of charge transfer rate

and equilibrium constants in the pulse radiolysis of liquids was studied

using the temperature-controlled radiolysis cell. These studies may be

divided into two parts: ( 1 ) kinetics of electron transfer from

nitroaromatic radical anions and ( 2 ) electron transfer equilibria between

nitro compounds, quinones, and oxygen.

Rate constants for electron transfer from various nitroaromatic

radical anions to other nitroaromatic compounds in aqueous solutions were

found to increase from "10® to "10® M

- 1 s~' upon increase in driving force

from 0 to -300 mV, while the activation energies decrease from "6 to "3

kcal/mol. Nitro compounds with ortho substituents exhibit lower electron

affinities due to rotation of the nitro group away from the ring plane.

Anion radicals of such compounds transfer their electron much more slowly

(k down to "10® M

- 1 s

-1

) despite the apparent increase in driving force (to

"550 mV). This behavior is rationalized by an increase in solvent

reorganization energies around these radical anions caused by localization

of the charge. In general, nitroaromatic radical anions donate electrons

much more slowly than other radical anions, in reactions with similar

driving forces, due to low self-exchange rates for ArN0

2 /ArN02

_

*

Temperature effects on electron transfer equilibria:

A- + B <=> A + B.-

were studied for the cases: (1) A = nitro compound, B = quinone; (2) A and

B are both quinones; (3) A = quinone, B = oxygen.

The question of interest here is whether the redox potentials obtained

at room temperature, which are known for many quinones and nitroaromatics

reflect differences in the heats of one-electron reduction of the aqueous

compounds, or whether entropy effects are also significant. The results

show that, in fact, the entropy contributions to the Gibbs free energy

change can be significant.

The entropy changes in the present equilibria are most likely due to

changes in solvation, and in particular, the solvation of the ions. In

both of the reactions of the type (AQS-)- + B <=> B- + AQS-, the entropy

159
change is negative. This is reasonable, since the reaction proceeds from a one-ion to a two-ion system, and increased ion solvation can lead to more

structured solvent.

By using the known enthalpy and entropy of hydration of 0

2 - we can calculate the corresponding values for the semiquinones and nitroaromatic

radical anions (if the values for the neutral compounds are known). These

studies are still in progress.

2. Kinetics and Radiation Chemistry of Aqueous Inorganic Solutions

(R. E. Huie and P. Neta)

This program includes research in two related areas: the

chemistry of small free radicals, and the aqueous phase chemistry of the

atmosphere. The work on small free radicals, supported by a contract with

DOE, is focussed on deriving basic information (e.g. redox potentials,

self-exchange rates) about simple free radicals in aqueous solutions.

These experimental results have application to understanding other redox

systems. For example, a study of the effects of substituents on the

one-electron oxidation of phenols was carried out using radical reactants

chosen so that their reactivity would be sufficiently great to allow

determination of the rate constants, but not so reactive that substituent

effects would be small.

The work on the aqueous phase chemistry of the atmosphere is focussed

on the chemistry of free radicals likely to enter or be formed in

atmospheric droplets, especially their reactivity toward other possible

constituents of the droplet. These results have direct application to

modelling of the chemistry of the atmosphere, particularly for

understanding the acidification of precipitation.

(a) Reactions of Oxidizing Radicals

Based on results from earlier work in this laboratory on the

chemistry of small free radicals, a study has been completed of the effect

of substituents on the rate of one-electron oxidation of phenol. The rate

constants for reactions of CIO?, NO 2 , and SOo- with phenol varied from

immeasurably slow (<10" 1 M

_1 s“') to values almost as great as the diffusion

controlled limit (>10^ M^s-1

), and depended on the redox potential of the

phenol or phenoxide ion and that of the inorganic radical. The results

showed that these one-electron oxidation reactions could be correlated with

the Hammett substituent constants and that the reactivity, in general,

could be correlated with the difference in redox potentials.

(b) Reactions of Reducing Radicals

During the past year, a study of some one-electron transfer

reactions involving the couple SC^/SC^" has been carried out. 3oth pulse

radiolysis and voltammetry (in collaboration with A. Harrlman of the Roya.

Institution, London) were employed. At a pH of 2, the one-electron redox

potential of S0 2 was measured to be -0.31 V. This value increased somewna*.

160
at lower pH. From the rate constants for the reduction of S 0

2 by the

methyl viologen radical cation, and the reduction of several metal

complexes by S0

2 , we have calculated self-exchange rates for S02/S02- . The

values span four orders of magnitude (ignoring one very low value for

IrCl6-). Apparently, the S02 /S02~ couple behaves like the 0

2 /02~ couple,'

possibly because of the great difference in solvation between the charged

and uncharged halves of the couple.

(c) Reactions of Methylperoxy Radicals

Under Section C.I., above, studies of the reactivity of

methylperoxyl and substituted methylperoxyl radicals were described,

primarily in relationship to their importance in biological chemistry.

Alkylperoxyl radicals are also of considerable importance in atmospheric

chemistry, and would be expected to play a role in the chemistry of

atmospheric droplets, possibly initiating the autoxidation of sulfite.

R02

+ SO3 2 ro2

+ SO^

Therefore, information was sought on the reactivity of these peroxyl

radicals toward sulfite. The carboxymethylperoxyl radical was found to

react with a rate constant of < 10 ^ M^s-1

. Since the reactivity of this

radical toward other reductants was found to be similar to that of

methylperoxyl, this limiting value can be assumed to be applicable to the

latter radical also. The trichloromethylperoxyl radical is known to be a stronger oxidant than the methylperoxyl radical, and the rate constant for

its reaction with sulfite was found to be 9 x 10 ^ M“ 1 s“

-'.

(d) Reactions of Atmospheric Interest

In the literature of atmospheric chemistry, papers dealing

with the role of radicals in droplet chemistry have begun to appear. These

reactions may be very critical in determining atmospheric aqueous

chemistry. As a result, rate constants have been determined for the

oxidation of sulfite by several radicals in aqueous solution, notably for

the reaction of OH with HSO^-XSO^ 2-

, which is an important process in

atmospheric chemistry. The rate constant determined for reaction with SO^ 2 was in good agreement with a value reported previously, but the value for

the reaction with HSO^-was lower than the previously-accepted value by

about a factor of two.

The chloride ion is a significant trace species found in atmospheric

droplets. This ion can scavenge strong oxidants producing the dichloride

radical, Cl 2~. A value of the rate constant for the reaction of this

radical with bisulfite which was about a factor of ten greater than that

reported previously has been determined. The earlier work may have been

complicated by the occurrence of a chain reaction which regenerated Cl 2 ~.

The reaction of SO^- with S(IV), in which radicals are produced by

reduction of S

2 0s

2 “, was also investigated. The results led to values for

the rate constants which were much lower than expected from comparison with

161
similar systems. It was suggested that a chain reaction takes place in this

system involving the reduction of the peroxydisulfate by the sulfite

radical to regenerate SO^".

An additional reaction of direct atmospheric significance is the chain

propagating reaction of SOc" with S(IV). In earlier work from this

laboratory, a rate constant for this reaction at pH 6.8 was determined.

During the past year, measurements were made at pH 8.7 and 1.9, to allow

the rate constants for reaction with SOo 2 " and HSO^" to be separated. A

rate constant of 1.3 x 107 M^s-1 was obtained for the reaction of SO^-

with S0^~. For the reaction with HSO^”, an upper limit of <3 x 10^ M

_1 s

-

^ was derived.

Related computer modelling studies have been carried out to determine

the sensitivity of simple models of the aqueous-phase atmospheric oxidation

of S0 2 to these kinetic results. An important conclusion is that when one uses these new values for the rate constants in the model, the effect of

added chloride on the chemistry is not great. Because of the slowness of

the S0^~ + HSOj” reactions, secondary reactions of this radical, including

self-reaction and reactions with other radicals, will be important. Some

of these reactions will be investigated in the coming year.

(e) Development of the Van de Graaff System

The additional pulse radiolysis work generated by the new EPA contract has put further pressure on the experimental capabilities at

NBS. Therefore, additional effort has been given to making the NBS Van de

Graaff accelerator into a working tool for kinetics studies. While this has

involved some instrument- and software-development, most of the work has

been concerned with solving a number of small problems expected with such a complex apparatus.

In addition to taking pressure off the Febetron, the use of the Van de

Graaff for pulse radiolysis studies affords some important advantages.

First, the high repetition rate permits signal averaging, so that radicals

with weak absorptions, such as N0 ? , can be monitored. Second, the shorter

overall optical train and the greater penetration depth of the electrons

permits measurements further into the UV, down to 220 nm. This allows one

to monitor radicals directly which previously could be followed only

indirectly, if at all. For example, the rate constant for the reaction:

S02- * 02 -> SO 2 + 02-

(k = 2.4 x 10^ M~^s _1

) has been measured by monitoring SOj- at 260 nm.

The solution handling and data collection procedures on the Van de

Graaff have been automated. In the coming year, procedures will be

developed to transfer the data from the Tektronix computer (which is also

used to control the experiment) to a separate computer for data analysis.

162
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in
El-Shall , M. S. , Kafafi, S. A., Meot-Ner (Mautner), M., and Kertesz, M.,

"Ionic Charge Transfer Complexes. 2. Comparative ab initio and

Semiempirical Studies on Cationic Complexes of Aniline+", J. Am. Chera.

Soc., 108, 4391 (1986).

Fahr A., and Laufer, A. H. , "Quantum Yield of Vinylidine(3B2 ) for the Vacuum

UV Photolysis of Acetylene and Ethylene ", J. Photochemistry 34, 261,

(1986).

Frenklach, M., Clary, D. W., Gardiner W. C., and Stein, S. E. , "Shock Tube

Pyrolysis of Acetylene: Sensitivity Analysis of the Reaction Mechanism

for Soot Formation" in"Shock Waves and Shock Tubes, Proceedings of the

15th International Symposium on Shock Waves and Shock Tubes" (D.

Bershader and R. Hanson, ed) Stanford University Press, Stanford CA.

285, (1986).

Hampson, R. , et.al., "Chemical Kinetics and Photochemical Data for Use in

Stratospheric Modeling. Evaluation Number 7," JPL Publication 85 -31 , July 1 , 1985.

Hampson, R. , et.al., "Present State of Knowledge of the Upper Atmosphere. An

Assessment Report", NASA Reference Publication 1162, May 1986.

Harnman, A., Neta, P., and Richoux, M. C., "Reactions of Magnesium

Porphyrin Radical Cations in Water. Disproportionation, Oxygen

Production and Comparison with Other Metalloporphyrins" , J. Phys.

Chem. , 90, 3444 (1986)

Harriman, A., Neta, P., and Richoux, M. C., "Catalyzed Decay of Oxidizing

Radicals" in "Homogeneous and Heterogeneous Photocatalysis" (E.

Pelizzetti and N. Serpone, editors), D. Reidel Publ. Co., 123, (1986).

Herron, J. T., Tsang, W., Stein, S. E., and Golden, "International

Conference on Chemical Kinetics," J. Phys. Chem., 90, 343 (1986)

Herron, J. T., and Tsang, W., "Chemical Kinetics - Theory and Experiment,"

J. Res.NBS, 389 (1986).

Hoffbauer, M. A., and Hudgens, J. W., "Multipnotn ionization Detection of

Gas Phase Benzyl Radicals" J. Phys. Chem., 89, 5152, (1985>.

Huie, R. E., "Chemical Kinetics of Intermediates in the Autoxidation of

SO2

", Fossil Fuels Utilization: Environmental Concerns, ACS Symposium

Series 31 9, 284 (1986) .

Huie, R. E. and Neta, P. , "Race Constants for One-Electron Oxidation by

Methylperoxyl Radicals in Aqueous Solutions", Int. J. Chem. Kinetics,

164
Huie, R. E. and Neta, P., "Kinetics of One-Electron Transfer Reactions

Involving C102 and N02

", J. Phys. Chem. 9£» 1193 (1986).

Jovanovic, S. V., Neta, P., and Simic, M. G., "One-Electron Redox Reactions

of Pyrasozlin-5-ones. A Pulse Radiolysis Study of Antipyrine and

Analogues", Mol. Pharmacol., 28_, 377 (1985).

Karpas, Z., Stevens, W. J., Buckley, T. J., and Metz, R., "The Proton

Affinity and Gas Phase Ion Chemistry of Methyl Isocyanate, Methyl

Isothiocyanate and Methyl Thiocyanate, J. Phys. Chem ., 89_, 5274

(1985).

Karpas, Z., "The Proton Affinity of H

2 se, SeCO and H 2 CSe and Reactions of

Positive Ions with H2Se", Chem. Phys. Lett. 120, 53 (1985).

Karpas, Z. and Jasien, P. G. , "The Proton Affinity of Hydrogen Telluride",

Int. J. Mass Spectrom. Ion Proc., 69_,

1 15 (1986).

Kurylo, M. J., Ouelette, P. A., and Laufer, A. H., "Measurements of the

Pressure Dependence of the H0 2 Radical Self Disproportionation

Reaction at 298 K" J. Phys. Chem., _90_, 437 , (1986).

Kurylo, M. J. and Ouelette, P. A., "The Pressure Dependence of the Rate

Constant for the Reaction H0 2 +N02+ M = H0 2N0(M=N2 , 02 at 298K, " J.

Phys. Chem., _90.» ^1 * (1986).

Langley, R., Hambright, P., Alston, K. , and Neta, P., "Kinetics of the

Reduction of Manganese( III )-Myoglobin by Dithionite", Inorg. Chem., 25_,

114 (1986).

Lias, S. G. , Karpas, Z., and Liebman, J. F., "Halomethylenes : Effects of

Halogen Su I. Thermochemistry and Structural Implications and Role in

Ion Solvation", in "Molecular Structure and Energetics" (J. F.

Liebman and A. Greenberg, editors), VCH Publishers, Inc.: Deerfield

Beach, FL, 71 , (1986)

Meot-Ner (Mautner), M.and El-Shall, M. S., "Ionic Charge-Transfer Complexes.

1. Cationic Complexes with Delocalized and Partially Localized Pi

Systems", J. Am. Chem. Soc., 1 08 , 4386 (1986).

Meot-Ner (Mautner), M. , Karpas, Z., and Deakyne, C. A., "Ion Chemistry of

Cyanide and Isocyanides. 1. The Carbon Lone Pair as Proton Acceptor:

Proton Affinities of Isocyanides", J. Am. Chem. Soc., 108, 3913 (1986).

Meot-Ner (Mautner), M. and Karpas, Z., "Ion Chemistry of Cyanides and

Isocyanides. 2. Alkylation of HCN and Cyanides by Oxygen and Sulfur

Compounds. Gas-Phase Synthesis and Reactions of Protonated

Isocyanides", J. Phys. Chem., 90, 2206 (1986).

165
Meot-Ner (Mautner), M. and Neta, P., "Kinetics of Electron Transfer from

Nitroaromatic Radical Anions in Aqueous Solutions. Effects of

Temperature and Steric Configuration, J. Phys. Chem. , 9£, 0986).

Meot-Ner (Mautner), M. , Neta, P„, Norris, R. K. , and Wilson, K.

,

"Temperature Effects on Rates of Dehalogenation of Aromatic Anion

Radicals", J. Phys. Chem., j9£, 1 68 (1986).

Meot-Ner (Mautner), M. and Sleek, L. W.» "The Ionic Hydrogen Bond and Ion

Solvation. 4. SH+...0 and NH+...S Bonds. Correlations with Proton

Affinity. Mutual Effects of Weak and Strong Ligands in Mixed

Clusters", J. Phys. Chem., _89, 5222 (1985).

Neta, P., Richoux, M. C., Harriman, A., and Milgrom, L. R., "Resonance

Stabilization of Zinc Porphyrin Pi-Radical Catioins", J. Chem. Soc.

Faraday Trans. 2, _82, 209 (1986).

Neta, P., Silverman, J., Markovic, V. , and Rabani , J., "Radiation-Induced

Reactions of Polymer Radicals with Ruthenium tris-Bipyridyl OH Adduct

in Aqueous Solutions Studied by Pulse and Gamma Radiolysis", J. Phys.

Chem., 90, 703 (1986).

Richoux, M. C., Neta, P., Christensen, and Harriman, A., "Formation and

Decay of Zinc Tetrakis(N-methyl-3-pyridyl)porphine Pi-Radical Cation in

Water", J. Chem. Soc. Faraday Trans. 2, 82_, 235 ( 1986).

Richoux, M. C., Neta, P. , and Harriman, A., "One- and Two-Electron Oxidation

of Lead(XI) Tetrakis(N-methylpyridyl) Porphyrins in Aqueous Solution",

J. Chem. Soc. Faraday Trans. 2, _82, 201 ( 1986).

Richoux, M. C., Neta, P., Harriman, A., Baral, S. , and Hambright, P., "One

and Two-Electron Reduction of Metalloporphyrins . Radiation Chemical,

Photochemical and Electrochemical Studies. Kinetics of the Decay of

Pi-Radical Anions", J. Phys. Chem., 9£, 2462 (1986).

Robaugh, D. A., Tsang, W. , Fahr A., and Stein, S. E. , "Ethylbenzene

Pyrolysis: Benzyl C-C or C-H Bond Homolysis" Ber. Bunsenges. Phys.

Chem. , 90, 77, (1986).

Robaugh, D. and Tsang, W. , "Mechanisms and Rate Constants for Hydrogen Atom

Attack on Toluene" J. Phys. Chem., ^0_, (1986).

Robaugh, D. and Tsang, W. , "Shock Tube Study on the Stability of Iodobenzene

and o-Iodotoluene" J.Phys. Chem., _9£, ( 1986).

Robaugh, D. A. and Stein, S. E. , "Stabilties of Highly Conjugated Radicals

from Bond Homolysis Rates" J. Amer. Chem. Soc., 1 08 , 3224, (1986).

Sieck, L. W. , "Thermochemistry of Solvation of N02

~ and C^H^NOp- by Protic

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166
Speller, C. V. and Meot-Ner (Mautner), M., "The Ionic Hydrogen Bond and Ion

Solvation. 3. Bonds Involving Cyanides. Correlations with Proton

Affinities", J. Phys. Chem., 8j_, (1985).

Stein, S. E., "Free Radicals in Coal Conversion" in "Chemistry of Coal

Conversion" (R. H. Schlosberg,ed) Plenum Publishing, 13. (1985).

Stein, S. E. and Fahr, A., "High Temeprature Stabilities of Hydrocarbons"

J. Phys, Chem., 89, 3714, (1985).

Stein S. E. and Brown, R. L., "Pathways to Graphite. Properties of Very

Large Benzenoid Hydorcarbons" in "Moleuclar Structure and Energetics"

(J. F. Leibman and A. Greenberg, ed.) VCH Publishers, Deerfield Beach,

FL, (1986).

Tsang, W., "The Stability of Alkyl Radicals," J. Am. Chem. Soc., 1 07 , 2872

(1985).

Tsang, W., "Thermodynamic and Kinetic Properties of the Cyclohexadienyl

Radical," J. Phys. Chem., 90_, 1152 (1986).

Tsang, W. and Hampson, R. F., "Chemical Kinetic Database for Combustion

Chemistry. Part 1. Methane and Related Compounds," J. Phys. Chem. Ref.

Data, 15., 1087 (1986)

Tsang, W., "Single Pulse Shock Tube Study on the Stability of

Perf luorobromethane" , J. Phys. Chem., £0, 414 (1986).

Tsang W., and Robaugh, D., "Single Pulse Shock Tube Studies on the Stability

of Aromatic Compounds" in "Shock Waves and Shock Tubes, Proceedings of

the 15th International Symposium on Shock Waves and Shock Tubes" (D.

Bershader and R. Hanson, ed) Stanford University Press, Stanford CA.

31 9, (1 986).

167
Publications in Progress

Alfassi, Z. B. , Harriman, A., Mosseri, S. and Neta, P., "Rates and

Mechanisms of Oxidation of ZnTPP by CCI

3O2 Radicals in Various

Solvents", Int. J. Chem. Kinetics, in press.

Braun, W. , Scheer, M., and Kaufman, V., "Measurement of Transient Gas

Temperature by Broadening of the Hg 61S0 - 63S1 Line", J. Res. NBS in

press

Braun, W. , Scheer, M. , and Cvetanovic, R. J., "Use of the Doppler Broadening

of the 254 nm Hg Absorpton Line as a Measure of V-RT Transfer in

Vibrationally Excited Gases, J. Chem. Phys. , submitted

Cvetanovic, R. J., "Evaluated Chemical Kinetic Data for the Reactions of

0(3P) Atoms with Unsaturated Hydrocarbons", J. Phys. Chem. Ref. Data,

submitted

Deakyne, C. A., Meot-Ner (Mautner), M. , Buckley, T. J., and Metz, R.,

"Proton Affinities of Diacetylene, Cyanoacetylene, and Cyanogen.

Experimental and ab initio Studies", J. Chem. Phys., submitted.

El-Shall, M. S. and Meot-Ner (Mautner), M., "Ionic Charge Transfer

Complexes. 3. Delocalized Pi Systems as Electron Acceptors and

Donors. Dimer Cations of Naphthalene Derivatives", submitted to WERB.

Fahr, A. and Laufer, A. H., "Collisional Quenching of Excited Vinylidine

(3B2), J, Phys. Chem., in press

Frenklach, M. , Gardiner, W. C., Clary, D., and Stein, S. E., "Effects of

Fuel Structures on Soot Formation Mechanisms" 21st Symposium on Combustion, in press

Hambright, P., Neta, P., Richoux, M. C., Abu-Gamra, Z., and Harriman, A.,

"Redox Chemistry of Water Soluble Vanadyl Porphyrins", J. Photochem.

,

in press.

Harriman, A., Christensen, P. A., Porter, G. , Morehouse, K. , Neta, P., and

Richoux, M. C., "Decay of High Valent Manganese Porphyrins in Aqueous

Solution and Catalyzed Formation of Oxygen", J. Chem. Soc. Faraday

Trans. 1, in press.

Herron, J. T., "Thermochemical Data on the Gas Phase Compounds of Sulfur,

Fluorine and Oxygen Related to Pyrolysis and Oxidation of Sulfur

Hexafluoride," J. Phys. Chem. Ref. Data, submitted.

Herron, J. T., "A Critical Review of the Chemical Kinetics of SF^, SF^, and

S

2 F 10 in the Gas Phase," Int. J. Chem. Kinetics, in press

168
Herron, J. T. f "S2 Fiq Formation in Computer Simulation Studies of the

Breakdown of SF^," IEEE Transactions on Electrical Insulation, in

press

Huie, R. E., and Neta, P., "Rate Constants for the Oxidation of Sulfite

Radicals in Aqueous Solutions'1 , Atmos. Environ., submitted.

Karpas, Z. and Lias, S. G. , "On the Mechanism of Formation of

Dialkylhalonium Ions in Alkyl Halides", J. Org. Mass Spectrom.

,

submitted.

Karpas, Z. and Meot-Ner (Mautner), M. , "Alkyl Transfer Reactions between

Protonated Alcohols and Ethers. The Gas Phase Alkylation of

Formaldehyde", J. Phys. Chem. , submitted.

Kurylo, M. J. and Ouelette, P. A., "Rate Constants for the Reaction H02N02+

N

2

= HO 2NO2

+ N 2

: The Temperature Dependence of the Fall off

Parameters", J. Phys. Chem. , (submitted to WERB)

Lias, S. G. , "Ion Kinetics and Energetics: The Physical Chemistry of Ions

in the Gas Phase", The Encyclopedia of Physical Science and Technology

(R. A. Meyers, editor), Academic Press: New York, in press.

Martinez, R. I. and Dheandhanoo, S., "Validation of Absolute Target

Thickness Calibrations in a QQQ Instrument by Measuring Absolute Total

Cross-Sections of Ne+(Ne,Ne)Ne+", Int. J. Mass Spectrom. Ion. Processes,

submitted.

Martinez, R. I. and Herron, J. T., "Stopped flow Studies of the Mechanisms

of Ozone-Alkene Reactions in the Gas Phase: Tetramethylethylene"

,

J. Phys. Chem., submitted.

Meot-Ner (Mautner), M. , "Multicomponent Cluster Ions. 2. Comparative

Stabilities of Cationic and Anionic Hydrogen Bonded Networks. Mixed

Clusters of Water-Methanol", J. Am. Chem. Soc., in press.

Meot-Ner (Mautner), M. and Deakyne, C. A., "The Ionic Hydrogen Bond and Ion

Solvation. 5. Predictive Relation for Heats of Hydration.

Hydrophobic Solvation of Ions", J. Phys. Chem., in press.

Meot-Ner (Mautner), M. , Rumack, D. T., and Nelsen, S. F., "Slow Organic

Electron Transfer Reactions", J. Am. Chem. Soc., submitted.

Meot-Ner (Mautner), M. and Sieck, L. W. , "Relative Acidities of Water and

Methanol and Stabilities of the Dimer Anions", J. Phys. Chem., in

press.

Meot-Ner (Mautner), M. and Sieck, L. W. , "The Ionic Hydrogen Bond and Ion

Solvation. 5. 0H...0- Bonds. Gas-Phase Solvation and Clustering of

Alkoxide and Carboxylate Anions", J. Am. Chem. Soc., in press.

169
Meot-Ner (Mautner), M. and Speller, C. V. , "The Filling of Solvent Shells in

Cluster Ions; Thermochan i cal Criteria and the Effects of Isomeric

Clusters", J.. Phys. Chem., in press.

Neta, P., "Reactions of Radicals with Biologically Important Molecules",

Chapter in a CRC book on Organic Radicals, in press.

Neta, P„, "Radiation Chemistry of Quinonoid Compounds", in "The Chemistry of

the Quinonoid Compounds" (S. Patai and Z. Rappoport, editors), Wiley,

in press.

Neta, P., Huie, R. E., and Harriman, A., "One-Electron Transfer Reactions of

the Couple S0 2 /S02- in Aqueous Solution. Pulse Radiolytic and Cyclic

Voltammetric Studies", J. Phys. Chem., submitted.

Neta, P. and Huie, R. E., "Rate Constants for Some Reactions of N03 in

Aqueous Solutions, J. Phys. Chem., in press.

Neta, P. and Ross, A. B., "Representative Rate Constants for Radical

Reactions of Biologically Important Molecules", in a CRC book on Organic Radicals, in press.

Okabe, H. and dicker, S., "Photochemistry of Diacetylene", J. Phys. Chem.,

accepted.

Sieck, L. W. , "Thermochemistry of Solvation of SFg- by Simple Polar Organic

Molecules in the Vapor Phase", J. Phys. Chem., in press.

Stein, S. E., Fahr A., and Mallard, W. G. , "Phenyl Radical Reaction with

Ethane, Ethnye and Benzene," 21st Symposium on Combustion" In press.

Stein, S. E., Griffith, L. L., Billmer, R. L., and Chen, R., "Anthracene

Pyrolysis" J. Org. Chem., submitted.

Stein, S. E., Brown, R. L., and Manka, M. , "Rate Constants for Hydrogen

Transfer by Diphenylmethyl and Fluorenyl Radicals" J. Phys. Chem.,

submitted.

Tsang, W. , "Chemical Kinetic Data Base for Combustion Chemistry. Part 2.

Methanol," J. Phys. Chem. Ref. Data, submitted.

Tsang, W. and Herron, J. T. , "Chemical Kinetics Data Base for Combustion

Modeling", Proceedings of the 10th International Codata Conference, in

press.

Tsang, W. "Fundamental Aspects of Key Issues in Hazardous Waste

Incineration" ASME Publication, in press.

Tsang, W. , Robaugh, D., and Mallard, W. G. , "Single Pulse Shock Tube Studies on C"N02 Bond Cleavage During the Decomposition of Some Aromatic

Compounds" J. Phys. Chem., in press.

170
6 . TALKS

Brown, R. L. , "Chemical Theory of Graphite" Carbon Conference

Lexington, Ky, April, 1986.

Brown, R. L., "Chemical Theory of Graphite" AFOSR Contractors’ Meeting

Alburquerque, NM, Mar., 1986.

Brown, R. L., "Huckel Molecular Orbital Theory Applied to PAH"

1st Symposium on the Quantum Chemistry of Polynuclear Aromatic

Compounds, NRL, Washington DC, June, 1986.

Cvetanovic, R. J., "Reaction of Oxygen Atoms with Olefins", Catholic

University of America, Washington, D.C., April, 1986.

Herron, J. T., "The National Bureau of Standards Chemical Kinetics Data

Base," International Symposium on Gas Kinetics, Bordeaux, France, July,

1986.

Herron, J. T., "A Chemical Kinetics Data Base for Combustion Chemistry,"

International Symposium on Combustion, Munich, West Germany, August

1986.

Hudgens, J. W. , "Spectroscopy of Free Radicals Using Resonance Enhanced

Multiphoton Ionization" Symposium Theoretical and Experimental Studies

of Transient species" 190th ACS Meeting, Chicago, 111. Sept., 1985.

Hudgens, J. W. , "Multiphoton Ionization of Free Radicals" Chemistry Dept.

University of Illinois, Urbana, Illinois, Sept. 1985.

Hudgens, J. W. , "Multiphoton Ionization of Free Radicals" Chemistry Dept.

Yale University, New Haven Conn., Jan, 1986.

Hudgens, J. W. , "Multiphoton Ionization of Free Radicals" Ballistics

Research Laboratory, Aberdeen Proving Grounds, Jan., 1986.

Hudgens, J. W. , "Resonance Enhanced Multiphoton Ionization Spectroscopy of

Reactive Intermediates" Gordon Conference on Multiphoton Processes,

June, 1986.

Hudgens, J. W. , "Multiphoton Ionization Spectras of BrO and CIO Radicals"

Gordon Conference on Molecular Electronic Spectroscopy, August, 1986.

Huie, R. E., "Reactions of Intermediates in the Autoxidation of S0 2

",

Department of Chemistry, University of the District of Columbia, March,

1986.

Huie, R. E., "Radical Intermediates in the Autoxidation of S0 2

", Argonne

National Laboratory, March, 1986.

171
Huie, R. E., "Radical Intermediates in the Autoxidation of S02

», Radiation

Laboratory, University of Notre Dame, South Bend, Indiana, March, 1986.

Huie, R. E., "Aqueous Phase Reactions of NOy, Symposium on Acid Rain, 191st

National Meeting, American Chemical Society, New York, N. Y., April,

1986.

Kurylo, M. J., "Flash Photolysis Kinetic Absorption Spectroscopy Applied to

the Study of Gas Phase H02 Reactions, Dept, of Chemistry, Catholic

University of America, October 1985.

Kurylo, M. J. , "Rate Constants for the Reaction H02 + NC>2 + M

-> H02 N02+ M: The Temperature Dependence of the Fall-off Parameters"

,

XVIth Informal Conference on Photochemistry, University of Colorodo,

June, 1986.

Lias, S. G., "Structures and Reactivities of C^^* Ions", Seventh East Coast

Symposium on Ion/Molecule Chemistry, University of Delaware, Newark,

Delaware, October, 1985.

Lias, S. G., "Competing Proton Transfer and Condensation Reactions", 191st

National Meeting, American Chemical Society, New York, N. Y., April,

1986.

Martinez, R. I., "Ozone-Alkene Reactions: Dimethyl Dioxymethylene" , 191st

ACS National Meeting, New York, NY, April, 1986.

Martinez, R. I. "Methodology for the Determination of the Absolute Total

Cross-Sections in a QQQ Instrument" 3^th ASMS Annual Conference on Mass Spectrometry and Allied Topics Cincinnati, OH, June, 1986.

Martinez, R. I., "Dioxymethylenes: A Source of Oxygen Atoms in Alkene

Ozonolysis?" 17th Informal Conference on Photochemistry, Boulder CO,

June 1986.

Martinez, R. I., "Methodology for the Determination of Absolute Total CrossSections in a QQQ Instrument and Its Application to In-Situ Target

Thickness Calibrations" 17th Informal Conference on Photochemistry"

Boulder CO, June, 1986.

Martinez, R. I., "Research Opportunities in Mass Spectrometry" Office of

Naval Research, Arlington, V A, July , 1986.

Mautner, M., "The Ionic Hydrogen Bond", Department of Chemistry, University

of Maryland, Baltimore County Campus, December 17, 1985.

Mautner, M., "The Ionic Hydrogen Bond and Cluster Ions", Molecular

Spectroscopy Division Seminar, National Bureau of Standards, January,

1986.

172
Mautner, M., "The Ionic Hydrogen Bond”, Department of Chemistry, University

of Southern Illinois, March 19, 1986.

Neta, P. , "Pulse Radiolysis Studies of Porphyrins. Application to Solar

Energy Conversion Systems”, Radiation Chemistry Symposium, First Pan

American Chemical Congress, San Juan, Puerto Rico, October, 1985.

Stein, S. E., "Chemical Fundamentals of Coal Char formation" Contractors'

meeting Gas Research institute, Chicago, Illinois, June, 1986.

Stein, S. E., "Molecular Orbital Theory of PAH" Contractor's Meeting, Gas

Research Institute, Chicago, Illinois, June, 1986.

Stein, S. E., "Chemistry of Polynuclear Aromatic Hydrocarbons .Chemistry

Department, West Virginia University, Morgantown WVA., May, 1986.

Stein, S. E., "Phenyl Radical Reaction with Ethane, Ethnye and Benzene,"

21st Symposium on Combustion, Munich, Germany, July, 1986.

Tsang, W., "The Reaction of Hydrogen Atoms with Phenol"

191st ACS Meeting, New York, NY, June, 1986.

Tsang, W., "The Stability of Nitroaromatic Compounds"

ARO Workshop on Nitramine Decomposition" Livermore, California

June, 1986.

Tsang, W., "Evaluated Kinetics Database for Combustion Chemistry,"

International CODATA Conference, Ottawa, Canada, July, 1986.

Tsang, W., "Chemical and Thermal Stability of Aromatic Compounds" Catholic

University, Sept., 1986.

173
7. CHEMICAL KINETICS DIVISION SEMINARS

Ross, D. S., Stanford Research Center, Palo Alto, CA, "A New View of Nitration

Chemistryn

, November, 1985.

Platz, M. S., Department of Chemistry, Ohio State University, Columbus, OH,

"Photochemistry and Photobiology of Aromatic Azides", November 1985.

Lowe, J. P.» Department of Chemistry, Penn State University, State College, PA,

"MO Theory of Substitution in Polymers and Chemisorption on Surfaces",

Frebruary 1986

Niki, H., Ford Motor Company, Detroit, MI, "FTIR Spectroscopic Study of the

Mechanisms for Atmospheric Reactions of Olefins”, April 1986

Dewar, M. J. S., Department of Chemistry, University of Texas, Austin, TX,

"Chemistry by Molecular Simulations", May 1986

Len, M. C., Naval Research Laboratory, "Application of Lasus to Chemistry, May

1986

Henglein, A., Hahn-Meitner Institute, Berlin, "Extremely Small Colloidal

Semiconductor Particles: Electron Transfer Reactions and Size

Quantization Effects", June 1986

Gimarc, B., University of South Carolina, Columbia, "Topological Charge

Stabilization", June 1986

Burrows, J. P., Max-Plank Institute, Germany, "Chemical Dynamics of Atmospheric

Reactions", July 1986

Bartmess, J. E., University of Tennesse, Knoxville, TN, "Gas Phase Ion

Chemicstry", July 1986

Plumb, I. Cc, CSIRO Division of Applied Physics, Sydney, Australia, "Gas-Phase

Reactions in Plasma Etching Systems", August 1986

Traeger, J. C. , University of Ottawa, Ottawa, Canada, "Studies of

Thermochemistry of Ions", August 1986.

Heicklen, J., Department of Chemistry, Pennsylvania State University, College

Park, PA"

Wellington, T. J., "The Role of the NO^ Radical in Atmospheric Chemistry:

Laboratory Kinetics and Field Measurements", September 1986

174
8 . TECHNICAL AND PROFESSIONAL COMMITTEE PARTIPATION AND LEADERSHIP

Hampson, R. F.

Member, NASA Panel for Data Evaluation

Member, CODATA Task Group on Chemical Kinetics

Huie, R. E.

Member, Environmental Protection Agency Grant Review Panel

Member, Atmospheric Chemistry Working Group, Subcommittee for

Atmospheric Research

Kurylo, M. J.

Member, NASA Panel for Data Evaluation

Lias, S. G.

Member, Organizing Committee of NATO ASI on ’’Structure/Reactivity and

Thermochemistry of Ions", June 29-July 11, 1986, in Les Arcs, France

Member, Editorial Board of the series, "Molecular Structure and

Energetics", VCH Publishers, Inc.

Member, Editorial Board of the NBS Journal of Research

Program Manager, Office of Standard Reference Data, NBS

Neta, P.

Member, International Commission on Radiation Units and Measurements

(Committee on Chemical Dosimetry)

Regional Editor, "Radiation Physics and Chemistry"

Sieck, L. W.

Member, Panel for Small Business Innovative Research Program of the

U. S. Department of Energy

Stein, S. E.

Member, Editorial Advisory Board, International Journal of Chemical

Kinetics

Tsang, W.

Committee of the 21st Symposium on Combustion

175
9. PROFESSIONAL INTERACTIONS, CONSULTING AND ADVISORY SERVICES

Herron, J. T.

collaborated with R. VanBrunt of the Electrosystems

Division on dielectric breakdown phenomena

collaborated with David Kahaner of the Scientific Computing

Division on computer modeling programs (with Walter Braun)

consulted with J. Troe and D. Baulch on international

co-operative efforts in data evaluation for combustion

chemistry

Hudgens, J. W.

collaborated with D. Bogan (Catholic University of America) on studies of fluorine reactions with ketene.

collaborated with J. Leibman (University of Maryland, Baltimore

county) detection of small free radicals.

consultative services to Ole Krogh (Tegal Corp. , Novato, CA) on the

REMPI detection of CF^ during the plasma etching of surfaces.

Huie, R. E.

consulted with Dr. G. Mills of Argonne National Laboratory on the

chemistry of sulfite derived radicals.

consulted with Dr. D. J. Jacob of Harvard University on the Mechanism

of SO 2 oxidation in clouds.

Kurylo, M. J.

consultative services to R. B. Timmons (U. of Texas, Arlington) on

H0 2 kinetics.

consultative services to D. Bogan (Catholic University of America) on

H0 2 kinetics.

Lias, S. G.

collaborated with Drs. John L. Holmes (University of Ottawa), John E. Bartmess (University of Tennessee), and Joel F. Liebman (University

of Maryland, Baltimore County Campus) on production of an evaluated

compilation of heats of formation of ions and related neutrals,

ionization potential, appearance potential, and electron affinity

data.

176
collaborated with Drs. Vincent G. Anicich (Jet Propulsion Laboratory),

Albert Viggiano (Air Force Geophysics Laboratory), and Jean Gallagher

(JILA) to organize compilation of data on ion/molecule rate

constants.

Levin, R. D.

serves as NBS EEO Counselor.

Martinez, R. I.

provided technical information and consultation regarding the

Martinez-Herron Desulfurization Process (US Patent No. 4,351 ,810) to

several international corporations.

collaborated with S. Kafafi, Cairo University (Egypt) on thermochemistry of dioxiranes (and their isomers) and of alkenoxy

radicals

.

initiated collaboration with several investigators who will

participate in interlaboratory round robin experiments designed by us

to evaluate the general utility of our kinetic method as a generic

standard for target thickness calibrations in QQQ instruments.

consulted with D. Stone and Maj . K. Den Bleyker of the US Air Force

regarding standardization of QQQ operating parameters for speciation

of unknowns by MS /MS analysis.

consulted with P. Dawson, NRC-Ottawa on ion trajectories within

quadrupole mass filters, especially as it relates to QQQ instruments.

consulted with J. Futrell (U. of Utah), C. Ng (Ames Laboratory), K.

McFee (Bell Labs), G. Dunn (JILA), and A. Phelps (JILA) regarding the

relative reactivities of the states of the A r ion.

consulted with E. K. Lee, U. C. Irvine, on the mechanism for the

Photooxidation of matrices, and the probable involvement of

dioxymethylenes

.

consulted with J. Sodeau (University of East Anglia) on experimental

desig to validate the formation of hyroxy-substituted methylene and

dioxymethylene during the photolysis of H

2 C0 and H2 C0/02 matrices,

respectively.

consulted with H. J. Akimoto (Japan Environment Agency) on the

chemistry of dioxiranes (and their isomers).

consulted with S. Trevino, US Army, on trajectory calculations and

associated kinetics related to simulation of detonation of highly

energetic materials.

177
consulted with H. Guard, D. Nelson, and K. Wynne of ONR on research

opportunities in real-time mass spectrometry

.

consulted with M. Dixon and J. Gray of Galileo Electro-Optics

regarding design of novel high-mass detector.

consulted with P. S. Berger, President o.f Teknivent Corp., on requisite design and operational characteristics for an MS/MS system

controller and data system.

Mautner, M.

collaborated with Dr. C. A. Deakyne, Air Force Geophysics Laboratory,

on studies of ion clustering energetics.

collaborated with Professor S. Nelsen, Department of Chemistry,

University of Wisconsin, on ion chemistry of hydrazines.

Neta, P.

collaborated with A. Harriman, Royal Institute, London, England, on kinetics of redox reactions of porphyrins.

collaborated with P. Hambright, Chemistry Department, Howard

University, on porphyrin reactions.

Sieck, L. W.

collaborated with the Analytical Mass Spectrometry Group of the

Organic Analysis Division, Center for Analytical Chemistry, NBS

concerning adduct ion formation in MS/MS.

collaborated with R. Van Brunt of the Electrosystems Division, NBS,

concerning electron transport mechanisms in SF^.

collaborated with Professor S. Nelsen, Department of Chemistry,

University of Wisconsin, on ion chemistry of hydrazines.

collaborated with I. Savers, Health and Safety Research Division, Oak

Ridge National Laboratory, on joint studies involving reactions of

sf6 ~.

Stein, S. E.

collaborated with M. Frenklach, Louisiana State University on soot

formation thermochemistry .

collaborated with W. R. Moore, West Virginia University on synthes.

s

of polynuclear aromatic compounds.

178
collaborated with K. Kishore, IIS, Bangalore, India, on pyrolysis of

polymers.

Tsang, W.

collaborates with A. Lifshitz (Hebrew University, Jeruslaem) under an Israeli-American Binational Foundation grant on studies dealing with

the thermal stability of organic molecules,

collaborates with F. Tully (Combustion Research Facility, Sandia

National Laboratory) on the interpretation of OH reactions with

olefins.

provided consultative services to Dan Chang (UC, Davis), G. Hahn

(KWU, Erlangen, Germany), M. Macintosh (Argonne National Laboratory)

on various aspects of hazardous waste incineration.

provided consultative services to G. Zimmerman (Zentralinsti tute for

Organische Chemie, DDR) on the thermal stability of organic

molecules.

179
10. VISITING SCIENTISTS

Alfassi, Z., of Ben Gurion University returned to Division and has spent

two months at NBS as a guest scientist working on pulse radiolysis.

Altstein, N.„ of the Weizman Institute of Science, Israel, is spending

two years at NBS as a guest scientist working on pulsed electron

sources

Bai, J. s of Dalian Institute of Cehmical Physics, Dalian, Liaoming,

People's Republic of China, is spending one year at NBS as a guest

scientist working on Photochemistry of planetary atmospheres.

Behar, D. , of Soreg Nuclear Research Center, Israel spent six weeks at NBS

working on Pulse radiolysis studies of electron transfer reaction and

the effects of polyelectrolytes on such reactions.

Chen, R., of West Virginia University has spent eighteen months at NBS as

a guest scientist working on free radical chemistry.

Dheandhanoo, S., of Georgetown University, has spent 10 months at NBS as a guest scientist working on obtaining and analyzing CID spectra of

selected target molecules.

Fahr , A., has spent one year at NBS under a cooperative agreement with

Georgetown University, working on thermolysis of aromatic compounds.

Harriman, A., of The Royal Institution, London, has spent one year at

NBS as a guest scientist working on pulse radiolysis.

9 He, Yu Zhong, of the Institute of Mechanics Academia Sinica, Beijing, has

spent one year at NBS as a guest scientist working on shock tube

studies on thermal stability of molecules.

Kafafi, S., of the University of Cairo has spent one year at NBS as a guest scientist working on polynuclear aromatic hydrocarbons

Kishore, K. , of Indian Institute of Science, Bangalore, India spent six

weeks at NBS as a guest scientist working on polymer pyrolysis.

Laufer, A. , of the Department of Energy has spent one day a week at NBS

working on free radical species.

LeMotais, B. , of the University de Paris-Sud, France spent one year at NBS

working as a guest scientist working on studies of electron transfer

processes carried out using the technique of pulse radiolysis.

Manka, M. , of Catholic University has spent one year at NBS as a guest

scientist working on thermolysis of organic compounds.

McNesby, J. R. , of the University of Maryland has spent five months at NBS

as a guest scientist working on high temperatues and non-equi ^ i br : uir chemical kinetics involving organic compounds relevant to combustion

and potential industrial chemical processes.

180
Mosseri, S., of Ben Gurion University of the Negev has spent one year

at NBS as a guest scientist working on pulse radiolysis.

Price, I. W., is working on electronics design projects.

Richoux, M.-C., of The Royal Institution, London, spent one year at

NBS as a guest scientist working on pulse radiolysis experiments.

Rumack, D., of the University of Wisconsin has spent one month at NBS

as a guest scientist working on mass spectrometry of hydrazine

derivatives.

Senthilnathan, V., of West Virginia University has spent seven months at

NBS as a guest scientist working on free radical reactions on high

temperature fluids.

181
.

.

*'

o

182
CHEMICAL THERMODYNAMICS DIVISION

S. Abramowitz, Chief

SUMMARY OF ACTIVITIES

Fiscal Year 1986

1 . INTRODUCTION

A. Objectives

Chemical Thermodynamics provides measurement techniques, concepts and

data on the energetics and equilibria of chemical processes. Chemical

thermodynamics is used to predict equilibria in chemical reactions,

thermodynamic properties of high temperature refractory materials and gases,

activities of aqueous solutions used in technologies varying from power

generation and electrorefining to biotechnology. This division develops the

models necessary for correlating structure with thermodynamic properties,

develops the science of calorimetry in order to obtain precise data from

the microwatt to megawatt levels, carries out precise thermodynamic

measurements, including those on Standard Reference Materials, develops

the measurement capabilities for molecular structure determinations and

critically evaluates thermodynamic data in all phases for the use of

industry, government and academia. A current emphasis is directed towards

the needs of the emerging biotechnology industry. In particular, this

division is developing the measurement and computational techniques for

obtaining biomolecular structures of proteins, enzymes, enzyme-substrate

complexes and DNA species using x-ray and neutron diffraction. The

thermochemistry of generic processes of interest to biochemistry and

biotechnology are being studied in order to develop standards and provide

key data, to develop quantitative models for the energetics of these

processes and estimation schemes of demonstrated reliability for the

concomitant thermodynamic properties. A new effort is being launched in the

coming year aimed at correlating structure and function for proteins.

This research will coordinate with the biothermodynamics and biomolecular

structure efforts in order to develop structure-function-energetics

correlations.

The objectives of the Chemical Thermodynamics Division include:

o Application of the science of calorimetry to the needs of

existing and new technologies through the design of novel

calorimeters and the development of improved procedures to obtain

enhanced measurement precision and accuracy.

o Development and certification of Standard Reference Materials for the use of existing and emerging technologies.

o Measurement of the thermochemica.1 properties of key chemical species

and processes including bioprocesses and phase transitions of aqueous

biomolecular species.

183
o Provision of critically evaluated compilations of the thermodynamic

properties of inorganic, organic and bioorganic compounds in the

gaseous, liquid, solid and aqueous phases.

o Development of estimation schemes for the prediction of thermodynamic

properties of organic, inorganic, and bioorganic species in the

gaseous, liquid, solid and aqueous phases.

o Development of measurement and computational methodology for the

determination of the structure of biomacromolecular species using the

techniques of x-ray and neutron diffraction.

In achieving these objectives Division scientists are encouraged to be aware of and to respond to the needs of industry, government and academic

institutions for measurement standards, accurate data and concepts in the

field of thermodynamics.

B. Organization and Staff

The Chemical Thermodynamics Division has four groups. An additional

group has been organized, this year, under the leadership of Alex Wlodawer

to guide the growth in the biomolecular structure group. Malcolm Chase

has assumed the leadership of the Chemical Thermodynamic Data Centers

Group, which includes the Chemical Thermodynamics Data Center and

Electrolyte Data Center. Dr. Chase has extensive industrial experience in

the evaluation of chemical thermodynamic data for both industrial ana military technologies. He brings to this position an awareness of the

needs of these technologies and will make the products of this group more responsive to those needs. Dr. Chase will also continue his activity as the director of the JANAF Ther-rnochemicfal Data Project. This change in

leadership will allow David Garvin to devote all his energies to the

evaluation of chemical thermodynamic data in support of national and

international data evaluation programs. The group structure is

o Biothermodynamics, S. Abramowitz, Group Leader

o Biomolecular Structure, A. Wlodawer, Group Leader

o Chemical Thermodynamics Measurements, E.S. Domalskl, Group Leader

o Chemical Thermodynamic Data Centers, M.W. Chase, Croup Leader

The division has 26 full-time staff, 1 part-time employee, 6 guest

workers, 7 students, 5 contractors and 1 consultant. This fiscal year two

additional members have joined the Biomolecular Structure Group. Dr.

Gilliland will be continuing work he began elsewhere on the maintenance

and development of a computer based database for the crystallization of

biomolecular species and will conduct research in biomacromolecular

structure and on means to systemize the crystallization of prote.'.ns and

other biomolecular species. Dr. Weber will conduct research on evaluating

the effects of selected mutations on the structures of proteins and

protein-substrate complexes. In addition the group has a postdoctoral

associate, three guest workers and a technician. Funds for one guest

worker and the technician are being provided by the Center for Advanced

184
Within NML we are cooperating with the Center for Analytical

Chemistry on several programs in the area of biotechnology including the

thermodynamics characterization of monoclonal antibody antigen

interactions and the use of NMR in speciating carbohydrates . We are also

collaborating with the Center for Basic Standards on temperature

measurements in combustion studies. We are cooperating in the planning

and carrying out of a research program in support of AFOSR needs in

cooperation with both IMSE and NEL.

Our staff has many interactions with voluntary standards

organizations and international societies such as ASTM, ANSI, ASME,

CODATA, IUPAC , and IAEA etc. This past year staff members participated in

the planning and formations of a new ASTM committee on Biotechnology.

Staff members hold memberships on diverse committees ranging from

environmental and health concerns to energy utilization and database

management. Members of the Biomolecular Structure Group organized a three-day Mid-Atlantic Protein Cystallography Workshop at NBS in May 1986.

The workshop was attended by about 80 scientists.

We are actively planning for the maintenance of a protein

crystallization database. Computing expertise for the necessary

programming for this task will be provided by the Chemical Thermodynamics

Data Centers Group. The differential scanning calorimetry effort has been

successfully integrated into the biothermodynamics efforts in this past

year. This laboratory is documenting standard procedures for calibrating

differential scanning calorimeters that have been designed for use with

biochemical samples. Work has continued in the measurement of the

thermodynamics of enzyme catalyzed reactions. The work on the five and

six membered monosaccharides has been completed and efforts will be made,

in the coming year, to construct estimation schemes for the prediction of

the thermodynamic formation properties for this class of compounds.

Efforts have begun in other areas including the measurement of the

thermodynamics of the reactions of monoclonal antibodies with antigens and

the use of microcalorimetry to characterize the rates of enzyme catalyzed

reactions and to measure enzyme activity.

Work will also continue on the determination of enthalpies of

formation of key phosphorus compounds and other biomolecular building

blocks including the development of predictive schemes for these

compounds. Benzoic acid will be recertified during this fiscal year.

Research to characterize the chlorinated organic species present in the

effluents resulting from the combustion of municipal solid waste will also

be continued.

185
Biotechnology (CARB) to support research of mutual interest. This group

has acquired state-of-the-art computing and x-ray detector equipment in

the last year. It also has access to additional equipment through its

collaboration with others including CARB and Genex.

Additional expansion is planned for FY87 in the area of protein

structure-function studies. A laboratory will be refurbished for

molecular biology work and will be used for protein synthesis and for the

investigation of the effect of changes in protein structure on function.

It is expected that this new activity will involve close collaboration

with the biothermodynamics and biomolecular structure programs.

The division participates in the work of the Office of Standard

Reference Data and the Office of Standard Reference Materials. In support

of the Standard Reference Data program, the Chemical Thermodynamics Data

Centers group evaluates thermochemical data for organic and inorganic

species, develops database management systems for chemical thermodynamics,

and develops critically evaluated data and reliable estimation schemes for

organic and biochemical species. In support of the Standard Reference

Materials program, the Thermodynamics Measurements Group maintains standards for

oxygen bomb and heat capacity calorimetry and develops new standards as needed. Benzoic acid is a best seller of the Standard Reference Material

Program. It is responsible for converting the chemical system of

measurements to the electrical system and is used to calibrate combustion

bomb calorimeters for the fuel industry, power generation industry and in

bomb calorimeter research laboratories.

The research needs of two federal agencies and one industrial trade

association are being addressed by the division. We receive funding from

the Department of Energy for determining the chlorine content of municipal

solid waste and optimizing conditions for the formation and destruction of

chlorinated organic species, and for the development of thermodynamic data

for flue gas clean-up in fossil fuel technology. Programs being pursued

for the Department of Defense include the provision of combustion

calorimetric data and estimation methods for the thermodynamic and related

properties of organic phosphorus compounds and development of

thermodynamic functions for species of importance to high temperature

technologies including rocketry, reentry, and energy production. We are developing computer algorithms for aqueous thermodynamics and providing

annotated bibliographies for the sources of the data for the Design

Institute for Physical Property Data (DIPPR), which is sponsored by AIChE.

We have finished the revision of a previous publication on the

thermodynamic data for biomass and waste incineration in cooperation with

the Solar Energy Research Institute (SERI).

In addition to the interactions which we have with other NBS programs

and federal agencies the division cooperates with other NBS units. Within

CCP we have a joint program with the Chemical Kinetics Division on database managment systems, with both the Chemical Kinetics

and Spectroscopy Divisions in developing and carrying out a research

program in support of the high temperature technology needs of AFOSR and

with the Surface Science Division in developing computer algorithms for

the interpretation of sputtering depth profiles.

186
2. BIOTHERMODYNAMICS

S. Abramowitz, E. Gajewski, R.N. Goldberg, W.H. Kirchhoff,

F.P. Schwarz, D. Steckler, Y.B. Tewari

A. Biochemical Thermodynamics

(R.N. Goldberg, E. Gajewski, D. Steckler, Y.B. Tewari)

The long term goals of this research are to provide understanding of

the thermodynamics of the key processes and interactions relevant to

biochemistry and biotechnology. This understanding is needed to predict

the feasibility of biochemical processes, optimization of product yields

and elimination of side reactions in industrial processes. The data are necessary to construct estimation schemes to reliably predict the thermochemical

properties of substances and processes for which measurements are not

available. The goals are realized by development of measurement and

computational methodology, determination of reliable thermodynamic values,

and establishment of the relationship between molecular structure and the

formulation of predictive methods.

The thermodynamic investigations include, where feasible, both

equilibrium composition and calorimetric measurements on carefully

characterized biochemical systems. Independent measurements of enthalpy

and equilibrium composition as a function of temperature enable the

reliable modelling of reactions outside of the temperature range of the

measurements. The effects of pH, metal ion concentration, ionic strength

and temperature on the equilibrium and enthalpy measurements are also

investigated. An equilibrium model of the system allows one to account

for the experimentally determined values and to predict these quantities

under a variety of possible conditions. The calculations require

identification of the individual molecular processes, activity coefficient

models to account for nonideality, and numerical solution of the

equilibrium equations which describe the system. The final set of

thermodynamic parameters makes possible the prediction of the

thermodynamic behavior of a system under a wide range of conditions beyond

those used for the measurements. The combined approaches of equilibrium

measurements, calorimetry and computer modelling is believed to be unique

to NBS

Written descriptions of the microcalorimeters, procedures and

software used in the studies of biochemical systems have been prepared.

The documentation includes a detailed description of the construction,

calibration, operation, performance and use of these calorimeters. The

software allows for the acquisition and treatment of data from three

microcalorimeters simultaneously. Software for the acquisition and

treatment of data from an isoperibol solution calorimeter, using a quartz

thermometer, is also described. Procedures for obtaining kinetic

parameters such as enzyme activity and rates of conversion of substrate to

product are also described with accompanying examples using glucose

isomerase.

Summaries of the accomplishments of the individual projects follow:

187
1. Thermodynamics of the Hydrolysis of Adenosine 5 ' -Triphosphate

The enthalpy of the hydrolysis of the enzyme catalyzed conversion of

adenosine 5 '“triphosphate (ATP) to adenosine 5 '“diphosphate (ADP) and

inorganic phosphate was investigated using microcalorimetry. There are five measurements of this equilibrium in the literature. Four of these

are in agreement „ All of them involve the use of coupled reactions to

obtain the Gibbs energy change, which is known to ± 1.5 kJ mol -1

. These

results are sufficiently accurate for our needs. Enthalpies of reaction

were measured as a function of ionic strength (0.05 to 0.66 mol kg-1

), pH

(6.4 to 8.8) and temperature (25 to 37 °C) in Tris/HCl buffer. The

measured enthalpies were adjusted for the effects of proton ionization

and metal ion binding, protonation, interaction with the Tris buffer and

ionic strength effects to obtain a value of AH = “20.5 ± 0.4 kJ mol-1

at

25 °C for the process:

ATP 14- + H

2 0 = ADP

3- + HP0J4 -

+ H

+

Since earlier investigations did not systematically investigate the

effects of pH, ionic strength or temperature the results obtained are currently the best value for the enthalpy change for this biochemical

process. The result of AC

p ° = -237 ± 30 J mol -1

K

-1

is the only

direct determination of this thermodynamic quantity.

2. Thermodynamics of Carbohydrate Isomerization Reactions

The thermodynamics of the enzymatic conversion of aqueous D-psicose to

D-allose was investigated using high pressure liquid chromatography . The

reaction was carried out in phosphate buffer at pH 7.4 over the temperature of 44.1 to 76.1 °C . From the temperature dependency of the equilibrium constants, the following results were obtained for the conversion

process at 25 C: AG° = -1.41 ± 0.09 kJ mol

-1

, AH° * 7.42 ± 1.7 kJ mol

-1 and

AGp° was estimated to be 67 ± 50 J mol -1K

-1

. An approximate equilibrium

constant of 0.3 was also obtained at 60 °C for the conversion of D-pslcose

to D-altrose. The kinetics of these reactions are not rapid enough to

permit a direct calorimetric determination of the enthalpy changes.

This study is a continuation of earlier studies of carbohydrate

isomerization reactions using the enzyme, glucose isomerase, which included

isomerizations of glucose to fructose, xylose to xylulose and ribose to

ribulose and arabinose. The possibility of other isomerization reactions

involving sorbose, galactose, tagatose and talose were also investigated.

Isomerization was not observed for the above carbohydrates.

The available information on the thermodynamics of the aldo/keto

isomerization of hexoses and pentose is summarized in Table 1 . With the

exception of the mannose/fructose system, all the results were determined

in this laboratory using both HPLC, for the determination of equilibrium

constants, and where feasible, microcalorimetry to determine both the

enthalphy and heat capacity changes. This represents the most complete

set of information on the thermodynamics of carbohydrate isomerization

reactions

188
The observed thermodynamic data for the hexoses and pentoses will be

coupled with other thermodynamic data such as enthalpies of combustion and

solution and heat capacities to estimate the thermodynamic formation

properties of the hexoses and pentoses. Available NMR and polarimeteric

data will be used, where appropriate, to obtain speciation information for

the solutions.

Table 1

Thermodynamics of isomerization reactions involving D-aldohexoses and

D-aldopentoses in aqueous solution 298. 15K

Process AG° AH0 AS0 AC

p °

(kJ mol -1

) (kJ mol” 1 ) (J mol” 1 K” 1 ) (J mol” 1 K" 1 )

Ribose-arabinose -3.44^0.30 -9.8±3.0a -21 .3

Ribose-ribulose 2.85±0. 1

1 1 .0±1 . 5 a 27.3

Xylose-xylulose 4.38q±0.031 I6.09±0.67a 39.2 40±23 a Arabinose-ribulose 6.29±0.34 20. 75+3.

a 48.5

Allose-psicose

Psicose-altrose

Alios e-altrose

-1 .41 ±0.09

*3*4

*2.0

7.42± i ,?

b 29.6 67+50 d

Glucose-fructose 0. 349±0. 053 2.78+0. 20a 8.15 76±30 c Mannose-fructose -2.72 0.0b 9.12

Glucose-mannose 3.07 2.78 +0.97

° Based on direct calorimetric measurements.

° Calculated from the temperature dependency of equilibrium constants.

c Calculated from the temperature dependency of enthalpies of reaction.

d Based on both an estimate and the temperature dependency of equilibrium

constants.

3. Equilibrium Studies of the Conversion of Trans-Cinnamic Acid and

Ammonia to L-Phenylalanine

The thermodynamics of the enzymatic conversion of aqueous

trans-cinnamic acid and ammonia to L-phenylalanine has been investigated

using high pressure liquid chromatography. The reaction was carried out

in 0.1 M Tris/HCl buffer containing ammonium chloride over the pH range 7.0

to 7.7, at ionic strengths from 1.0 to 2.1 mol kg

-1

in the temperature

range of 12 to 43 °C. Analysis of the HPLC data using an estimated heat

capacity change of 50 kJ mol

-1

K**

1 and an ion size parameter of 1.6

mol“ 1/2 kg" 17^ leads to an equilibrium constant of 0.86 ± 0.22 at 25 °C

for the process

Trans-cinnamic” acid + NH l4 + = L-Phenylalanine±

We were unable to bring about a sufficiently rapid reaction to permit a direct calorimetric measurement of the enthalpy of this reaction. The use

of these thermodynamic parameters in an equilibrium model allows for the

189
prediction of values of the apparent equilibrium constant as a function of

pH, temperature and composition. These data are useful for optimizing the

yield of phenylalanine. The available thermochemical data for this

generic type of reaction (ammonia elimination and the formation of a double bond) can be rationalized in terms of a scheme which views the

entropy changes for related processes to be comparable and then attributes

differences in Gibbs energy changes to the enthalpy changes which can be

influenced by resonance stabilization of the double bond which is formed.

This study complements an earlier one on the conversion of fumaric acid

and ammonia to aspartic acid.

Microcalorimetric Measurement of Enzyme Activity

In addition to thermodynamic studies, the microcalorimetric

instrumentation can be used for the determination of enzyme activity. If

the substrate is present in large excess relative to enzyme, the reaction

will be slow and accompanied by a steady rate of heat production per unit

time given by

dq/dt = (dn/dt)/AH

where AH is the molar enthalpy of reaction and (dn/dt) is the number of

moles of substrate converted per unit time. The quantity (dn/dt) is a measure of the enzyme activity and can be determined from the measured

power (dq/dt) if the enthalpy of reaction is known. This technique may

prove valuable for the measurement of the activity of creatine kinase.

Currently, the activity of this enzyme is measured spectrophotometrically

with a precision of about 16?. The procedure requires the coupling of

three enzyme catalyzed reactions to produce an increase of absorbance at

340 run. A single step process can be used to measure this process in a microcalorimeter

.

Creatine Phosphate + ADP => Creatine + ATP

Results obtained have confirmed the literature results for the enthalpy of

this reaction. Also the measurement of enzyme activity in aqueous buffer

solutions have yielded results having an imprecision less than 10?.

Measurements of this activity in human serum will require steps to

eliminate and/or correct for possible chemical interferences in the

measurements

.

5. The Hydrolysis of Glucose 6-Phosphate and Fructose 6-Phosphate and

the Isomerization of Glucose 6-Phosphate to Fructose 6-Phosphate.

G6P_“2 = G + HPOiJ2 F6P“2 = F + HP0u 2

G6P~2 * F6P"2

Here glucose and fructose are abbreviated as, G and F,

respectively. The aim of this research is to obtain enthalpy, heat

capacity and Gibbs energy changes for these processes. The results will

be examined in conjunction with the thermodynamic data obtained previous.)'

for the hydrolysis of ATP of glucose and fructose, and the phosphor y . a t : >n of glucose and fructose by ATP.

190
To date, enthalpy measurements have been made on the first two

processes as a function of pH, temperature and concentration of magnesium

chloride and of Tris/HCl buffer. A preliminary set of measurements have been

made on the third process. After completion of the measurements on the

third reaction, the necessary corrections will be made to obtain the

enthalpy changes and the formalism applied to the Krebs cycle will be used

to obtain the best consistent set of thermodynamic parameters for the above

reactions, phosphorylation of glucose and fructose by ATP, and hydrolysis

of ATP

6. Antigen-Antibody Interactions

A study of ant igen-anti body reactions has been started, in

cooperation with the Center for Analytical Chemistry, using monoclonal

antibodies. This should aid in the molecular interpretation of the

thermodynamic properties of the reaction. A sample of a monoclonal antibody, has been obtained. The antibody has a molecular weight of about

150,000 daltons and is specific for E-N-E dinitrophenyl-L-lysine (2,4

DNP) . An affinity column is being used to purify the monoclonal antibody.

We plan to measure the enthalpy of the antigen-antibody reaction using

microcalorimetry and to measure the equilibrium binding using dialysis

techniques. Differential scanning calorimetry will also be used to

characterize both the bound and unbound antibody.

7. Plans for Next Year

Thermodynamic formation properties of the five and six membered

monosaccharides will be determined using available literature, estimation

methods and data from ours and others research. The study of the

thermodynamics of the reactions of glucose and fructose with ATP and the

isomerization of glucose 6-phosphate to fructose 6-phosphate will be

completed. The thermodynamics of the reactions of a monoclonal antibody

with its antigen will be completed. An examination will be made of the

thermodynamics of the most important processes currently used industrial

biotechnology. The available thermodynamic data will be given, best

available values will be recommended and, where appropiate, experiments

suggested. A thermodynamic investigation of the enzymatic conversion of

penicillin G to 6-aminopenicillanic acid and phenylacetic acid will be

initiated. Equilibrium measurements will be made using HPLC and, if

kinetics allow, microcalorimetric studies will also be pursued.

B. Differential Scanning Calorimetry

(F. P. Schwarz and W. H. Kirchhoff)

Differential scanning calorimetry, provides thermodynamics information

on biological systems which characterizes the interactions and

conformational changes of biological molecules in solution. Studies of

the effect of ligand concentration on the transition temperature and

enthalpy of protein, such as human serum albumin, yield information on

the binding energetics of the substrate to the enzyme. Comparison of the

transition enthalpies and temperatures of synthetic oligonucleotides

in solution yield information on the effect of the nucleotide sequence on

the conformational stability of DNA species in solution.

191
1. Temperature and Enthalpy Standards for Differential Scanning

Calorimetry

(F. P. Schwarz)

Differential scanning calorimetry standards for temperature and

enthalpy are needed to validate comparisons of data from different

laboratories. A differential scanning calorimetric standard should

exhibit a well characterized transition in the temperature range from 0 to

100 °C , the normal operating temperature range for biological studies,

with an accuracy in the transition enthalpy of ± 0.10 meal and a temperature accuracy of ± 0.10 °C. It is also desirable to use a biological solution as a standard since many of the differential scanning

calorimeters contain fixed cells which are filled through small capillary

tubes. Ribonuclease A is a candidate. Ribonuclease A is an enzyme

consisting of 124 amino acid residues (G.M.W. = 13.700). In buffer

solutions, ribonuclease a exhibits an unfolding transition with a transition temperature and enthalpy depending on the pH of the solution.

It is readily available in relatively high purity and is highly stable.

Furthermore, its concentration can be readily determined by several simple

spectroscopic methods.

Solutions of ribonuclease A in a HCL-glycine buffer were prepared,

dialyzed, analyzed, and thermally scanned on a differential scanning

calorimeter to evaluate the suitability of ribonuclease A as an enthalpy

and temperature standard. The calorimetric results from solutions prepared from four different samples of ribonuclease A were determined with a computer-controlled , heat flow differential scanning calorimeter. The

solutions ranged in concentration from 0.7 to 1.7 mM and a glycine buffer

concentration of 0.1 and 0.2 M. A straight baseline was interpolated

under the transition peak to obtain the enthalpy of transition. The transition enthalpies exhibited a linear dependence on the transition temperature, ranging from 66.0 ± 0.4 kcal/mole at 37.4 ± 0.1 °C (pH - 1.9), to

110.0 ± 0.5 kcal/mole at 64.0 ± 0.1 °C (pH = 4.2), with a standard deviation of 2.47 kcal/mole. The enthalpy determinations are in good agreement

with values reported in the literature. The results are independent of the

source of the ribonuclease A and the concentration of the buffer. The solutions are stable when stored in a refrigerator and can be analyzed by

measuring the UV absorption at 278 nm at a pH of 7.0. An error analysis

revealed that the major source of error was in determining the temperature

limits in the integration of the enthalpy transition peak. It is anticipated that a computer algorithm based on the two state model, being developed by W.H. Kirchhoff, to fit the entire thermal scan, will further reduce

the standard deviation in the linear fit of the enthalpy to the temperature.

In summary, from the standpoint of ease of preparation, ease of

characterization of the transition properties of ribonuclease A, and

stability, ribonuclease A is an acceptable standard for the calibration of

differential scanning calorimeters. The value of a ribonuclease A standard for measurement accuracy of the transition enthalpy and

transition temperature is expected to be improved by the algorithms being

developed.

192
2. Studies of the Thermal Stability of Synthetic, Quasi palindromic

DNA Sequences in Solution.

(M. Miller, F.P. Schwarz, E. Appella (NIH) , and W. H. Kirchoff)

Oligonucleotides consisting of prepared palindromic sequences

have served as model systems for studying the effects of environmental

variable (e.g. pH, temperature, electrolytic strength, etc.) on the

stability of various forms of DNA - duplex (Z or B double-helix

structures), cruciforms and hairpin loops. The palindromic sequences, which

have the property of being self-complementary enabling the

oligonucleotides to form exactly matching double-helices or exactly

matching ends for stabilizing loop structures, have been extensively

studied by crystallography, differential scanning calorimetry,

UV spectroscopy and NMR. From these studies, the stabilities of all possible

nearest-neighbor configurations have been computed and from this limited

data base, the stability of any double-helix form of DNA may be estimated

from its base-pair sequence.

We have begun to study a series of quasipalindromic sequences in

order to determine the effects of mismatches on the stability and structure

of DNA. In addition, spectroscopic and calorimetric measurements on systems with small enthalpies of reaction provide very broad transition

envelopes which can further test mathematical models for the description

of phase transitions in small systems. This work complements structural

work being conducted in the Biomolecular Structure Group of the division.

The species studied, along with their duplex and hairpin forms are shown

below.

1

3

~mer 17-mer 15~mer

AATTa CGCG CGCGCG AATTA CGCGCG CGCG AAATTT

TTAA GCGC GCGCGCa TTAA GCGCGC GCGC a tttaaa

T T T

T A T A T

A A A A T

(SC GEC A A

CEG CEG GEC

GEC GEC CEG

CEG CEG GEC

GEC o

in o CEG

One of the variables in the study of these species is the total

concentration of DNA strands. At high concentrations, the duplex form is

favored. At low concentrations, the hairpin form is favored. The high

concentration forms are most easily measured with a differential scanning

calorimeter, the low concentration forms with a uv spectrometer. Both

techniques were used and transitions between the species were analyzed.

The van* t Hoff enthalpies of transition were most accurately determined

from the UV data. The 15“mer was found to form the most stable duplex

form at low temperature and was selected for crystallographic studies. The

thermodynamic data have been interpreted in terms of the relative

193
strengths of G2C vs A=T base pairs. Circular dichroism measurements

indicate the presence of the Z form of the duplex and observed transitions

have been tentatively ascribed to Z-B transitions.

3. The Effect of Ligand Concentration on the Thermal Stability of Human

Serum Albumin

(F.P. Schwarz and A. Shrake)

Serum albumin is the most abundant protein in blood plasma, and

information on its thermal stability can be used to improve commercial

preparations of blood plasma. A detailed differential scanning

calorimetry study has been completed on the dependence of the thermal

stabilization of human serum albumin on the concentration of alkanoate

anion ligands in solution. The increase in the thermal stabilization of

serum albumin is monitored by the increase in its denaturation temperature

and in its denaturation enthalpy in the presence of increasing ligand

concentration. Two trends in the thermal stabilization were observed:

(1) The optimum denaturation temperature increased from 66.1 °C in the

absense of ligand to 76.1 °C in the presence of formate and then to 79.0 °C

in the presence of acetate, propionate, and butanoate.

(2) The optimum denaturation temperature increased to 81 .2 °C in the

presence of pentanoate and monotonically thereafter with increasing carbon

chain length to 88.8 °C for the decanoate anion. An increase in thermal

stability with chain length is anticipated since the binding constants of

the alkanoate ligand to the serum albumin increase with chain length. The

departure of propionate and butanoate from this behavior have been

explained by assuming two different types of binding sites for the ligand to

the serum albumin: (1) A large number of sterically hindered binding

sites which bind only small ligands (formate to butanoate) and (2) a small

number of large binding sites which bind all the ligands from formate to

decanoate.

For FY 87, a number of studies are being planned which should serve as prototypes for assessing the applicability of DSC to the measurement of

protein-substrate binding energies. The studies currently under

consideration include: the thermal stability of monoclonal antibodies and

their complexes with antigens; the thermal stability of the avidine

and its unusually strong complex with biotin (vitamin H), and the effects

of structural alterations on the thermal stabililty of chymotrypsin and

trypsin and their respective proenzymes, chymotrypsinogen and

trypsinogen

4. Calculational Methods for the Characterization of Phase Transitions

in Biomolecules

(W. H. Kirchhoff)

Computer programs have been written for analyzing phase transition? in

biomolecules as measured by calorimetry or spectroscopy. The purpose of

the programs is to characterize the measurement process and to determine

the limits within which simple thermodynamic theories can duplilcate

temperature profile measurements. Since the same theories are applied tc

both spectroscopic and calorimetric profiles, we may be able to separit*

instrumental effects from effects due to the non-ideality of true phase

transition behavior.

194
The basis for the description of the spectroscopic and calorimetric

profiles is the explicit dependence of the concentration of species on temperature. Phase transitions can be considered to be chemical reactions

between initial and final states and can be written most generally as:

A <=> nB

and the concentration of species in states A and B is expressed in terms

of the equilibrium coefficient

K = [B] n and its temperature dependence d[lnK]/dT = -AH/RT2 .

. [A]

The enthalpy change, AH, is expressed as a power series about the standard

state temperature, T

0

:

AH = AH0 + AC

p

°(T-T 0 ) + ...

The expression for the differential scanning calorimetry heat capacity,

dQ/dT, is

dQ/dT = **AH(dNA /dt) + NA CpA + NgCpg + baseline parameters

while the expression for the temperature dependence of the spectrum of a biomolecule undergoing a phase transition is given by:

I = I A

[A] + Ib^ + baseline paramenters

„ • were I A and I B are the absorption coefficients or scattering intensities

for the two species (which themselves may be expressed as power series in

temperature). Simple algebra provides explicit expressions for dQ/dT and

for I as functions of temperature.

Computer programs have been written for fitting these expressions by

the methods of non-linear least squares to the experimental data. From

the spectroscopic data, T

Q and AH 0 can be obtained, though the data are generally not sensitive enough to determine AC °. In the cases tested thus

far, which have included the main phase transition in lipid bilayers, DNA

fragments, and ribonuclease , the data have been fit to within experimental

error. As a corollary, additional information may be obtainable from

spectal measurements only through improved sensitivity, precision and

temperature control.

From the calorimetric data, T

Q , AH°, ACp°, and N, the number of

moles of material present in the cell, can be determined. This approach

differs from traditional approaches to the analysis of calorimetric data

in that the baseline is a varying function of composition, and hence

temperature. A so-called calorimetric enthalpy is not calculated.

Instead, the van't Hoff enthalpy, AH°, and the number of moles, N, are

deemed the fundamental quantities to be determined. Although the fit of

the model to experimental data seems excellent on casual inspection (the

observed and calculated profiles are indistinguishable in graphical

depictions) the difference between the calculated and observed profiles

shows distinct trends and the standard deviation of the fit is an order of

magnitude greater than the scatter in the data. This systematic error

may be due to diffusion and other dynamic effects which have not been

195
included in the analysis, the inadequacy of a simple power series in

describing the instrumental background or a breakdown in the purely two

state nature of the transition in ribonuclease A. Work in the coming year

will focus on distinguishing between instrumental effects and effects due

to the limitations of the purely thermodynamics model. The programs will

also be expanded to include values of n greater than 1 , the only case for

which the programs have thus far been tested.

The computer programs have been written in standard Fortran 77 for

personal computers compatible with the IBM AT and XT computers. In

developing the programs, some degree of portability had to be sacrificed

for ease of use. The lack of portability is related directly to the

graphical displays that accompany the analysis. At this time, no standard

protocols for graphical displays for Fortran-based programs exist. The

programs are currently being distributed on a limited basis to those

individuals who are willing to share their experience with the programs

and who can offer critical reviews of the thermodynamic models, the

statistics of the data analysis, the robustness of the algorithms, and ease of use.

The function for the spectral profiles is known as the logistic

function and is commonly encountered in chemistry and other fields.

Consequently, the spectral fitting program has been written in a more general manner for wider dissemination. It has been successfully used

to analyze sputter depth profiles through interfaces where a simple

diffusion model gives rise to the logistic function. The program has been

distributed to laboratories performing depth profile analyses and is

gaining in popularity.

196
3. BIOMOLE CULAR STRUCTURE

A. Wlodawer, G. Gilliland, R. Harrison, M. Miller,

H. Savage, I. Weber

The Biomolecular Structure Group has developed an active program in

measurement and analysis of the structure of biological macromolecules. We

are developing new methods of X-ray and neutron structure determination

and are applying these and other, more conventional, methods to selected

structures of proteins and nucleic acids. Our general aim is to advance

the understanding of the structure-function relationship in macromolecules,

in particular by modifying the structure using genetic technology, by

binding of ligands and by studying families of closely related proteins

with different properties. We are also interested in the interactions of

macromolecules with solvent, and such studies can particularly benefit

from the availability of neutron diffraction data.

The physical facility available to us includes a well-equipped

general purpose laboratory for protein purification, crystal growth and

mounting, including a walk-in cold room, as well as computer and graphics

areas. Instrumentation include a flat-cone neutron diffractometer located

on the NBS Reactor, a conventional X-ray generator with two Buerger

precession cameras (useful for preliminary data collection, but not for

intensity measurements), and a gas-flow crystal temperature controller

with a range of -80 °C to +60 °C. In the reporting period, we had no facilities for quantitative x-ray measurements, owing to the slow delivery

cycle of a Nicolet area detector. For these reasons our capability to

collect data was limited to the time donated to us by Genex Corporation,

in collaborative efforts with Dr. Gary Gilliland, who subsequently joined

our group in August 1986. Our computing facility includes an IBM4381

shared with the Quantum Chemistry Group of the Molecular Spectroscopy

Division, a dedicated Evans and Sutherland Graphics facility which was upgraded this year from PS330 (vector graphics) to PS3^0 (vector and

raster screens). This modification enables us to create both dynamic

line drawings as well as static space-filling pictures. We have

implemented programs for hard copy output of the images generated using

various graphics programs. A recent upgrade to our computational facility

includes a MicroVAX II equipped with a large disk and a tape drive, which

will be dedicated to processing area detector data.

A number of problems initiated previously were continued in the last

year and several new ones were initiated. Those individual projects on which significant progress was achieved are summarized below.

A. Structural Studies of Mutations in Catabolite Gene Activator Protein

(I.T. Weber)

Catabolite gene activator protein (CAP) regulates transcription in E. coli in response to the level of cyclic adenine monophosphate (cAMP)

which is an allosteric activator of CAP. CAP recognizes and binds to

specific sequences of DNA at several operons, causing the stimulation or repression of transcription of cAMP-dependent genes. The crystal

structure of a dimmer of CAP with bound cAMP has been determined at 2.5A

resolution and refined to an R factor of 0.207.

197
Several laboratories are investigating mutations in the crp gene

that produces CAP. Three CAP mutants, 91, 220 and 222, that function in

the absence of cAMP have been subjected to crystallization trials in order

to study the structural changes associated with these mutations in amino

acid sequence. Both CAP 91 and 222 form crystals with cAMP. CAP 91

also crystallizes in the presence of adenosine, an alternate activator for

this mutant.

X-ray intensity data have been obtained for the crystals of CAP91

with cAMP which are isomorphous with the crystals of wild type CAP. These

data have been refined to 2. 4 A resolution and an R factor of 0.186. The

CAP91 structures are very similar although the Ala to Thr mutation is

clearly visible. There also is a movement of Cys178. There are no significant differences around cAMP-binding sites. Smaller differences

have been located by a vector average of the differences in atomic

coordinates. These differences are located far from the site of mutation,

in the hinge region between the two domains in the CAP subunit and in an adjacent loop between two 6 strands. These differences suggest that the

Ala 144 to Thr mutation in CAP91 produces structural changes that

propagate through the hinge region towards the DNA-binding site.

The CAP91 structure is being investigated in the absence of cAMP and

in the presence of the analog, adenosine. Other CAP mutants will be

studied.

B. Predicted Structure for Two Domains of the Regulatory Subunit of

cAMP-dependent Protein Kinase

(I.T. Weber) *

The mammalian cAMP-dependent protein kinase Is an important

regulator of many biochemical reactions. In the inactive state the

holoenzyme consists of a complex of two regulatory subunits and two catalytic subunits. This is activated by the binding of cAMP to the regulatory subunits which then dissociate from the catalytic subunit. The

active catalytic subunit phosphorylates other proteins. The regulatory

subunit (R) contains two domains that bind to cAMP and have amino acid

sequences that are homologous with the sequence of catabolite gene

activator protein (CAP) from the bacterium, E. coli .

The crystal structure of the cAMP-binding domain of CAP has been used

to model the cAMP-binding domains of the regulatory subunits. The amino

acid sequence for the R-subunits was fitted into the CAP structure using a computer graphics system. The predicted R structure was overall very

similar to CAP. The model structure was evaluated by comparison with

other experimental evidence including photolabeling with 8-azido cAMP,

the binding of cAMP analogs, and fluorescence quenching. This gave good

agreement and the predicted structure of the regulatory subunits can be

used as a model for site directed mutagenesis.

C. Structural Studies of Anti-tumor Amidohydrolases

(I.T. Weber, A. Wlodawer and R.W. Harrison)

Three homologous bacterial amidohydrolases with anti- tumor properties

have been crystallized: a glutaminase-asparaginase from Ac Inetobactor

glutaminasif icans (AGA) , a glutaminase-asparaginase from Pseudomonas ’*

A

198
(PGA) and an asparaginase from Vibrio succinogenes (VA) . These enzymes in

solution are tetramers with subunit molecular weights of ca. 34,000

dal tons. AGA crystallizes in space group 1222 with one subunit per

asymmetric unit. PGA crystallizes as a tetramer in space group P2^ 2-j 2i

and VA crystallizes in the same space group with a dimer in the asymmetric

unit.

Native data are available to 2.9A resolution for AGA and MIR data on

three derivatives (5.3 to 4.0A) permitted the direct phasing of 2617

reflections. Phase improvement and extension to 2.9A resolution for an additional 4784 reflections was achieved by two complementary techniques

of density modification. These are the method of B.C. Wang which

flattens the solvent region and improves protein connectivity, and the

method devised by R.W. Harrison that maps the distribution of density

values onto a Gaussian distribution with the same mean and standard

deviation. By examining electron density maps produced by the two

methods it proved possible to trace a polypeptide chain, although the

connectivity is ambiguous in several places. Since the amino acid

sequence has not yet been determined, the type of amino acid was estimated from the shape of the electron density, and these coordinates

were refined to an R factor of 0.30. The AGA polypeptide chain folds into

two domains. The first amino terminal domain, contains a five-stranded 6 sheet

and four of helices. The second domain has four of helices and several

6 strands. This model for the AGA structure has been used to phase the PGA

data.

Intensity data have been obtained to 2.5A resolution for the PGA

crystals using a Nicolet-Xentronix area detector at Genex Corporation.

The starting point for phase determination has been rotation and

translation function techniques using the AGA map. This solultion was confirmed by using the AGA polyalanine coordinates. The rotation function

has also been solved for VA. A starting PGA model was produced by

rotation and translation of an AGA tetramer and this was refined to

improve the phases. The tetramer model phases are being used as a prior

in the maximum entropy technique that is under development by R.W.

Harrison and the new electron density map is being intepreted. An active

site inhibitor has been soaked into the PGA crystals in order to locate the

active site of the enzyme.

D. Comparison of Two High Resolution Structures of Bovine Pancreatic

Trypsin Inhibitor

(A. Wlodawer, with J. Deisenhofer and R. Huber (Max Planck Institute,

Munich)

)

While it has been known for a long time that the structure of a protein in a crystal is similar to that present in solution, the limits of

discrepancy have not been rigorously established. The availability of

two distinct crystal forms for bovine pancreatic trypsin inhibitor

(BPTI) made it a system of choice for such studies.

The structure of deuterated crystals of form II of BPTI has been

refined using X-ray and neutron diffraction data. These crystals belong to

space group P2

1 2 1 2, a=74.1A, b=23.4A, c=28.9A and the packing of the

molecules is related to form I structure previously solved in Munich by

rotation of about 45° around y. X-ray intensities were collected on form

199
II crystals by the Munich group using standard dif fractometry , while

neutron data extending to 1.8A resolution were collected at NBS. Joint

restrained refinement using both types of data was performed by J, Walter

and A. Wlodawer, resulting in a final model characterized by R values of

0.200 (X-ray) and 0.197 (neutron).

The two available high resolution structures of bovine pancreatic

trypsin inhibitor, refined in two distinct crystal forms, have now been

compared. After superposition, the molecules show an overall

root-mean-squares deviation of 0.40 A for the atoms in the main chain,

while the deviations for the side chain atoms are 1.53 A. The latter

number decreases to 0 . 6 1 A when those side chains which adopted drastically different conformations are excluded from comparison. The discrepancy between atomic temperature factors in the two models was 6.7 A

2

, while their general trends are highly correlated. About half of the

solvent molecules occupy similar positions in the two models, while the

others are different. As expected, solvents with the lowest temperature

factors are most likely to be common in the two crystal forms. While the

two models are clearly similar, the differences are significantly larger

than the errors inherent in the structure determination. This study

established the limits of discrepancy of atomic coordinates of proteins

which can be expected to result from differences in crystal packing.

E. High Resolution Refinement of Ribonuclease A (A. Wlodawer, with G. Gilliland and B. Finzel (Genex Corporation),

A. Svensson and L. Sjolin (Chalmers Polytechnic)).

The structure of ribonuclease A, was reinvestigated using a new set of

X-ray diffraction data extending to 1.26 A, the limits of detectable

diffraction. The X-ray diffraction data were obtained from two

phosphate-free crystals which were isomorphous with previously reported

monoclinic crystals containing phosphate, or perhaps sulfate. The data were collected using an area detector, the Xentronics-Nicolet image

proportional counter at Genex, and included 129,694 observations of 25,732

unique reflections out of the total of 31.730 possible at 1.26' A. The data

scaled with a weighted least squares R-factor on intensity for

symmetry-related observations of 0.05, with 23,398 of the measured unique

reflections having significant intensity (F>2o(F)).

One of the first significant observations with the new data was the

detection of a large number of side chains with multiple conformations.

The structure was highly refined (R = 0.15) and was modeled with 13 residues having discrete multiple conformations of side chains. These residues are widely distributed over the protein surface, but only one of

them, Lys 61 , is involved in crystal interactions. The discrete

conformers have no unusual torsion angles and their interactions with the

solvent and with the atoms of the protein are similar to those residues

modeled with a single conformation. For three of the residues, Val 43,

Asp 83, and Arg 85, two correlated conformations are found. The observed

plasticity in the protein surface will be of significance in analyzing

structure-function relationships and in performing protein engineering.

Other new observations resulting from this refinement, in particular

the details of the structure of ordered solvent, are still being analyz--:!.

200
F. Structure of the Solvent in Crystalline BPTI

(R. Harrison and A. Wlodawer)

Neutron data for bovine pancreatic trypsin inhibitor (BPTI) have been

collected for crystals soaked in both deuterated and hydrogenous solvents.

Deuterated data extending to 1.8A resolution have been available for some

time, while hydrogenous data were collected recently. This data 3et was virtually complete to 1.8A resolution, with 3^16 reflections showing

observed intensity.

Since deuterium and hydrogen have greatly different scattering lengths

it should be possible to use the difference between the scattering from

deuterated and hydrogenous crystals to determine the positions and

occupancies of exchangeable and solvent hydrogens. With X-ray diffraction

data, differences in the scattering due to a change in the crystal such as the addition of a substrate can be used directly via a difference Fourier

synthesis to show the location and orientation of the changes in the

molecule or the complex. Because the differences are much larger with

deuterium-hydrogen exchange, such a simple treatment is not correct when

applied to neutron diffraction data. The problem with a simple treatment

is the choice of the phase of each term used in the difference Fourier

synthesis. With small differences in the scattering there are only small

differences in the phase of the reflection. However, the phases of the

deuterated data and the hydrogenous data determined by independently

refined models are quite different, and there is no a priori reason to

choose one or the other.

We have attempted to resolve this problem by constructing an enhanced

model of the scattering from the protein. The scattering is treated as coming from two non-overlapping regions. Scattering from the part of the

molecule that should not be altered by solvent exchange is required to be

the same in both the hydrogenous and deuterated models, and scattering

from everywhere else is independently refined for each model. Requiring

that the structure in the non-exchanged regions of the map be the same for

two different sets of data results in an improved model for the protein.

The solvent regions are required to be featureless when far (>4 A) away

from the protein. In addition a correction to the F(000) term of the

Fourier series is refined. These procedures should result in a significantly enhanced model for the solvent near the protein surface.

The structure of this local solvent is critical to the stability and

function of proteins. The structure of solvent in BPTI is now analyzed in

these terms.

201
G. Crystallization of Synthetic Fragments of DNA

(M. Miller, A. Wlodawer, and E. Appella (NIH))

We have been crystallizing a series of DNA oligonucleotides predicted

to form structures deviating from the classical double-helix. A 13 -mer d(CGCGAATTACGCG) derived from the self-complementary dodecaraer

d(CGCGAATTCGCG) by inserting an extra adenosine in the 9th position f*~om

the 5 '“end was synthesized as a model of a frame-shift mutation. This

sequence was expected to form an improper duplex with the unpaired adenine

residue either looped out or intercalated into the double helix. The

crystals that were grown were disorderd (or unstable). Our solution

studies (done in collaboration with F. Schwarz and W. Kirchhoff of the

Biothermodynamic's Group, see separate report) showed that the duplex

undergoes a transition to a single stranded hairpin loop in the temperature

range 0 - 6 °C. Subsequently we found that a 15~mer d(CGCGAAATTTACGCG) forms

a much more stable duplex. The inserted nucleotides are now separated by an AT sequence two base pairs longer. Crystals of this material have

been grown by the vapor diffusion technique at A °C. The space group is

1222 with a=36.9 A, b=53°8 A, and c=t02.7 A. We are modifying the

conditions of crystal growth with the aim of preparing a sufficient

number of them for data collection. We have been also continuing our efforts to find a DNA oligomer which would crystallize in the form of a single stranded hairpin loop, but so far with little success.

H. Application of Repulsive Regularities Found in Water Structures.

(H. Savage)

Water structures in crystal hydrate systems have been studied in

order to categorize the repulsive interactions between different classes

of atoms (Nature 322, 717,(1986)). These interactions are divided into

four groups (RR1 - RR4).

RR1 : 0...0 repulsion of the H-bonds (H-bonds may bend, if necessary, to

within a certain limit).

RR2 : 0...0 repulsion between non-bonded water oxygens (minimum contacts

of 3 .I-3 . 6 A depending on orientations).

RR3 : H2...01 repulsion between H2 and 01 of the configuration

01-H1 . . .02-H2 (minimum contacts of 3.0A).

RR4

j

H...H repulsions (minimum contacts of 2.1 A).

(where HI, H2 , etc, refer to atoms belonging to two distinct water

molecules

)

202
These repulsive restraints explain several of the basic features

found in water structures. For example, they can be used to describe the

different structures found in the ice phase diagram. The

pressure-temperature phase space can be divided into 4 separate regions

(Fig 3-1) with respect to which of the repulsive restraints RR2 and RR3 are fully strained:

Region 1 : H2

.

. .01 remote contacts

,

Region 2: 0 .

.

..0 non-bonded contact

H2

.

. .01 remote contacts

Region 3: H2

.

. .01 remote contacts-,

Region 4: 0 . . . .0 non-bonded contacts

H2

.

. .01 remote contacts

for a single lattice of H-bonds

for two interdigitating lattices of

H-bonds

In region 1 the RR3 contacts are fully strained, but the non-bonded

RR2 0...0 contacts are not (all >3.5A). Thus, a reduction in volume can

only take place with respect to reducing the RR2 contacts. In region 2

both the RR2 and RR3 contacts are at their limit and further contraction

at higher pressures has to take place by the formation of interpenetrating

lattices of H-bonds (self-clathrates) . Compression of the ’double'

lattice follows along similar lines to that of the single H-bond lattice

case; firstly the RR3 contacts are fully strained (region 3). and then

both the RR2 and RR3 contacts are at their minimum limits (region 4).

In regions 1 and 3 the non-bonded RR2 interactions are not fully

strained and it is possible that some disorder of the water oxygens may be

present. This has been found in some recent ultra-high resolution neutron

diffraction experiments carried out at the Institute Laue-Langevin on ices

Ih (Kuhs and Lehmann, 1986) and VI (Kuhs and Finney, 1986). In ice Ih the

position of the oxygen was found to be disordered by up to 0.04 a, while in

Ice VI variations of up -0.1 5A are present.

I. Plans for Next Year

We are planning to commission the X-ray diffraction instrumentation

within the next few months. The system will consist of a Nicolet area

detector mounted on a Huber diffractometer, with controlling electronics

locally adapted by T. Buckley. When fully operational, this facility will

obviate the need for the use of X-ray data collection facilities.

203
Temperature

Fig. 3.1o Division of the pressure-temperature ice phase diagram into

four regions with respect to the RR2 and RR3 repulsive limitations

20A
Scientifically, we are planning a concerted effort directed to

improving the ability to grow protein crystals in a predictable and

reproducible manner. To that effect, we will implement a crystallization

data base, originally developed by G. Gilliland at NIH, which lists all

published conditions for growth of macromolecular crystals. We will

develop software, in cooperation with the Chemical Thermodynamics Data

Center's Group for manipulation and updating of this data base.

205
4. CHEMICAL THERMODYNAMIC MEASUREMENTS

E.S. Domalski, S.S. Bruce, K.L. Churney, T.J. Buckley, J. Colbert,

E. Diaz, D . A. Ditmars, D.R. Kirklin, A.E. Ledford

A. Large Sample Combustion Calorimetry

(E.S. Domalski, J.C. Colbert, K.L. Churney, J.E. Diaz, A.E. Ledford,

S.S. Bruce, and T.J. Buckley)

This research is being performed in support of the Resource Conservation and Recovery Act and is funded by the U.S. Department of Energy.

The purpose of this work is to provide measurement methods, standards, and

baseline data for establishing calorific (heating) values and optimal

combustion conditions for the control of pollutants for municipal

solid waste (MSW) from various sources. Current emphasis is directed

toward monitoring the fate of chlorine from input through MSW combustion.

The presence of trace amounts of chlorinated organic compounds (i.e.,

dioxins) in the effluent and fly ash has hindered the construction and

operation of MSW incinerators used for the generation of steam and

electric power.

During FY 1 98-4 » samples of MSW were obtained from Brooklyn, NY, and

Baltimore County, MD to generate data on the chlorine content of MSW.

Quantitative information of this type is meager and is needed to evaluate

the methods that have been proposed for reducing the emission of

chlorinated dioxins and furans from incinerators . The main methods

proposed are: (1) removal of the responsible components of the waste, (2)

proper incinerator design, and (3) efficient operation of the incinerator.

The results of the sampling study, which were evaluated in 1985, showed

that all combustible components of MSW contained chlorine. Our study has

shown that removal of plastics from MSW is not sufficient to reduce the

chlorinated organic species formed during the combustion of MSW to

negligible levels.

During FY 1985, studies were conducted dealing with laboratory and

field data for the calorific value of MSW. The calorific value of the MSW

that is needed in a performance or acceptance test is the heat liberated in

the actual incineration process, however, the combustion of the organic

fraction of MSW is incomplete in this process. The calorific value

determined in laboratory tests is for conditions of complete combustion.

Currently, no data are available for validating methods either for the

measurement of incomplete combustion or the making appropriate

calculations to correct for incomplete combustion. To obtain such data,

the heat liberated for varying degrees of complete combustion was determined by burning microcrystalline cellulose and synthetic MSW in

O

2 /N 2 mixtures containing 100, 50, 35, and 21 mole % O 2 in the 0 2 in the

2., 5 kg capacity flow calorimeter. The synthetic MSW is mlcrocrystall lne

cellulose which contains 20 mass % silica as the noncombustible component.

The particle size of the silica and combustion conditions were such that the

amount of char formed in the combustion of the synthetic MSW in air was about 5 % of the mass of the ash, the approximate value for the amount of

char formed in MSW incinerators. Gaseous hydrocarbons and CO were monitored as a measure of gaseous products of incomplete combustion. The

combustion results are being examined to establish the methods for the

determination of calorific corrrections for incomplete combustion.

206
Also during FY 1985, studies were carried out to develop procedures

needed for the determination of the threshold conditions for the formation

and for destruction of organic chlorine compounds during MSW combustion.

The purpose of this study is to determine if we can reproducibly form

and/or destroy these compounds and, if so, whether the combustion

conditions in a large, laboratory-size combustor can be sufficiently

well-characterized to allow application of the results to design or operation of real-world MSW incinerators.

An EPA modified method 5 (MM5) gas and particulate sample train for

sampling the product gas and trapping both particulates and volatile

organic chlorine compounds was constructed and installed as part of the

combustion flow calorimeter. Procedures were developed by S. Chesler and

R. Parris of the NBS Organic Analytical Research Division for separating

the organic chlorine compounds trapped in the MM5 train into chemical

classes of increasing clarity. The organic chlorine compounds were formed

in the combustion of synthetic MSW doped with 1.5 mass % polyvinyl

chloride (PVC) in 35 mass % O 2/65 mass % N£. A qualitative analysis using

gas chromatography with an electron capture detector was carried out on

the separated organic chlorine product formed in the combustion of PVC

doped synthetic MSW. Dioxin or furans were not found but could have been

present below the detection of the instrumentation (several ppb), but

substantial quantities chlorinated benzenes, chlorophenols , and

chlorinated biphenyls (PCB's) were detected.

In FY 1986, significant accomplishments were made in the following areas

1. Gram-size Test Samples to Characterize 2.5 kg Increments

An experimental test was conducted to verify the method

used to calculate the heat exchange between the 2.5 kg capacity flow

calorimeter and its environment. The test showed that the overall heat

exchange corrections to the experimental data were negligible, less than

0.1?, despite significant departures from conventional gram-size

combustion calorimeter operating conditions. The results were used to

complete an evaluation of the bounds of systematic errors in the calorific

values determined in the FY 1 98-4 study involving gram-size test samples

prepared from kilogram-size parent increments. The results of the error

analysis are reported in a manuscript describing the 2.5 kg flow

calorimeter and appears in the September 1986 issue of the NBS Journal of

Research

A summary of the results of the study concerning gram-size test

samples from kilogram-size increments was prepared and published in the

proceedings of the Twelfth National Waste Processing Conference sponsored

by the American Society of Mechanical Engineers (ASME) held in Denver, CO,

June 1986.

2. Chlorine Content of MSW

The results of the chlorine content of MSW study completed

in FY 1985 are in press for a 1986 issue of Chemosphere devoted to papers

presented at the 5th International Symposium on Chlorinated Dioxins and

207
Related Compounds held at the University of Bayreuth, West Germany,

September, 1985 and also appear in the Proceedings of the Twelth National

Waste Processing Conference sponsored by the American Society of Mechanical Engineers (ASME).

Four samples of MSW from Baltimore County, MD and Brooklyn, NY which were analyzed in the 1985 chlorine content study were sent to R. Wingender

of Argonne National Laboratory for determination of the presence and

amounts of chlorinated dioxins, furans, and related compounds (e. g. PCB’s

and chlorophenols) . Input composition data of this type are not clearly

established for MSW and are essential to establish how much dioxins or furans are formed during the incineration process.

3.

Development of Corrections for Incomplete Combustion

The determinations of the calorific value and moisture content

of the cellulose burned in the study to develop methods for correction for

incomplete combustion were carried out. The .determinations provide

necessary auxiliary data to convert laboratory results so that they have a closer correspondence to real-world incinerator conditions. The

combustion results obtained in the study for development of corrections

for incomplete combustion were summarized and appear in a second manuscript

published in Chemosphere (see following section)

4.

Threshold Condition for Formation/Destruction of Organic

Chlorine Compounds

The results of the FY 1985 combustion of synthetic MSW

doped with PVC appear in a second manuscript in press for Chemnosphere

,

devoted to papers presented in the 5th International Symposium on chlorinated Dioxins and Related Compounds.

5.

Modifications to Apparatus and Procedures

A number of hardware and software changes were made as a result of the shift in emphasis of the experiments from calorimetry to

controlled combustion studies and chlorine monitoring. The changes were

as follows:

o To better simulate combustion conditions in real-world

incinerators, the combustor of the 2.5 kg capacity flow

calorimeter was modified so that the CO produced in the

combustion of synthetic MSW in air could be reduced to less

than 1000 ppm. (In the FY 1985 study to develop corrections

for incomplete combustion, the CO was in the 10,000-15,000 ppm

range.) This was accomplished in a sequence of experiments in

which various sources of heat loss from the combustion zone

(i.e. region near the burning sample) were successively

reduced, the most critical of which amounted to providing

insulation between the combustor and combustor enclosure in

the region below the reaction zone baffle. The option of

burning synthetic MSW in dispersed rather than in pellet form

208
was not explored in order to have a capability of studying the

formation or destruction of dioxins under various conditions

in the absence of fly ash.

o To minimize the time necessary to break down, reassemble, and

leak check the gas supply and sampling lines in a calorimetric experiments, the combustor was permanently

mounted on a frame outside the 2.5 kg capacity flow

calorimeter. Auxiliary cooling sources were built for the

outside of the combustor enclosure, for the heat exchange coil

for the product gas, and for the collector for the water

liberated in the combustion reaction to replace the cooling

originally provided by the calorimeter water.

o Two oxygen detectors have been installed to improve

the characterization of inlet and exit gas streams to the

combustor. Backup CO and C02 detectors (NDIR) were installed in

the product gas analysis train to provide redundancy and loss

of data due to detector malfunction.

o To improve the collection of trace chlorinated organic

species, the MM5 train was redesigned and is being rebuilt in

cooperation with R. Wingender of Argonne National Laboratory,

who will carry out the dioxin analysis in subsequent

experiments. Changes are oriented towards improving the

efficiency of recovery of organic chlorine compounds and

reduction of possible contamination of the XAD-2 resin (used

to trap gaseous organic chlorine compounds) prior to analysis

by gas chromatography and mass spectrometry

0 To upgrade monitoring of the detectors for 0

2 , CO and Co2

, a new

thirty channel scanner was installed. Since each combustion

experiment now tends to be quite different in terms of the

need for and time sequence for monitoring the various

detectors, the original software for data acquisition for the

fixed routine of a calorimetric experiment has become

obsolete and has had to be replaced. We were fortunate to

have a guest computer scientist from the Twente University of

Technology, Netherlands, to help us in redesigning the data

acquisition software. As a result of Mr. Rukkers three and a half month stay with us, we have a well designed data

acquisition system which can be modified rapidly to fit the

varying demands of any particular laboratory experiment.

Other software for data analysis and plotting was developed

by two summer students (S. Sung, R. Metz).

In the initial phase of the combustion experiments of

this study, we are currently carrying out a set of chlorine

mass balance experiments. The aim of these experiments is to

determine the degree to which suitable clean up procedures

will ensure that organic chlorine compounds detected in the

combustion products of a given run are formed from chlorine

containing compounds burned in the same rather than in

previous runs.

209
During FY 1987 we plan to complete the remaining auxiliary measurements

and analysis of the study for development of corrections for incomplete

combustion. The initial phase of the study of threshold conditions for

the formation/destruction of chlorinated organics will be completed with

an attempt to determine the combined recovery efficiency of the combustor

plus the MM5 sampling train for chlorinated organic compounds. In the

second phase of the study, we plan to evaluate the use of calcium oxide

binder in densified pellets of processed MSW as a possible method for

reducing dioxin emissions from combustion of refuse. In the third phase of

the study, we plan to resume our study of the combustion of synthetic MSW

doped with inorganic as well as organic chlorine compounds.

Because the combustor of the 2.5 kg flow calorimeter cannot be

economically altered to provide all the combustion conditions that must be

studied in the threshold study, a new laboratory- si ze , two stage

incinerator was purchased in FY 1986. It is our plan to instrument this

unit and conduct trial experiments toward the latter part of FY 1987.

B. Calorimetric Update on SRM Coals 2682, 2683, 2684 and 2685

(J.C. Colbert)

The annual calorimetric update was performed on SRM Coals 2682, 2683,

2684 and 2685 to determine if there has been any change in the calorific

value of these coals due to sample degradation as a result of aging or normal oxidation. Sixteen unopened bottles of coals were received from

OSRM, four of each of the latter SRM’s. One measurement was made for

residual moisture and one for calorific value. The original certified

value for sulfur was used in making the calculations since this

constituent remains constant with time. All of the measurements were made

in random order with one duplicate measurement for SRM 2684. The sampling

procedure and run protocol was designed by R.C. Paule, NML Statistician.

Good agreement (<50 Btu/lb) was obtained between calorific values

obtained for SRM 2683, 2684, and 2685 and their 1985 certified values,

however, the average calorific value for SRM 2682 was 300 BTU/lb higher

than the average result for 1985.

As a further check on the results, an additional set of four unopened

coals were measured with only one sample giving a high calorific value.

These eight coal samples were sent to an outside testing laboratory by

the OSRM. The results of our lab and the outside lab agree to within 7 Btu/lb. The final statistical evaluation of the data led the OSRM to

remove the calorific value certification from SRM 2682. This is

due to a larger variability in the sample than anticipated, resulting in a larger variability in the calorific value than was predicted. It appears

that the bottled material maybe degrading at an uneven rate, the cause of

which is unknown at this time. Another parameter which should be examinee!

is particle size variability in SRM 2682, within and between bottles,

since particle size variability can influence the dispersion of results.

210
C. Bomb Calorimetric Measurements for Biotechnology

(J'.C. Colbert and E.S. Domalski)

The enthalpy of combustion of the crystalline monsaccharides D-ribose

and 2-deoxy-D-ribose (2-deoxy-D-erythro-pentose ) have been determined by

combustion bomb calorimetry. The standard molar enthalpies of combustion

(A

ch) and formation (AfH) at 298.15 K for crystalline D-ribose are:

-2349.47 ± 0.95 kJ/mol and -1047.23 ± 1.66 kj/mol, respectively.

Similarly, for 2-deoxy-D-ribose, A

C H = -2527.39 ± 0.98 kJ/mol and AfH = -869.31 ± 1.68 kJ/ mol. Proton NMR and C— 1 3 NMR studies were conducted by

B. Coxon of the Center for Analytical Chemistry, to determine the anomeric

composition of the crystalline sugars. The crystalline D-ribose sample

consisted of 64.4 mass % beta-pyranose, 35.4 mass % alpha- pyranose , and

0.2 mass % beta-furanose anomers. The sample of 2-deoxy-D-ribose was made

up of 98.8 mass % beta-pyranose, 0.5 mass % alpha-pyranose , and 0.7 mass %

beta-furanose anomers.

Combustion bomb calorimetric studies are in progress on crystalline

hexaglycine. Elemental analyses on this compound for carbon, hydrogen,

and nitrogen from two independent testing laboratories indicates that it

is the hemihydrate. An examination of the literature combined with some

preliminary calculations on diglycine, triglycine, and tetraglycine shows

that the energy of the peptide bond in these compounds is constant. If

one extends this energy constancy to hexaglycine, then the energy or enthalpy of hydration can be estimated as a result of conducting the

combustion calorimetric measurements. This value for the enthalpy of

hydration should provide some useful insight into the magnitude of

hydration forces between an oligopeptide and water under conditions of

initial bonding interaction.

Previous bomb calorimetric measurements in this laboratory on

crystalline adenine, guanine, purine adenosine, guanosine dihydrate,

D-ribose, and 2-deoxy-D-ribose provide the basis for establishing several

energetic cycles for the formation of nucleosides as well as indicating

research paths in which to pursue combustion bomb calorimetric

measurements on key compounds. Three key compounds which are immediate

candidates are: deoxyadenosine , deoxyguanosine, and nebularine.

Energetic differences between ribose/deoxyribose , adenine/adenosine,

guanine/ guanosine, and purine/ nebularine moieties in nucleoside formation

could be established more precisely than are presently available and could

be regarded as standard reference value points for thermodynamic

assessments involving reaction processes of nucleosides.

D. Estimation Methods and Combustion Calorimetry an Organic Phosphorus

Compounds

(D.R. Kirklin and E.S. Domalski)

Precise enthalpies of formation are not available for important

industrial and biochemical compounds that contain phosphorus.

Experimental determination of these properties for some of. the compounds

is not feasible because of their toxicity or limited availability. The

objective of this research is to develop correlation and estimation

schemes which are needed to predict enthalpies of formation at 298 K for

211
compounds that have no reported experimental values. Also, combustion

calorimetric determination of enthalpies of combustion will be conducted

on key organic phosphorus compounds.

Precise and accurate enthalpies of formation are necessary to develop

an adequate correlation and estimation scheme. However, there is a lack

of precise and accurate thermodynamics literature data on organic

phosphorus compounds. The existing thermodynamic data for organic

phosphorus compounds, which are based upon bomb calorimetric data, are often inaccurate due to several problems associated with the combustion

calorimetry of organic phosphorus compounds. Until the present time,

there is only one set of data in the literature which has adequately

addressed all of these problems. These data were obtained by Harrop and

Head (J. Chem. Thermodynam. 9_, 1067 (1977).) on crystalline

triphenylphosphine oxide.

There are four major problems associated with the combustion

calorimetry of organic phosphorus compounds. The first problem is the

selection of an unreactive crucible material. Platinum crucibles, which

work well with most organic compounds, are unsuitable because platinum

reacts with organic phosphorus compounds at high temperatures. The second

problem is that organic phosphorus combustion samples usually do not burn

completely in a bomb combustion experiment. Phosphorus compounds are used

commercially as flame retardants for various fabrics because of their

resistance to burning. When phosphorus compounds burn in oxygen they

produce oxides of phosphorus which dissolve in the water in the bomb to

form various kinds of phosphoric acids. These phosphoric acids have

appreciable energies of dilution and are produced as various

concentrations in different parts of the bomb. Therefore, the attainment

of a homogeneous solution of uniform concentration of these phosphoric

acids constitutes the third problem area. The fourth problem is that the

bomb solution must be analyzed to determine, qualitatively and

quantitatively, the speciation of phosphorus acids formed as rapidly after

the calorimetric measurement as possible because of slow oxidation of all

phosphoric acids present to H^PO^.

The solution to the above mentioned problems are straightf orward , but

most laboratories are not equipped to handle them. Gold crucibles are found to be unreactive with organic phosphorus compounds but have a relatively low melting point. A sufficiently massive gold crucible

performs well in most experiments. The problem of incomplete combustion

can be overcome by determining the amount of carbon dioxide produced or by

measuring the amount of carbon residue formed. The problem of obtaining a homogeneous solution of the phosphoric acids can only be solved by using a rotating bomb calorimeter. Most laboratories use static bomb calorimeters

and therefore cannot obtain a homogeneous bomb at the end of the reaction

period. The qualitative and quantitative analysis of bomb solutions can

be only done by various forms of chromatography . Harrop and Head used

paper chromatography, however, this method is very slow and not very

quantitative. Ion chromatography seems to be ideally suited to solve this

problem because it is quanti tative v and offers reasonable precision.

The MBS bomb calorimetry laboratory has a rotating bomb calorimeter

that utilizes sample sizes on the order of 100-200 milligrams. The

laboratory has equipment for measuring the amount of carbon dioxide

212
produced during each combustion experiment. A DIONEX 2000i Ion

Chromatograph was borrowed from the DIONEX Corporation to check the

feasibility of analyzing the bomb solution composition for the various

forms of phosphoric acids.

A set of measurements on triphenylphosphine oxide was made in the

NBS rotating bomb calorimeter. Negligible amounts of carbon residue were produced. The carbon dioxide analyses verified these results. A DIONEX

2000i Ion Chromatograph was utilized to analyze the homogeneous bomb

solution for the various oxyacids of phosphorus. Orthophosphor ic acid,

H^POij, pyrophosphoric acid, H4 P2 O

7

, and tripolyphosphoric acid, H^P^Oiq*

were observed to be produced in the following percentages, respectively:

76.3, 20.0, and 3.7. The analysis means that 59.9 % of the total

phosphorus was quantitatively converted to orthophosphoric acid while

31.4 % and 8.7 % of the total phosphorus was converted to pyrophosphoric

acid and tripolyphosphoric acid, respectively. These values were used to

determine the amount of energy that would be needed to hydrolyze the

condensed phosphoric acids to orthophosphoric acid.

A correction of -11.08 J/g for the hydrolysis of condensed phosphates

to orthophosphate was added to our experimental energy of combustion, -35 , 778.15 ± 5.06 J/g, for triphenylphosphine oxide to calculate the correct

energy of combustion, -35,789.2 ± 5.06 J/g. This value agrees very well

with the previous reported value of -35,789.6 ± 6.0 J/g by Harrop and

Head. (J. Chem. Thermodynam. 9, 1067 (1977)). These authors have reported

the only precise combustion data for an organic phosphorus compound which

was based on a comprehensive analysis of the products of combustion, which

included the quantitative determination of condensed phosphoric acids

present in the bomb solution from a rotating bomb calorimeter. Bedford

and Mortimer (J. Chem. Soc. 1622 (i960)) reported an energy of combustion

of -35,943 ± 45 J/g based upon measurement using a static bomb

calorimeter

.

Experimental measurements were also made on triphenylphosphine. The

methods and procedures established during the triphenyl phospohine oxide

were utilized. The sample was vacuum dried for 12 h and found to contain

0.0077 % moisture. The sample was investigated with no further

purification. The mean of seven measurements yielded a value of

-39,200.73 ± 3.85 J/g for the internal energy of combustion without a correction for the hydrolysis of condensed phosphates to orthophosphate.

Assuming that the condensed phosphates were produced in the same

proportions as for the triphenylphosphine oxide would require an additional correction of -11.08 J/g. This would make the actual value

determined to be -39,211.81 J/g. However, the actual correction for the

hydrolsis of condensed phosphates must be determined on a set of

combustions of triphenyl phosphine and will be performed during fiscal

year 1987 when the combustion calorimetry laboratory receives a DIONEX Ion

Chromatograph. The internal energy of combustion reported by Bedford and

Mortimer is -39,245.8 ± 36.7 J/g based upon measurements using a static

bomb calorimeter.

213
Future plans include bomb calorimetric measurements on other key

organic phosphorus compounds. These measurements will provide the data

necessary to determine estimation parameters for other organic phosphorus

compounds. Proposed compounds are triphenyl phosphate, tri-n-octyl

phosphine oxide and tricyanophosphine.

E. Drop Calorimetry of Non-Reacting Systems Below 2800 K

(D.A. Ditmars)

This activity is a continuation of a calorimetric research program

whose goals are:

o to obtain accurate thermodynamics data on non reacting refractory

materials in either the solid or liquid state up to 2800 K.

o to measure the specific heat at temperatures above 273 K of

well-characterized materials of the highest attainable purity for which

existing C

p

data are insufficient or in conflict and which are: (a)

critical to energy and space related technology, or (b) especially suite

as a model on which to test refined lattice-dynamic calculations of

thermodynamic properties.

o to produce and support high- temperature calorimetric standard

reference materials (SMR's) for heat capacity and for differential

thermal analysis (DTA) calorimetric measurements.

The number of facilities, nationally, which can sustain programs of

high- temperature calorimetric research is seriously diminishing at a time

of increasing needs for just the data produced through this type of

investigation. There is a constant demand for thermodynamic data on new materials capable of functioning acceptably in the harsh environments

associated with space propulsion systems or upon re-entry, new energy

technologies and defense-generated needs for materials to enable space

systems to withstand overt aggression. Also, the existing thermodynamic

data on some elements is often not accurate enough to allow a meaningful

test of theories which have recently been formulated to calculate

thermodynamic functions directly.

The Chemical Thermodynamics Division has available two operative

precision drop calorimeters for the ranges 273“1200 K (isothermal,

phase-change calorimeter) and 1200-2800 K (adiabataic receiving

calorimeter). These are being used in research intended to provide

calorimetric measurements at the highest accuracy on materials related

to the high temperature applications mentioned above. Every effort is made

to coordinate this research with that of another NBS facility

(very-high-temperature pulse calorimeter) in order to provide the capacity

for continuous coverage of high- temperature thermodynamics studies up to

5000 K or above on especially important systems. We have in addition an operative high- temperature discrete-heating adiabatic calorimeter (300-80C

K) and we maintain in reserve a low-temperature (4-300 K) adiabatic

calorimeter for possible future research needs.

214
In order that NBS thermal data and that of other high- temperature

investigations can be fairly interccmpared and assessed for accuracy, we

maintain a continuing effort to update or extend the range of coverage of

high- temperature standard reference materials. In recognition of the

growing need for accurate DTA temperature and enthalpy standards, we attempt to identify systems whose thermal properties can be measured by

both conventional calorimetric and DTA techniques.

We have concentrated our experimental and data-analysis activity in

FY 1986 among the alkaline earths Ca, Sr, and Ba and have continued our work on pure Cu. Of the alkaline earths, calcium is of particular

economic and biological importance, yet the literature thermodynamic

functions for calcium are certain to be seriously in error due to sample

impurity effects. The situation of the thermodynamic functions for

strontium is similarly unclear for no original published heat-capacity

data exists for this element above room temperature. This is unfortunate,

as knowledge of the thermodynamic properties of strontium compounds

figures prominently in assessing the course and effects of potential

nuclear power accidents.

In the conduct of thermodynamic research on these alkaline earth

metals, one must confront the effects of low, but virtually irreducible,

oxide and hydride impurity levels which nevertheless exert a substantial

influence on the phase relationships among the allotropes of Ca and Sr

and on Ba. Thus, a large fraction on ones total effort must be devoted

obtaining pure samples, maintaining their integrity, and obtaining

credible analysis for the oxygen and hydrogen present.

Our prior (FY 84) heat-capacity data on calcium, measured partly at

NBS (T>300 K) and partly at the U.S. Geological Survey in Reston, VA (in

the cryogenic range) employed two calcium samples of differing oxygen and

hydrogen impurities. Of these data, only those in the high- temperature

fee region (715>T>300 K) were obtained using the sample of lower purity.

Comparison at NBS with enthalpy data obtained in the fee region for the

high-purity sample led to the conclusion that the earlier NBS

high- temperature data were subject to serious and uncorrectable systematic

error arising from the method of encapsulation. Therefore, in FY 86 we repeated the entire fee series of measurements on the higher-puri ty

sample. In addition, a number of enthalpy measurements were made at

closely and carefully-spaced temperatures throughout the fcc-bcc

transition region. This new fee data for calcium was analyzed in FY 86

and shown to merge, uncorrected, with the cryogenic data mentioned above.

The enthalpy data for calcium in the fcc-bcc transition region indicated

not a sharply temperature-resolved transition, but one occurring gradually

over a 5 or 6-degree interval. This, we have interpreted using a model in

which a trace contaminant (in this case CaH2

) enters into ideal solution

with each of two allotropes of calcium. The results (Fig 4.1) indicate a lower

temperature for the fcc-bcc transition temperature (710 K) than current

values proposed in the literature (716 to 720 K)

.

Analysis of the strontium sample we had obtained from Prof. Westrum of the

University of Michigan measured in FY 86 showed an unacceptably high level

of hydrogen contamination. Therefore, we obtained in FY 86 a new,

215
specially-prepared , diff usion-distilled strontium sample from the

Metallurgy Department of Iowa State University. At the same time, we obtained a similar sample of barium.

Considerable effort was expended in FY 86 on the encapsulation of these

materials and preparation of them for purification of hydrogen as well as for oxygen and hydrogen analyses. To bring this about, we developed a cooperative arrangement with the Metallurgy Division of the Naval Research

Laboratory (Wash. D.C.) for the use of their electron-beam

materials-processing facility.

In FY 87 we plan to extend the heat capacity measurements on calcium

through the melting point into the liquid range. Also, purification and

analysis of the strontium and barium samples will be carried out and

measurement of their heat capacity in the solid range begun. Heat

capacity measurements on the purified barium sample in the cryogenic range

will concurrently be performed. In FY 86 we collaborated with a guest

worker from Brock University (C. Plint, Ontario) to complete measurements

on the heat capacity of highly-pure, polycrystalline copper ( NBS Special

Research Material 5 : a low- temperature heat capacity standard) up to 1173

K. We plan to extend these measurements in FY 87 to the melting point and

to begin the analysis of our data and comparison to the extensive

literature data available on copper. These copper data will have potential value in extension of the temperature range of the copper heat-capacity standard and in establishing more accurate heat capacity data against

which to test new theoretical model in the calculation from first principles of the thermodynamic properties of fee metals.

T/K H/J mol

*

1

(a) (b)

Fig. 4.1(a): Idealized Ca-CaH 2 phase diagram including 2-phase region

near peritectoid. Overall CaH2 concentration (Cq) = 0.24 mol % j (b): Schematic measured enthalpy function for Ca containing

0.24 mol % CaH 2 in solution. = 714 K, T 2 = 720 K, Ttr

= 710 K .

216
5 . CHEMICAL THERMODYNAMIC DATA ACTIVITIES

M.W. Chase, D.M. Bickham, D. Garvin, C.R. Jackson, T.L. Jobe, Jr.

W.L. King, D.B. Neumann, V.B. Parker, D. Smith-Magowan, R.H. Wood,

(Consultant), D.D Wagman (Guest Worker), E.D. Hearing, R.H. Nuttall,

R.H. Schumm, N. Young, and S.D. Wasik (Contractors)

The goal of this work is to provide reliable values of thermochemical

and thermophysical properties of chemicals, both inorganic and organic. The

values are intended to be useful throughout science and industry. Because of

the widely differing needs of users, emphasis is placed in this work on generic information and methods of wide applicability. Two data centers carry

on this function: the Chemical Thermodynamics Data Center (CTDC) and the

Electrolyte Data Center (ELDC). Both are partly supported by the NBS Office

of Standard Reference Data (OSRD).

The data group now consists of five thermochemists, a computer systems

manager, two computer programmers, a chemical information specialist, a clerk, a consultant and a guest worker. In addition, four thermochemists do

special tasks under contract.

The work of the two data centers is inter-linked. Together they cover the

evaluation of thermochemical properties of chemical reactions, thermal functions of chemical species and thermophysical properties of solutions. These

activities are being extended by extramural collaborations: participation in

the CODATA Thermodynamic Tables project to build an international set of

recommended values, and, cooperative work with the University of Delaware on

methods for correlating thermophysical properties of solutions.

A major expansion of the data centers occured during the year. The JANAF

Thermochemical Tables project was moved to NBS from the Dow Chemical

Co., Midland, MI. Dr. M.W. Chase, leader of the JANAF project, became a member of the data center staff, and, at the end of the year, head of the

Chemical Thermodynamics Data Centers Group.

The data centers are supported by a vigorous computer group which

manages the mini- and microcomputer facility used by five CCP data

activities

The outputs from the centers are published in the Journal of Physical and

Chemical Reference Data, the Journal of Research of NBS, CODATA Special

Publications, Handbooks of DIPPR, and proceedings of various meetings. The

annual index to the thermochemical literature on inorganic compounds that is

prepared at NBS is published in the Bulletin of Chemical Thermodynamics.

Most of our prime activities are described in the following paragraphs.

Topics in progress which will not be discussed further are:

o Installation of the computer program GAMPHI (calulates activity

coefficients) on a microcomputer

217
o Final selection and documentation of the CODATA key values for

chemical thermodynamics

o Preparation of recommendations for the solubility of eleven types of

organic compounds in water

o Converted network calculation programs (CATCH) to be operational on the NOS CYBER (from the NBS UN IV AC); these programs are necessary for

the evaluation of the calcium and key values results for CODATA and the

rubidium network

A. Chemical Thermodynamics Data

1 . Thermochemistry of Compounds of Iron

(V.B. Parker)

The evaluation of the thermochemical properties of iron compounds

is being undertaken as part of a larger project, sponsored by CODATA, that

will include thermal functions and the analysis of several binary systems.

The thermochemical analysis is well underway. A reaction catalog (listing of

pertinent measurements, each expressed as a chemical reaction, together with

the values of the properties measured) has been assembled. It contains the

evaluated thermochemical data on the reactions of the "key” iron compounds.

A "key" compound is a species whose thermochemical properties are of

strategic importance because many other compounds are dependent upon Its

thermochemical properties. The properties of this compound may, in turn, be

dependent upon those of other compounds (from various reaction paths). This

group of compounds and its interconnections comprises the "key network".

The thermochemistry of iron compounds is complex. An example of this

complexity 13 shown in Figure 5.1, which indicates the enthalpy relationships

among the key compounds. A similar diagram, not shown, Indicates the Gibbs

energy relationships and measured entropies. Considering the Importance of

iron and its compounds, the disarray of the data for the basic thermochemical

relationships is disturbing. Calculations of the same property via different

paths in the network yield discordant values. This is demonstrated in the

following brief analysis of the thermochemical properties of Fe

+2 (aq) and

Fe+3 (aq) in their standard states at 298.15 K. The cited reactions are from

the network shown in Figure 5.1, the values are from individual studies or combinations of them. The enthalpy data are given first for the two ions and

then the Gibbs energy data. The tentative selected values made to date

conclude the presentation. The state designation "ao" means standard state.

All thermochemical values are in kJ/mol.

Enthalpy of Formation: For the determination of the enthalpy of formation of

Fe+3 (ao) the measurements on the following reactions are used.

(1) Fe(cr) + 1.5H2 02(ao) + 3H+ (ao) - Fe+ 3( a o) + 3 HtO(1)

(2) FeCl

3 (cr) = Fe+3 (ao) + 3Cl“(ao)

218
(3) Fe(cr) + 1.5Cl2 (g) = FeCI^Ccr)

(4) Fe(cr) + 3HC1( in 12.73 H

2 0) + 0.5H2 02 (1)

+ h

2 o(i)

Values obtained are:

From Reaction A

fH°(Fe+3 ,aq)

( 1 )

( 2 ) (2)

(3)

(4)

and

and

(3)

(4)

“46„6±0.8

-53.8±0.9

“57. 0±1 .0

FeCl^Ccr ) + H2 (g)

AfH°(FeCl

3 ,cr

)

“396.02±0.14

“399. 24±0. 35

The agreement of the results in each column is not as good as anticipated,

based on the claimed reliability of the individual studies.

Similarly a more extensive set of measurements may be used for the

of the enthalpy of formation of Fe+2 (ao). A similar conclusion is

The resulting values show too much scatter; much larger than would

expected based on interpretation of the individual studies.

In a third independent path, the difference between the enthalpies

formation of ferric and ferrous ion can be determined from:

(5) Fe+2 (ao) + 0.5H2 02 (ao) + H

+ (ao) = Fe+3 (ao) + H2 0(1)

(6) Fe+2 (ao) + H

+ (ao) = Fe+3 (ao) + 0.5H

2 (g).

Again, from a collection of six results, the scatter in this enthalpy of

formation difference is too great, casting suspicion on the results.

determination

obtained,

have been

of

Gibbs energies of formations: The Gibbs energies of each of these species can

be determined (independently) from cell measurements (7), equilibria and

solubilities (8-10).

(7) Fe(cr) + 2HT (ao) = Fe

T ^(ao)

(8) Fe+2 (ao) + 2Tl(cr) = Fe(cr)

(9) (1/3) Fe

3

01| (cr) + 2H

+ (ao)

+ (4/3) H

2 0(1)

(10) FeS04 :7H2 0(cr) = Fe

+2 (ao) +

The Gibb’s energy of the ferrous

+ H

2 (g)

+ 2Tl+ (ao)

+ (1/3) H

2 (g) = Fe

+2 (ao)

S04 "2 (ao) + 7H2 0(1)

ion Af>G°(Fe+2 ,ao) is determined to be:

219
from (7) from reaction shown

“80 . 1 4±0 . 20 —7 8 . 7 ± 1 .5 (8)

“90. 1 1 ±0,80 “9Q.0±5.0 (9)

“78. 8±0. 5 “90.6±1 .2 (10)

“84. 91 ±0.20

These numbers should exhibit much greater agreement. On the basis of the EMF

data alone, a value A

fG°(Fe+2 ,ao) of“80.14± 0.20 would be selected, using a study in which great care was taken to avoid electrode contamination by

preparation) and 02(g). The more negative values from (9) and

(10), however, cast suspicion on this choice.

The Gibbs energy of formation of ferric ion, -11.4±1.5 kJ/mol can be

obtained from:

(11) Fe0QH(cr, alpha) + H

2 0(1) = Fe+3 (ao) + 3 0H“(ao)

where A

fG°(Fe00H, cr ) is dependent upon AfH°(Fe3 04,cr) and

S°(Fe00H, cr, alpha).

Independently, the half cell

(12) Fe+2 (ao) + H

+ (ao) = Fe+3 (ao) + 0.5H2 (g)

for which agreement among the various investigations is excellent,

yields A( A

fG°(Fe+3 (ao)“A fG°(Fe+2 ,ao) ) = 74.27±0.20.

Selected values. Tentative selections have been made, based on the data given

above:

Fe

+2 (ao)

Fe+3 (ao)~Fe+2 (ao)

so that:

Fe+3 (ao)

FeCl 2 (cr

)

FeCl

3 (cr)

FeS0i| :7H2 0(cr)

A

fH°

“91 .5±1 .0

“49 . 0±2 .

0

-342. 8±1 .1

“396 . 0±2 .0

“3013- 7±0.

3

A(A fH°) A(A fG°)

42.5±1 .5 74 . 27±0 . 20

It is hoped that further analysis of the data, and the inclusion of more

data, based on current measurements, will help establish the selections above

and clarify the situation, particularly that for A fG°(Fe+2 ,ao) . The

following experimental data would be useful.

Activity coefficients for aqueous FeSOjj solutions. Those used now for

A sol G0( FeS C) 4 :7 H2 0, C r ) are estimated from NiSOq, but it is not known how good

this analogy is.

220
IRON

KEY

NETWORK -

ENTHALPY o

QJm3 w oa3

C5

00 ja3

00

Fig.

5.1.

Iron

Key

Network—

Enthalpy .

Measured

processes

are

shown

Dy

ai

connecting

the

substances.

(The

numbers

on

the

arrows

refer

toa

larger

reaction

catalog

than

that

discussed

here,

and

are

not

the

same

as

those

the

text).
o The A

fG°(Fe+2 ,ao) value, now -80.14 ± 0.20 from EMF data

should be verified.

0 A solH solH ( FeC1 3» cr ) is needed as a function of concentration in water

and aqueous HC1. The present data are not of high enough quality to

permit confident extrapolation to the standard state.

o A fH°(FeCl 2 ,cr), A fH°(FeCl

3 ,cr ) , and A rH° for FeCl 2 (cr) + 0.5 Cl 2 (g) * FeCl2 (cr) should be redetermined. The FeCl 2 /FeCl couple is important

outside the iron system as auxiliary data in redox reactions. The "NBS

Tables" and others use ArH 0

= -57.5, but there are conflicts in data

in the uranium halide thermochemical network which might be a result

of using this value.

2. JANAF Thermochemical Tables

(M.W. Chase)

This project was transferred in February 1986 from The Dow Chemical

Company, Midland, MI to the Center for Chemical Physics at the National

Bureau of Standards. Since that time, most of the effort has been directed at

the establishment of JANAF resources within the Chemical Thermodynamics Data

Centers. This includes the calculational programs, the literature and data

files, and the backup information for the existing tabulations. In parallel

with this, the third Edition of the JANAF Thermochemical Tables has been

completed, at Dow Chemical, and sent to the American Institute of Physics for

publication later this year in Journal of Physical Chemical Reference Data.

In our data evaluation activities reviews and thermochemical tables are being prepared for three classes of species: the alkaline earth metals, their

monohydroxides and their dihydroxides. For the 3rd Edition of the JANAF

Thermochemical Tables, the calcium thermal functions were estimated to be

intermediate between those for magnesium and strontium; the strontium thermal

functions being based on unpublished enthalpy data of Stephens and Roth.

However, there now is additional information available from the recent heat

capacity study of calcium by Robie (USGS) and the enthalpy studies of calcium

and strontium by Ditmars. The low temperature study by Robie is in

qualitative agreement with the recent JANAF analysis. However, the

experimental results yield a considerably different Cp curve in the region

below -20 K, raising the entropy of calcium at 298.15 K by - 1.5 J/(mol K)

above our recommendations. When the analysis of new information is completed,

the thermodynamic functions of the metals will be much more firmly based. We

will then be in a better position to judge the reliability of the existing

enthalpy data for barium.

The alkaline earth monohydroxides have been studied experimentally

during the last few years. A thorough spectroscopic study has been carriec

out for the magnesium, calcium, strontium, and barium species by Harris et

al. and Bernath et al . These studies have yielded structures and two of the

three vibrational frequencies v-|

, and v2

. In all cases, v-^ , the 0-H stretch is

assumed to be -3650 cm-1 in comparison with the-alkali metal hydroxides. Now

the thermal functions, in particular the entropy, are well-established,

comparison with the previously available entirely-estimated values. This

222
results in the entropy at 298.15 K being shifted by 2.5 J/(mol K). However,

for the case of beryllium, we still must rely on theoretical calculations for

the structure and the vibrational frequencies.

Our review of the alkaline earth dihydroxide species is nearing

completion. The full analysis of these species is limited by the lack of low

temperature heat capacity data for Sr (0H) 2 and Ba(0H)2 and high temperature

enthalpy data for Be(0H) 2

. The low temperature data for Be(0H)2 has been

measured in USSR, is available through VINITI (Russian Depository of

Technical Data), and will enhance the quality of the beryllium dihydroxide

thermal functions. The gas phase dihydroxide species are estimated based on comparisons with the gaseous difluorides, dichlorides and the monohydroxides.

With more reliable data avalilable on these latter species, the resulting

gaseous dihydroxide thermal functions (still estimated) should be much

improved.

In addition, information has been collected for the analysis of the

alkaline earth oxides, sulfides, sulfates, carbonates, and the halides. For

each of these classes of species, annotated bibliographies exist and are

being updated continuously. Data summaries are in preparation for these

classes of species.

3. Thermochemical Properties of Compounds of Rubidium

(V.B. Parker, W.H. Evans, R.L. Nuttall)

The thermochemistry of rubidium compounds has been summarized in a paper accepted for J. Phys. Chem. Reference Data. This paper presents a catalog of the 420 measurements on 250 substances used in the preparation of

the rubidium table in the "NBS Tables of Chemical Thermochemical Properties”.

It represents a comprehensive survey of thermochemical measurements on rubidium compounds. Included are enthalpies of reaction, Gibbs energies of

reaction, based on equilibria and cell potentials, and entropies. For each

process a comparison is made between the observed value and that calculated

from the ”NBS Tables". A feature novel to thermodynamic tables is that

estimated reliabilities are given for the recommended values for each

measured process.

4. Thermodynamic Properties of Compounds of Calcium

(D. Garvin, V.B. Parker)

The first volume of a new series of tables of evaluated

thermodynamic properties of chemicals is being published this year. It is the

"CODATA Thermodynamic Tables. Selections for Some Compounds of Calcium and

Related Mixtures. (A Prototype Set of Tables.)", D. Garvin, V.B. Parker and

H.J. White, Jr., editors. This is the report of the CODATA Task Group on Chemical Thermodynamic Tables and covers six years of work by an international team of data evaluators. NBS has taken the lead, providing

evaluated thermochemical data, a definitive analysis of the CaCl 2 ~H 2 0 system,

some thermal functions, extensive "catalogs of data", technical editing and

preparation of the final book. Its contents are summarized below.

Recommended values are presented for chemical thermodynamic properties of

selected compounds of calcium and their mixtures. These have been prepared in

accord with and as a test of a plan developed by the CODATA Task Group on

223
CODATA THERMODYNAMIC TABLES

Substance Molar mass Af H'(0 K) Af H* 4fG* H*-H*(0) S g.mor ^ ........... - KJ.mol' 1 -- J.Cmol .K)-1 -

Mg(cr) 24.5030 0 0 0 4.996 32.671 24.869

COOATA Key Value £840003

.

±0.030 ±0.100 ±0.100

Mg<l) 24.3050 4.790 14.044 9.788 a 1.633 34.309

Extrapolated from high ±1.000 ±1 .200 ±1.000 ±2.000 ±3.000

temperature.

Mg<g) 24.3050 145.901 147.10 112.521 6.197 148.649 20.786

COOATA Key Value [84CC03

.

£0.800 ±0.80 ±0.800 ±0.002 ±0.005 ±0.001 MgO(cr) 40.3044 -597.422 -601.60 -569.311 5.160 26.950 37.237

COOATA Key Value [84C003

.

±0.300 ±0.30 ±0.30 ±0.020 ±0.150 ±0.200

MgF2 (er) 62.3018 1120.297 -1124.2 -1071.051 9.920 57.200 61.587

COOATA Key Value C84C003

.

±1.200 ±1.2 ±1 .300 ±0.060 ±0.500 ±0.2

Ca(er) 40.0800 0 0 0 5.736 41.588 25.929 CODATA Key Value [84C00)

.

±0.040 ±0.400 ±0.300

Alpha

Ca(er2) 40.0800 1.056 0.614 0.792 a 43.070 25.951

Beta, extrapolated from ±0.300 ±0.800 ±0.300 ±0.700 ±1.200

high temperature.

Ca(l) 40.0800 7.788 6.619 13.524 a 45.510 35.000 Extrapolated from high ±1.000 ±1.200 ±1.000 ±2.000 ±3.000

temperature.

C*<g> 40.0800 177.339 177.80 144.020 6.197 154.887 20.786

COOATA Key Value [84COO3

.

±0.800 ±0.80 ±0.810 ±0.002 ±0.004 ±0.001

Ca*(g) 40.0795 767.152 773.81 732.057 6.197 160.650 20.786

±0.830 ±0.83 ±0.84 ±0.002 ±0.002 ±0.001 Ca^lg) 40.0789 1913.645 1926.50 1880.210 6.197 154.887 20.786

±0.920 ±0.92 ±0.930 ±0.002 ±0.005 ±0.001

Ca

+^(ao) 40.0789 -543.0 -552.807 •56.2 281.38

COOATA Key Value [84COO]

.

±1.0 ±1.100 ±1.0 ±5.0

Ca2 <g) 80.1600 341.982 341.7 289.819 11.190 257.185 36.577

±1.800 ±1.7 ±1.800 ±0.100 ±1.500 ±0.500 CsG(er) 56.0794 631.594 -634.92 603.297 6.750 38.100 42.049 COOATA Key Value [84 COO 3

.

±0.900 ±0.90 ±0.920 ±0.060 ±0.40 ±0.400

CaO(g) 56.0794 24.623 23.5 0.974 8.953 219.718 32.455 ±8.000 ±8.0 ±8.000 ±0.001 ±0.020 ±0.010

Fig. 5.2. Selected values for A

fH°>

A

fH°(0 K) at 0.1 MPa. First page of

the CODATA Thermodynamic Tables.

A-Go, H°-H°(0 K), S°. C

p

° at. 298

a 5 page table of thermochemi ca

224
Chemical Thermodynamic Tables. All values in the present table are mutually

consistent and are consistent with the CODATA Key Values for Thermodynamics.

The values are recommended for general use.

The evaluated data are for common compounds of calcium (element, oxide,

hydroxide, peroxide, fluoride, chloride, sulfate, nitrate and carbonate,

their hydrates and their ions in aqueous solution) and for three systems:

Ca-Mg, CaCl 2-KCl and CaCl2-H2 0.

Forty one tables of thermal functions (heat capacity, entropy, enthalpy and

Gibbs energy functions) are given for those compounds of magnesium, calcium

and potassium for which the properties have been evaluated in this

work. Twenty four tables of thermal functions are given for auxiliary substances. Each table spans the temperature range 0 to 4000 K, to the extent

that data are available. Formation properties at 298.15 K (enthalpy and Gibbs

energy of formation) are given for 68 compounds of calcium, magnesium and

potassium plus the relevant values of 54 auxiliary substances. A sample page

from the formation property table is given in Figure 5.2.

For each of three binary systems recommendations are given for mixing

properties (enthalpies and Gibbs energies), partial molar or excess

properties of the components (activities, enthalpies, heat capacities) and

phase transformation data. All selections of data are accompanied by

uncertainties, and are documented. Detailed lists of the measurements used in

the evaluations are given for the thermochemical, alloy and aqueous solution

sections

.

The preparation of this compendium involved work at five geographically

separated institutions, assembly of machine readable data bases, transfer of

data by magnetic tape and interactively, and extensive development of com- puter programs for both thermodynamic calculations and document preparation

and printing.

5. Needs for Thermochemical Data

(D. Garvin, V.B. Parker)

In the course of work on the CODATA Key Values for Thermodynamics

and the CODATA tables on calcium compounds, deficiencies in the presently

available thermodynamic data have become apparent. Very brief summaries of

these are given here. Publication of this material is planned, in order to

alert the thermodynamic and spectroscopic communities to these needs.

(a) K

2 (g): Dissociation Energy. The 1930’s spectroscopic data

(used in a Birge-Sponer extrapolation) , the vapor pressure data and recent

theoretical calculations do not agree (range 4 kJ). Current spectroscopic

techniques are adequate for the solution of this problem.

(b) Ca(cr): Thermal Properties. Ditmars (NBS) and Robie (U.S.G.S)

have measured the heat capacity of Ca up through the alpha-beta transition.

On the basis of preliminary results, their work leads to a value for S(298.15

K) that is 1.5 J/(mol.K) greater than the CODATA Key Value, to different heat

capacities for the alpha and beta forms, a lower T fus , 71 0 K versus 716 K,

and a revised A trHAtrH. (Only the liquid remains to be done). These data, if

accepted, will change selections for all species whose properties depend on high temperature data, such as Ca(g), a CODATA Key Substance, CaH 2 ( cr ) f and

225
possibly Ca(0H)2(cr) and CaCO^Ccr). Gibbs energies of calcium compounds will

also change. However, these changes, <0.5 kJ/mol of Ca, usually are less than

the uncertainties in the values themselves.

(c) CaCl2.nH20(cr ) , n= 1,2, 4, 6: Heat Capacity. These hydrates are

the stable forms of the salt in equilibrium with aqueous solutions, -50 to

+175 °C. For none of them are there low temperature C

p

data from which

entropies can be calculated. Instead, the entropies are calculated from

enthalpy and Gibbs energy of solution data, and the resulting values of S do

not show the smooth variation that might be expected. Recent measurements by

Meisingset and Gronvold treat the hexa- , tetra- and di-hydrates above 288 K

and can be combined with low temperature data to provide the thermal

functions needed for a modern optimization of the CaCl 2-H20 system. Such data

will also be useful in the development of estimation methods.

(d) CaF2 (cr): Solubility and Thermal Properties. Existing

measurements give pK

sp values varying from 11.6 to 8 at 298.15 K. The likely

value is 10.6, although the most recent extensive study gives 11.6.

Solubility should be studied between 298 and 500 K (to allow for geochemical

applications) , from both under- and over-saturation as a function of ionic

strength, acid concentration, particle size, time to reach equilibrium,

source and preparation of the samples. Choice of method will be important.

In addition this substance has a lambda-type transition in the heat

capacity at 1424 K. There are enthalpy measurements, but these are insufficient to define the transition. Heat capacity measurements are needed.

(e) Ca(0H)2(cr): Enthalpy of Formation. The "best" data lead to

AfH values that do not mesh well with those for CaCO^ and CaO. Nor do the

Gibbs energy data (solubility and high temperature decomposition). Enthalpy

of solution and solubility studies should be repeated.

(f) Ca4 ^(aq,std. state): Entropy and Enthalpy of Formation. This

Key Substance has surprisingly poorly defined properties: S to ±1.0 J/mol K,

AfH to ±1.0 kJ/mol . Its properties are based on those of Ca(0H)2, CaSO^,

CaCO^ and Ca(N0^)2 and their aqueous solutions. The spread in values from

system to system is larger than within each system. Any type of

experimentation that would improve the properties of Ca+2 (aq) would be

useful

.

(g)

CaO(cr) and MgO(cr): Enthalpy of Fusion. Both of these

substances melt above 3000 K. Measurements of T fus have proved to be very

difficult, the melting point of CaO may still be in dispute. The enthalpies

of fusion are derived from phase boundary information: d(ln a^)/dT- Af us

H

1 /R.

Older values are 77 kJ/mol for MgO (from the Mg0-Zr02 system) and 52 kJ mol

for CaO (Ca0“Zr02 system), in both cases assuming ideal solutions. A recent

optimization of the MgO-CaO system [Chand and Howald, 1982] selected values

of about 58 kJ/mol for both, allowing for non-ideality in the liquid and

solid phases. Unfortunately, phase boundaries in the CaO-MgO system are very

poorly delineated and are based in part on studies that lead to incorrect

melting points. A comparative study of other binary systems should be made.

226
(h) CaMg2

: Thermochemical and Thermophysical Data. The analysis of

this system in the CODATA Thermodynamic tables showed that the data are in

very poor shape. Enthalpy data above 298 K show large scatter, a new study is

needed. This may indicate that the limited low temperature heat capacities

need to be remeasured. Enthalpies of fusion measurements disagree, and are

not consistent with mixing data and enthalpies of formation. Almost any

attack would help.

B. Electrolyte Data

1. Electrolyte Data: The Calcium Chloride-Water System

(D. Smith-Magowan)

Evaluation of data on the physical and chemical properties of

aqueous electrolytes is done by the Electrolyte Data Center with two

fundamental objectives: (1) to provide reference data for use in scientific

and technical applications and (2) to present data and analyses which will

highlight challenges for future experimetal or theoretical investigations.

The results of a study of the CaCl2 -H2 0 system provide an example of the

realization of these two goals.

A correlation of experimental data on the heat capacity of CaCl

2

solutions as a function of temperature and composition has been combined with

separate NBS correlations of excess Gibbs energy and excess enthalpy as functions of composition at room temperature to create a "skeleton table" of

values for all three properties throughout the temperature range

273-1 5~373 - 1 5 K and composition range 0-11 molal. The heat capacity correlation

was made using a model-independent spline fit on the T-x surface. The other

two correlations used the Pitzer formulation (although this was not

essential). The apparent molar heat capacities are shown in Figure 5.3. The

maximum with respect to temperature in the apparent molar heat capacity is

found in other salts and is analogous to the trends observed for excess

volume. This behavior has not yet been interpreted in terms of the structure

of the solutions.

The resulting values for the excess properties C ex

, Hex and Gex are considered to be the most accurate representation of the experimental data

available and cover the broadest range of composition of any study presented

to date. The procedure includes the systematic treatment of data on aqueous

systems at elevated temperatures, where the pressure is greater than one atmosphere. The effect of pressure has routinely been neglected in most

previous treatments of the data for this system. Comparison with previous

correlations where the effect of pressure has been neglected reveals a tangible systematic error in those studies.

Heat capacity data are lacking or of low quality in several temperature-composition regions. Below 298.15 K, the evaluation is based on scattered, imprecise data at intermediate compositions. More accurate measurements at all concentrations are desirable, but measurements below 1 molal

and above 8 molal are imperative if the correlations are to be improved. This

is an important temperature region as the structure of water and of solutions

is changing rapidly with temperature. Data at high concentrations (7 molal

to saturation) are needed at all temperatures. Experimental values are not

available, even at 298.15 K and estimates had to be made in our work, based

227
m

o O o o o o

lQ in m m m m

i V— CM m

( L _(» i°w)r)/^‘d

o

228

Fig.

5.3*

Apparent

molar

heat

capacity

for

calcium

chlori

de-water

mixtures,

273“373

K.
on a small set of measurements at 323 and 348 K. The high concentration

region is important because, more often than not, the industrial applications

involve concentrated solutions.

Enthalpy of dilution data are available only at or near 298.15 K. There is

only one published study that covers any large range of concentrations at

other temperatures (273 and 323 K). Above 298 K there are no data that reach

the saturation line. Most useful would be a study at 373 K, from 0 molal to

saturation, and a study at 323 K from 0 to 4 m, to validate the existing study.

For both C

p

and data from 373 K to the critical line will be welcomed.

This study has also raised a significant problem for the theoretical

interpretation of thermodynamic properties of electrolytes concerning the

permittivity (dielectric constant) of H

2 0(1). It was necessary to choose a consistent formulation for the Debye-Huckel limiting law slopes Ax

(activities), AH

( enthalpies ) and Aj (heat capacities). Later on Ay (volumes)

will be required. The limiting law slopes for all properties can be

calculated for any temperature or pressure provided that the density, the

permittivity and their derivatives with respect to temperature and pressure are known. The Haar-Gallagher-Kell equation of state for water (NBS-NRC Steam

Tables) is nearly a universal standard for the PVT properties of water. There

are available, however, several formulations for the dielectric constant of

water all of which represent the experimental measurements equally well, at

least superficially. Our first selection was the dielectric constant

correlation of Uematsu and Franck, because of the wide range of temperature

and pressure at which it is applicable, the extensive data base considered,

and its status as a standard.

A reviewer of the work pointed out that the formulation of Bradley and

Pitzer should be used as it more accurately reproduced the measured

permittivity values and derivatives at temperatures below 298.15 K.

(Differences in the calculated D-H limiting law values are inconsequential

for the Gibbs energy or enthalpy, but are quite dramatic, 30% , for heat

capacity.) The reviewer’s comment appears to be correct, and, because of our concern for fitting the lower temperature data, we have adopted his

suggestion for the present.

An ensuing examination of the available experimental permittivity data,

however, indicated they are not accurate enough for our purposes especially

below 298.15 K. There are several detailed studies that show similar trends

with temperature, but the studies disagree in absolute value. Thus it is

difficult to establish the second derivative. The data are compared in Figure

5.4. The trend with temperature (below 298.15 K) in the Bradley-Pitzer

formulation is steeper than in the Uemetsu-Franck treatment, and is closer to

the trends in the principal studies. It is clear, however, that this

important property of an important substance needs to be redetermined.

229
deviations

from

79BRA/PIT

iid/vaa6z - dxa

230

The

two

correlations

represented

by

solid

points

are

compared

to

the

79

BRA/PIT

correlation.

Four

experimental

data

sets

represented

by

open

points

are

compared

to

the

BRA/PIT

correlation.
2. Krebs Cycle Thermodynamics

(D. Smith-Magowan)

The thermochemical analysis of the reactions comprising the Krebs

cycle has continued during the year. The value of the network method for

obtaining thermochemical properties for metabolic substrates has been shown

in several aspects of the work thus far.

Inconsistencies in the results for several reactions suggested, after some

thought, that the value of the reduction potential for the Nicotinamide

Adenine Dinucleotide/Nicotinamide Adenine Dinucleotide (NAD/NADH) couple

(0.311 ± 0.006 V from potentiometric measurements), which is widely adopted

and was input to the network, must be in error. This is indeed the case as our subsequent investigation revealed. It was discovered that an error in

the formation data for the reduction of acetaldehyde to ethanol obtained from

the compilation by Stull, Westrum and Sinke leads to an error in the

interpretation of equilibrium measurements for alcohol dehydrogenases from

which this potential has been deduced. Recent equilibrium measurements for

the acealdehyde/ ethanol system have been used to obtain a more reliable value

for the NAD/NADH potential (0.3165 ± 0.001 V) that is more consistent with

the other reactions of the Krebs cycle.

For many of the substances involved in the Krebs cycle it is virtually

impossible to obtain an estimate of the Gibbs energy of formation in solution

by the more traditional approach of combining enthalpy of reaction and heat

capacity determinations (to get entropies) for the pure substance with

measurements of the solubilities (to get A sol G), because the necessary data

are lacking. Lactic acid, for example undergoes polymerization in aqueous

solution, making it impossible to measure its solubility accurately. Using

the power of the network analysis, which includes reactions linking lactate

with pyruvate, oxaloacetate, and acetate, a value for Gibbs energy of

formation (-519.77 kJ/mol) has been obtained that is accurate to ±0.4

kJ/mol. Similar situations can be quoted for other substances.

The Krebs cycle is common to almost all aerobic respiration pathways, which

implies, at least in principle, that the network can be extended to encompass

metabolic substances of unlimited complexity. If this is indeed possible,

it could be the most reliable way to quantify and relate the subtle effects

of changes in structure, in solution, of the complex substances that

biotechnology seeks to exploit.

3. Electrolyte Solution Properties Data Base

(D. Smith-Magowan)

A computer database of thermodynamic properties for electrolytes

is being developed for the Design Institute for Physical Property Research

(DIPPR) . DIPPR is sponsored by AIChE and is a consortium of about 50 major

chemical companies that support various research projects depending upon

their individual interests. The database will consist of a collection of the

activity, enthalpy, heat capacity and volume properties for electrolyte

solutions supplemented by computational utilities to aid the engineering

application of these properties. These utilities will provide the ability to

calculate values of properties for simple binary solutions using several

different models for extrapolation, prediction, or comparison; the

231
calculation of properties for ternary or more complex mixtures; and methods

for integrating these properties to obtain consistent sets of properties for

a range of temperature, pressure and composition.

Tempera ture-Density-Composi tion Correlations of Excess Properties

(D. Smi th-Magowan

)

The correlation of thermodynamic properties of electroytes as a function of temperature, pressure and composition is underway using an algorithm that simultaneously treats temperature, density and composition as independent variables. The experimental data for calcium chloride are being

used as a test case so that comparison with the CODATA skeleton table can provide an indication of the quality of the performance of this algorithm.

The choice of density as an independent variable instead of pressure is made

because of the PVT behavior of water at elevated temperatures. As the

critical point is approached, the compressibility of water increases greatly

and the excess thermodynamic properties of binary electrolytes appear to show

corresponding trends. For example, the apparent molar heat capacity (at

constant pressure) of aqueous NaCl seems to diverge to a value of negative

infinity as the temperature of the critical point (674 K) of water is

approached. A polynomial in temperature to fit such behavior requires terms

of very high order. The heat capacity at constant density (or volume) on the

other hand, is not divergent and can be fitted with a less complicated

expression.

C„ Thermodynamic Properties of Organic Compounds

(E.S. Domalski, E.D. Hearing, J.F. Liebman, D. Garvin)

1. Prediction of Properties

An estimation method developed by S.W. Benson and coworkers for

calculating thermodynamic properties for gas phase organic compounds from

structural group parameters has been extended to the liquid and solid phases

for hydrocarbons. The work is in the process of being reviewed for

publication in the Journal of Physical and Chemical Reference Data.

The group parameters for hydrocarbons in gas, liquid and solid phases at

298.15 K have been tested in 1267 comparisons with experimental data. For 527

comparisons with enthalpy of formation data, the average difference is ± 2.8

kJ/mol. The average differences for 396 comparisons for heat capacity and 3^4

comparisons for entropy in all three phases are ±2.6 and 3-1 J/(mol.K),

respectively. The publication will include examples of the method of

calculation, total symmetry numbers and methyl corrections for hydrocarbons

plus a bibliography on the development of estimation methods since 1932.

This estimation procedure is now being extended to C-H-0 compounds in the

gas, liquid and solid phases at 298.15 K, and it is planned to apply it tc

C“H“N and C-H-N-0 compounds.

2. Thermochemistry of Organic Compounds of Interest in

Biotechnology

.

A preliminary machine-readable data base has been complied for

evaluated data on the chemical thermodynamic properties of a thousand or- compounds at 298.15 K. Four general classes of compounds are covered, ai. f

232
interest to researchers in biotechnology, namely: ( 1 ) amino acids, peptides

and related compounds, ( 2 ) heterocyclic nitrogen compounds, ( 3 ) heterocyclic

oxygen compounds, and (4) heterocyclic sulfur compounds. The properties

covered are enthalpy of combustion, enthalpy of formation, heat capacity,

entropy, Gibbs energy of formation and the logarithm of the equilibrium

constant of the formation reaction. The data base is now being annotated.

Publications are planned for each section.

3. Enthalpies of Combustion of Components of Natural Gas.

Recommended values have been prepared and published for the

enthalpies of combustion of the C

1 -Cg alkanes, C 2 - C

3 alkenes, acetylene,

benzene and C

3 - Cg cyclolkanes. In addition to the thermochemical data,

corrections are given for non-ideal behavior of the gases. This work has

been incorporated in a handbook on properties of natural gas for use in the

liquified natural gas industry (prepared for the International Group of

Importers of Liquified Natural Gas, GIIGNL) , included in the Gas Producer

Association standards, recommended to ASTM, discussed withan ISO Task Group,

and reported on at an industry conference on "Gas Quality". In the course of

this work it has been noted that thermochemical data for the hexanes are conflicting. Predicted enthalpies of combustion (and formation) of

2 , 2 -dimethyl and 2 , 3 -dimethyl alkanes tend to be outliers in estimation

schemes. That is true for the hexanes 2, 2-dimethylbutane and 2,3“dimethyl

butane. Their enthalpies of combustion also are the least well defined of

those for the lower molecular weight hydrocarbons. Calorimetric,

isomerization equilibrium and correlation results spread by 2.5 kJ/mol.

Combustion calorimetry on these two hexanes (now known only from relative

measurements) could lead to a solution of the general problem of how to treat

such isomers.

D. Automating Data Center Procedures

(D.B. Neumann, D.M. Bickham)

Automation efforts in the Chemical Thermodynamics Data Centers are

oriented toward providing for the following needs: (a) data analysis, (b)

on-line access to data and bibliography, (c) transfer of data to other media

or other data bases, (d) re-formatting data for publication, and (e)

graphical presentation of data.

This year, three generic solutions to data center problems have been developed. The problems are: search for and retrieval of chemical data,

bibliographic data management, and, printing and publication of results. The

solutions are applicable to the work of all the CCP Data Centers.

1. Search and retrieval systems.

A general keyed access search-retrieval system called SETKY-GETKY

has been written and implemented on the HP-1000. It is suitable for indexed

material containing either text or tabular material.

SETKY-GETKY provides rapid access to free formatted textual or tabular

material stored in large data files on the mini-computer. As a "keyed access"

system it permits the user to create editable files with the usual system

editor. Index commands, or "keys", are placed into the file by the user.

233
SETKY is then invoked. It reads the original file and creates a file of keys

that will be searched. The key file contains only the keys and the physical

disc positions of the text in the original file to which the keys refer.

In its on-line mode the user invokes GETKY with a key or an approximate

key. The GETKY program rapidly searches for the key in the key file. Using

the physical disc position retrieved from the key file, GETKY retrieves, by

direct access in tne original file, the indexed item of text and displays it.

If the key cannot be found, Getky returns the 20 keys alphabetically nearest

to it and prompts the user to select one.

There are several aspects of the system that has made it unique and highly

useful for Data Center work:

Text related to a key may be obtained from within programs, i.e. the

GETKY functions are callable from user programs. This has been used to

build retrieval systems for the JANAF Thermochemical Tables and the

CTDC abstract files.

The original text files can be used for text processing as well as for

on-line or programmatic retrieval. This has been accomplished by

choosing the syntax of the index commands in the original files to be

compatible with the TEXED system currently used for text formatting of

reports and papers. This feature has been used in building a system for

printing the CODATA Thermodynamic Tables.

The original file remains accessible, may be corrected or expanded by

its owner. (This is much easier than when a Data Base Management System

is used .

)

The number of index items per entry is unlimited.

SETKY-GETKY is written in FORTRAN 77.

It is expected that these programs will be transferable to other systems

such as the NBS Cyber or micro-computers such as the IBM-PC/XT, or AT. It may

prove advantageous to use it as the search system for data distributed on floppy discs.

A users guide for SETKY-GETKY is being published in the proceedings of

the 1986 International Users Group for Hewlett-Packard minicomputers. The

applications of the system to date are (1) in printing a large section of the

CODATA Task Group on Chemical Thermodynamic Tables, (2) a combined users manual and on-line help system for the HP-1000 was created, (3) a retrieval

system for the JANAF Tables, (M) the NBS Telephone Book on-line, and (5) a retrieval system for abstracts of thermochemical data.

The motivation to create the SETKY-GETKY system was to automate CTDC's

large data base of literature extracts, some 50,000 in number. In F io6 a section of this data base was re-formatted for this application. Using this

section as a test we expect to remove remaining problems from the retrieval

system and put the entire data base on line in early F Y i 987 . At that point

retrieval by substance formula, property, name, Wlsswesser line notation,

and registry number will be possible.

234
2. Common Bibliographic System.

A bibliographic system for CTDC and the other Data Centers, DB-BIB, was placed on-line and is being tested. Initial test applications are with a small

Ion-Energetics bibliography and a bibliography of sputtering data (Surface

Chemistry Division). The goal of this effort is to load, as an on-line

searchable data base, all 60,000 -70,000 CTDC bibliographic citations. This

is necessary to permit the more efficient preparation and publication of

reaction catalogs such as that for rubidium thermochemistry, which is now in

press.

3. Printing and Text Formatting Utilities. A program utility,

(called PTTL) , for printing using the 0SRD laser printer was written by CTDC.

This system is now in use by the Atomic Spectra Data Center, the Kinetics

Data Center, and is used heavily by CTDC. Its function is to provide for suband super-scripts, Greek and math symbols, italics, bold, various line

spacing needs, as well as a general and consistent input technique for Data

Center staff. 0SRD staff have made a number of improvements to this utility.

A utility for formatting reports containing text as well as tabular

material, called TEXDA, was implemented by CTDC on the 0SRD and CTDC

mini-computers. It is an expansion of TEXED distributed by the International

HP Users Group. A User’s Guide covering both these utilities is in preparation

by 0SRD

.

M. CTDC Abstracts Data Base.

Twenty six hundred current articles on thermodynamics were

abstracted during the ten months Nov 1985 through Aug 1986. The process for

doing this has been refined to make use of the Chemical Abstracts Data Base.

Articles of interest are selected by inspection of CA or of high-yield

journals. This is done by a contractor and by CTDC staff. The abstracts of

the articles are retrieved from CA and then a decision is made by CTDC staff

about the usefulness of each article and how it is to be abstracted. Copies

of the articles to be retained are obtained, if possible, and microfilmed.

Each article is indexed for its thermodynamic data content (in terms of

substance and property studied), either from the article or its abstract,

depending upon the subject and on the availability of the original. This

material becomes part of the computerized CTDC Abstracts Data Base.

This data base is the ready reference used in the Center when

evaluations of data are made. In addition, it is used to answer questions

from the public.

All of the Abstracts Data Base since 1970 is machine-readable. During

the year new programs have been written for processing the input. The

programs have been tested extensively and are being used in a production

mode. They have also been used to prepare indexes for the Bulletin of

Chemical Thermodynamics. CTDC has processed the material for the inorganic

index (prepared here), the organic index (prepared at Texam A&M Univ.), and

the organic mixture index (prepared at Univ. Paris) into a form that can be

handled by the index formatting programs of the Bulletin. The programs used

here have also been supplied to the editor of the Bulletin who plans to do

the entire processing task next year.

235
6 . PUBLICATIONS

(a) Publications of Past Year

Churney, K.L., E.S. Domalski, A.E. Ledford, Jr., J.C. Colbert, S.S. Bruce,

T.J. Buckley, and M.L. Reilly, "Assessing the Credibility of the

Calorific Value of Municipal Solid Waste", Proceedings of the 1986

National Waste Processing Conference, ASME, New York, 1986.

Bitmars, D.A., Flint, C.A. and Shukla, R.C., "Aluminum (I): Measurement of the Relative Enthalpy from 273 to 929 K; Derivation of Thermodynamic Functions for Al(s) from 0 K to Its Melting Point", Int. J. Thermophysics 6 , 495 (1985).

Domalski, E.S., Churney, K.L. , Ledford, A.E., Bruce, S.S., Buckley, T.J.,

Parris, R«, and Chesler, S.N., "Monitoring the Fate of Chlorine from

MSW Sampling through Combustion", Proceedings of the EPRI Seminar on Municipal Solid Waste as a Utility Fuel, EPRI, Palo Alto, CA, (1986),

14pp.

Domalski, E.S., Churney, K.L., Ledford, A.E.,Jr. and Reilly, M.L., "MSW

Calorimetry", Mechanical Engineering 1 08 , 32 (August, 1986).

Domalski, E.S., A.E. Ledford, Jr., S.S. Bruce, and K.L. Churney, "The

Chlorine Content of Municipal Solid Waste from Baltimore County, Maryland,

and Brooklyn, New York", Proceedings of the 1986 National Waste Processing

Conference, ASME, New York, NY, 1986.

Domalski, E.S., "NBS Research Program in Municipal Solid Waste Combustion",

Proceedings of the Biofuels and Municipal Waste Technology Division, U.S.

Department of Energy, 1986, 28 pp.

Evans, W.H., Grimes, J.J., Jobe, T.L., Young, N.W., Foreman, R. , Thompson, R.C.

and Seymour, C.L., "Substance - Property Index Section III. Inorganic

Substances", Bull. Chem. Thermodynamics, 26, pp 219-286 (1983).

Evans, W.H., Grimes, J.J., Jobe, T.L., Young, N.W., Foreman, R., Thomspon,

R.C., and Seymour, C.L. "Substance - Property Index Section III. Inorganic

Substances", Bull. Chem. Thermodynamics, 26, pp 473“542 (1983).

Gajewski, E., Goldberg, R.N. and Steckler, D.K. "Thermodynamics of the

Conversion of Fumarate to L(-)Malate", Biophys. Chem., 22, 187 (1985)

Garvin, D., Domalski, E.S., Wilhoit, R.C., Somayajulu, G.R., and Marsh, K.N.,

"Physical Properties of Pure Components of Natural Gas", in ’Gas

Quality', van Rossom, G.J., editor, Elsevier Science Publ., Amsterdam,

1986, p.59.

Garvin, D. and Parker, V.B., "CODATA Chemical Thermodynamic Data Bases for

Science and Technology", in 'Scientific Program and Abstracts, Tenth

International CODATA Conference', CO DATA Bull, 6_1_ 48 (1986),

Garvin, D., and White, H.J., Jr., "Comprehensive, Consistent Thermodynamic

Tables", in 'Thermodynamic Databases', CODATA Bull 58_, 1, (1986 .

236
Goldberg, R.N., Gajewski, E., Steckler, D.K., and Tewari , Y.B.,

"Thermodynamics of the Conversion of Aqueous 1-Aspartic Acid to

Fumaric Acid and Ammonia", Biophys. Chem. 24_, 13 ( 1986).

Goldberg, R.N. and Parker, V.B., "Thermodynamics of Solution of S02 (g) in

Water and of Aqueous Sulfur Dioxide Solutions", J. Res. NBS, 9£, 341

(1985).

Johnson, W.H. and Prosen, E.J., "Determination of Enthalpies of Combustion and

Formation of Substituted Triazines in an Adiabatic Bomb Calorimeter",

J. Res. NBS, 90, 295 (1985).

Karpas, Z. , Stevens W.J. Buckley, T.J. and Metz, R. , "The Proton Affinity and

Gas Phase Ion Chemistry of Methyl Isocyanate, Methyl Isothiocyanate and

Methyl Theocyante" , J. Phys. Chem., 89_, 5274 (1985).

Kirchhoff, W.H., Chambers, G.P., Fine, J., "An Analytical Expression for

Describing Auger Profile Shapes of Interfaces.", J. Vac. Sci. Tech. A4

,

1666 (1986).

Kirchhoff, W.H., "A National Program of Measurement Services and Standards

for Biotechnology at the National Bureau of Standards, Planning Report

22 (Revised)", February, 1986.

Kirchoff, W.H. "Who Needs Standards," Chemtech J_6, 280 (1986).

Kirklin, D.R. and Domalski, E.S., "Estimation Methods and Combustion

Calorimetry on Organic Phosphorus Compounds", Proceedings of the 1985

Scientific Conference on Chemical Defense Research U.S Army, Research

Directorate, CRD&EC Aberdeen Proving Ground, 1986.

Miller, M.M., Wasik, S.P., Guang , G.L. Shiu , W.Y. and MacKay , D., "Relations

Between Octanol-Water Partition Coefficients, Aqueous Solubility and

Biocentration Factors", Enviromental Science and Technology, 19, 522

(1985)

Neumann, D.B. "Data Base Management Systems, Part I. A Quick Overview",

Non Bibliography Data Banks in Science and Technology, S. Schwarz, D.G.

Watson , 0. Alvfeldt, eds. ICSU Press, 1985, p. 139.

Neumann, D.B., "Data Base Management Systems, Part II, An Application to

Scientific Technical Data and its Associated Bibliographic Data",

Non-Bibiographic Data in Science and Technology, S. Schwarz, D.G.

Watson, 0. Alvfeldt, Eds., ICSU Press, 1985, p. 153-

Owens, J.W., Wasik, S.P. and DeVoe, H., "Aqueous Solubilities and Enthalpies

of Solution of n-Alkylbenzenes" , J. Chem. Eng. Data, 3_T_, 47 (1986)

Savage, H. , "Repulsive Regularities of Water in Ices and Crystalline

Hydrates", Nature 322, 717 (1986).

Schwarz, F.P. "Biological Standard Reference Materials for Calibration of

Differential Scanning Calorimeters: Di-alklyl-Phosphatidylchol ine in

Water Solutions," Thermochim. Acta 106 , 347 (1986).

237
Shukla, R.C., Plint, C.A. and Ditmars, D.A., "Aluminum( II ) : Derivation of

C

v

o from C

p

and Comparison to C v

o Calculated from Anharmonic Models",

Int. J. Thermophysics, 6_, 517 (1985).

Steckler, D.K., Goldberg, R.N., Tewari , Y.B., Buckley, T.J. "High Precision

Microcalorimetry: Apparatus, Procedures, and Biochemical Applications"

J. Res. NBS 91, 113 (1986)

.

Steckler, D.K., Goldberg, R.N., Buckley, T.S. "Computer Software for

Acquisition and Treatment of Calorimetric Data", NBS Tech Note 1224,

UoS. Government Printing Office, Washington, D.C. (1986).

Tewari, Y.B. and Goldberg, R.N., "An Investigation of the Equilibria Between

Aqueous Ribose, Ribulose, and Arabinose" , Biophys. Chem. 22, 197 (1985)

Tewari, Y.B., Steckler, D.S. and Goldberg, R.N., "Thermodynamics of the

Conversion of Aqueous Xylose to Xylulose", Biophys. Chem. 22, 18

(1985).

Weber, I.T. and Steitz, T.A., "The Crystallization of rec A protein from

proteus mirabilis , J. Mol. Bio. 188 , 109 (1986).

Wlodawer, A., "A Facility for Data Collection and Processing at the National

Bureau of Standards Reactor", in Methods in Enzymology, H.W. Wyckoff,

C.H.W. Hirs, and S.N. Timasheff, eds., Academic Press: New York, 114 , 551 (1988).

Wlodawer, A., Borkakoti , N. , Moss, D.S. and Hawkin, B. , "Comparison of Two

Independently Refined Models of Ribonuclease A", Acta Cryst., B42 , 379

(1986).

238
(b) Publications in Progress

Bickham, D.M., Neumann. D.B., "Setky-Getky User ' s Manual" , NBS-IR,

( in press)

Bickham, D.M., Neumann D.B., "Setky-Getky. A Keyed Access System for the

HP-1000." Proc. INTEREX North Am. Conf., (in press).

Bickham, D.M., "User Manual for the Chemical Thermodynamics Data Center

Hp-1000 mini-computer", NBS-IR (1986), (in press).

Chase, M.W., Davies, C.A, Downey, J.R., Frurip, D.J., McDonald,

R.A., and Syvervd, A.N., 'JANAF Thermochemical Tables, Third Edition,

Phys. Chem. Ref. Data, 1_4> Supplement No. 1 , 1985, (in press).

Churney, K.L., Ledford, A.E., Jr., Reilly, M.L., and Domalski, E.S.,

"A Multi-Kilogram Capacity Calorimeter for Heterogeneous Materials",

J Res NBS (in press).

Colbert, J.C. Domalski, E.S., and Coxon, B. , "Enthalpies of Combustion of

D-Ribose and 2-Deoxy-D-ribose , J. Chem. Thermodynamics, (in press).

Ditmars, D.A., "Drop Calorimetry above 300 K" , McGraw-Hill/CINDAS Data Series

on Material Porperties, Chap 13. Compendium of Thermophysical Property

Measurement Methods, Vol. I, Plenum Publishing Corporation, 1986,

(in press)

Domalski, E.S., Churney, K-.L. Ledford, A.E., Jr., Bruce, S.S., "Monitoring

the Fate of Chlorine from MSW Sampling Through Combustion, Part I: Analysis of the Waste Stream for Chlorine", Chemosphere (in press).

Domalski, E.S., Churney, K.L., Ledford, A.E, Jr., Bruce, S.S., Buckley, T.J.,

Parris, R.M., and Chesler, S.N., "Monitoring the Fate of Chlorine from

MSW Sampling through Combustion, Part II: Combustion Studies",

Chemosphere (in press)

Domalski, E.S., and Hearing, E.D., /'Estimation of Thermodynamic Properties of

Hydrocarbons at 298. 15K", J. Phys. & Chem. Ref. Data, (submitted).

Domalski, E.S., Jobe, T.L., Jr., and Milne, T.A., "Thermodynamic Data for

Biomass Conversion and Waste Incineration", (submitted).

Garvin, D., Parker, V.B., and White, H.J., Jr., editors 'CODATA

Thermodynamic Tables: Selections for Some Compounds of Calcium and

Related Mixtures. (A Prototype Set of Tables)', CODATA Special Report,

1986, 370 pp., (in press).

Garvin, D., Schumm, R.H., Parker, V.B., and Nuttall, R.L., "Thermochemical

Properties at 0 and 298. 15K", in 'CODATA Thermodynamic Tables:

Selections for Some Compounds of Calcium and Related Mixtures. (A

Prototype Set of Tables).' CODATA Special Report, 1986, section 6.2, pg.

100-196, and section 7.1, pg 216-318, (in press).

239
Gurvich, L.V., Yungman, V.S., Chase, M.W., and Bergman, G.A., "Thermodynamic

Properties of Individual Substances", in ’CODATA Thermodynamic Tables.

Selections for Some Compounds of Calcium and Related Mixtures. (A

Prototype Set of Tables).’ CODATA Special Report, 1986, section 6.1,

pg. i42“179 , (in press).

Gajewski, E., Stockier, D.K., Goldberg, R.N., "Thermodynamimcs of the

Hydrolysis of Adenosine 5’ - Triphosphate to Adenosine 5 ' - Diphosphate,"

Jo Biol. Chem., (in press).

Harrison, R. , "Sayres Equation is a Chernov Bound to Maximum Entropy", Acta

Crystallographica , (in press).

Miller, M., Apella, E., Schwarz, F.P., Kirchhoff, W., Sussman, J., "Possible

Conformations in Solution for Synthetic Quasi palindromic DNA

Sequences.", (submitted).

Parker, V. B. , Evans, W.H., Nuttall, R.L., "The Thermochemical Measurements

on Rubidium Compounds; A Comparison of Measured Values with those

Predicted from the NBS Tables of Chemical Thermodynamic Properties", J. Phys. Chem. Ref. Data, (in press).

Raghavan, N.V. and Wlodawer, A., "Neutron Crystallography of Proteins,"

Methods in Experimental Physics, (in press).

Roy, S. , Weinstein, S. , Borah, S. , Nickol, L. , Appella, E. , Sussman, J.L.,

Miller, M, Shindo, H. Cohen, J.S., "The Mechanism of Olignonucleotide

Loop Formation Solution", Biochem., (in press).

Savage, H. and Wlodawer, A., "Determination of Water Structure Around

Biomolecules Using X-ray and Neutron Diffraction Methods", Methods in

Enzymology (Biomembranes), (in press).

Savage, H. "Water Structure in Vitamin B-12 Coenzyme Crystals II, Biophysical

Journal", (in press).

Savage, H. "Water Structure in Crystalline Solids: Ices to Proteins Water

Reviews", (in press).

Smi th-Magowan , D., Garvin D., Parker, V.B., Nuttall, R.L., and Staples, B.R.,

"The Aqueous System CaC1 2 H

2 0", in ’CODATA Thermodynamic Tables.

Selections for Some Compounds of Calcium and Related Mixtures. (A

Prototypoe Set of Tables).' CODATA Special Report, 1986, section 6.5,

pg. 216-243, section 7.3, pg. 326-342, (in press).

Smi th-Magowan, D., editor, "Bibliographies of Industrial Interest:

Thermodynamic Measurements on the Systems C02 ~H 2 0, CuCl-H 2 0, NH^-H 2 0,

ZnCl 2“H2

0, H^POjjHr^O. " NBS Special Publication (in press).

Svensson, A., Sjolin, L. Gilliland, G.L., Finzel, B.C., Wlodawer, A., "Multiple

Conformations of Amino Acid Residues in Ribonuclease A", (submitted .

Tewari, Y.B., and Goldberg, R.N., "Thermodynamics of Carbohydrate

Isomerization Reactions: The Conversion of Aqueous Allose to Psicose",

Biophys. Chem., (in press).

240
Tewari, Y.B., and Goldberg, R.N. "An Equilibrium Study of the Conversion of

L-Phenylalanine to Trans-Cinnamic Acid and Ammonia.", J. Phys Chem., (in

press )

.

Weber, I.T., "The Structure of Catabolite Gene Activator Protein Crystallized

with Cyclic Amp" in Methods of Enzymology (Hormone Action) Cyclic

Nucleotide Action and Degradation, J.D. Corbin and R.A. Johnson, eds,

(in press)

.

• Weber, I.T., Steitz, T.A., Bubis, B. Taylor, S.S., "Predicted Structures of

the c AMP Bindine Domains of the Type I and II Regulatory Subunits of a

c AMP-dependent Protein Kinase, (submitted).

Wlodawer, A., Deisenhofer, J., Huber, R., "Comparison of Two Highly Refined

Structures of Bovine Pancreatic Trypsin Inhibitor", J. Mol. Biol.,

(In press)

.

Wlodawer, A. and Sjolin, L. "Experience with the Use of a Neutron Data

Collection Facility Equipped with an Area Detector.", Les Editions de

Physique, (in press).

Zielinski, W.L., Miller, M.M., Ulma, G. and Wasik, S.P., "GLC Separation of

Polychlorinated Biphenyl Isomers Between a Nematic Liquid Phase and a Non-Polar Base", Analytical Chem., (in press).

241
7. Talks

Abramowitz, S„, "Thermodynamic Properties of High Temperature Materials", Air

Space Technology Center, Albuquerque, NM, November 19, 1985.

Abramowitz, S„, "Biochemical Research in Support of NBS' Biotechnology

Program", Center for Chemical Engineering, Boulder, CO, September 15,

1 986*

Abramowitz, S., "NBS* Biotechnology Program", Thermochemical Brigham Young

University, Provo, UT, 89602, September 24, 1986.

Bickham, D.M., "SETKY-GETKY , A Keyed Access System for the HP-1000", INTEREX

North Am. Conf., Detroit, MI, September 28-October 3* 1986.

Buckley, T.J., "Formation and Reactions of Hydrocarbon Ions Under Ionospheric

Conditions." The 1985 AFOSR Scientific Conference on Laser-Material

Interaction in Obscuration Research, Albuquerque, NM, November 19, 1985.

Buckley, T.J., "Design of a Real Time Data Acquisition for Combustion

Calorimetry", 41 st Annual Calorimetry Conference, Somerset, NJ, August

18, 1986.

Chase, M.W., "JANAF Thermochemical Tables", AFOSR/AFRPL Rocket Propulsion

Research Meeting, Edwards Air Force Base, CA, September 9-11, 1986.

Churney, K.L. , "Assessing the Calorific Value of Municipal Solid Waste",

Twelfth National Waste Processing Conference, Denver, CO, June 4, 1986.

Churney, K.L., "Design and Performance Tests of a Multi-kilogram Capacity Flow

Calorimeter", 41 st Annual Calorimetry Conference, Somerset, NJ, August 18,

1986.

Domalski, E.S., "The Chlorine Content of Municipal Solid Waste", Derwood

Lions Club, Derwood MD , May 20, 1986.

Ditmars, D.A., "Heat Capacity of Solid Calcium; a Tour de Force of

Equilibrium Macrocalorimetry" , Chemical Thermodynamics Seminar, NBS,

Gaithersburg, MD , September, 30, 1986.

Domalski, E.S., "The Chlorine Content of Municipal Solid Waste from Baltimore

County, MD , and Brooklyn, NY", Twelfth National Waste Processing

Conference, Denver, CO, June 4, 1986.

Domalski, E.S., "Monitoring the Fate of Chlorine from MSW Sampling through

Combustion", DOE/EPRI Seminar on Municipal Solid Waste as a Utility

Fuel, Madison, WI, November 22, 1985.

Domalski, E.S., "A Status Report of Research Activities on the Combustion

Calorimetry of MSW", Solar Energy Research Institute (SERI), June, 4,

1986 .

Domalski, E.S., "Monitoring the Fate of Chlorine from MSW Sampling through

Combustion", Acid Gas and Dioxin Control for Waste-to-Energy Facilities

Conference, Hyatt Regency, Crystal City, V A, November 26, 1985.

242
Gajewski, E., "The Enthalpy of Hydrolysis of Adenosine 5' - Triphosphate",

76 th Annual Meeting of the American Society of Biological Chemists,

Washington, DC, June 12, 1986.

Gajewski, E., "Thermodynamics of the Conversion of L-Aspartate to Fumarate

and Ammonia", 5 th International Symposium on HPLC of Proteins, Peptides,

and Polynucleotides", Toronto, Ontario, November 6, 1985.

Garvin, D., "Physical Properties of Pure Components of Natural Gas", 1 st

International Congress on Gas Quality—Specification and Measurement of

Physical and Chemical Properties of Natural Gas, Groningen, the

Netherlands, April 22-25, 1986.

Goldberg, R.N., "A Computerized Database of Activity and Osmotic

Coefficients", Nuclear Regulatory Commission, Silver Spring, MD,

December 1985.

Goldberg, R.N., "A Computerized Database of Activity and Osmotic

Coefficients", Office of Standards Reference Data Advisory Panel,

December, 1985.

Goldberg, R.N., "Thermodynamics of Enzyme-Catalyzed Reactions", Chemical

Thermodynamics Division, NBS, Gaithersburg, MD, March, 1986.

Goldberg, R.N., "Thermodynamics of Enzyme-Catalyzed Reactions", Laboratory

of Metabolism, NIH, Rockville, MD, May, 1986.

Goldberg, R.N., "Thermodynamics of Enzyme-Catalyzed Reactions",

Laboratory of Metabolism, NIH, Rockville, MD , May, 1986.

Goldberg, R. N. , "Current Research in Chemical Thermodynamics", ICI , Runcorn,

Cheshire, United Kingdom, July 7, 1986.

Goldberg, R.N., "Thermodynamics of Enzyme-Catalyzed Reactions", University of

Newcastle-upon-Tyne, United Kingdom, July 9, 1986.

Goldberg, R.N., "GAMPHI-A Database of Activity and Osmotic Coefficients",

University of Newcastle-upon-Tyne, United Kingdom, July 10, 1986.

Goldberg, R.N., "Thermodynamics of Enzyme-Catalyzed Reactions", University of

Glasgow, United Kingdom, July 11, 1986.

Goldberg, R.N., "Thermodynamics of the Conversion of L-Aspartate to Fumarate

and Ammonia", 9

th IUPAC Thermodynamics conference, Lisbon, Portugal,

July 18, 1986.

Goldberg, R.N., "The Enthalpy of Hydrolysis of Adenosine 5 ' -Triphosphate"

,

gtn iupac Thermodynamics Conference, Lisbon, Portugal, July 18, 1986.

Goldberg, R.N., "The Enthalpy of Hydrolysis of Adenosine 5 ' -Triphosphate"

,

Ml 3 ^ Calorimetry Conference, Somerset, NJ, August 21, 1986.

243
Goldberg, R.N., "Thermodynamics of the Conversion L-Plenylalanine to

Trans-Cinnamic Acid and Ammonia”, ACS Middle Atlantic Regional Meeting,

Baltimore, MD , September 2, 1986,

Goldberg, R.N., "Thermodynamics of the Hydrolysis of Adenosine

5 ' -Triphosphate” , ACS Middle Atlantic Regional Meeting, Baltimore, MD

,

September 2, 1986,

Harrison, R., "A Common Sense Guide to Maximum Entropy”, Mid-Atlantic

Protein Cystallography Workshop, NBS , May 15-17, 1986.

Kirchhoff, W.H., "An Analysis Program for the Characterization of Interface

Profile Shapes", 8 th Symposium on Applied Surface Analysis, University

of Dayton, Dayton, OH, June 4, 1986.

Kirchhoff, W.H. , "A Computer Program for Describing the Denaturation of

Biopolymers, as Measured by Differential Scanning Calorimetry, in Terms

of a Two State Model", 41 s *' Calorimetry Conference, Somerset, NJ , August

22, 1986.

Kirklin, D.R., "Estimation Methods and Combustion Calorimetry on Organic

Phosphorus Compounds", 1985 Scientific Conference on Chemical Defense

Research, Aberdeen Proving Ground, MD, November 22, 1985.

Kirklin, D.R., "Enthalpies of Formation of Organic Phosphorus Compounds",

41 st Annual Calorimetry Conference, Somerset, NJ, August 21, 1986.

Miller, M., "Oligomers of DNA", Mid-Atlantic Protein Crystallography

Workshop, NBS, May 15-17, 1986.

Newmann, D.B., "The Chemical Thermodynamics Data Center Bibliographic Data

Base System", Chemical Thermodynamics Division Seminar, April, 1986.

Newmann, D.B., "The Application of the IMAGE/1000 Database Management System

to Scientific Data", Baltimore-Washington HP-1000 Users Group,

Baltimore, MD, November 15, 1985.

Parker, V.B., "CODATA Chemical Thermodynamic Data Bases for Science and

Technology", Tenth International CODATA Conference, July 15, 1986,

Ottawa, Canada.

Smith-Magowan, D., "A Database of Thermodynamic Properties of Aqueous

Electrolyte Solutions with Computational Procedures for Industrial

Applications", AIChE National Meeting, Chicago, IL, November 1985.

Smith-Magowan, D., "Effects of Temperature, Pressure and Composition on the

Thermodynammic Properties of Electrolytes", International Association

for Properties of Steam, Dusseldorf, W. Germany, Sept 22-26, 1986.

Tewari, Y.B., "Thermodynamic Investigations of Reactions Catalyzed by Glucose

Isomerase", Indian Institute of Technology, New Delhi, India, October

29, 1985.

Tewari, Y.B., "Thermodynamic Investigations of Enzyme Catalyzed Reactions",

Indian Institute of Technology, Bombay, India, November, 21, 1986.

244
Tewari , Y.B., "Thermodynamics of Carbohydrate Isomerization Reactions:

Conversion of Aqueous Allose to Psicose", 4l s t Calorimetry Conference,

Somerset, NJ, August 21, 1986.

Tewari, Y.B., "Thermodynamics of the Conversion of L-phenylalanine to

Trans-Cinnamic Acid and Ammonia", 41 st Calorimetry Conference, Somerset,

NJ, August 21 , 1986.

Tewari, Y.B., "Thermodynamics of Carbohydrate Isomerization Reactions: The

Conversion of Aqueous Allose to Psicose", ACS Middle Atlantic Regional

Meeting, Baltimore, MD, September 2, 1986.

Weber, I.T., "The Analysis of Protein Structure from Crystallographic Data".

The Structure of Catabolite Gene Activator Protein and its Complex with

DNA " , Course on Protein Structure and Function, Les Diablerets,

Switzerland, September 30 to October 3, 1985.

Weber, I.T., "Model for the Complex of Catabolite Gene Activator Protein and

Its Site in Lac Operon" , Series on the Relation between DNA Structures

and their Interactions, NIH, Bethesda, MD, March 19, 1986.

Weber, I.T., "The Structure of a Mutant of Catabolite Gene Activator

Protein.", Mid-Atlantic Protein Crystallography Workshop, NBS,

Gaithersburg, MD , May 15-17, 1986.

Weber, I.T., "The Crystal Structure of a Mutant of Catabolite Gene

Activator Protein.", Gordon Conference: Diffraction Methods in Molecular

Biology, New Hampshire, June 30-July 4, 1986.

Wlodawer, A., "A Novel Method for the Determination of Solvent Structure in

Protein Crystals", Max-Planck-Institut , Munich, West Germany, January

28, 1986.

Wlodawer, A., "High Resolution Studies of Proteins Using X-ray and Neutron

Diffraction", University of Washington, Seattle, WA, June, 3. 1986.

Wlodawer, A., "Bound Solvent in Proteins: Improvement of Fourier Maps by

Protein Averaging Combined with Flattening of the Solvent", Gordon

Research Conference, Andover, NH, June 30, 1986.

Wlodawer, A., "Bound Solvent in Proteins - a Novel Technique for its Analysis",

Tenth European Crystallographic Meeting, Wroclaw, Poland, August 5,

1986.

Wlodawer, A., "High Resolution Refinement of BPTI and R ibonulcease"

,

Department of Crystallography, Birkbeck College, University of London,

England, August 15, 1986.

Wlodawer, A., "X-ray and Neutron Diffraction Studies of Proteins and Nucleic

Acids", NBS Staff Research Seminar, September 5, 1986.

245
8. Chemical Thermodynamics Division Seminars

Kamlet, M.J., Navel Surface Weapons Center, Silver Spring, MD, "A General

Equation for Correlation and Prediction of Solute-Solvent Interaction

in Chemical and Biological Systems'*, October 1 , 1985.

* Bott, R., Genentech, Inc. South San Franciso, CA, "Protein Engineering,

Modification of the Oxidative Stability of Subtilisin'', October 18,

1985.

Ditmars, D.A., NBS, Gaithersburg, MD, "Heat Capacity of Solid Calcium: a Tour de Force of Macrocalorimetry" , September 30, 1986.

* O'Leary, T.J., NIH, Bethesda, MD, "Spectroscopic and Calorimetric Studies

of Biomembranes", October 24, 1985.

* Osman, R. , Department of Physiology and Biophysics, New York, NY, "A New

Mechanism of Action of Superoxide Dismutase", November 7, 1985.

* Rein, R., Department of Biophysics, Roswell Park Memorial Institute

Buffalo, NY, "Multistep Modeling of Bioactive polypeptides in

3“Dimensions" , November 14, 1985.

* Hyde, C., NIH, Bethesda, MD, "Three Dimensional Structure of Aspartate

Aminotransf erase and Substrate Complexes", December 18, 1985.

Thompson, P.T., Chemistry Department, Swarthmore College, Swarthmore, PA,

"Progress Towards the Development of Simple Potential Functions for

Solute-Solute Interactions in Non-electrolyte Aqueous Solution",

January 13, 1986.

* Goldberg, R.N., NBS, Gaithersburg, MD, "Thermodynamics of Enzyme Catalyzed

Reactions", February 21, 1986.

* Wlodawer, A., NBS, Gaithersburg, MD, "Structure of a 'Standard' Protein

Bovine Pancreatic Trypsin Inhibitor at High Resolution", February 28,

1 986 o

Neumann, D. , NBS, Gaithersburg, MD, "A Bibliographic Database for the

HP-1000 Mini-Computer", March 5, 1986.

Roy, R., Drury College, Springfield, MO, "Thermodynamics of Mixtures of

Strong Electrolytes: Applications of Pitzer's Equations", March 20,

1986.

* Gitomer, W. , NIH, Bethesda, MD, "The Estimation of the Free Mitochondrial

Ca2+ Concentration in Vivo", April 15, 1986.

* Zeyfus, M., Department of Biological Chemistry, Pennsylvania State

University, University Park, PA, "Compact Domains of Proteins", April

17, 1986.

246
Pember, S., Department of Chemistry, Pennsylvania State University,

University Park, PA, "Mechanism and Structure of Chromobacterium

Violaceum Phenyl Alanine Hydroxylase", April 22, 1986.

Harman, J.G., NIH, Bethesda, MD, "Structure - Function Analysis of Cylic

AMP Receptor Protein", May 12, 1986.

McKenney, K., NIH, Bethesda, MD, "Protein Structure Function Studies Using

Synthetic Oligonucleotides", May 14, 1986.

Tweedy, N.B., Department of Chemistry, Pennsylvania State University,

University Park, PA, "Effects of Point Mutations on Protein Folding",

May 21 , 1986.

Biotechnology Seminars
9. TECHNICAL AND PROFESSIONAL

COMMITTEE PARTICIPATION AND LEADERSHIP

Abramowitz, S.

Member

,

Energy

ASTM Commitee E-38 on Resource Recovery, Subcommittee E 38 .OI

Bickham, D.

Member

,

Chase, M.

Baltimore-Washington HP-1 000 Users Group

Vice-chairman, ASTM Committee E-27 on Hazard Potential of Chemicals

Consultant, CODATA Task Group on Chemical Thermodynamic Tables,

Corresponding member, Engineering Science Data Unit - Physical Data

and Reaction Committee

Churney, K.L.

Member, ASTM Committee E~37 on Thermal Measurements

Member, ASTM Committee on Hazard Potential of Chemicals, Subcommittee

E-27. 02 on Thermal Stability

Member, ASTM Committee E -38 on Resource Recovery

Colbert, J.C.

Member

,

Energy

ASTM Committee E -38 on Resource Recovery, Subcommittee E38.01

Member

,

ASTM Committee D-05 on Coal and Coke

Ditmars, D.A.

Member, ASTM Committee E37.05 on Thermal Measurements/Thermophysical

Properties working group I (Thermodynamics) Task Group 1.5 (Drop

Calorimetry ) , 1.6 (Adiabatic Calorimetry)

Division Safety Officer

Member, Standards Committee, U.S. Calorimetry Conference

Domalski, E.S.

Member

,

E-27. 07

ASTM Committee E-27 on Hazard Potential of Chemicals, Subcommittee

Computational Methods

Member

,

ASME Research Committee for Industrial and Municipal Wastes

Member

,

3“38.01

ASTM Committee E -38 on Resource Recovery, Subcommittee

Energy

248
Garvin, D.

Secretary, CODATA Task Group on Chemical Thermodynamic Tables

Member, ASTM Committee E -38 on Resource Recovery

Member, ASTM Committee E-27 Hazard Potential of Chemicals

Kirchoff, W.H.

Immediate Past Chairman, ASTM Committee E-47 on Biological Effects

and Environmental Fate

Member, ASTM Committee E-48 on Biotechnology

Titular member, IUPAC Commission 1.1. on Physicochemical Symbols,

Terminology and Units

Kirklin, D.R.

Member, ASTM Committee E -38 on Resource Recovery, Subcommittee

E-38 . 01 on Energy, Subcommittee E-38 . 02 on Research

Director, U.S. Calorimetry Conference

Neumann, D.

Member, Hewlett-Packard HP-1000 International Users Group

Member, Baltimore-Washington HP-1000 Users Group

Parker, V. B. Consultant, IAEA Committee on Chemical Thermodynamics of Actinide

Elements and Compounds,

Member, Subcommittee IAEA. WG. 01 Actinide Halide Thermodynamics.

Corresponding member, CODATA Task Group on Chemical Thermodynamic

Tables

Member, Chemical Thermodynamimcs Advisory Committee on Aqueous

Solutions Data Base, (Lawrence Berkeley Laboratories, Sidney

Phillips)

Smi th-Ma gowan , D

.

Organizing Committee of the ’International Conference on Thermodynamics of

Aqueous Solutions with Industrial Applications’, Airlie House, May

1987.

,

Member, International Association for the Properties of Steam

Wlodawer, A.

Treasurer, Neutron Special Interest Group of the American Crystallographic

Association

Member, Apparatus and Standards Committee, American Crystallographic

Association

249
10. PROFESSIONAL INTERACTIONS, CONSULTING

AND ADVISORY SERVICES

Abramowitz, S.

Collaborated with I.W. Levin, National Institute of Arthritis and

Metabolic Disease, NIH, on vibrational analysis of small molecules

and some biological species.

Formulated cooperative research program on high temperature

thermodynamics with AFOSR.

Interacted with the following agencies and organizations regarding

the NBS program in Biotechnology: National Aeronautic and Space

Administration (NASA) , National Academy of Science (NAS) , National

Science Foundation (NSF), Office of Technology Assessment (OTA).

Chase, M.

Reviewed and planned for physical property data issued by

Engineering Science Data Unit.

Participated in the development of ASTM Standard on "Calculation of

Hazard Potential Figures of Merit for Thermally Unstable Materials"

prepared by ASTM. Committee E-27 on Hazard Potential for

Chemicals

.

Supplied thermal functions to the Therdynamic Research Center, Texas

A & M University, for inclusion in the TRC Hydrocarbon and

Non-hydrocarbon Tables.

Collaborated with AIP on the design and publication of the JANAF

Tables, 3rd edition.

Prepared tables of thermal functions for the CODATA Thermodynamic

Tables and for CODATA Key Values for Thermodynamics, and

participated in meetings of the CODATA Task Group on Chemical

Thermodynamic Tables.

Interacted to obtain data needed for development of theoretical

concepts used in the JANAF Tables with J.L. Haas, Jr, United States

Geological Survey (USGS) , T. Chart, & A. Dinsdale, NPL, U.K., M.H.

Rand, AERE, Harwell, U.K., L. Brewer, U. CA, Berkley, P.F. Bernath,

AZ State U., and D.O. Harris, U. CA, Santa Barbara, CA.

Reviewed an extensive series of articles on Isomer Group Thermodynamics

(R . A. Alberty , MIT).

Churney, K.L.

Interacted with R. Wingender of the Analytical Chemistry Lab of

Argonne National Laboratory, Argonne, IL on analysis of effluent

fractions from combustion measurements for chlorinated dioxins and

related compounds.

250
Colbert, J.C.

Interacted with ASTM Committee D-05 on Coal and Coke and its

Subcommittee 21.02 on Methods of Analysis. Membership and active

participation with subcommittee members on the evaluation of

calorimetric procedures for determining the calorific value of coal

and coke.

Cooperated in research with B. Coxon of the NBS Organic Analytical

Research Division on bomb calorimetric and NMR studies of D-ribose

and 2-deoxy-D-ribose.

Ditmars, D.

Cooperated with R.A. Robie of the U.S. Geological Survey, Reston,

VA, on preparing a sample of pure calcium and measuring the heat

capacity of the solid phases from MK to the melting point, 1112K.

Interacted with Commission on Standardization of Thermophysical

Preperty Measurements of the European Thermophysical Properties

Union. This Commission is sponsoring and coordinating the assembly

of a two-volume compendium of apparatuses and techniques for the

measurement of thermophysical properties. One chapter has appeared

in press on a survey of high temperature drop calorimetry. Another

chapter on hardware design is in preparation.

Cooperated with C.A. Plint, Physics Department, Brock University,

Ontario, Canada, on measurement of the high-temperature heat capacity

of pure copper.

Cooperated with the investigator on U .S. -Yugoslav cooperative research

project being carried out at NBS (Chemical Thermodynamics Division)

and at Boris Kidric Institute, Belgrade (Institute for Thermal

Engineering and Energy Research).

Provided advisory service to U.S. Naval Weapons Ordinance Center, Crane,

Indiana on calorimetry hardware, techniques for studying low-level

degrading reactions in solid propellants and explosives.

Domalski, E.S.

Cooperated with engineers involved in solid waste disposal, solid

waste processing, and resource recovery from the ASTM Committee E -38

on Resource Recovery and The ASME Research Committee on Industrial

and Municipal Wastes concerning combustion characteristics of waste

materials

.

Participated in the USUK collaboration for Waste Combustion.

Areas of interest are : (1) chlorine content analysis of municipal

solid waste, (2) calorific value data derived from U.S. and U.K. one

kilogram-capacity calorimeters , and (3) combustion studies on threshold conditions for the f ormation/destruction of chlorinated

species

.

Interacted with the U.S. Department of the Army, Chemical Research

and Development (CRDC), Aberdeen Proving Ground, Maryland to carry

out combustion calorimetry and develop estimation methods for organic

phosphorus compounds (CRDC) has continued in FY 1986.

251
Negotiated for the publication of a compilation entitled:

"Thermodynamics Data for Biomass Conversion and Waste Incineration",

prepared at NBS, compiled at the Solar Energy Research Institute, and

funded by DoE, as an ASME document.

Interacted with engineers from Combustion Engineering (J. Orcutt and

D. Borio) during a visit to the large sample flow calorimeter

facility and through discussion of plans for future research on monitoring chlorine during MSW combustion.

Gajewski, E.

Interacted with Anne Plant, Center for Analytical Chemistry,

purification of monoclonal antibodies.

Garvin, D.

Worked with CODATA on the preparation of thermodynamic data bases, jointly

with groups at AERE, Harwell, U.K., (M.H. Rand), LIPCM-ENSEEC

,

Grenoble, France (I. Ansara), Univ. of Sussex, Brighton, UK, (J.B.

Pedley), and TERMOCENTER Akad. Nauk, Moscow, USSR (L.V. Gurvich, V.A.

Medvedev, V. Yungman), and US Geolog. Survey, Reston, VA, USA (J.L.

Haas, Jr.).

Visited British Gas, London Research Station, London, U.K. (A.E.

Humphreys) regarding calorimeter design.

Selected values for properties of components of natural gas:

Thermodynamic Research Center, Texas A & M Univ., College Station,

TX, (K.N. Marsh, R. Wilhoit).

Participated in completion of the handbook for calculation of properties of natural gas for the International Group of Importers of

Liquified Natural Gas (GILGNL) , NBS, Boulder, CO, (D. Mann).

Interacted with international standards (Chemical) community. Observer at

IUPAC General Assembly, Lyons, France, Commission 1.3 [Nomenclature],

1.2 [Thermodynamics], 1.4 [Chemical Kinetics], and II. 3 [High

Temperature Chemistry].

Attended DOE Contractor’s Meeting for Department of Energy on clean

up of coal combustion stack gases, assessment of industry needs.

Goldberg, R.N.

Met with Richard Veech, National Institutes of Health, general

discussions on the thermodynamics of enzyme-catalyzed reactions.

Met with Richard Virdins, University of Newcastle-upon-Tyne, United

Kingdom, to discuss possible work in the penicillinase reaction.

Met with Arthur Carrington, University of Newcastle-upon-Tyne, United

Kingdom, to discuss pH Standards.

Discussed with Yung-Chi Wu, Center of Analytical Chemistry, the

treatment of electrochemical data.

252
Kirchhoff, W.H.

Collaborated with I.W. Levin, et. al. Laboratory of Chemical Physics,

National Institute of Arthritis, Diabetes and Digestive and Kidney

Diseases on thermodynamic properties of lipids.

Worked with J.D. Fine, Surface Science Division, on the statistical

analysis of depth profile data.

Neumann, D.B.

Collaborated with Freeman, Oklahoma State Univ. on the publication of

the Bulletin of Chemical Thermodynamics.

Interacted with A. Maczynski, Institute for Physical Chemistry,

Polish Academy of Sciences, Warsaw, Poland - Protocal for the

international exchange of chemical thermodynamic data - IUPAC

sponsored activity.

Participated in Task Group meetings at Ottawa, July 1986. CODATA

Task Group on Chemical Thermodynamics Tables.

Provided computer programs to Office of Standard Reference Data to

assist in the production of camera ready documents and tables, acted

as consultant for the planning of automation activities at NBS and

DOC.

Consulted witn J.W. Gaazuk, Division 5-4 1 , on graphics for

publication

.

Consulted with D.J. Orser, Division 739, on presentation of topology

of phase diagrams.

Consulted with G. Klopman, Dept of Commerce, on oceanographic data

(Netherlands) to the NBS computer.

Parker, V.B.

Consulted with E. Busenberg and N. Plummer, USGS, Reston, VA

concerning the thermochemistry of BaC03(cr) and the selection of the

"best values" for the enthalpy of formation at zero K; also

concerning Ba

+ ^ (aq. std. state) and values for the enthalpy of

formation at 0 K and the entropy.

Consulted with John Haas, USGS Geological Survey, concerning the

thermochemical behavior of iron oxides.

Discussed with V. Medvedev, Institute for High Temperatures and I. Khodakovsky, Vernadsky Institute for Geochemistry and Analytical

Chemistry, Moscow, the evaluation of the thermochemistry

of key iron compounds.

Held discussions on USA/USSR Science exchange: Exchange of data,

calculational methods and interpretations of data between the Chemical Thermodynamics Data Center and a similar group at the Institute

for High Temperatures, Moscow.

253
Collaborated with members of the CODATA Task Group on the

preparation of Chemical Thermodynamic Tables: Preparation of

thermodynamic data bases, jointly with groups at AERE, Harwell, U.K.,

(M.H. Rand), LIPCM-ENSEEG, Grenoble, France, (I. Ansara), and

TERMOCENTER Akad. Nauk, Moscow, USSR, (L. V.Gurvich, V.A. Medvedev, V. Yungman), and USGS, Reston, VA, USA (J. Haas Jr.)

Held discussions, provided advice and guidance to Phillips,

Lawrence Berkeley Lab. and M. Siegel, Sandia National Lab. on the

need for and the construction of thermodynamic data bases for

modelling in geothermodynamic equilibrium calculation in aqueous

solutions

.

Provided advice and guidance on handling uncertainties in thermodynamic

data to NRC, DOE, and USGS at a panel meeting Dec. 17, 1985 at

NRC Silver Spring, MD.

Collaborated with D.D Wagman, former NBS staff scientist, on chemical

thermodynamic key values and thermodynamic tables.

Schwarz, F.P.

Collaborated with I.W. Levin, Laboratory of Chemical Physics,

National Institute of Arthritis, Diabetes and Digestic and Kidney

Diseases on the thermal properties of lipids.

Collaborated with A. Shrake, Office of Biologies, FDA on the thermal

stability of serum albumen.

Smith-Magowan , D.

Collaborated with R.H. Wood, University of Delaware, on the development of

methods for the correlation and theoretical interpretation of the

thermodynamic properties of aqueous solutions at elevated temperatures

and pressures.

Interacted with S.L. Miller, Univ. of California, San Diego, on the

correlation of equilibria comprising the Krebs (tricarboxylic acid)

cycle and associated metabolic pathways. Joint manuscript is in

preparation.

Interacted with J.O.M. Levelt-Sengers , Thermophysics Div, NEL, NBS; on the

interpretation the properties of aqueous electrolytes near their

critical points.

Interacted with P.T. Thompson, Swarthmore College, on the calculation

of virial coefficients of small organic compounds in aqueous

solution.

Provided advice to Dewey, Reynolds Metals Co., Richmond, Va; on the

vapor pressure and enthalpy of concentrated NaOH solutions at

elevated temperatures.

Provided advice to J. Erwin, SWRI, San Antonio TX, on the electrical

conductivity of aqueous mixtures of CO 2

.

254
Provided advice to R.L. Truitt, Dallas TX, on the formulation of

colloidal suspensions of magnetic materials.

Provided advice to W. Kelly, Nuclear Regulatory Commission, on the

data for aqueous solutions used in codes to predict the stability of

nuclear waste storage deposits.

Tewari, Y.B.

Held discussion with and interacted with Dr. William Gitomer of the

Laboratory of Metobilism at NIH on the equilibrium measurement for

the process: hydrolysis of glucose 6-phosphate.

Weber, I.T.

Held discussions and interacted with Dr. Sancar Adhya, NIH, on the

crystallization and structural studies of coli gal repressor.

Held discussions and interacted with Professor Herman Ammon,

Department of Chemistry, University of Maryland, on structural

studies of glutaminase-asparaginases from several bacterial sources.

Collaborated with Dr. Gary Gilliland, Genex Corporation, Gaithersburg,

MD, on data collection from crystals of catabolite gene activator

protein.

Interacted with Dr. Keith McKenny, NIH, on the crystal structures of

mutants of catabolite gene activator protein.

Interacted with Dr. Alan Peterkofsky, NIH, on the crystal structures

of several mutants of catabolite gene activator protein.

Interacted with Professor Thomas Steitz, Department of Molecular

Biophysics and Biochemistry, Yale University, New Haven CT, on crystallization of rec A protein and on refinement of the structure

of catabolite gene activator protein.

Interacted with Professor Susan Taylor, Department of Chemistry,

University of California, San Diego CA, on the prediction of the

structure of the regulatory subunit of mammalian cAMP-dependant

protein kinase.

Interacted with Dr. Susan Wickner, NIH, on the crystallization of

* O’-protein that is required for transcription in phage X.

Wlodawer, A.

Collaborated with Professor Robert Huber, Max Planck Institute,

Martinsried, West Germany, on the comparison of two crystal forms of

bovine pancreatic trypsin inhibitor.

Collaborated with Professor Lennart Sjolin, Chalmers Polytechnic,

Gothenburg, Sweden, on the structural investigations of ribonuclease

and bovine pancreatic trypsin inhibitor.

Collaborated with Dr. Franz Schmid, University of Regensburg, West

Germany, on crystallographic studies of porcine ribonuclease.

255
Collaborated with Dr. David Moss, University of London, England, on comparisons of independently refined structures of bovine

ribonuclease.

Collaborated with Professor Herman Ammon, University of Maryland, on crystallographic studies of glutaminase-asparaginases from several

bacterial sources.

Collaborated with Dr. Giuseppe Zaccai, Institute Laue-Langevin,

Grenoble, France, and Dr. Martin Gellert, NIH, Bethesda, MD, on the

low-angle neutron scattering studies of gyrase and gyrase-DNA com- plexes .

Collaborated with Dr. Ettore Appella, NIH, Bethesda, MD, on crystallization of DNA fragments.

Collaborated with Dr. Joyce Jentoft, Case Western University, OH, on crystallographic studies of the RNA-binding protein from the phage

PP12.

Collaborated with Dr. Gary Gilliland, Genex Corporation,

Gaithersburg , MD, on crystallographic studies of a sweet protein,

monellin, and on high resolution refinement of ribonuclease.

Collaborated with Dr. Matthew Pincus, Brooklyn Polytechnic, on crystallography of covalent complexes between ribonuclease and

nucleotides.

256
1 1 . VISITING SCIENTISTS

The Thermodynamics Division has been host in the past year to the

following scientists who have worked with NBS scientists on problems of

mutual interest.

Liebman, J.F., University or Maryland-Baltimore County, Baltimore, MD,

completed an evaluation of enthalpies of formation of amino acids,

peptides, heterocyclic and related compounds. He is an expert on techniques in estimating thermodynamimc properties of organic

compounds and on strain energies in organic compounds.

Miller, M., University of Warsaw, Poland, Dr. Miller is working on the

crystallographic structure of proteins and DNA fragments.

Nachmann, J., Weizmann Institute of Science, Rehovot, Israel. Dr. Nachmann

is a protein crystallographer conducting neutron and x-ray

diffraction measurements of macromolecules of biological importance

in the Biomolecular Structure Group of the Division

Nuttall, R., Former NBS employee, is an expert on solution thermodynamics

and evaluation of thermochemical data. Dr. Nuttall participated in

developing the data for electrolyte data bases and catalogs of

measurements of thermochemical data.

Rukkers, K. , graduate student in the Department of Applied Physics, Twente

University of Technology, Enschede, Netherlands, spent three and a half months (Feb-May 1986) providing assistance to the large sample

flow calorimetry group improving the data acquisition and data

handling procedures.

Savage, H. , National Institute of Health, Bethesda, MD. Dr. Savage is

working on neutron diffraction of protein hormones and the structure

of bound water in biological systems.

Schumm, R.H., Former NBS employee, is an expert on the evaluation of

thermochemical data. Mr. Schumm evaluated data on sulfur compounds

relevant to flue gas desulfurization.

Shrake, A., Food and Drug Administration, Washington, D.C. Dr. Shrake is an expert in the area of thermodynamics of phase transitions in proteins

and protein ligand complexes of biological interest.

Thompson, P.T., Swathmore College, Swathmore, PA. Dr. Thompson is an expert on the interaction of organic species with water in terms of

hydrophobicity . He performed both experimental and theoretical

research during his sabbatical at NBS during calendar year 1985.

Wagman, D.D., Former NBS employee, is an expert on the evaluation of

thermodynamic data. Mr. Wagman has prepared the CODATA key values

for thermodynamics.

257
Wasik, S.P., Former NBS employee, is an expert on the evaluations of

solubility data for organic species in aqueous and mixed media. Dr.

Wasik evaluated data on the thermodynamic properties of alkanes in

aqueous media.

Weber, I., University of Maryland, College Park, MD. Dr. Weber is working

on the molecular structure of complex Diomolecules using both x-ray

and neutron diffraction.

Wood, R.H., Chemistry Department, University of Delaware, Newark, DE,

worked with the staff on solution thermodynamics, theory and

experiment; electrolyte theory of weak electrolytes, speciation

calculations, molecular interactions in solution; and the

solubilities of non-electrolytes in aqueous solution as a function

of concentration and temperature.

258
MOLECULAR SPECTROSCOPY DIVISION

A. Weber, Chief

SUMMARY OF ACTIVITIES

Fiscal Year 1986

1 . INTRODUCTION

A. Goal

This Division is a discipline oriented unit and its goal is to be at the

forefront of modern theoretical and experimental spectroscopy in order to:

Advance spectroscopic measurement methods and techniques

Develop models, theoretical concepts and quantum theoretical

methods for predicting molecular properties and interactions

Obtain reliable reference spectroscopic data for NBS, government,

research community and industrial needs

Understand and model fundamental chemical processes

Provide state-of-the-art frequency standards

Transfer forefront spectroscopic expertise to other NBS Divisions,

other government agencies, industry and the research community.

Within the framework of these general goals the Division also follows

three specific thrusts which are part of the overall program of the Center

for Chemical Physics - Properties of Weakly Bonded Systems, Biotechnology,

and Energy Transfer. Properties of weakly bonded systems are obtained for

small atomic and molecular complexes held together by van der Waals and

hydrogen bond forces in order to develop a data base to understand

conformation, thermodynamics, and reactivity of such systems. The objectives

of our thrust in biotechnology are to develop and implement methods for the

study of metal interactions in proteins and nucleic acids using primarily

quantum mechanical techniques, while the major effort of the third thrust is

directed to the study of vibrational energy transfer.

This summary contains a report of the activities of each of the three

groups within the Division during the past year and demonstrates how they are meeting the above objectives.

259
B. Organization

To carry out its work the Molecular Spectroscopy Division is organized

into three working groups: High Resolution Spectroscopy (HRS), Laser

Photochemistry (LPC), and Quantum Chemistry (QC). The permanent Division

staff is augmented by that of postdoctoral fellows and guest scientists.

During the past year we have had fourteen guest scientists and four post

doctoral fellows engaged in Division projects. In addition, two members of

the Surface Science Division participated in the work of the LPC group. A list of the guest scientists, their permanent affiliations, and their

activities is given in Section 10 of this report.

C. Division Programs

To be able to respond to the present and projected needs of NBS, the

Center for Chemical Physics (CCP), and the user community, a significant

fraction of the Division's effort is directed toward achieving and

maintaining the expertise of its staff in their discipline oriented fields,

and into maintaining its experimental facilities at the state-of-the-art

level. We must remain at this level of expertise in spectroscopic

measurements, theory, and interpretation in order to respond quickly to

provide standards, serve national technical needs, and to insure adequate

response to future, unknown problems. This approach is justified by the past

and present applications of experimental and theoretical spectroscopy by our Division. These applications also provide much of the direction and

motivation for our efforts. Remote sensing for industrial and atmospheric

monitoring, laser chemistry, and combustion diagnostics are a few of the many

important high technology areas that depend on modern spectroscopic

techniques

.

As described in Section 2, the work of the HR group involves experimental

and theoretical applications of molecular spectroscopy for character izing gas

phase molecules, primarily in the infrared (rotation-vibrational) and

microwave (rotational) spectral regions, the development of frequency

standards for the infrared, and the development and application of new experimental techniques for high resolution spectroscopy. The emphasis of

these studies is in the applications of our expertise to problems in

structural chemistry, atmospheric chemistry, chemical analysis, radio

astronomy and the properties of weakly bound molecular species.

The environmental problem posed by the pollutants of the earth's

atmosphere, especially the role played by trace constituents in the

chemistry of the upper atmosphere, are of major concern and a portion of the

group's activities is devoted to providing critically needed data to help

solve some of these problems. In this effort our activities are guided by

the needs of the environmental research community, and are conducted with t.he support of NASA and AFGL. These efforts will continue to play an important

role in the work of the HR group during the coming years.

260
Weakly bound molecular complexes, i.e., van der Waals and hydrogen bonded

molecules have received considerable attention in our laboratory during the

past year and will continue to do so in the future. The Division is in a unique position of having available personnel and instrumentation that

permits such studies to be performed using any and all of the facilities from

the microwave to the near infrared region of the spectrum in a concerted

attack on the problems posed by these weakly bound systems. These

experimental efforts are buttressed by the analytical and computational

theoretical expertise available in the Division.

The Division is the home of the NBS Molecular Spectra Data Center. This

Center, supported by the Office of Scientific Reference Data and staffed by

members of the HR group provides evaluated data on molecular rotational

spectra in the microwave region and develops evaluated infrared spectra to be

used as standards in calibrating diode lasers and infrared laser

spectrometers. This work is based on the needs of the user community. Thus

the work on infrared standards is a response to requests from the

instrumentation industry, industrial research laboratories, applied

technological user groups, and government agencies and laboratories.

Improvements in the stability of diode lasers have emphasized the need for

accurate calibration standards. The absorption frequencies of N

2

0 that

involve the lower energy levels are now being tied to the cesium frequency

standard. This work has been made possible through the joining of the unique

facilities of the Time and Frequency Division of NBS/Boulder with our spectroscopic expertise. Other collaborations, with non-U. S. research groups

exist as well in an effort to develop the most extensive and accurate set of

frequency calibration data. A recent activity is the critical evaluation and

tabulation of the vibrational and electronic energy levels of transient

molecules. Section 2. A of the HR group report describes the various

activities of the Data Center.

The LPC group primarily does quantum-state specific studies of molecular

dynamics. A common factor in the research of this group is the role of

energy transfer in the spectroscopy and kinetics of molecules. Three major

activities are pursued: Condensed Phase Energy Transfer, Laser Diagnostics

of Surface Dynamics, and Dynamics of van der Waals Molecules. As described

in Section 3. A in the first of these the direction taken is the study of

vibrational energy transfer. This research was extensively discussed in the

Annual Report for FY85 and the research outlined and proposed there has been

pursued successfully during the past year in the determination of the rates

of energy transfer from vibrationally excited chemical bonds in liquids,

solids, and on molecules bound to surfaces.

In the second major activity the goal is to obtain an understanding of

the energy transfer and chemical dynamics occurring at metal surfaces at a fundamental level. This work is done in close collaboration with staff

members of the Surface Science Division. This collaboration has resulted in

the creation of an experimental facility to perform state-resolved studies of

261
thermally and laser desorbed molecular processes at well characterized

surfaces. Details about this year's accomplishments are presented in Section

3.B.

The capability to perform time resolved spectroscopic measurements at

the picosecond level has been turned to good advantage in the study of

vibrational predissociation of van der Waals molecules. The experiments are performed in the time domain and thereby yield a direct measure of the

lifetimes of the predissociating states. This work is described in Section

3.C of the LPC group report.

The field of Quantum Chemistry continues to experience new developments

which extend the range of reliable and useful calculations to complex

polyatomic systems. The stabilities, conformations, spectroscopy and

reactivity of complex molecules, clusters, ions, radicals, and transition

states, among others, are successfully investigated by the Quantum Chemistry

group. The ability of the QC group to attack large scale computational

problems using ab-initio rather than semi-empirical methods is significantly

enhanced by the dedicated IBM M 38 I superminicomputer located in the Molecular

Structure and Modeling Facility of the Molecular Spectroscopy Division.

A major effort of the QC group described in Section M.A is in the field

of theoretical calculations on biomolecules. The goal of this program is the

theoretical calculation of the energetics, spectroscopy, and reaction

behavior of biomolecules with emphasis on the role of metal interactions in

biomolecules. Ab initio methods are used to the exclusion of semi-empirical

methods to insure predictability. The program is developed on three levels.

At the first and fundamental level is the development of an ab initio

electronic structure, reaction field method and code which will allow quantum

mechanical calculations on systems of the order of 1000 atoms. Molecular and

statistical mechanics is used to provide conformation for quantum models and

to determine the environment for a reaction field approach. At the second

level accurate ab initio calculations of small prototype systems provide data

on a wide range of properties which also contributes to the large theoretical

data base required in the reaction field code. At the third and applied

level, model calculations that relate to specific problems of current

interest are undertaken. The reaction field code development is the major

thrust of this program.

During the last few years the three groups have been engaged in the study

of the properties of van der Waals and hydrogen bonded complexes. This

activity is continued using the experimental and theoretical expertise

represented in each group and the individual group reports give detailed

description of the work done. Only free complexes (i.e., gas phase) are investigated in order to obtain clearly interpretable data on molecules which

are unperturbed by molecular interactions that exist in the condensed phase.

Thus the HR group reports on its studies of the resolved microwave rotation

and infrared rotation-vibration spectra while the LPC focusses its attention

on the dynamics of vibrational pre-dissociation. In many cases the

interpretation of the experimental results is aided by the analytical and

262
computational theoretical studies performed in the HR and QC groups. The

work done by the three groups on weakly bound complexes constitutes therefore

a Division wide effort in which the groups are participating in a mutually

supportive and beneficial manner. The study of weak molecular interactions

as exemplified by the van der Waals and hydrogen bonded molecules is a field

of considerable present and future interest and our Division is expected to

fully participate in these investigations during the coming years (cf. the

Pimentel Report "Opportunities in Chemistry," National Academy Press,

Washington, D.C., 1985, and the more recent Brinkman report on "Physics

Through the 1990s," National Academy Press, 1986).

D. Collaborations

The Division staff conducts its research in collaboration with

postdoctoral associates, members of the Surface Science and Time and Frequency Divisions as well as with many non-NBS visiting scientists. Some of

these use the facilities of the Division and are appointed Guest Scientists

at NBS. Section 10 of this reports lists the names, affiliations, and

activities of the guest scientists who collaborated with us during the past

year. Further collaborations exist with other scientists associated with

universities from the U.S. and abroad whose names are given in the various

project descriptions and appear as co-authors of many of the publications and

talks listed in Sections 5 and 6 of this report.

E. Other Agency Support

Among the several goals of the Division are the services provided to

various agencies of the government and private industry which in turn support

some of the work done in the Division. The various agencies of the

Department of Defense (ONR, ARO, AFGL, AFOSR) , NASA, DOE, as well as the

National Foundation for Cancer Research are among those that sponsored some

of the research done during the past year.

In the remainder of this Annual Report are the individual group reports

(Sections 2, 3, 4), the listings of publications and talks (Section 5, 6),

Division seminars (Section 7), outside professional activities by the staff

(Section 8), professional interactions and consultations by the Division

staff (Section 9), and guest scientists (Section 10).

263
2. HIGH RESOLUTION SPECTROSCOPY GROUP

N. Craig, G. T. Fraser, C. W. Gillies, J. T. Hougen, M. E. Jacox,

W. J. Lafferty, F. J. Lovas, A. G. Maki, W. B. Olson, A. S. Pine,

G . Rotter, R. D. Suenram, G. A. Thompson, A. Weber, and J. Zozom

The work of this group spans a variety of spectroscopic topics many of

which are a part of programmatic efforts . Accordingly the activity

reports are grouped into five separate sections: Calibration and Data

Center Activities, Spectroscopy for Environmental Studies, Spectroscopy of

Hydrogen-bonded and van der Waals Complexes, Matrix Isolation

Spectroscopy, as well as General Spectroscopy and Theory. Each section is

concluded with a brief statement of work planned for the coming year. The

descriptions list the scientists active on the projects. These include

NBS staff, guest scientists, as well as, outside collaborators.

A. Calibration and Data Center Activities

We collect under this heading the work of the group connected most

closely with the core mission of NBS, namely the production and

dissemination of compilations of accurately measured frequencies or wavenumbers for use as secondary standards, and of critically evaluated

molecular constants for use in other disciplines. Occasionally, spectral

fitting programs, for use in reducing data in other laboratories are also

proceeded. The group devotes a significant portion of its effort each

year to this program, and frequently collaborates with workers in other

laboratories. Outputs of the program serve needs spanning the microwave

to the ultraviolet spectral regions.

1 . N

2 o Frequency Measurements Extending Calibration Data into the

2800 cm" 1 Region

(A. G. Maki, J. S. Wells, and A. Hinz)

In a continuation of our collaborative work with Joe Wells (NBS,

Boulder) we have this year measured the frequency of several important hot

band transitions in the 1257 to 1335 cm” 1 region. These data were used to

provide a finer comb of calibration features in this region, but their

most important contribution has been to tie more energy levels of N

2 0 to

the cesium frequency standard. From these accurate energy level

determinations, it is possible to obtain accurate transition frequencies

outside the area of direct measurement. In particular, these new frequency measurements allow us to extend our calibration tables to the

2800 cm

- region, which was the primary goal of this year's work.

This work has also given us the opportunity to compare

our frequency measurements with frequencies derived from wavelength

measurements coming from various other laborator ies . It appears that the

264
recent work reported by Toth (JPL) using the Brault interferometer at Kitt

Peak gives wavenumber values that are consistently close to those we measure. Toth’s accuracy seems to be largely due to the calibration

procedure he has been using based on frequency measurements of several

bands

.

Some of the hot band measurements that were made this past year will

assume greater importance next year if we are able to measure some of the

other transitions that are on our agenda. These measurements will provide

frequency values for new energy levels and this will lead to new

calibration bands in the 2300 to 3000 cm

- "

1 region. This work is supported

by NASA.

2. OCS Heterodyne Measurements for Calibration from 1866 to 1920 cm

-1

(A. G. Maki, J. Wells, and A. Hinz)

Another advance in the development of OCS absorption lines as convenient frequency standards was made by the heterodyne measurement of a number of transition frequencies in the 1866 to 1915 cm

- *

1 region. These

measurements have allowed us to prepare an improved calibration table for

this region and also provide a good measure of the energy levels for the

1 2 °0 state from which other transition frequencies can be calculated.

This work is supported by NASA.

3. Recommended Rest Frequency List

(F. J. Lovas and G. Rotter)

The first revision of the paper originally entitled ’’Recommended

Rest Frequencies for Observed Interstellar Molecular Microwave Transitions

- 1984 Revision" was published in the January 1986 issue of J. Phys. Chem.

Ref. Data. While the manuscript was in the publication process, we continued to update the spectral entries through 1985 so the title was modified to 1985 Revision" to reflect the content more accurately.

The next revision of this paper is planned for 1988, so the

literature search of radio astronomy papers and data evaluation of new

microwave studies of these species will continue. Last year preprints

were widely distributed and very favorable responses were received. Since

the manuscript was published in January, several requests for magnetic

tape copies have been received and very recently Professor K. R. Lang of

Tufts University requested permission to reproduce the frequency list in a forthcoming book Astrophysical Formulae .

4. Microwave Spectral Tables

(F. J. Lovas, G. Rotter, and R. S. Suenram)

The general search for all papers dealing with microwave spectral

data continues. Reprints or photocopies of all pertinent reports are obtained and filed according to empirical formula. These files are the

source of data for spectral evaluation reported in the various publication

series which the data center produces.

265
Work continues on the Part III of the Microwave Spectral Table

series. This involves the spectra of simple hydrocarbon species C

xhv

. During the current year we have been carrying out evaluations on species

exhibiting internal rotation from methyl groups. This project is slated

for completion in September 1986 and appears to be on schedule. This is

part of the long range plan to develop a microwave spectral atlas, so care

is taken to keep all the coding compatible with previous compilations in

this series.

We continue to up-date our computer files on diatomic and triatomic

species. Since the publication of Part I. Diatomic Molecules, 21 new

species have been added and the spectra for 3^ species have been augmented.

Similarly for Part II. Triatomic Molecules, spectra for 15 new species

have been added and the data on 30 other species have been updated.

5c Update of Landolt -Bernstein Structural Tables of Free Polyatomic

Molecules

(J. H. Callomon, E. Hirota, K. Kuchitsu, and W. J. Lafferty)

A project to update the Landolt-BOrnstein compilation,

"Structure Data of Free Polyatomic Molecules," has just been completed.

This effort includes all structural data of gas phase molecules reported

in the literature since the last volume was published in 1976 up to the

end of 1985. It includes structures obtained by microwave, infrared, Raman,

and visible spectroscopy as well as electron diffraction techniques. About

1500 new or improved structures are included in this work which has been a collaboration between workers in England, Japan, and the United States.

The new volume is expected to be in press in early 1987.

6. Vibrational and Electronic Energy Levels of Transient Molecules

(M. E. Jacox)

All of the data previously compiled on the ground-state

vibrational energy levels of polyatomic transient molecules have been

transferred to a new IBM PC-AT computer system. This system not only is

much more efficient, but also will facilitate possible future development

of a version of the tables amenable to digital search. The tables of

ground-state vibrational energy levels have been kept current; new or revised tables have resulted for approximately 75 molecules per year.

Matrix effects on the electronic spectra of diatomic molecules

have been surveyed in a paper entitled, "Comparison of the Electronic

Energy Levels of Diatomic Molecules in the Gas Phase and in Inert Solid

Matrices," to be published in a forthcoming issue of Journal of Molecular

Structure honoring Professor George C. Pimentel. Electronic band origins

and vibrational band spacings in excited electronic states have been

compared for the approximately 230 electronic transitions of diatomic

molecules which have been observed both in the gas phase and in rare-gas

or nitrogen matrices. With few exceptions, valence transitions and the

266
associated vibrational band spacings are shifted by less than about 1? in

neon matrices. Somewhat larger shifts, often to longer wavelengths,

result from isolation of the molecule in a heavier rare gas or a nitrogen

matrix. The perturbation of Rydberg transitions by the matrix, the

effects of charge-transfer interaction with the heavier rare-gas matrices,

and the behavior of the potential curve of the matrix-isolated molecule in

the vicinity of the dissociation continuum are discussed.

With partial support from the NBS Office of Standard Reference

Data, experimental data are being critically evaluated and compiled for

the electronic energy levels of transient molecules possessing from 3 to

6 atoms. Both gas-phase and inert matrix data will be included. A wide

variety of observation techniques, including high resolution absorption

spectroscopy, laser-excited fluorescence, multiphoton ionization, and

photoelectron spectroscopy, are being surveyed. Energies of band origins,

fundamental vibration frequencies, rotational constants (A, B, C), and

radiative lifetimes are among the properties now being entered. When

complete, the tables will include well over 150 molecules.

7. Future Plans

Further work in our frequency standards effort is to

systematically develop the N

2

o spectrum and energy levels for use as frequency calibration bench marks by heterodyne frequency measurements of

the 10°0-02°0 transitions near 1060 cm

-1 and the 10^0-01 '0 transitions

near 1635 cm

-1

. When combined with other frequency measurements made

earlier in this program, these new measurements will provide the first

frequency data on the 02°0-00°0 transitions near 1168 cm

-1 and thereby

will provide improved data for the 10°0 and 01 °0 levels of N

2 0.

Evaluation of microwave spectra data will continue to focus on the

two major projects in progress. The radio astronomy literature is

continually searched for new observations to be included in the next

revision of the Recommended Rest Frequency compilation. When the current

work on the Microwave Spectral Tables - Part III on simple

hydrocarbons is finished, we will begin evaluation of the next group,

hydrocarbons containing oxygen.

The compilation of the electronic spectral data tables is nearing

completion. It is planned to submit these tables to the Journal of

Physical and Chemical Reference Data late in FY87.

Revisions and additions to the tables of ground-state vibrational

energy levels will continue to be kept current. It is also planned to

submit a supplement to these tables to the Journal of Physical and

Chemical Reference Data late in FY87. This supplement will include a master index, in order to facilitate a complete search of the experimental

literature on the vibrational and electronic spectra of polyatomic

transient molecules.

267
B. Spectroscopy for Environmental Studies

Many small molecules play a significant role in the chemistry of the

earth's atmosphere. As such, they are of significant interest to agencies

like NASA, DOD and the CMA (Chemical Manufacturer's Association). The

interest of these agencies generally focusses on molecular spectroscopy

as a remote sensing tool and for the determination of concentration

profiles. Consequently, the emphasis in this section is on band analyses „ as well as the important information on line intensities, line widths,

line shapes, and the effect of pressure on these quantities. As in all

branches of spectroscopy, the very narrow band width of infrared laser

sources now permits quite reliable studies of phenomena involved in

spectroscopic concentration determinations.

1 . N

2

- and Air-Broadening in the Fundamental Bands of HF and HC1

(A. S. Pine)

N

2 - and air-broadened lineshapes of HF and HC1 transitions in the

v=1«-0 bands have been measured at T=295 and 202 K with a high-resolution

difference-frequency laser spectrometer. Pressure broadening and shifts

and collisional narrowing parameters have been extracted by least squares

fitting of several collisional profiles to the spectra. Figure 2.1 shows

the observed lineshape of the R(0) line of HF as a function of N

2 pressure

fit to Voigt and Galatry (soft collision model) profiles. At low

pressures, the collisional, or Dicke, narrowing effect causes deviations

from the Voigt profile having a Doppler-fixed Gaussian component and

yields a measure of the diffusion constants for the hydrogen halides in

the buffer gases. The pressure broadening parameters, r, were effectively

linear with pressure for the Galatry collisional narrowing model as they

should be, whereas the Voigt fits were highly nonlinear as shown by the

ratios of r for the two models in Fig. 2.1. At high J, where the pressure

shifts are comparable to or larger than the broadenings, a slight

asymmetry is observed in the lineshapes which is attributed to statistical

correlation between velocity- and state-changing collisions. Fig. 2.2

indicates this asymmetry for the P(9) line of HF at P(N 2

) ~ 5^ Torr fit

to the formally symmetric Voigt, soft and hard collisional narrowing

profiles

.

The ratio of air-to-N

2 broadening varies systematically with

rotational levels and is always somewhat larger than that given by the

relative quadrupolar contributions of 0

2 and N2

. The temperature

variations in the broadening coefficients are also J dependent, deviating

significantly from T

_1// ^ and exhibiting opposite behavior for HF and HC1.

These effects are summarized in Fig. 2.3 as a function of the rotational

index m. This work is supported by NASA.

268
INTENSITY

(ABSORBANCE)

INTENSITY

(ABSORBANCE)

Fig. 2.1 Lineshape of HF as a function of N

2 pressure fit to Voigt and

soft collision models.

269
0S1 o

270

The P(9)

line

of

HF

shown

fit

to

the

Voigt,

hard,

and

soft

colllslonal

narrowing

models.
Broadening Coefficient Ratios

Fig. 2.3 Ratio of the air-to-N

2 broadening of HF and HC1 as a function of

temperature and rotational index, M.

2. Measurements of Collisional Interference in Nitrous Oxide

(A. S. Pine)

We have been making a number of collsional lineshape studies in

support of a NASA program to monitor the upper atmosphere for trace

contaminants using sensitive infrared techniques. One of the major

uncertainties is how to interpret the observed profile of a dense

unresolved spectrum, such as occur for the strong, characteristic Q-branch

and band-head features used for monitoring various species. When spectral

lines overlap due to collisional broadening, the resulting envelope may

not be the simple addition of individual component lineshapes if the

collisions actually transfer excitation between energy levels involved in

the unresolved transitions. This nonadditivity is a collisional

interference effect, akin to motional narrowing, variously known as line

coupling, line mixing or rotational collapse, and is well known for

densities approaching the condensed phase. However, in the range of

pressures below lO^Pa, pertinent to atmospheric and stratospheric

conditions, the deviations from additivity are typically small and subtle

271
and require exceptionally high resolution, good signal-to-noise ratio and

wide linear dynamic range as well as precise scanning control in order to

be reliably measured.

Collisional interference at subatmospheric pressures has been observed

recently using high resolution coherent Raman gain techniques for the Q

branches of N

2 , CO and NO and in the infrared for Q branches of CO2 using

diode lasers and Fourier transform interferometers. In the present work

we have performed measurements on N

2

Q with a precision tunable

difference-frequency laser system. Preliminary transmission spectra of

the Q branch of the v-j + combination band of N2 O as a function of

pressure are shown in Fig. 2.4 illustrating the high quality of the data.

0 0 —»

' i

«

1 — —•

F » —

i —-*—r—• *—- 1— *— t — 1 r—

'

2799.00 2790.50 2798.00 2797.50 2797 00 2796.50 2796 00 2795.50 Wavenumber/cm - l

Fig. 2.4 Transmission spectra of the Q branch of the v

1 + V2 combination

band of NpO as a function of pressure.

The wavenumber scale is linear and reproducible to £ 5 x 1 0 ^ cm

1 using

digital scanning servo control; the signal-to-noise ratio and the linear

dynamic range are £ 1000:1 using real-time division of the transmitted

light by the incident light. The 0$ transmission baseline is stable to

within Q.1? and the 100? transmission baseline is reproducible to within

1$. This latter baseline uncertainty is the principal source of error in

these measurements, particularly for the higher pressure traces where the

troughs between the lines exhibit strong absorption and there is no clue

as to the position of the baseline over an extended spectral range. The

baseline is then determined from a sequential empty cell trace. However,

272
trace-to-trace variations in the relative sample and reference beam

channels arise predominantly due to drifts in the interference fringes of

the two detectors windows and filters (the sample cell windows are mounted

at Brewster’s angle to minimize reflections) and to beam wander from

pressure-induced displacements and from thermals drifts of the

phasematching oven for the LiNbO^ nonlinear optical mixing crystal. The

phasematching fluctuations are peculiar to the difference-frequency laser,

but the other problems are common to any high-resolution transmission

measurements. We are now developing a digitally-tuned F-center laser

system with enough power to do direct optoacoustic absorption (rather than

transmission) spectroscopy in order to improve the baseline

reproducibility for collisional interference and for wing measurement.

This work is supported by NASA.

3. Heterodyne Frequency Measurements for Nitric Oxide (NO)

(A. G. Maki, J. S. Wells, and A. Hinz)

For certain measurement applications, especially those involving

laser techniques, it is often important to know quite accurately the

frequencies of the absorption lines of NO. By using heterodyne frequency

counting techniques we have measured 28 transitions of NO from 1750 to

1930 cm

-1

. With the help of other measurements in the literature,

especially microwave and radio frequency measurements, we have determined

an improved set of constants to describe the infrared spectrum of NO.

With these constants, very accurate tables of energy levels and transition

frequencies have been prepared for NO. This work is supported by NASA.

4. New Measurements and Analysis for Nitric Acid (HNO,)

(A. G. Maki, A. Fayt, J. Wells, Wm. B. Olson, and A. Goldman)

Over the past several years we have been involved in the

measurement and analysis of the spectrum of nitric acid with the goal of

producing an atlas or compilation of transition frequencies and

intensities. Such a compilation is very useful for the analysis of remote

sensing data being accumulated in various programs run by NASA and other

agencies. As an example, Dr. Linda Brown (JPL) has taken our latest

line-list for the v

2 band of HNO

3 (near 1723 cm

-1

) and added it to the

data bank she has accumulated to help her in the analysis of ATMOS data.

She was very pleased with the accuracy and completeness of our data. Dr.

A. Goldmann (University of Denver) has also been very anxious to use our data on nitric acid and from time to time requests an updated copy of our latest data.

This past year new diode measurements were completed on the high

rotational transitions of the vr band of HNO

3

. These measurements, when

combined with microwave and earlier infrared measurements from this

laboratory, provided a more accurate set of ro-vibrational constants for

the v

2 band that enabled us to calculate an improved line-list. This

improved line-list, consisting of about 12,000 entries, has been

273
circulated to various interested parties and will be included in the next

version of the AFGL-trace gases tape, which is the major data source for

most atmospheric workers.

The analysis of the highly perturbed v

5 and 2v9 bands has been

sucessfully accomplished by using a new computer program which fits data

for two asymmetric rotor bands that are coupled through Fermi resonance

and certain other resonances* This analysis allows us to fit even the

most highly perturbed transitions with an overall standard deviation of

0.0007 cm

" 1 which is the accuracy expected since a number of transitions

used in the fit are known to be overlapped even though a diode laser with

nearly Doppler limited resolution was used for the measurements. Fig. 2.5

shows a particularly clean portion of the P-branch region of vc in which the

transitions are identified. In this figure it is easy to see now the

perturbation shifts the K

a < 13 transitions to high frequencies while it

shifts the K

a > 1

3

transitions to low frequency.

hno3 v*

869 4 869 6 869 6 WAVENUMBERS (cm- 1 )

Fig. 2.5 Region of the P-branch in the band of nitric acid.

Because of a high degree of correlation between some constants, this

work will not be complete until a few more carefully chosen transitions

are measured to try to reduce the correlation as much as possible. Then

it will be necessary to test a new computer program which has been written

to prepare an atlas of line positions and intensities for these two bands.

We can anticipate that a complete line-list will be ready for the 850 - 930 cm

”

1 region of HNO^ within the next year. An important part of this

work will be the determination of the relative signs and magnitudes of the

transition moments for and 2vg. This work is supported by NASA.

274
5. Rotational Intensity Dependence Measured for CIO

(A. G. Maki, J. B. Burkholder, P. D. Hammer, C. J. Howard,

G. Thompson, and C. Chackerian)

New frequency and relative intensity data on CIO have been

determined using some diode laser measurements from this laboratory and some FTS measurements from the NOAA-Environmental Research Laboratory in

Boulder, CO. Last year we described the reasons for this work, namely the

need to verify the line positions and intensities in a search for the

reason for discrepancies between infrared and microwave measurements of

atmospheric CIO. After the work was begun here, it was learned that NOAA

was making similar measurements and we joined forces.

One of the goals of this work was to measure the rotational

dependence of the intensities of the fundamental infrared band of CIO.

The rotational dependence is related to the ratio of the dipole moment of

CIO to the vibrational transition moment. Since the transition moment

seems to be small and the dipole moment is known to be fairly large, it was expected that the rotational dependence would be significant and

could, in fact, be used to determine the transition moment. Our

measurements did not require a knowledge of the concentration of CIO

whereas all previous techniques had involved a measurement of the

concentration of CIO in the absorption cell; a difficult and controversial

measurement.

This work is now completed and a manuscript has been prepared but

the results can be summarized as follows:

o The CIO line frequencies are now known with greater accuracy,

especially for the P-branch lines. While the new line positions are different

from the old by as much as 20 MHz, the difference is not enough to

reconcile the problems with the field measurements.

o The rotational dependence of the line intensities is now known,

but it only affects the derived concentration of CIO by 10 to 1 5% whereas

the discrepancy is larger than that.

o From the rotational dependence, the transition moment has been

derived and it agrees with the previous value of 11.8 cm" 2 atm -1

, although

the present results are not as accurate as we had hoped for.

o By several arguments, including a determination of the

temperature from intensity measurements, it has been shown that the

laboratory measurements involve CIO that is in thermodynamic equilibrium

at room temperature.

o It has been shown that both the infrared and microwave field

measurements involve CIO transitions that originate from the same vibronic

state which is the lowest vibronic state.

275
The net results of this work is that we are unable to explain the

problems with the field measurements, but the problems do not come from

the laboratory data. This work is supported by NASA.

6. Analysis of the Spectrum of H

2

0 2 (W. B. Olson, Re H. Hunt, A. G. Maki, and J. W. Brault)

Rotational constants of the CG and 1G torsional states and the

matrix element coupling these states have been determined by fitting to a model of two coupled asymmetric rotors. The fitted data were primarily

combination differences. Those for the OG torsional state were formed

from published values of submillimeter wave transitions for low values of

K

a , and those for high Ka (up to Ka = 10) were obtained from assigned

transitions in the vc OH stretching band. There are as yet no assigned

submillimeter transitions involving the 1G torsional state, and all of the

combination differences for this torsional state were obtained from the

assigned transitions in the torsional hotband + v^CIU) - (1G).

Combination differences alone do not supply enough information to

determine all the relevant parameters, i.e., they do not give direct

information on the energy difference between the origins of the OG and 1G

torsional states. The rotational-torsional energies of the OG state for

K

a

= 8 are only about 3 cm

-1 above those for Ka

«= 6 in the 1G torsional

state at low J, but because of the perturbation the levels of the two

states are pushed apart, the separation increasing with increasing J to

about 7 cm~‘ at J = 25. Mixing of the wavef unctions of the OG, K

a

- 8

levels with those of 1G, K

a

= 6 through the perturbation leads to

perturbation enhanced transitions from 1G, K

a

* 6 to the state with K a * 7. Although these could be considered normally allowed transitions of a difference band, no transitions can be observed at J values lower than 15.

It is only at this and higher values of J (to 25) that the wavefunction

mixing is sufficiently large so as to provide sufficient intensity that

the transitions may be observed. Differences between the normal

transitions from OG, K

a

= 8 to Ka

= 7 in and the perturbation enhanced

transitions from 1 G, Ka

= 6 to the same upper state levels provides direct

information on the separation of the lower torsional state origins.

We obtained valuable supplementary information by assignment of

the weak spectrum of the sum band from the OG state to vjj(IU).

Direct differences between levels of the OG and 1G torsional states were obtained by differences of transitions with the same J and K

a in the OG

and 1G torsional states to the same upper state level in the vr + ( 1 U

)

vibrational-torsional state. Final constants are not yet available, but

the fit is quite satisfactory at the present stage of refinement. The

origin of the 1G torsional state is 25^.550 cm

-1

, about 0.35 cm

1 above

the value obtained from the medium resolution far infrared spectrum. Our

experimental value for the matrix element for the interaction of the OG

and 1G torsional states proves to be only 1 5% higher than the value

calculated by Hunt, Leacock, Peters, and Hecht [J. Chem. Phys. £2. 19"’

276
(1965)]. Considering the complexity of their model and uncertainties in

parameters required for input for their calculations, the agreement with

our experimental value may be considered excellent.

7. Future Plans

In the coming year an atlas of absorption line frequencies and

intensities will be completed for the vc and 2\>q bands of HNO3 near 880

cm

-1

. This atlas will include all the transitions to these two states

from the ground state including those transitions that are strongly

perturbed by the effects of the Fermi resonance between these two states.

We also expect to complete a paper describing the analysis of the spectrum

of the and 2V9 bands and also to complete a paper on the analysis of the V3

and v]| bands near 1300 cm

-1

. This work is needed by various laboratories

that are studying the concentration of nitric acid and nitrogen oxides in

the atmosphere in connection with the ozone problem as well as the

greenhouse effect.

By using a long path cell we should also like to make some heterodyne measurements on some of the weaker bands of OCS such as I^O-OO&O (1372 cm

-1

) 03^ - 00°0 (1573 cm" 1 ) and 00°1-02°0 (1015 cm

-1

).

These measurements would locate more energy levels with respect to the

ground state and would give us frequency data for the 520 cm" 1 and 2100

cm" 1 regions, as well as other regions.

We also expect to have new Fourier transform spectra of the lowest

frequency fundamental band of S0

2 near 500 cm

-1

. Both frequency and

relative intensity measurements will be made on this band and the goal

will be to produce a set of band constants that will enable us and others

to accurately calculate the infrared spectrum of S0 2 in the 400-600 cm” 1 region for any temperature appropriate to an atmospheric path.

Understanding atmospheric S0 2 , is, of course, important for understanding

the acid rain problem.

C. Spectroscopy of Hydrogen-bonded and van der Waals Complexes

The program of study of hydrogen-bonded and van der Waals complexes

initiated several years ago now represents a significant fraction of the

group's total effort. Continuning studies using a difference frequency

laser spectrometer in the 3 micron region, the BOMEM Fourier transform

spectrometer in both the mid- and far- infrared, and studies using the

pulsed beam Fourier transform microwave spectrometer are reported. The

major efforts this year deal with structural determinations of weakly

bound dimers from microwave spectra and potentials derived from extensive

infrared spectra. This program has benefitted greatly this past year from

collaborations with guest workers. We certainly plan to continue work in

this direction for the forseeable future.

277
1 . Rotational Spectrum and Structure of CF^H-NH^

(G. T. Fraser, F. J. Lovas, R. D. Suenram, D. D. Nelson, Jr.,

and W. Klemperer)

The rotational spectrum of CF^H-NHj has been obtained using a pulsed nozzle Fourier transform microwave spectrometer . A symmetric top

spectrum is observed that is consistent with free internal rotation of the

NHj subunit against the CF 3H subunit. Rotational transitions have been

measured for both the ground and first excited internal rotor state of the

complex. The spectroscopic constants which have been obtained include: B

Q - 1996.903(2) MHz, Dj = 3.46(12) kHz, and eQ

q

N * - 3-186(8) MHz. From the

quadrupole coupling constant of the nitrogen nucleus , eQ

q

N

, the bending

amplitude of the NHo unit is determined to be 22.57(10)°. The hydrogen

bond length is 2.314(5) A and the weak bond stretching force constant is

0.066(2) mdyn/A. The bond length and stretching force constant for

CFgH-NHo are similar in value to those determined for HCCH-NH 3 (2.33 A and

0.070 mdyn/A, respectively).

2. Rotational Spectrum of the Hydrogen-bonded Formami de-water Dimer

(H. D. Suenram, F. J. Lovas, G. T. Fraser, J. Zozom, and C. W.

Gillies

)

The characterization of hydrogen bonding between peptides and water

molecules is one of the most challenging problems in modern science. The

fundamental peptide-water hydrogen bonding may be exemplified by the

prototypical formami de-water species. To date most of the information

available on these systems has been provided by ab Initio calculations.

Now for the first time the complex of these two species has been

investigated experimentally by employing a pulsed molecular beam

Fabry-Perot microwave spectrometer with a heated pulsed nozzle.

Based on the ab initio calculations of Jasien and Stevens, [J.

Chem. Rhys. 84 , 3271 (1986)], we have investigated the rotational spectrum

of the lower energy form of the formamide-water complex. A planar cyclic

double hydrogen bonded structure was calculated to be the lowest energy

form, and the observed spectrum is in excellent agreement with this

conclusion. The rotational constants obtained are listed in Table 2.1.

Comparison of the 1 nuclear electronic quadrupole coupling constants

between the complex and formamide indicates that the complex is slightly

non-planar with an angle of 16.8° between the planes of the subunits. The

structure of the complex is illustrated in Fig. 2.6.

278
H

Table 2.1 Molecular constants determined from the microwave spectra of

NH 2 CH0-**H2

0 and NH 2 CH0 • • -H0CH

3

Parameter NH2 CH0***H2

0

Value (MHz)

NH 2 CH0* • «H0CH3

Value (MHz)

A 1 1 227. 91 3(3*0 10186.69(15)

B 4586.997(2) 2088.86(8)

C 3258.872(3) 1764.18(6)

eQ<

>aa

1 .330(5) 1 .287(7)

eQ%b 2.038(5) 2.026(6)

e

«<lco -3-3685(5) -3.313(6)

4 t-vw -0.1095 uA

2 -5.05 yA 2

279
3. Microwave Spectrum and Properties of the Methanol-Formamide Dimer

(F. J. Lovas, R. D. Suenram, G. T. Fraser, J. Zozom, and C. W.

Gillies

)

Recent ah initio calculations on formamide-water and

formamide-methancl performed by Jasien and Stevens of the Quantum

Chemistry Group [J. Chem. Phys. 8£, 3271 (1986)3 indicated that the most

stable form of each is a double hydrogen bonded planar ring structure.

The results of the formamide-water study discussed above are quite

consistent with the theoretical structure, although evidence for slight

non-planarity is given.

Since the methanol complex is expected to have a structure similar

to that of the water complex, we have examined formami de-methanol. The

spectra were obtained in a pulsed beam Fabry-Perot microwave spectrometer

with a heated nozzle containing liquid formamide. Rotational assignments

'were considerably aided by the unique hyperfine structure. The rotational

analysis provided the rotational and hyperfine constants shown in Table

2.1. The rotational constants are consistent with the ring structure, but

the out-of-plane moment and hyperfine constants indicate that the complex

is non-planar (disregarding the methyl group).

With the monomer geometries fixed, a rotation of 15° about the HO

axis (moving the CH^ group out of the plane of the remaining atoms)

provides good agreement with the observed moments of inertia. The

structure of the complex is shown in two views Figs. 2.7. The internal

rotation of the methyl group has also been observed. Analysis of the A-E

splittings provides a barrier to internal rotation of 231 cm

-1

, which is

about 38% lower than in free methanol.

Fig. 2.7 Structure of the formamide-methanol dimer (a) top view (b) side

\ lew

.

280
4. Microwave Spectra and Structures of the van der Waals Complexes

Ar-Formamide and Ar-Methanol

(C. W. Gillies, J. Zozom, G. T. Fraser, R. D. Suenram, and F. J.

Lovas)

During the course of characterizing the formam id e-water and

formamide-methanol complexes, we detected the spectra of two additional

complexes. One of these showed 1 nuclear quadrupole hyperfine structure

while the second exhibited no splittings. By using Ne as the carrier gas

in place of Ar in the pulsed beam expansion, it was clear that each

species contained Ar.

Assignment of the hyperfine structure on the first species

provided a unique rotational state assignment for the Ar-formamide

complex. Spectral fitting provides the distortion free rotational

constants A = 10725.32 MHz, B * 1771.58 MHz and C = 1549.53 MHz. These

constants indicate a non-planar structure ,as shown in Fig. 2.8 with the Ar

at 45° to the formamide plane.

Based on chemical evidence we identify the second species as Ar-methanol and have assigned the J = 3 ~ 2 and J = 4 - 3 a-type R-branch

transitions. The rotational constants are consistent with a T- shape

structure as illustrated in Fig. 2.9. A number of strong unassigned lines

remain which we believe is evidence for near free internal rotation of the

methanol subunit.

Fig. 2.8 Structure of the Argon formamide complex.

281
Fig. 2.9 Structure of the Argon-methanol complex.

5. Nearly Free Internal Rotation in Ar-CH^Cl Determined from its

Microwave Spectrum

(G. T. Fraser, R. D. Suenram, and F. J. Lovas)

observed, at H kHz resolution, using a pulsed nozzle Fourier transform

microwave spectrometer. The observed spectra are consistent with a T-shaped complex in which the methyl group is undergoing nearly free

internal rotation. Analysis of the ground (A-state) internal rotor state

spectrum for Ar-CH^Cl using an asymmetrical top Hamiltonian produces the

spectroscopic constants listed in Table 2.2 for both the 35^ ancj 37 q^

isotopic forms. A combined analysis of the ground and excited internal

barrier to internal rotation. The Coriolis interactions in the E-state

also allow the determination of |eQqab | for Ar-CH-^Cl as 13-0(3) MHz.

The symmetry axis of the CH^Cl subunit is nearly perpendicular (-82°) to

the line joining the centers of mass of the two binding partners. The

isotopic data indicate that the Cl end of the methyl chloride is tilted

toward the argon. The distance between the centers of mass of the two

subunits is 3-7825 A for Ar-CH^ ^C1 and 3-7839 A for Ar-CH^ 37 qi implying

an Ar-Cl distance of 3-750 A. Centrifugal distortion analysis yields a weak bond stretching force constant of 0.0157 mdyn/A and stretching

frequency of 3^-6 cm

-1 for Ar-CH^ 35 ci.

Rotational spectra of Ar-CH^ci, for both Cl isotopes, have been

rotor states (E-state) places an upper bound of 20 cm" 1 on the three fold

3.7826 A

97.5 C

o

Fig. 2.10 Structure of the Argon-methylchloride complex.

282
Table 2.2 Asymmetric rotor constants (in MHz) for the A internal rotor

states of ArCH^^ci and ArCH^^Cl.

ArCH

3

35 cl ArCH

3

37ci

A 1 3633 * 020( 1 4) a 13436. 8700(56) a

B 1593.5683(79) 1565.075(12)

C 1420.4572(52) 1395.6126(36)

0.01216(14) 0.01280(41 ) *JK 0.1 381 (48) 0.1392(13)

0.00096(17) 0.00150(15)

h jjk -0.00058(25) • • •

eQ<w 34.895(30) 27.432(27)

' eQ %b -72.185(25) -56.799(19)

eQq00 37.290(35) 29.367(25)

a. Experimental uncertainties are reported as two standard deviations

from the least squares fits.

6. The Microwave Spectrum of the K=0 States of Ar-NH^

(D. D. Nelson, Jr., G. T. Fraser, K. I. Peterson, K. Zhao,

W. Klemperer, F. J. Lovas , and R. D. Suenram)

The microwave spectrum of Ar-NH^ has been obtained using molecular

beam electric resonance spectroscopy ana pulsed nozzle Fourier transform

microwave spectroscopy. The spectrum is complicated by nonrigidity and

most of the transitions are not yet assigned. A AJ=0, K=0 progression is

assigned, however, and from it the following spectroscopic constants are obtained for Ar-^NH^ (B + C)/2 = 2876.849(2) MHz, Dt = 0.0887(2) MHz,

eqQaa

= 0.350(8) MHz, and y a

= 0.2803(3) D. For Ar- 1 *NH

3 we obtain:

B + C)/2 = 2768.701(1) MHz, and Dj = 0.0822(1) MHz. The distance between

the Ar atom and the 1 it NH

3

center of mass, , is calculated in the free

internal rotor limit and obtained as 3*8358 A. The weak bond stretching

force constant is 0.00840(2) mdyn/A which corresponds to a weak bond

stretching frequency of 34.6(1) cm

-1

. The NH^ orientation in the complex

is determined primarily on the basis of the measured dipole moment

projection and the quadrupole coupling constant. It is concluded that the

Ar-NH^ intermolecular potential is nearly isotropic and that the NH

3 subunit undergoes practically free internal rotation in each of its

angular degrees of freedom. Spectroscopic evidence has been obtained

which indicates that the NH^ subunit also inverts within the complex.

These conclusions concerning the internal dynamics in the Ar-NH^ complex

283
Si =8=

(Fraser et al. t J. Chem. Phys. _8 £, 2535

7 # van der Waals Potentials from the Infrared Spectra of Rare Gas HF

Complexes

(G. T. Fraser and A. S. Pine)

The rare gas-hydrogen halide (Rg-HX) van der Waals complexes

Last vear we reported high-resolution tunable infrarea laser

the rare gas-HCl species including the °^®r vations

within a predissociation, manifest as a s a

p nbrational motion from the

band, and of the large-amplitude bending or “^“^“““tsent work we anomalously strong bend-stretch combination band.

g Jsing a difference-frequency

1* laser toVecord the HF stretching fundamentals v,.

of r-t Kr- and Xe-HF under therma Fig.

2?l" 1 P

along

S

wi th

S

simulations' calculated from the measured and^predicted^^

rovibrational constants for the v-, fundamental nd \j-| 3

Fig. 2.11 ;trum of the Xe-HF van der Waals complex

1 length of 80 m and a temperature of T

d) and calculated (bottom).

for an absorption

211 K; observed

284
Rotational structure has been observed up to or approaching

rotational predissociation, permitting us to model the effective radial

van der Waals potentials for these complexes. For example, Ar-HF is found

to predissociate by tunneling through the centrifugal barrier at J=40 in

the ground vibrational state, leading to the empirical potentials shown in

Fig. 2.12. These potentials provide good estimates for the binding

energies, Dq, and the van der Waals stretching frequencies, V3, in the

Model Radial Potential

r/A

Fig. 2.12 Empirical potentials for Ar-HF derived from spectroscopic data.

ground (v^o) and excited (v-|=1) states of the molecules. For v-|=0 in

Ar-HF, Kr-HF and Xe-HF, we find Dq = 102, 133, and 1 81 cm

-1 and = 39.2,

41.1, and 43.4 cm

1 respectively. The modes characterized by the model

potentials aid in the assignment of the + V

3

- V

3 hot bands observed in our spectra. The band centers for the v

1 fundamentals are all

down-shifted in frequency from the isolated HF monomer by Av «= -9.654,

-17.518 and -29.185 cm

-1

for the Ar, Kr , and Xe complexes respectively,

indicating that the van der Waals bonds are some 10 to 15? stronger in the

excited vibrational state. This increased vibrational attraction also

results in a contraction of the van der Waals radial coordinate manifest

in the larger rotational constants observed for v-j ; AB/Bq = +0.35, +1.00

and +1.75? for Ar-, Kr-, and Xe-HF. We have also observed the Q branch of

the v-, + \>2 stretch-bend combination band in Ar-HF some 70.2 cm

-1 above

the v-j fundamental with a large negative AB/Bq = -2.00? implying a strong

anisotropy in the potential.

285
8 c NATO-Advanced Research Workshop

(A.. Weber)

A NATO-Advanced Research Workshop on "Structure and Dynamics of

Weakly Bound Molecules Complexes was conducted in Acquafredda di Maratea,

Italy in September 1986. The purpose of this Workshop was to bring

together researchers active In the field of high resolution spectroscopy

and dynamics of van der Waals and hydrogen-bonded molecular complexes in

order to assess the present state of knowledge, to communicate directions

and progress of research already underway and to indicate directions,

potential and level of effort needed for future research. Seventy

scientists from nearly all NATO countries participated in this Workshop.

The topics taken up included the determination of structures by microwave,

molecular beam electric resonance, high resolution infrared,

and visible spectroscopy, rotational and vibrational predissociation

determined from spectral line widths and from time dependent

photodissociation experiments, determination of potential energy surfaces

from experimental data and from ab initio calculations, as well as stability and dissociation dynamics. The proceedings of the Workshop will be

published in the NATO-ASI series of publications.

9. Future Plans

During the past year the pulsed beam Fourier transform microwave

spectrometer (FTMWS) has provided rotational spectra of both new dimers

and van der Waals complexes. Further work in this direction will continue

next year. A number of dimer studies have been started, but are not yet

complete due to the complexity of the observed spectra. These include

studies of CH 0 NH 2 -H 2

O, CH

3 OH-NH

3 and several new species observed in Ar/03

expansions. We hope to complete the assignment of these spectra during

the coming year.

We will also test several new molecular beam designs. One design

allows mixing two beams in the nozzle exit channel for the study of dimers

of species which react, e.g., ammonium halides. A second design will

provide a dc electric discharge in the beam exit channel which we hope

will generate free radical species.

One of the major thrusts during FY87 will be the development of a pulsed laser ablation system which can be used in conjunction with the

FTMWS to study molecular species that are normally non-volatile. The high

power pulsed laser has been ordered and the pumping system is in place.

All that remains is to design a vacuum chamber to allow the laser-target

to be interfaced with a pulsed nozzle and the FTMWS.

A second area of major emphasis will be to investigate the

feasibility of Incorporating a cryogenically cooled, extremely low noise

mixer device in the FTMWS. Theoretically improvements in signal-to-nolse

with this type of device could be two or three orders of magnitude.

286
Infrared investigations will also be performed on molecular-beam

adiabatically-cooled systems. A pulsed molecular beam apparatus is now

under construction and will be used for absorption spectroscopy with the

aid of various tunable lasers. A cw-molecular-beam laser resonance

apparatus is now under development and scheduled for completion during the

coming year for vibrational predissociation measurements. Also under

development is a high resolution tunable F-center laser system for high

power excitation of van der Waals complexes for vibrational

predissociation studies.

D. Matrix Isolation Spectroscopy

1 . Fluorine-Atom Reaction Study

(M. E. Jacox)

Some years ago, the infrared spectra of cis- and trans-HOCO were obtained in this laboratory by the reaction of photolytically generated OH

with a CO matrix. These species are of considerable interest to the

combustion scientist, since the OH + CO reaction is the principal process

by which C0 2 is formed in combustion systems. Because HOCO can hydrogen-bond to the CO matrix, it was desirable to obtain the spectra of

its rotamers in an argon matrix. However, molecules cannot diffuse

through solid argon under the conditions necessary for effective matrix

isolation. Therefore, it was not feasible to study the OH + CO reaction

in solid argon. Preliminary studies, outlined in the Annual Report for

FY85, have shown that the reaction of F atoms with HCOOH provides a suitable source of trans-HOCO. Early in FY86, further isotopic studies on

the F + HCOOH system were conducted using the Beckman IR-9 infrared

spectrophotometer

.

2. Excited Argon-Atom Reaction Studies

(M. E. Jacox)

As was reported in the Annual Report for FY85, a good yield of

trans-HOCO can also be obtained by codepositing the Ar: HCOOH sample with a beam of argon atoms excited in a low-power microwave discharge. This

method of preparation of trans-HOCO has the advantage of eliminating

contributions of HOCO«**HF from the spectrum. Detailed isotopic studies

of trans-HOCO formed in this system were also performed using the Beckman

IR-9. However, the product yield on deuterium substitution was relatively

low. Therefore, completion was deferred until the BOMEM Fourier transform

system can be used. The greater frequency accuracy of this experimental

system will be valuable for the determination of carbon-13 and oxygen-18

isotopic shifts. In turn, these isotopic data will permit derivation of an improved vibrational potential function for trans-HOCO.

The accessibility of the near infrared spectral region using the

BOMEM system made possible a detailed series of experiments on the

interaction of excited argon atoms with acetylene. Previous studies in

this laboratory have shown that this sampling configuration provides a

287
consistently high yield of the HC 2 free radical, an important intermediate

in astrophysical and combustion systems. Extensive deuterium- and

carbon-isotopic substitution studies spanning the 700-7900 cm' 1 spectral

region were conducted at a resolution of 0.2 cm

-1

.

The mid-infrared studies yielded a more precise value of 1846.2 cm

-1

for the CC-stretching frequency of HC 2

. Several weak absorptions between

2100 and 3400 cm" 1 were also assigned to HC 2

. An absorption at 3610 cm

-1 has previously been assigned (M. E. Jacox, Chem. Phys. ]_, 424 (1975)) as the CH stretching fundamental of HC2

. Although this value is anomalously

high for a CH-stretching fundamental, the observation of Fermi resonance

with the first overtone of the CC-stretching fundamental for H

12C and

for H ^C2 indicates that the energy level of HC 2 which contributes this

absorption must be of E

+ vibronic symmetry.

Recently, Curl, Garrick, and Merer (R. F. Curl, P. G. Carrick, and

A. J. Merer, J. Chem. Phys. 82_, 3479 (1985)) have assigned prominent

gas-phase absorptions at 3796, 4012, and 4108 cm

-1 observed by

color-center laser spectroscopy in a discharge through polyacetylene to

combination bands arising from the ground state of HC 2

. Counterparts of

these three bands at 3806, 4022, and 4134 cm

-1 are prominent in the matrix

experiments, consistent with such an assignment. The corresponding

absorptions for the carbon-13 substituted species were also observed in

the matrix experiments.

2 The matrix studies have provided the first observation of the A n - A

2

I+ absorption band system of HC 2 in the 4200-7900 cm

1 spectral

region. As is evident from Fig. 2.13, a rich spectrum is obtained. The

product absorptions shown in trace (b), the soe o,--um obtained in an

Fig. 2,13 HC 2 (DC 2

) aosorption spectrum Detweer. --jO and 7200 cm observed on codeposition of Ar : C

2

H

2 ~d

n sampl| with a beam of

excited |rgon atoms. (a) Ar : C

2H 2#

= 800 + Ar ; (b) Ar : HCCD - 200 + Ar ; (c) Ar: C

2 D2

= 150 + Ar .

288
experiment using an HCCD sample, are the sum of those characteristic of

C

2h 2 samples (trace (a)) and C 2 D 2 samples (trace (c)), supporting the

assignment of all of the peaks in this spectral region to HC 2 and DC 2

. There are concentrations of peaks at intervals of approximately 1500 cm

-1

, appropriate for a progression in the upper-state CC-stretching frequency.

The superposed structure is contributed by extensive perturbation by high

vibrational levels of the ground state. Although the ground-state bending

vibration has not yet been directly observed, both it and the bending

fundamental of HC

2 in the A

2 n state are expected to occur at very low

frequencies, as has been observed (C. Fridh and L. Asbrink, J. Electron

Spectrosc. Relat. Phenom. 119 (1975)) for the isoelectronic species

HCN +

. Such perturbations in the spectrum of N0 2 are well known. Their

occurrence for HC 2 helps to explain the properties of the emission

spectrum observed on photolysis of acetylene in the gas phase. Depending

on the photolysis wavelength, several workers have observed unstructured

emission by HC 2 at wavelengths from the near ultraviolet to the cutoff of an InSb detector in the mid-infrared. Anomalously long lifetimes, between

about 5 and 30 ys, are typical. Douglas (A. E. Douglas, J. Chem. Phys.

45, 1007 (1966)) has considered the increase in fluorescence lifetime

which is associated with extensive interaction between two electronic

states.

Although a detailed assignment of all of the matrix data has not

been possible, the shifts on carbon-13 substitution appear to be

sufficiently regular that correlations can be made with reasonable

certainty. The isotopic shifts indicate that most of the peaks involve

CC-stretching excitations. Of particular interest is a peak at 4622 cm

-1

, which shifts by 103 cm

-1 for H^C2

. it is difficult to explain such a large shift except by postulating that two quanta of CC-stretching

vibration are excited in the transition. Such an assignment would place

the origin of the transition some 3000 cm

-1 lower, or near 1600 cm“ ' . A

definitive assignment must await rotational analysis of the gas-phase

absorption spectrum. Because all of the absorptions which are observed in

the matrix experiments must arise from the X(000) state of the molecule,

the data should be useful in the analysis of spectra of HC 2 obtained in

future gas-phase studies in other laboratories.

3 . Reaction Intermediates in the Decomposition of Energetic Materials

(M. E. Jacox)

As a part of a project on the spectroscopic characterization of

reaction intermediates in the decomposition of energetic materials,

supported in part by the Army Research Office, studies of the products of

the H + HCN reaction were also conducted on the B0MEM system. This

reaction is of especial interest because H

2 CN is a potential intermediate

in the decomposition of the solid propellants HMX and RDX. Preliminary

studies had provided evidence for the formation of CN and of three CH 2X

species (presumably H

2 CN and cis- and trans-HCNH) when H atoms produced by

a microwave discharge through an Ar:H 2 mixture react with HCN in an argon

matrix. BOMEM observations between 700 and 4000 cm

-1 were conducted with

289
a resolution of 0.2 cm" 1

. The peak at 1336.6 cm

-1

, which appeared even when low-energy H atoms were formed by the mercury-arc photolysis of HI, was shifted by only 0.1 cm

” 1 on carbon -13 substitution, but by 3.0 cm

-1 on nitrogen-15 substitution. This behavior is similar to that of the 1500

cm

” 1 CH 2 "scissors" fundamental of H 2 CO. Since H 2 CN is calculated to be

the most stable isomer and since it has been identified in earlier studies

of the esr spectrum of products of the mercury-arc photolysis of Ar:HCN:HI

samples, the assignment of the 1336.6 cm”' peak to the CH 2 "scissors"

fundamental of H

2 CN is strongly indicated. The carbon-13 isotopic shift

of the 31 0^4 cm

” 1 peak, tentatively attributed to a HCNH species, requires

its assignment to a CH-stretching fundamental. Carbon-13 and nitrogen-15

isotopic shifts were also observed for the 886.3 cm

” 1 absorption,

contributed by a photochemically unstable HCNH species, probably the cisrotamer. Despite the greater sensitivity of the BOMEM interferometer,

other infrared absorptions which can be assigned to these three products

have not been identified. The interferometer system was also used for

survey scans of the 4000-8000- and 10 , 000 -20,000 cm

” 1 spectral regions,

but no absorptions which could be assigned to the analog of the red bands

of the isoelectronic species HC0 were detected.

In a preliminary Ebert scan of the ultraviolet spectrum which

results on 122-nm photolyis of an Ar:HCN sample, moderately intense

absorptions appeared at 34990 (overlapped by the OH A-X 1-0 absorption) and

35436 cm” 1

. These two peaks correspond closely with gas-phase absorptions

previously attributed to H

2 CN, formed on flash photolysis of several more complicated precursor molecules. Several less intense peaks extending to

37764 cm

” 1 may have been contributed by previously unidentified bands of

H

2 CN. Further studies are needed to confirm this identification.

In an earlier study in this laboratory, the nitromethyl free

radical, CH 2 N02 » was stabilized by the reaction of F atoms with CH

3 NO 2 in an argon matrix, and the first spectroscopic data for this species were reported. Most of the vibrational fundamentals were observed for five

isotopic species of nitromethyl, and a tentative vibrational assignment

was proposed. The wealth of data available from these experiments

suggested that a detailed normal coordinate analysis should be feasible.

Among the important questions which such an analysis would address are whether the molecule is asymmetric, as had been proposed as a result of a recent ab initio calculation, and whether the unpaired electron

contributes to partial double-bond character for the CN bond. A least-squares force constant adjustment calculation has recently been

conducted. All of the observed frequencies can be fitted very well for a planar C

2 v molecular structure. The vibrational assignment proposed in

the earlier experimental paper has been somewhat revised. The magnitude

of the CN-stretching force constant is appropriate for a single bond. A manuscript presenting the detailed results of the normal coordinate

calculations is being prepared for publication.

290
A manifold has been designed and constructed to permit matrix

isolation sampling of low vapor pressure materials by controlling the

pressure of argon with which they are in equilibrium. This manifold will

be used for studies of the spectra of products of the photolysis of phenol

and nitrobenzene, also a part of the current ARO project.

4. Future Plans

During the coming year, highest priority must be given to the

completion of a number of important projects which have already been

discussed. These projects include BOMEM studies of the infrared spectrum

of trans-HOCO and Ebert studies of the electronic spectra of the H + HCN

reaction products. Detailed studies of products of the photolysis of

benzene, phenol, and nitrobenzene be conducted using the BOMEM system.

Studies of the products of the reaction of 0 atoms with these three

molecules will also be conducted.

Studies begun in 1985 on the reaction of SiH^ with H, Cl, and 0

atoms produced in a discharge are also planned. The potential

stabilization of SiHn and SiHn

0 species is of interest in relation both to

basic chemical research and to applied studies of plasma etching.

Infrared studies of interesting and important F-atom reaction

systems- e.g., F + cyclopropane—will continue to be conducted. However,

emphasis will now be placed on UV-visible studies of F-atom reaction

products, for which there is a substantial backlog.

For some time, it has been planned to use a beam of excited neon

atoms as a source of 16.6-16.8 eV energy for the production of small

molecular ions, to be trapped in a neon matrix. This energy range should

make possible the preparation of significant concentrations of such small

molecular cations as HC0 +

, H

2

o

+

, NHo , and CH4, not accessible in the

11.5-11.8 eV energy range provided by a beam of excited argon atoms. It

is hoped that later in FY87 the excited neon atom experiments, which may

provide much previously inaccessible information on the vibrational and

electronic spectra of molecular ions, can begin.

E. General Spectroscopy and Theory

In addition to the previously described programmatic activities a variety of research problems are pursued in response to special

opportunities, and special interests of the staff and outside guest

scientists. The following are descriptions of such projects of a general

nature

.

291
1. Fourier Transform Measurements of High Temperature Species;

Infrared Gas Phase Spectra of LiCl, LiH, and LiD

(W. B. Olson, G. A. Thompson, A. G. Maki, and A. Weber)

The new transfer optics for the BOMEM described below have allowed

us to make high temperature measurements of the infrared spectrum of

several compounds produced in a high temperature oven. So far we have

measured the Av=1 transitions of the two species LiH and LiD and the four

naturally abundant isotopic species of LiCl.

A portion of the spectrum of LiCl containing 95$ ^Li is shown in

Fig. 2.14. The complete spectrum contained over 2500 identified

transitions for the various isotopic species. Vibrational transitions

ranged from v=1-0 to v=8-7 and rotational transitions for J values up to

75. These transitions were fit to a set of Dunham potential constants

that included 9 isotopically invariant terms and 4 terms to allow for

isotopic shifts due to the break-down in the Born-Oppenheimer

approximation. The standard deviation of the fit was 0.00027 cm

-1 which

is what we expect considering the slightly larger than normal Doppler

linewidth of these high temperature spectra.

700.0 720.0 740.0

WAVENUMBER (cm- 1 )

Fig. 2.14 A portion of the spectrum of 6 LiCl at 830°C. The locations of

a number of band heads are indicated above the spectrum.

292
A portion of the spectrum of LiD is shown in Fig. 2.15. This

spectrum is much more sparse than that of LiCl and shows the advantage of

LiD

i—.—.—.—.—i—i—.—i—*—i—.—i—i—i—i—i—i—i—i—

800.0 875.0 950.0 1025.0 1100.0

WAVENUMBER (cm- 1 ) Fig. 2.15 A portion of the absorption spectrum of LiD at 750 C C. The wave

number scale applies to the upper spectrum.

using a broad-scanning FTS instrument for making these measurements.

Earlier measurements using a diode laser spectrometer were very slow

because the lines were so far apart, the electronic tuning range of the

spectrometer was quite small, temperature tuning was slow, and there were

many gaps in the coverage.

The standard deviation of the fit of the LiH and LiD spectra

(0.0076 cm

-1

) was worse than that of LiCl because the Doppler width was larger and there seems to be more of a problem with break-down of the

Born-Oppenheimer approximation. To investigate this further, we hope to

measure the pure rotational spectrum of LiH at high J values to get better

measurements on the higher centrifugal distortion constants.

2. Hydrogen Migration Tunneling Effects in the Rotational and

Vibrational Spectrum of Protonated Acetylene C

2Ho

+ (J. T. Hougen)

The influence of a possible hydrogen atom migration in protonated

acetylene, on the high-resolution vibration-rotation spectrum of

this ion was investigated. The migration model, which derives from ab initio

calculations, consists of a planar structure with the three hydrogen atoms

moving on an elliptical path around the two carbon atoms. Symmetry

considerations for this ion were considered in terms of the

permutation-inversion group G

2 ^. A method for calculating energy levels

for a highly idealized model of this ion can be found in the early

293
microwave literature. In this idealized model, an equilateral triangle of

three hydrogen atoms performs internal rotation about a dumbbell of two

carbon atoms, with all atoms remaining in the same plane. This model

gives rise to a symmetric rotor top, an asymmetric rotor frame, and a six-fold barrier to the internal rotation motion. An alternative method

of calculating the energy levels of this ion, involving a more recently

proposed algebraic tunneling formalism, shows that qualitatively similar

results are obtained even when the hydrogens do not retain the form of a rigid equilateral triangle during their migration motion. Energy level

diagrams, nuclear spin statistical weights, selection rules for electric

dipole transitions, etc. were developed. It is hoped that the patterns

described in the present work will aid in identifying and interpreting any

spectrum of C

2 Ho

+ obtained as a result of ongoing efforts elsewhere to

record its spectrum.

3. The Torsional-Wagging Tunneling Problem and the Torsional-Wagging

Rotational Problem in Methylamine

(N. Ohashi and J. T. Hougen)

A theoretical formalism is presented for fitting rotational energy

levels in isolated (unperturbed) vibrational states of methylamine. This

formalism is obtained by recasting and extending theoretical studies in

the earlier literature, which were undertaken to help analyze the

methylamine microwave spectrum. The present formalism is applicable when

both the NH 2 umbrella (wagging) motion and the CH

3 internal rotation

(torsion) motion take place near the high-barrier limit and leads to the

usual Fourier sine and cosine series expansions for molecular energy

levels. The derivation is separated into two parts, one treating the

large-amplitude vibrational problem (the torsional-wagging problem) by

itself, the other treating the torsional-wagging-rotational problem. In

both treatments, permutation-inversion group and extended group ideas are used to determine the allowed terms in an effective rotational-tunneling

Hamiltonian operator and to block diagonalize the matrix representation of

this operator for a near-prolate symmetric top. Application of the method

in detail to the methylamine spectrum is planned for a later study.

4. Far-Infrared Spectrum of Methylamine

(N. Ohashi, W. J. Lafferty, and W. B. Olson)

The far-infrared spectrum of CHoNH 2 has been recorded in the

region 50 to 350 cm

” 1 on the NBS BOMEM Fourier transform spectrometer with

a resolution of about 0.004 cm” 1 . The torsional band as well as pure

rotational transitions originating in higher K

a levels fall in this region

of the spectrum. This molecule is of more than passing interest since it

has two large amplitude motions, the NH 2 ~wag and the OU-torslon, and the

spectrum is rather complex as a result. Assignment of the pure rotational

transitions is complete at this point, and the stronger B-, (B 2

)«-B 2 (Bi ) and

E-j^-E-j components of the torsional band have been assigned. A small

portion of the spectrum of the torsional band is given in Fig. 2 . 16 where

the line assignment of two components of the r Q ^ - and r Q^- transitions is

294
indicated. Ohashi and Hougen have recently derived approximate energy

level formulas for CH

3 NH2 , and a computer program is being written to fit

the data and extract the molecular constants. Preliminary fits show that

the torsional splitting in the torsional vibrational state is about 30

times larger than in the ground state, and, somewhat suprisingly, the

inversion splitting in the excited state is about 3 times greater than it

is in the ground state.

PRESSURE 10 Torr PATH 20 cm C H^N H

^ TO R S I O N

RESOLUTION 0.005 cm" 1

251.58

H \- 252. 00 252 '. 50 2531 09 253. 50CM-1

Fig. 2.16 A small portion of the torsional band of CH^N^ taken with a resolution of 0.005 cm

-1 showing the line assignments of the

Q-branches of two components of the K=5”4 and K=6~5 subbands.

5. Transfer Optics System Design

(W. B. Olson)

An efficient transfer optics system has been designed and

constructed to couple the BOMEM FTS to an existing heat pipe in order to

obtain infrared absorption spectra of species which can only be seen in

295
the gas phase at high temperatures. This system has enabled the high

resolution observation of several bands of LiCl and LiH leading to

improved vibrational and rotational constants for these species.

The necessity of efficient and practical transfer optics for the

heat pipe was the "mother of the invention" of a fairly general and

powerful approach to transfer optics design via a "system" concept of

first order design, through analytical equations directly coupling

required throughput or entendue to the ray transfer matrix of an optical

system c The necessary ray transfer matrix for the system is uniquely

determined (except for sign), and one can relatively rapidly calculate

required distances and focal lengths of spherical mirrors required to

implement a practical system.

With a single optical element, in our applications a concave spherical

mirror, one has no degrees of freedom with which to make the design

convenient. With each added optical element one gains two degrees of

freedom to adjust features. With three optical elements one can specify

all four distances in the system to convenient or practical values, and

from these calculate the focal lengths required for each of the three

mirrors. This is the method used for the heat pipe transfer optics system

design. The resultant optical system for the heat pipe works well, but no precise explanation can be given of the function of the individual optical

elements in simple, familiar terms.

6. Analysis of Infrared Spectra of SiH^D

(R. Schaefer, R. Lovejoy, W. B. Olson, and G. Tarrago)

An analysis of the V

2 parallel band of ^SiH^D has been nearly

completed through the collaborative efforts of Ron Schaefer and Roland

Lovejoy of Lehigh University, W. B. Olson of NBS, and Ginette Tarrago of

the University of Paris, South. For a complete analysis the interactions

of Vg with the parallel and perpendicular components of 2v$ had to be

taken into account by simultaneous solution of a secular determinant

containing all three vibrational states. Three different types of

perturbations giving readily evident displacements of absorption line

positions in V

2 were found to be due to pertur bations with the

perpendicular component of 2v^.

The perpendicular component of 2v^ proved difficult to assign

because it was so weak, and additional spectra were run with a pressurepathlength product a factor of ten higher than that used for the initial

runs. This also increased the intensity of many other weak lines

from unidentified hot bands and silicon isotopes. Two techniques for

getting assignments, and checking them through the quality of the least

squares fit, and the success of using molecular parameters from the fit to

calculate new line positions at higher values of J and K eventually lead

to a reasonably complete set of assignments for this weak band. Many o'.

296
the strongest lines in 2vg are actually perturbation allowed transitions

which get their intensity from the parallel component of 2vg through the

1-type doubling matrix element.

The secular determinant used for this work contained all possible

matrix elements through the fourth order of the twice transformed

Hamiltonian. A number of the higher order terms were found to be

insignificant, while others of high order are significant, but did not

make major contributions to the energies of any of the levels.

The values of the major low order molecular parameters of 2vg are

in quite satisfactory agreement with those of the vg fundamental. The

origin of the v

2 band is at 1593-962 cm

-1

, and that of 2vg is at 1557-258

cm '. An article describing this work in detail is being prepared for

publication.

7. Future Plans

In the coming year we plan to exploit the optical system used for

the high temperature Fourier transform experiments to obtain Fourier

transform measurements of other systems unstable under normal room temperature conditions. We shall try to observe the far infrared spectrum

of several systems such as the pure rotational spectrum of LiH and -the

spectrum of compounds with low frequency vibrations (e.g., NaCl). We shall

also try to observe the spectrum of compounds produced in an electric

discharge with the hope that this may enable us to look at the spectrum of some metal oxides or hydrides.

Theoretical studies will focus further on large amplitude motions.

Topics to be examined are the CH

2

NH2 microwave and far infrared spectra

both in terms of pure rotational spectra and torsional spectra. The water

dimer Hamiltonian and spectral consequences will be examined in further

detail.

297
3* LASER PHOTOCHEMISTRY GROUP

D. F. R„ Burgess, Jr., M. P. Casassa, R. R. Cavanagh, L. B. Elwell,

E. J. Heilweil, D. S. King, and J. C. Stephenson

This group primarily does quantum-state specific studies of molecular

dynamics. A common factor in the research described below is the role of

energy transfer in the spectroscopy and kinetics of molecules. Research on molecular dynamics of molecules on surfaces is done in collaboration with the

Surface Science Division.

A. Condensed Phase Energy Transfer

(M. P. Casassa, R. R. Cavanagh, L. B. Elwell, E. J. Heilweil, and J. C.

Stephenson)

The major effort in the condensed phase energy transfer program has been

directed at the study of vibrational energy transfer (VET). During the past

year we have successfully measured the rates of energy transfer from

vibrationally excited chemical bonds in liquids, solids, and in molecules

bound to surfaces.

This research area was extensively discussed in the 1985 Annual Report.

The present report does not repeat last year's lengthly discussion of

experimental detail and program rationale. In summary, we used a picosecond

infrared pump/probe method to perform time-resolved measurements of the

vibrational energy relaxation rate ('T'

1 “ 1 ) for the high frequency modes of

species chemisorbed on a silica (Si0 2 ) surface in a variety of chemical

environments. Previously, energy transfer rates have been measured for the

vibrations of many molecules in the gas phase, and for a few molecules in

liquids and low temperature solids. However, our experiments were the first

to measure vibrational energy transfer rates for vibrations on surfaces.

A summary of some surface T-j results is given in Table 3»1« These data

were limited to vibrations with frequencies v>2500 cm* 1 since the psec ir

pulses necessary to cause transient bleaching of the surface vibrations were generated in a Nd-YAG-pumped LiNbO^ OPA (LiNbO^ only transmits v>2500 cm

-1

). The data suggest the following conclusions. T-| times are longer than most

people expected prior to these measurements. Energy relaxation rates (T^ 1 ) are much slower by factors of 100-2000, than would be deduced from spectral

bandwidths of these surface vibrations. At the vacuum interface, the MCH

(M=B, Si, Al, Zn) and MOD stretching vibrations relax via anharmonic coupling

to spatially adjacent vibrational modes, particularly the M-0-H bending mode.

One reason BOH relaxes faster than SiOH is that its local accepting modes art

higher in frequency and hence a better match to the OH stretch. The faster

relaxation of NH 2 and OCHo vibrations ,1s consistant with energy transfer from

the NH stretches to the NH 2 bend and similarly from the CH stretches to the

CH bends (with which the CH stretches are known to couple strongly via Fermi

resonance). It is reasonable that T-| of OH in the commercial zeolite ZSM-5

298
Table 3.1 T

1 decay times at room temperature for various surface vibrations

System v( cm

-1

) T

1 (ps) k(10 9 s" 1 ) Notes

SiOH/vacuum vOH = 3750 220±20 4.9 Pressed Si02 disk

SiOH/CCljj vqh=3690 1 59±1

6

6.3 Dry Si02 dispersion

SiOH/CF2Br2 vqh=3690 140±30 7.1 M

SiOH/CH2 ci 2 vqh = 3660 1 02±20 9.8 it

SiOH/C 6H 6 vqh=3625 87+30 1 1.0 If

SiOH/C 6 D 6 voh=3625 80±30 12.0 ff

SiOH/H2 0/CCl]4 vqh=3690 56±10 18.0 SiOH Tt

,

-5H 2 0/100A2

physisorbed

SiOD/vacuum vod =2760 1 55±1 6 6.5 OD T., with 67$ OH re- placed by OD

BOH/vacuum

boh/cci 4

v0H = 3700 -70 -14.3

SiNH 2 /vacuum

SiNH 2 /CCli!

vNH = 3460

3520

£20 250 Pulsewidth limited

signal, AT/T -5$ for

both stretches

SiOCH^/vacuum v=2860

3000

<5( ?) >280 ( ?) No pulse saturation

observed for any

CH-stretching mode

OH on zeolite

ZSM-5/CCl^

(Si/Al=3600)

voh =3690 1 40±25 7.1 Pressed disk CCl^

saturated

OH on ZnO Voh-SW £10 2100 AT/T0“1 2$ pulsewidth

limited

ZnO, no OH 3600-3750 <10 2100 Electronic excitation

of free carrier

absorption AT/T

-10$.

299
is the same as on fumed Si0 2 , since the high Si/Al ratio (*3600) of this

particular sample precluded any appreciable bonding of OH on aluminate

sites. The very rapid relaxation of OH on the semiconductor ZnO surface may

not be caused by anharmonic coupling to adjacent vibrational modes but by

coupling to electronic excitations of impurity states in the ZnO.

Relaxation rates for the surface vibrations increase in the presence of

solvents (solid/liquids vs. solid/vacuum interface). The increase in rate is

minor for solvents like 001^ which have no resonant high frequency modes,

( VC-C1 = 770 cm

-1 is the highest fundamental). An increase in rate of about

a factor of 2.5 occurs for benzene which has many nearly resonant

( v

0H"* benzene V 1 + vij, etc.) internal vibrational states which could accept

some or all of the OH quantum. Alternatively, vibrational relaxation rates

may increase in the presence of solvents which perturb the 0H(v-0 * 1)

absorption through hydrogen bonding or van der Waals interactions. The

dependence of T^ for surface vibrations on chemical environment, temperature,

and other factors previously mentioned is always qualitatively in the

direction expected by analogy to T-j data in homogeneous phases. However,

standard first order perturbation theory calculations (e.g., solid state

multiphonon relaxation theory) do not quantitatively agree with these trends.

During the past year a new picosecond dye laser was constructed for the

purpose of generating tunable ir pulses for v < 2500 cm' 1

. This enables us to pump and probe interesting surface vibrations such as CO bound to metals.

For vibrational relaxation on a metal surface, it is thought that a qualitatively different energy transfer mechanism, damping by excitation of

electron-hole pairs in the metal, may be dominant. If this is true, then

perhaps the broad spectral bandwidths ( -5~50 cm' 1 FWHM) observed for high

frequency vibrations on metals are really due to T

1 broadening, as has often

been assumed. A direct time-resolved measurement of vibrational relaxation

for a molecule on a metal surface is crucial to assessing the importance of

this damping mechanism, and for understanding surface spectroscopy and

kinetics

The new laser is a synch-pumped tunable dye laser pumped by the second

harmonic (532 run) of the rejected trains of ps pulses from our acti vely-passi vely modelocked 10 Hz ps Nd-YAG laser. A single pulse from the

dye laser is cavity-dumped, amplified to -500 yJ/pulse and mixed in a LilO^

crystal with a single 532 nm pulse derived from the same 10 Hz YAG.

Typically pulses of -25 ps duration, 20 yJ, and tunable throughout the CO

stretching region (-H cm' 1 FWHM), are generated by this system. These pulses are sufficient to perform pump/probe ir saturation measurements of T 1 for

C0(v=1) bound to small metal particles (e.g., Pt) on an insulator support

(e.g., Si02

). The Pt particle size (or other transition metal) can be

controlled so that CO will chemisorb to either isolated metal atoms or larger

crystallites. Measurement of T-j for CO on the surface of supported metai

particles should begin mid October 1986.

300
Initial experiments with the new laser system have involved measuring

for stretching vibrations of CO bound to transition metal atoms (metal

carbonyl complexes) dissolved in CCl^ and other solvents. In terms of

vibrational spectroscopy, the inorganic carbonyls are analogous to

surface-bound CO (the assignment of surface CO sites as "bridge-bonded” on "terminal" frequently involves comparing the surface vibrational frequencies

with corresponding metal carbonyls). Figure 3*1 shows ir pump-probe

saturation data giving T

1 for the F-j u C0(v=1) mode of Cr(C0)6 in carbon

tetrachloride and hexane solutions. T-j is very long (T-j 3 490 ps corresponds

to 20,000 vibrational periods) and is clearly unrelated to the 8 cm

-1 FWHM

infrared Lorentzian bandwidth. We expect a similar lifetime for CO bound

to isolated surface metal atoms on a dielectric support. A wide variety of

metal carbonyls and nitrosyls are available and are excellent model compounds

to answer questions about VET mechanisms, such as: is there a "heavy atom

effect"; is T-j for bridge-bonded CO different from terminal CO?; how is

vibrational energy exchanged among modes of different ligands (adsorbates)

bound to the same or neighboring metal atoms?

Fig. 3.1 Vibrational relaxation times for the F 1u C0(v=1) mode of

Cr(C0)^ in solutions of hexane and carbon tetrachloride.

Studies of related energy transfer processes at semiconductor surfaces

have also recently begun in collaboration with Dr. Claude Sandroff of AT & T

Bell Laboratories. The luminescence decay times of "exciton-like" electronic

301
states of extremely small (S 30A diameter) and planar Pbl

2 and PbBr 2 colloidal particles suspended in organic solvents are being measured.

Preliminary experiments for Pbl 2 and PbBr 2 in alcohol, using the third

harmonic of the picosecond Nd + 3 : YAG (355nm for Pbl 2 ) and the second harmonic

of the synchronously pumped dye laser ( 31 0 nm for PbBr

2 ) as excitation pulses,

have yielded ca. 1100 and 900 ps lifetimes, respectively. These emission

lifetimes were measured with a streak camera system. It is believed that

measurements of this sort will reveal mechanisms for light-induced chemical

reactions occurring at the liquid-surface interface. These include, for

example;, charge-transfer and oxidation-reduction reactions that are known to occur at semiconductor surfaces.

Using the LiNbO^ OPA system, a study of the T-j relaxation times of

0H(v=1) and 0D(v=l) vibrations of silanol, R^SiOH, and alcohol, R^COH,

molecules in solution was completed. The results are summarized in Table

3.2. They may be compared to the surface OH results in Table I and the OH in

crystalline mica results in Table 3*3* Most of the liquid phase results can

be understood in terms of an isolated binary collision (IBC) model frequently

used to interpret gas phase collisional VET rates. The fact that T-j for

(CH^gSiOH < Tj for (CgH^oSiOH, even though the latter molecule has 500 times

the total density of vibrational states, shows clearly that factors other

than the total vibrational state density are important in determining T

1 . The deactivation of hydroxyls of R^MOH and R

3 MOD (M=C,Si) were simply

modelled using the assumption that 0H(v=1) or 0D(v=1) energy is initially

transferred to the eleven vibrations involving the OH bond and the

neighboring four tetrahedral bonds of the central M atom. Data were analyzed

by considering the frequencies of those particular accepting modes, and by

using the propensity rules that energy transfer will be nearly resonant, and

that processes involving the fewest vibrational quantum number changes

(n=number changing) will be most probable. Because of their different

vibrational frequencies, there are many more nearly resonant relaxation

channels, involving lower values of n, for the alcohols (n Z 4) than for the

silanols (n 2. 5). This may explain why the R^COH and R^COD molecules relax

much faster than corresponding silanols. The observation that the R^SiOD

molecules relax more slowly than the R^SiOH species is consistent with energy

transfer occuring predominantly to the SiOH bending motion, and is not

consistent with transfer primarily to the Si-0 stretching vibration. Similar

analysis for the methanols (CH^OH, CHoOD, CD^OH, CD^OD) suggests that energy

transfer to the CH (CD) stretching vibrations or to the C-0 stretch are probably not dominant relaxation channels.

302
Table 3.2 lifetimes for the OH and 0D(v=1) stretching vibration in

alcohols and silanols in dilute CCl^ solution (SO. 007 mole

fraction) at 298 K. Error limits are ±o, or 10$ of T 1

f

whichever

is greater.

SILANOLS3 v0H,0D^ cm_1

}

T 1 (ps) ALCOHOL3 v0H,0D( cra_1 > T

1 (ps)

Me

3 SiOH 3690 205 ± 21 Me3 C0H 361 4 < 6 b

Me

3 SiOD 2722 245 ± 25

Et

3 SiOH 3689 185 ± 19 Et 3 C0H 3622 < 6

b

Et

3 siOD 2722 224 ± 22 Et 3 C0D 2673 < 20 b

6

3 SiOH 3675 206 ± 21 cp 3 C0H 3609 < 1 5

b

9

3 SiOH 2712 292 ± 29

9 2 Si(0H) 2 361 0,3679 80 ± 15 ch

3

oh 3641 15 - 30 b

4> 2 Si ( 0D ) 2 2665,271

0

134 ± 14 ch

3 od 2685 52 ± 17

cd

3

oh 3642 73 ± 7

cd

3 od 2690 79 ± 17

EtOH 3625 70 ± 10

pOH 3610 5 - 20 b

bOD 2665 1 5 - 25 b

c

6 f

5od 2640 < 1 5

b

aMe=-CH

3

, Et=-CH 2 CH

3

, <f>=-C 6 H

5

^Limits on T-| were deduced from computer simulation.

303
Table 3-3 T-, vibrational lifetimes of the OH(v-l) stretching fundamental

mode of hydroxyl ions in natural crystalline micas at 298 K.

Uncertainties in T-j are ±1o. Where applicable, the samples are labelled by their Smithsonian Institution identification numbers.

Muscovite v0PA

( cm" 1 )

Tt (ps) Biotite v0PA

( cm" 1 )

T-] (ps)

104935 3591 88 ± 16 82063 3691 198 ± 15

10501

3

3648 90 ± 15 03647 3691 244 ± 15

105051 3591 83 ± 18 03675-1 3691 220 ± 18

3675 85 ± 8 3575 125 ± 11

B1 6862 3675 105 ± 36 Ruggles 3591 72 ± 20

Ruggles 3591 79 ± 8 Unknown 3540 64 ± 5

3675 114 ± 13

For comparison to the surface (Table 3-1) and liquid (Table 3-2) phase

results, new results were obtained for the 0H(v=1) T

1 lifetime of hydroxyl

ions located within the two-dimensional crystalline layers of natural

Muscovite and Biotite micas. Briefly, these silicate crystals are composed

of a sheet of metal cations octahedrally coordinated to OH" ions which is in

turn sandwiched between two covalently linked SiOjj tetrahedral layers. This

composite layer is further stacked upon others (creating several polymorphs)

to form the mica. Excess negative charge in these stacked layers is

neutralized by intercalated K

+ ions which give micas their easily cleaved

sheet-like character. With Al

+ 3 ions in the octahedral layer, the chemical

composition of Muscovite is best represented as [KO^Si^^ + Al-j

/

2 >02(0H

)

Al 2 (0H)02<Si3/2 + Al-|/ 2

> 03 ] n

. Since its aluminum ions occupy two of three

possible octahedral sites (two Al +

3 and one vacancy), Muscovite is called a dioctahedral mica. Because Biotites generally have all three octahedral sites

filled (e.g., by Mg +2 in Phlogopite), their chemical composition may be

written as [K0o<Sig/2 + A1-] /2>02 (0H)Mg3(0H)02<Si3^2 + A1 1/2 >03^n and they are called trioctahedral~micas . Substitutions for Mg * in Phlogopite (by Fe” and

Al

+ 3, for example) gives rise to other forms of the Biotite family.

T-j values for the micas are given in Table 3-3- At room temperature, the

average 0H(v=1) vibrational population lifetime (T^±o) for OH in Muscovite

is 92 ± 13 ps. For Biotite samples, absorptions arising from two distinct

lattice sites yield T-, = 221 ± 23 and 87 ± 33 ps, respectively. These energy

dissipation times are comparable to those observed for the surface OH, liquid

silanols, and OH in amorphous fused silica. In the micas the MOH bending

304
frequency is in the 800-900 cm

-1 range (like surface OH) while the M-OH

stretch in the micas is lowered to 400 - 500 cm

-1 (much lower than the

stretch in silanols or for surface OH). Thus the similarily of T-, may again

be consistent with energy transfer to the MOH bend being a dominant channel.

The observed trends in T

-] (Muscovite and Biotite low frequency site vs. Biotite high frequency site) can be rationalized in terms of local site

structure and hydrogen bonding. The high frequency trioctahedral Biotite

sites have the longest T-j (221 ps) and are least hydrogen bonded because

their out-of-plane orientation leads to little 0-H0 interaction with the

octahehral layer oxygens. The Muscovites and lower frequency Biotite hydroxyl

sites are dioctahedral sites with broader, lower frequency absorption,

reduced 0-H0 distance (3-5A) and increased H-bonding and a correspondingly

shorter T-j

.

The crystalline micas are also attractive samples for measuring

transient vibrational populations by picosecond coherent anti-Stokes Raman

scattering (CARS). Such measurements will give independent confirmation that

the ir pump-probe experiments yield correct T-| times. Also the CARS probing

may determine what vibrational modes accept the energy following deactivation

of the high frequency 0H(v=1) mode. The 10 Hz dye laser described above and

the 532 nm doubled Nd-YAG form the CARS probe pair. The 0H(v=1) level is

initially pumped by the LiNbO^ OPA. Large CARS signals have been produced from

crystalline mica when the dye laser was tuned to make the pulse pair resonant

with the OH v=0 -> v=1 transition. We do not yet (mid September 1986) have

time-resolved population data using this approach.

The preceeding successfully completed experiments and those now being

done are all steps toward answering the questions 1) What is T^ , for a molecule on a metal surface? 2) What are the pathways of energy transfer

(i.e., where does the energy go)? 3) How is VET at surfaces related to

chemistry? With continued support from the Air Force Office of Scientific

Research, we anticipate continuing progress toward understanding these and

other important questions in condensed phase energy transfer.

The most significant questions for us to answer in the area of energy

transfer for molecules on surfaces are: 1) What is T-j , for a molecule on a metal surface? 2) What are the pathways of energy transfer (i.e., where does

the energy go)? 3) How is VET at surfaces related to chemistry? The

experiments outlined below are planned to answer these questions.

We have several different strategies for measuring T^ for a molecule

on a metal surface. One approach is to perform our usual one color IR

pump/probe time-resolved bleaching experiment for molecules on supported

metal clusters. Another approach involves IR excitation of a molecular

(e.g., pyridine) bound to the surface of a metal (e.g., Au) particle

suspended in liquid as a sol; this would be followed by anti-Stokes Raman

scattering (surface enhanced) as a time dependent probe of vibrational

population. These experiments require infrared and visible laser pulses of

305
suitable energy, bandwidth, frequency, and duration. We have two suitable

laser systems which generate the difference frequency, cuIR , = between two

visible laser pulses in non-linear crystals. For frequencies u> IR> 1800 cm

-1 we use LilO^ and for lower frequencies 900 < iojr < 1800 we have tried AgGaS2

« In addition, a new hybrid 10 Hz pulsed Nd-YAG laser, presently under

construction, should generate -8 ps, 1.06 micron pulses, and hence much

shorter dye, 532 nm, difference frequency ir , and 0PA ir pulses than the

present apparatus produces. These shorter pulses should improve the time

resolution by more than factor of four compared to the current 1 0 Hz ps laser

system. Ir pump-probe measurements of T

1 for C0(v-1) on dispersed supported

small metal particles are being attempted with this new laser source. The

successful T-| experiments on "model compounds" like the metal carbonyls will

continue. Anti-Stokes Raman scattering measurements to determine the pathways

(accepting modes) involved in the VET will be done, first for homogeneous

model compounds such as metal carbonyls in solution and crystalline micas.

It is possible that the dispersed supported metal samples may scatter so much

light as to make any anti-Stokes experiments impossible. If so, we may still

be able to perform such time-resolved measurements on molecules bound to the

surface of colloidal metal particles in liquid suspensions.

B. Laser Diagnostics of Surface Dynamics

(D. Burgess, Jr., R. R. Cavanagh, L. B. Elwell, and D. S. King)

This program is directed at understanding energy transfer and chemical

dynamics occuring at metal surfaces at a fundamental level. The approach is

to apply state-resolved diagnostics, shown over the last decade in gas phase

reaction and beam scattering experiments to provide a tremendous wealth of

information about intermolecular potential energy surfaces to issues in

surface chemistry. Thermally driven processes that have been characterized

(i.e., kinetics, binding site occupation, etc.) by more conventional surface

science techniques have been chosen for study because of their ubiquitous

role in heterogeneous chemistry. From the viewpoint of chemical physics,

elucidation of the rates and mechanisms for energy flow from a molecule into

a nearby surface (dissipation) or vice versa (fluctuation) are key to a fuller, fundamental, knowledge of surface controlled chemical processes.

A collaboration between CCP Molecular Spectroscopy and Surface Science

Divisions has resulted in the creation of an experimental facility to perform

such state-resolved studies of thermal, molecular processes at well

characterized surfaces. The facility includes two ultra-high vacuum (UHV)

chambers. The major chamber, for oriented single crystal work, includes

traditional surface sensitive analytic tools such as mass spectrometry, ion

sputtering, low-energy electron difraction and Auger electron spectroscopy.

The second chamber, a test chamber for laser desorption experiments, is much

smaller in scale. Two laser systems are currently available. A near transform limited excimer-pumped dye laser is dedicated to measurements of

vibrational, rotational, spin-orbit, and lambda doublet distributions,

orientational effects, and kinetic energy distributions for molecules (e.g.,

NO) desorbing from surfaces. This system is used as the state-resolved

diagnostic both for thermal and laser-induced desorption. For the

306
laser-induced thermal desorption (LITD) studies we are using a YAG laser

(temporarily borrowed from the Center for Radiation Research) capable of

producing either nanosecond or picosecond duration pulses to probe the time

scale required to achieve equilibrium.

1. Adsorbate-Adsorbate Interactions: (NO + NH^/PtOll) Thermal

Desorption

In FY85 measurements of the internal state distributions for NO

thermally desorbing from Pt (111) were measured both for an extensive

(10-fold) range in NO coverage and under the influence of co-adsorbed CO.

Unlike the earlier, apparently non-equilibrium dynamics exhibited by the

N0/Ru(001) system, the results of the work on the N0/Pt(111) system may be

summarized as follows: 1) the rotational levels and spin-orbit states are characterized by a common rotational temperature; 2) although the kinetic

parameters describing the desorption process change significantly with

coverage and the presence of co-adsorbed CO, the rotational degree of freedom

of the desorbing NO is always nearly fully accommodated with the surface

temperature; 3) there was no measurable alignment of the desorbing species.

In terms of the observable dynamics there was no manifestation of

adsorbate-adsorbate interaction, i.e., no substantial deviation from full

accommodation. In both the NO-NO and NO-CO systems the adsorbate

interactions are weak-to-moderate in strength. The co-adsorption system

(N0+NHo)/Pt ( 1 1 1 ) was chosen for study in FY86 since it had been shown by TPD

and EELS studies that there is a stable, surface bound complex formed upon

co-adsorption of NO+NH^ on cold Pt (111). Thermal desorption of NO and of NK^

occurs simultaneously at a temperature much higher than characteristic of

either species, implying that the rate-limiting step in the co-adsorbed

system is dissociation of the more strongly bound complex.

Although the kinetics for NO desorption from Pt (111) were significantly

altered by the interaction with co-adsorbed NH^ there was no significant

deviation from near-complete rotational accommodation with the surface.

For surface temperatures of 150 to 400 K and NO coverages of 5 % to

saturation, the rotational temperature of the desorbed NO was 90 ± 5 % of the

instantaneous surface temperature and independent of the amount of

co-adsorbed NHo. This imples that disruption of the NO/NH^ complex leads to

NO molecules which are able to accommodate with the surface prior to

desorption

.

2. Laser-induced Desorption: N0/Pt(foil)

Thermal desorption techniques probe surface processes occuring under

conditions of thermodynamical equilibrium. This is to say that external

heating rates of 1-10 K/s are much slower than rates for energy transfer in

condensed phases. To attempt to learn the important time scales for

molecular energy transfer at surfaces we have implemented a program in

laser-induced thermal desorption. Here it is hoped that sufficiently rapid

307
temperature jumps (heating laser pulse durations of 1 0~® to 2 x 10” 11 s) will

allow desorption or other surface processes to compete favorably with energy

exchange or relaxation processes characteristic of thermal processes.

A major concern in all experiments where a laser is used to heat a surface is the accurate determination of the surface temperature. Classical

heat conduction equations have been employed to establish the surface

temperature in the past, and are currently being used to analyze the

desorption yields obtained in this laboratory. However, experimental efforts

to validate the surface temperature actually achieved due to laser heating are sparse. A direct measure of the laser perturbation of the surface properties

would offer the most satisfactory probe of the heating effects. Attempts at

exploiting the resulting time dependent black-body radiation as a signature

of the surface temperature have not been successful. The choice of our initial system for study, NO/Pt using 3“8 nanosecond heating-laser pulses, was based on our earlier results for NO/Pt thermal desorption wherein we have always observed near-complete rotational accommodation. Our naive

expectation was that desorbed NO would exhibit rotational and

translational accommodation and thereby give us an in situ probe of the

response of such a surface in other laser-heating experiments.

The experiments were performed on a 25 x 12 x 0.25 mm polycrystalline

Pt foil in a small UHV test chamber (base pressure 2 x 10” 10 torr). A frequency-doubled, 3 ns FWHM YAG laser was used to heat the surface. A spatially homogeneous portion of the collimated laser beam irradiated a 1.5 mm diameter portion of the surface with 0.5 mJ/pulse at near normal

incidence. The density of desorbed NO in specific (V, J, 0) states above the

surface was probed using a frequency-doubled dye laser (0.05 cm

-1 bandwidth,

9 ns FWHM) tuned to the (0-0) or (1-1) vibronic bands of the NO A-X

electronic transition. The 1 mm diameter probe beam was aligned parallel

to the surface at a distance of 4 mm. LEF from desorbed molecules in a 1.5 mm long portion of the probe beam was detected with f/2.5 collection

optics, spatial masks, spectral filters, and a solar-blind photomultiplier.

The platinum surface was initially flashed clean to 1300 K, cooled to

200 K, and then exposed to a saturation dose of NO. A background pressure of

4 x 10~9 torr NO was maintained during the experiments to stabilize the

surface NO concentration, which would otherwise have been slowly depleted by

the LITD process. Time of flight (TOF) distr

butions were obtained by

scanning the time delay between the desorption laser and the probe laser in

0.1 ysec increments. At the 30 mJ/cm2 incident energy density used, the

surface temperature jump was calculated to be 120 K from the optical and

thermal properties of platinum and the laser pulse FWHM. This implies a maximum surface temperature of T

m =320 K.

Representative TOF distributions for desorbed NO in v=0 with low (25

cm”

1 ) to moderate (662 cm” 1 ) rotational energy are shown in Figure 3-2. The

observed LEF/T0F signals correspond to maximum molecular densities of about 5 x 10~° torr in the probed region as determined by comparison to LEF s.gnais

with NO flowing through the chamber. The prompt onset and early maximum

308
exhibited by the molecules in the J=19.5 rotational state became increasingly

more apparent as higher quantum states were probed. These data and TOF

spectra for 16 other rotational states with 25 < ER < 2162 cm

- "

1 suggest that

there are at least two distributions of NO desorbing from the surface: a "fast" component with moderate internal excitation and a slower component

with a "colder" internal energy distribution. To characterize the

translational and rotational energy distributions of the desorbed NO, all of

the TOF spectra were fit to the sum of two velocity distributions, each of

the form P(v) = v^exp[-( a+bv+cv2

) ] , which reduces to a Maxwell-Boltzmann

distribution for b=0.

For all quantum states with 25 < E

R < 2162 cm

- ”' , the slow component

was fit by a distribution with a mean kinetic energy of <ET>=52±5 meV, while

<Ej> for the fast component continuously increased from 240 ± 35 meV to 460 ± 50 meV with increasing E

R

. Maxwell-Boltzmann distributions with these

average energies are characterized by effective translational temperatures

<ET>/2k of 300 K and ranging from 1400 to 2650 K, respectively. However, the

observed distributions were not Boltzmann. Each had a slightly larger energy

spread <E^>/<ET

>^ than would a Maxwell-Boltzmann distribution. The

relative populations for the rotational levels were determined by their

magnitudes in the TOF fits. The rotational populations for states with 25

< E

R < 662 cm

- "

1 were well characterized by Boltzmann distributions with

temperatures of 410 ± 50 and 170 + 20 K for the fast and slow components,

respectively. The energetic NO molecules contributed 21 ± 3 % to the

integrated desorption flux under these experimental conditions.

TOF distributions were measured for desorbed N0(v=1,J) states with E

R

< 133 cm

-1

. These were dominated by a single velocity distribution with <ET

> = 290 ± 25 meV. The N0(v=1) rotational distribution was estimated from an excitation spectrum taken at 3 ysec delay and including transitions from 7

different rotational levels. A value of T

R (v=1)=155 ± 75 K was obtained.

Comparison of the integrated population in v=1 to the v=0 fast component

yielded a ratio of 0.054 ± 0.027, consistent with Ty=900 K.

To summarize the N0/Pt(foil) laser-induced thermal desorption results,

at near saturation coverage from a platinum foil two components were

observed. Although the mean kinetic energy of the less energetic component

is comparable to the maximum surface temperature, its rotational temperature

is significantly lower than the surface temperature. Such incomplete

rotational energy accommodation has been observed in conventional TDS

experiments for N0/Ru(001) and discussed in terms of dynamical factors in the

adsorption potentials. A dramatic departure from accommodation was exhibited

by the energetic NO, with its high translational energy. While this is

consistent with exit channel effects which have been invoked for thermally

activated H

2 recombination and CO oxidation reactions at metal surfaces, it

is also consistent with a sudden ( non-thermal) desorption channel.

Apparently, at heating rates of 10 10 K/s new desorption channels compete

favorably with thermalizing energy relaxation pathways even under mild

temperature jump conditions. This work is supported in part by the U.S.

Department of Energy.

309
TIME-OF-FLIGHT Cpsec)

Fig. 3-2 Desorbed nitric oxide LEF signal as a function of time delay

between heating and probe laser pulses for different quantum

states. Spectra are normalized to NO at 29^ K. Two-component

fits to the data are also shown, a) J-19.5, <ET

> - 450 and 60 meV;

b) J-12.5, <Et

> = 330 and 53 meV; c) J-3.5, <ET

> - 235 and 47 meV.

3. Future Plans

This work will be directed towards exploring in more detail

laser-induced thermal desorption (LITD). "Non-equilibrium" behavior has been

observed for NO desorbing from Pt foils at low initial surface tempeatures

when driven by 3 ns, visible heating-laser pulses. We hope to answer speculations regarding the physical origin of this non-equilbri urn dynamics

(i.e., secondary desorption channels, recombinatory desorption, coverage

dependent adsorbate interactions, binding site effects, or electronic effects)

by exploring LITD results as a function of heating-laser pulse length,

wavelength and energy, of surface morphology using single crystals, and of

initial surface temperature, coverage and co-adsorbates.

310
One of the long range goals of this program is to study recombination

reactions on surfaces. For technical reasons, this is difficult by thermal

desorption techniques. Experiments currently underway entail the use of a variable pulse length heating laser (10 ns to 25 ps on loan from Radiation

Physics for four months). These experiments should ellucidate the

contribution from recombinatory desorption to the observed N0/Pt(foil) LITD

signals (described above).. It is anticipated that LITD will provide a powerful

technique for detailed study of recombination rections.

C. Dynamics of van der Waals Molecules

(M. P. Casassa, L. B. Elwell, D. S. King, and J. C. Stephenson)

There has been substantial recent theoretical interest in the vibrational

predissociation of van der Waals (vdW) molecules, but very few experiments

that have looked at either the final product state distributions or obtained

real time measurement of the dissociation lifetimes. We have recently

studied the vibrational predissociation of the nitric oxide vdW dimer,

including picosecond time-resolved measurements of the lifetime following

excitation of the symmetric (v^) and antisymmetric (vjj) stretching modes, and

measurements of the complete distribution of energy in NO product fragments

following v^ excitation.

Vibrational predissociation of van der Waals molecules occurs because,

in general, the constituent molecular vibrational levels lie above the vdW

bond energy. Vibrational excitation and subsequent vibrational energy flow

lead eventually to rupture of the weak van der Waals bond. While such

systems have had great appeal as models for vibrational dynamics, the

previously available lifetime data are based on indirect measurements. In our experiments, picosecond infrared pulses excited the symmetric (v^ = 1 ) or antisymmetric ( = 1 ) stretching modes of the NO dimer. The formation

times of the NO fragments ejected upon vibrational predissociation were measured by laser excited fluorescence (LEF) using picosecond time-delayed

ultraviolet laser pulses. A remarkable dependence of the predissociation

lifetime on the vibrational mode initially excited was observed.

The NO dimer has C symmetry with a 2.236 A N-N separation and a 99.6°

0-N-N bond angle. The dimer bond energy is 800 ± 150 cm

- "

1 . Photodissociation spectra have been reported for excitations of the symmetric

v-j (vibrational symmetry A-| ) and antisymmetric (B 2 ) N-0 stretching

fundamentals at 1870 cm

-1 and 1789 cm

-

', respectively. The low frequency

modes associated with the vdW bond are 90 (A 2

), 170 (A-j), 198 (B 2

), and 263

( A-j ) cm

- ”

1 . We used laser-excited fluorescence (LEF) spectroscopy (using a frequency doubled C0 2 laser for photolysis and a 1 0 ns probe dye laser) to

determine the internal state distribution and kinetic energy of the NO

photofragments. For fragments with internal energy E int < 400 cm

-1 (representing a 97 ^ of all products), the rotational states were adequately

represented by a Boltzmann distribution with TRot = 110 K * for both spin

orbit states. The two spin orbit states, F

1 = NO 2 n -)/ 2 and F

2

= NO 2

n-^/ 2

»

311
were formed with equal probability. The lambda doublet states were formed

with equal probability. The average product internal energy was <E. = 135 ± 25 cm

" 1

. n

Doppler profile measurements were made for fragments in the F

2 (J=3.5)

state. Profiles measured with the propagation direction of the probe laser

parallel or perpendicular to the electric vector of the photodissociation

laser were indistinguishable. This indicates the angular flux of the NO

photodissociation fragments was essentially isotropic. The observed Doppler

profiles were "top hat" (rectangular) in shape with 0.165 ± 0=01 cm

-1 FWHM.

The top hat shape implies a narrow kinetic energy distribution, a condition

imposed by the photon energy and E int distribution [assuming the dimers

initially equilibrated with the beam (T - IK)]. Computer modeling (including

the fragment internal state distributions) of the observed Doppler profiles

gave an average kinetic energy <EK

> = 400 ± 50 cm

-1 for each NO.

Conservation of energy gives a bond energy D Q

= 800 ± 150 cm

-1

, which may be

compared to the value D Q = 590 ± 80 cm

-1 calculated from infrared intensity

measurements.

For the lifetime measurements , dilute mixtures of NO in He or H

2 were expanded through a pulsed valve operating at 4 Hz with a .75 mm diameter

orifice. The observed LEF signals scaled with expansion conditions as for NO mole fractions 0.005 £ X £ .02 and nozzle stagnation pressures

3 S P ^ 10 atm. This is the same scaling behavior attributed to (N0 ) 2 previously. The conditions used for the lifetime measurements were shown by

mass-spectrometry and final-state energy distribution measurements to produce

cluster signals dominated by NO-dimer, and exhibit rotational cooling (of

uncomplexed monomer) to -1 K.

Picosecond infrared (ir) and ultraviolet (uv) laser pulses were derived

from two visible dye lasers synchronously pumped by a frequency-doubled,

modelocked cw YAG laser. One dye laser was set at u^-17, 341 cm

-1

. The

second dye laser was tuned to u

2

= 15,471 or 15,552 cm" so that the

frequency difference, a>o = cu-] - u2 , coincided with either the v-] or vij fundamental. Dye amplifiers pumped by a frequency-doubled, 2 ns Q-switched

YAG laser amplified both lasers to produce visible picosecond pulses at 20 Hz

with typical pulse energies of 0.7 mJ (aj-j) and 0.3 mJ (gj2

). Bandwidths of

these pulses were 3 cm

" 1 FWHM with autocorrelation widths of 7.5 ps FWHM and

a cross - correlation width of 10 ps FWHM. Infrared pump pulses of 4pJ were obtained by difference frequency mixing uj.| and <j2 in LUO3

. The ir pulses

were focused to a 0.3 mm diameter beam waist to vi brationally excite the

beam-cooled (N0) 2

. Ultraviolet probe pulses were produced by frequencydoubling w

2 in KDP and then summing 2w2 with residual 1.064 nm from the

Q-switched YAG in KD P. These pulses traversed a variable optical delay and

were focused to a 0.15 mm beam waist colinear with the ir pump beam.

Probe pulses polarized at the magic angle to the ir pump pulses traversed

the beam at a time t D , relative to the pump pulses, exciting those NO

fragments formed in the J = 1.5-7. 5 levels of the X^n ^/ 2 state (P 2 band head

region), resulting in LEF signals directly proportional to the number o

r NO

312
fragments formed during the time t D

. Previous studies showed that these

probed states 1) are not appreciably populated by uncomplexed monomer in the

expansion, 2) are formed with high probability in the (N0) 2

v-| photolysis,

and 3) are not favorably formed in the 1870 cm

-1 photolysis of other NO

complexes. The LEF signal and pump and probe pulse energies were recorded

for each shot with a computer based data acquisition system. LEF signals

were normalized to the uv probe energy. Shots with ir energy falling outside

a ±20? acceptance window were rejected. For each data point, a delay setting

was randomly selected and 100 accepted shots were averaged.

1 1

1 L 0. .1 .2

Delay time (t D

) /ns

Fig. 3*3 Time-resolved appearance of NO fragments following excitations of

either the symmetric (v-|) or antisymmetric (v^) stretching

fundamentals of the NO dimer. Note the 20-fold difference in time

axes. The solid curves are least-squares fits of a simple

exponential decay function with unimolecular decay rate k uni = 1/Typ. Although only short time measurements are included for the

rapidly rising data, there was no change in signal for delays

between 150 ps and M ns.

Results for (N0) 2 v-](v=1) and vij ( v= 1 ) photodissociations are shown in Fig.

3-3. A dramatic difference in dissociation rates for these two modes of

nearly equal energy is immediately apparent (Note the 20-fold difference in

time axes). Only short-time measurements are shown for the rapidly rising vjj

data; no further increase in signal was observed for delays between 150 ps

and 4 ns

313
If the ir laser excited an ensemble which dissociated with a single

unimolecular rate constant, k uni = 1 /typ, the expected fragment appearance

behavior would be:

S(tp) = S( t[) = a5 ) [

1 -exp( tp/typ) ] •

Of course non-exponential or multi-exponential decay could occur. Non-linear

least-squares fits of single exponential decays to the data, shown as solid

curves, yield lifetimes of 880 ± 260 ds for v-, and 39 ± 8 ps for vi*. These

lifetimes represent average values for a distribution of rotational levels.

Assuming that the ir bandwidth is 4=5 cm

- "' (convolution of two 3 cm

-1

Gaussians), the pump laser interacts with all (N0 ) 2 rotational levels

expected to be populated in the molecular beam (If Trot = 1 K, levels with

J

TT =3 , K

a "£2 account for 95? of the population). Each vibrationally-excited

rotational level could have a distinct predissociation lifetime. However,

with the present signal-to-noise, the data at many different expansion

conditions are adequately fit by the same single exponential time constant.

Including additional exponentials with different decay times did not

significantly improve the fit to the data (i.e., reduce chi square).

That ( 1 789 cm

-1

) decays much faster than v-, ( 1870 cm

-1

) is

inconsistent with standard statistical theories of unimolecular reaction

which predict unimolecular rates to increase with reactant internal energy.

On the other hand, models of vibrational predissociation involving pure V-T

energy transfer correlate increased lifetime with increased energy release,

and predissociation from releases 81 cm

-1

more energy than v^. However,

theory quantitatively predicts a much smaller difference (factor of £ 2 ) between v-| and V 4 than was observed. In the case of (N0 ) 2 » the

predissociation might be nonadiabatic since the 2

n configurations of the NO

fragments combine to form several low-lying electronic states in the dimer.

Nonadiabatic effects have been suggested to explain the anomalously large

collisional cross-section observed for vibrational deactivation of N0(v-1) by

N0(v=0). The different overall symmetries of the v

1 and V 4 levels of the

dimer 1 A-j ground state may constrain coupling to low lying repulsive

state(s), causing the observed difference in lifetimes. Ongoing measurements

of product energy distributions following V 4 dissociation and lifetimes for

states of different vibrational symmetries (e.g., combination bands involving

the vdW modes) might elucidate the source of the difference in v-| and vq

predissociation rates.

Future progress in this area depends critically on our ability to

obtain additional funds, either internal or from other agencies, to cover staff salaries and operations. During 1987 we hope to measure the

vibrational predissociation rates following excitation of particular

vibrational modes of several vdW dimers, and also to measure the distribution

of energy (electronic, vibrational, rotational, translational) in the products.

Candidate molecules are:

314
1900 cm

- ’

1 CoHii ^ q *N0 — tt

1870 cm 1

CO-NO 2046 cm

-1

C

2H2 -C 2

D 2 3282 cm

-1

i

C 2 H4( vj+vq) -NO

C

2 Hi|-N0(v=1)

C0( v=1 ) -NO

x C

2H 2

( V3=1 ) -C 2

D 2

C 2 H4 + NO (J,Q,A)

C 2H4 + NO ( J, Q, A)

C0( 0) +N0( v=1 or v=0,J,fi,A)

C2H2 (v,J) + C 2 D 2 (v,J).

Many other vibrations in C

2H2 , C 2

D2 , and C 2HD complexes can be studied. In

several systems vibrational energy transfer across the vdW bond (a fast

process according to some theoretical calculations) may occur and can be

readily detected by LEF. A high resolution (e.g., transform limited,

15 ns pulses) tunable infrared laser source, similar to the low resolution ps

ir difference frequency system, is necessary for obtaining good

photodissociation spectra on the same molecular beams used for the

time-resolved measurements.

D. Photophysical Studies of Photosensitizers

(D. S. King, in collaboration with D. F. Heller and J. Krasinski of

Allied Corporation and R. S. Bodaness of National Center for Health

Services Research, 0HTA)

Many photosensitizers, such as hematoporphyrin derivative (HPD), are known

to produce excited-singlet molecular oxygen which is then responsible for

ensuing oxidation reactions. Chemically, HPD has received significant

interest because it preferentially binds to tumor tissue and can be used for

tumor localization (fluorescence) and photochemotherapy. Conventional tumor

photolocalization techniques use blue to ultraviolet excitation sources which

are severly attenuated by tissue absorptions, limiting detection and

• treatment to exposed surface layers. We have persued a more universal

approach which takes advantage of the two-photon spectroscopy of HPD.

Two-photon excited fluorescence spectra were taken using either a Qswitched YAG with a 20 ns output pulse duration at 1064 nm or a Q-switched

alexandrite laser with 55 ns pulse duration, tunable in the 730 to 780 nm range. Second harmonic generation was also used to directly excite the

sample at 532 or 375 nm. The evidence for two-photon excitation consists of

both the similarity of the fluorescence spectra recorded following, for

example, excitations at 1064 nm (two-photon absorption) and at 532 nm (onephoton absorption), and the quadratic intensity dependence of the two-photon

fluorescence signals. Calibrations to determine the two-photon cross-sections

were made from single-photon fluorescence data, using the known single-photon

absorption coefficients and fluorescence quantum yields. The two-photon

excitation cross-section at 750 nm (of 1.5 x 10

-2^ cnr s) was approximately

100-fold greater than that at 1064 nm; we attribute this to a resonant

enhancement contribution from the HPD S-] state.

315
In the alexandrite laser excitation experiments the HPD two-photon

fluorescence was of sufficient intensity to be observed by eye in a darkened

room through a single dielectric filter. This implies potential usage of

such two-photon techniques for tumor localization at substantial tissue

depths since there is an approximately one-thousand fold increase in tissue

transmission at 750 nm as compared to 400 nm. Since the two-photon

absorption rate is proportional to the square of the laser intensity, the

application of picosecond laser pulses should greatly increase the efficiency

of the two-photon absorption process, permitting the use of substantially

reduced laser pulse energies to achieve equivalent ends. Use of 50 ps, 1 mJ

pulses available from a pulsed, mode-locked alexandrite laser oscillator will

only deliver 2 % of the energy dose used in the present two-photon

experiments, however the two-photon excitation rate should be enhanced a million-fold in relation to excitation by a 50 ns pulse of the same energy.

This should lead to complete saturation of the HPD two-photon absorption.

Such experiments are planned for Spring 1987.

316
U . QUANTUM CHEMISTRY GROUP

H. Basch, D. Beveridge, W. Fink, N. Goldgaber, P. J. Jasien, P. S. Julienne,

M. Krauss, B. Lengsfield, M. Mezei, F. H. Mies, K. J. Miller,

R. Osman, W. J. Stevens, and L. Vahala

The Quantum Chemistry Group develops and applies atomic and molecular

structure and scattering methods to chemical and spectroscopic problems where

experiments are difficult to perform or so complicated that the theory is

needed to model the results. The activities of the group encompass three

broad areas: the study of the structures and properties of large

biomolecules, accurate quantum mechanical calculations on small molecules,

and atomic and molecular scattering theory.

The biomolecular research is a result of the NBS biotechnology initiative

and represents a new direction for the group. Initial work in this area has

focussed on the development of methods for accurately predicting the

electronic structure, energetics, and properties of small pieces (eg., active

sites) of large molecules. This research has resulted in new techniques for

the decomposition of molecular electrostatic potentials and polarizabilities

into transf errable fragment components that will be used to construct

effective Hamiltonians for the small parts of the biomolecules to be studied

quantum mechanically. During the past year, several collaborations with

other groups have been initiated which will concentrate on applications of

newly developed theoretical techniques to interesting problems in

biochemistry. The Molecular Structure and Modeling Facility IBM4381 computer

is used for these large scale calculations.

9 The determination of accurate electronic structures and properties for

small molecules has been a central focus of the group's activities for many

years. Our unique capability for handling heavy atoms through the use of

effective core potentials has allowed the study of a variety of interesting

molecules including transition metal oxides and heavy rare-gas dimers. The

accomplishments for this year include state-of-the-art calculations on chromium oxide and silicon carbide, and a complete set of calculations of the van der Waals potentials for the homonuclear and mixed rare-gas dimers.

In the area of scattering theory, new methods have been developed for the

determination of cross-sections and fragment state distributions associated

with the collisonal broadening and photodissociation of small molecules in

the presence of both weak and strong radiation fields. In addition,

significant progress has been made in the area of multichannel quantum defect

theory and non-adiabatic half-collision amplitudes, with specific

applications to broad-band continuum spectroscopy.

317
A. Theoretical Calculations on Biomolecules

1 . Development of an Ab Initio Reaction Field Program

(W. J. Stevens, H. Basch, and M. Krauss)

Although the methods of modern quantum chemistry and the machines on which calculations are carried out have evolved dramatically in the last ten

years, it is still not feasible to determine the geometric and electronic

structures of very large molecules (> 20-30 atoms) by ab initio techniques.

However, in large molecules such as proteins, it may be possible to learn a great deal about chemical properties by looking at the detailed electronic

structure of a small part of the molecule (the active site), while treating

the remainder of the system as a perturbing environment that plays only an indirect role in the chemistry. During the past year we have modified the

HONDO electronic structure program to include a reaction-field Hamiltonian

that allows the study of an active molecular fragment, "A”, in the field of a molecular "spectator” environment, "S”. The Hamiltonian is written

h

a

= ha

+ v AS

where V^ describes the interaction of the active electrons with the

spectator part of the system. Assuming the interaction of "A" with ”S" is

non-bonding (i.e., no covalent bond, no charge-transfer ) , the interaction

terra in the Hamiltonian may be broken down into three pieces: electrostatic,

polarization, and orthogonality and exchange repulsion. Our desire is to

represent each of these interactions by one-electron operators in the

Hamiltonian of the active part, so that the difficulty of the calculation is

primarily dictated by the complexity of the active fragment "A".

Our analysis of the electrostatic potentials of the spectator molecules

is based on localized molecular orbitals (LMO). Accurate SCF calculations

are carried cut for prototypical molecules containing specific functional

groups. The molecular orbitals of the prototype are localized by some appropriate method (e.g., the Boys method). The electronic contribution to

the electrostatic potential is the sum of the contributions from each LMO.

The electrostatic potentials of LMOs catagorized by functional groups are found to be reasonably transferrable from one molecule to another. The

electrostatic potential of each LMO is approximated by a multipole expansion

at its center of charge. The molecular potential is then represented by a distributed set of LMO expansions. This distributed expansion produces an accurate representation of the molecular electrostatic potential for LMO

expansions that include only the centers of charge and the first few moments.

We have modified the HONDO code to include the potentials of such

distributed charges and second moments in the Hamiltonian, and test

calculations are now being done to determine the accuracy for a variety of

prototypical systems.

The polarization of "A" by "S" occurs naturally when the Schroeding^r

equation is solved for the wavefunction of "A" using a Hamiltonian that

contains the electrostatic potential of ”S”. However, the determination :f

318
accurate interaction energies requires that "S" also is polarized by the

electrostatic potential of "A". In addition, there is a self-consistent

effect in the mutual polarization of the two parts of the system.

Fortunately, the self-consistent part of the polarization has been found to

be small (-10?). For the energy contribution due to the dipole

polarizability of "S" we evaluate the expression

< T A li,j ?i • ?j a ("S")| f A

>

where is the electric field due to electron i in fragment ,! A", and

a( ,f S") is the dipole polarizability of fragment "S". This energy term is

evaluated as a perturbation once the wavefunction for "A" is known. Putting

the operator directly into the Hamiltonian of "A” is not possible, because

second order effects related to dispersion are improperly introduced. The

polarizability of the fragment "S" is constructed from fragment LMO

polarizabilities. We have developed a coupled Hartree-Fock scheme which

allows the total calculated polarizability of a molecule to be rigorously

represented as a sum of LMO polarizabilities. A series of calculations has

shown the LMO polarizabilities for functional groups to be reasonably

transferrable from one molecule to another. Distributing the LMO

polarizabilities in the fragment "S" helps take into account the

inhomogeneous nature of the electronic field due to "A". Higher order

polarizabilities may be added in the same fashion if necessary. Currently,

the HONDO code incorporates spherically averaged LMO polarizabilities in the

Hamiltonian of "A", and work is proceeding to incorporate tensor

representations.

Exchange repulsion and orthogonality between "A" and "S" must be

included in the Hamiltonian of "A" in order to prevent the collapse of the

"A” wavefunction into the "S" region. A rigorous evaluation of the exchange

interaction requires two-electron operators and a knowledge of the wavefunctions of "A" and "S" . In the *case of atoms, it has been shown that a one-electron effective potential can be constructed which accurately mimics

the exchange repulsion between the valence electrons and the frozen core. Our group has used such potentials extensively in calculations on systems

containing heavy atoms. We are developing analogous procedures for molecular

systems where the fragment "S" is treated like the frozen core in the atomic

case. A prototypical all-electron calculation is done in which the fragment

"A" is optimized with the fragment "S" held frozen. The wavefunction of "S"

is taken as a product of frozen LMOs which are obtained from independent

calculations on "S" alone. Then the frozen LMO exchange operators in the

Hamiltonian of "A" are replaced by one-electron effective potentials. The

parameters defining the potentials are adjusted until the orbitals and energies of "A” match those obtained from the all-electron calculation using the

frozen "S" and the correct exchange operators. Since the derivation of the

effective potentials is based on LMOs, transf erability from molecule to

molecule is expected. Calculations are underway to test this hypothesis.

319
2. Modeling of Fe and Mn Superoxide Dismutases

(R. Osman, W. J. Stevens, M. Krauss, and H. Basch)

This research is part of a long term objective to understand the

biochemical and biophysical role of metals in enzymatic mechanisms of

metallo-enzymes . Quantum mechanical calculations are carried out on models

of the enzymes active site, with and without the substrate, in order to

ascertain whether proposed mechanisms are reasonable from an energetic point

of view. The complexity of the model and the sophistication of the quantum

mechanical approach are chosen to produce energetics that are reliable enough

to determine which of several proposed pathways may be energetically the most

favorable. The electronic structure of the model active site is analyzed to

provide insight into the interactions that favor one pathway over another.

Three different superoxide dismutases have been chosen for study. They are Cu,Zn-SOD, Fe-SOD, and Mn-SOD. The availability of their crystal

structures enables the construction of models of their active sites. Osman

and Basch have previously studied Cu,Zn-SOD (J. Amer. Chem. Soc. 1 06 , 5710

(1984)) and have suggested a new mechanism of action that is quite different

from the ones proposed previously. Their quantum mechanical calculations

indicate that a single superoxide (

0

2 ) cannot reduce the cupric ion because

of an arginine group (Arg-141), positioned near the copper, that forms a strong hydrogen bond with the superoxide. Thus, superoxide forms a relatively stable complex with Cu,Zn-S0D that is subsequently reduced by

another superoxide in solution. The reduced complex undergoes an internal

oxidation-reduction coupled to a proton transfer that results in regeneration

of the original enzyme and the formation of the products of the dismutation

reaction. The proposed mechanism is in agreement with all known kinetic

measurements of the enzymatic reaction. The mechanism is based on the

special poperties of the copper ion in the active site and its surroundings

in the protein (particulary Arg-141).

Fe-SOD and Mn-SOD, while similar in structure to each other, are quite

different in structure from the Cu,Zn-S0D. The proposed mechanism of action

of these enzymes is also based on the reduction-oxidation cycle which is

consistent with the kinetic studies of the dismutation reaction. However,

the details of the reaction are not understood, and analogy to the Cu,Zn

enzyme may not be warranted. The recent availability of crystal structures

for these enzymes offers an opportunity to perform quantum mechanical

calculations on models of the active sites.

We have begun the calculations by determining effective core potentials

for the Fe and Mn atoms which allow their inclusion in the model active sites

as valence-only systems. In addition, the core potentials have been modified

to reproduce accurate -> M

+

^ ionization potentials. Crystal structures

indicate that the metal ion is pentacoordinate , with three hystidines, one aspartate, and one water (or OH ) acting as ligands. In our initial models

we have replaced the hystidines by ammonias and have considered only the five

ligands directly bonded to the metal ion. More complex models will be

320
developed using a reaction field approach to incorporate regions of the

enzyme that do not participate directly in the reaction but do influence the

energetics by virtue of their electrostatic potentials.

3. Frozen Fragment Studies of Hydrogen Bonding

(W. J. Stevens and W. Fink (UC Davis))

In a recent series of articles (J. Chem. Phys. 1983, 78 , MO 66 ; J.

Chem. Phys. 1985, 83_, 735; J. Chem. Phys. 1986, 84_, 5687) Reed and Weinhold

have proposed an energetic decomposition of hydrogen bonding interactions

based on a "natural bond orbital" analysis. The conclusions reached through

this analysis are that the electrostatic attraction and exchange repulsion

energy components of the hydrogen bond nearly cancel each other, and the

charge-transfer interaction determines the shape of the potential energy

surface and the structure of the complex. The charge-transfer analysis is

similar to the HOMO-LUMO charge-transfer interaction proposed by Klemperer

and coworkers, but differs in that the orbitals involved are the localized

lone-pair orbital as electron donor and the unoccupied X-H antibonding

orbital as electron acceptor. The amount of charge transferred is very small

(a few thousandths of an electron), but the energy contribution is said to be

several kcals/mol. This analysis is contrary to the widely accepted proposal

of Buckingham and others that the structure and energetics of hydrogen

bonding is determined primarily by electrostatics.

One of the problems with a decomposition of the interaction energy

between two molecules is that the orthogonlity , exchange, and charge-transf er components are difficult to unravel because they all involve the overlap of

the molecular wavef unctions . The analysis is also confused by a superposition effect that occurs when the virtual orbitals from the basis set

of one fragment help to improve the occupied orbitals of the other fragment.

Even though the analysis of Reed and Weinhold appeals to be remarkably

consistent for a wide variety of hydrogen bonded complexes, it is not

impossible that the component of the energy that has been assigned to

charge-transfer is really a mixture of other effects.

In collaboration with the group at the University of California at

Davis, we have modified the HONDO program to allow for the selective freezing

of molecular fragments in an all-electron calculation. It is also possible

to selectively eliminate unoccupied virtual orbitals from the basis set. We

have used this program to study the water dimer and to assess the importance

of charge-transf er in the hydrogen bond interaction. The molecules in the

dimer are labelled "A" and "B". Using a fully optimized hydrogen bonding

geometry at the double-zeta plus polarization level, the energy is calculated

by selectively freezing the wavefunction of either "A" or "B" and optimizing

the wavefunction of the unfrozen molecule. The frozen wavefunction is

obtained from a calculation on an isolated water molecule. Charge-transfer

cannot occur from the frozen water to the variationally active water. We

have also eliminated the virtual orbitals from the frozen water basis set so that charge-transf er cannot occur from the variationally active water into the

unoccupied space of the frozen water. With all of these constraints, our

321
preliminary calculations have found that the hydrogen bond energy in the

frozen molecule calculations is within 20% of a fully variational hydrogen

bond energy„ Also, a significant portion of the missing energy can be traced

to the lack of polarization in the frozen molecule. Although many more hydrogen bonded systems need to be studied, our tentative conclusion is that

charge-transfer does not determine the structure and energetics of hydrogen

bonded complexes.

A. Monte Carlo Studies of Solvated Biomolecules

(D. Beveridge, M. Mezei, W. J. Stevens, and M. Krauss)

This research project has been initiated to explore the interface

between ab initio quantum mechanical studies of large molecules and

simulation of molecules in the liquid state using the Metropolis Monte Carlo

method. The first step in this project has been to install the Hunter

College MMC program for Metropolis Monte Carlo simulations on the Molecular

Structure and Modeling Facility IBM4381 computer and the Consolidated

Scientific Computing System CYBER205 computer. The MMC program, developed by

Mezei and Beveridge, is a state-of-the-art program for simulation of a dilute

aqueous solution with a force-bias option for convergence acceleration, and a proximity analysis option for assigning the solvent molecules in each

N-particle configuration of the system to individual atoms of the solute.

The MMC program uses intermolecular potential functions based on several

current prescriptions. These functions are hardwired into the code, but the

introduction of new potentials is easily accomplished. The results of the

computer simulation include the calculated thermodynamic internal energies,

heat capacities, and various structural and energetic molecular distribution

functions. Some new methods for free energy simulations are also included.

The accuracy of the results of computer simulations of dilute aqueous

solutions is dependent on the intermolecular potential functions that are used to evaluate interaction energies and energy derivatives between

molecular constituents. The functions currently used in programs such as MMC are based on pairwise-additive interaction potentials between points in the

molecules (usually the atoms) that are derived either empirically or from ab

initio quantum mechanical calculations. The form of the potentials is kept

simple (6-12 plus a coulombic term) because of the computer time required to

carry out the simulations. Potentials derived by fitting quantum

mechanically calculated potential energy surfaces have been restricted to

low-level SCF calculations, such as ST0-3G, due to the expense of accurate

calculations on complex molecules. Our high-speed computing resources and

recently developed methods for simplifying ab initio calculations on large

molecules (such as the reaction field approach) will enable us to examine the

dependence of the Monte Carlo simulation results on the accuracy of the

potentials. Benchmark calculations are planned for several small amides in

aqueous solution. We will also explore the use of distributed molecular

polarizabilities in the evaluation of interaction energies as a method for

incorporating many-body effects in the simulation. This will be particular;/

important in the study of solvated ions.

322
Quantum mechanical calculations of the properties and reactivities of

molecules in solution or of molecular fragments imbedded in very large

molecular systems are limited by the statistical nature of the perturbing

environment at nonzero temperatures. Part of the collaboration between the

NBS and Hunter College groups will be to explore the use of snapshot

distributions from converged Monte Carlo simulations to construct models of

the solvent environment in reaction field studies of prototypical molecules.

5. Binding of Pt Complexes to DNA

(H. Basch, M. Krauss, K. J. Miller (RPI))

Preliminary calculations on the binding of cis-Pt

,

(R=H,

methyl, and cyclopropyl) to a tetramer duplex were reported in last years

report but research has expanded on this problem because of new experimental

results reporting the binding of PtOlH^ to a pGpG segment (S. E. Sherman et

al.. Science 230 , 412 (1985)), that suggested Pt(NH2)»»»0P H-bonds

significantly stabilize the complex. This research was initiated to

determine if binding energies could account for the very different anti-tumor

potencies between the methyl derivative and both Pt(NHn) 2 and the cyclopropyl

derivative. We concluded in the preliminary results which combined SCF

calculations of model binding energies with molecular mechanics

conformational energy analysis that the binding energy varies smoothly with

substitution. The constrained molecular mechanics energy minimization did

not show direct hydrogen bonding between the amine ligand and phosphate which

is a feature of the Pt-pGpG crystal structure.

Two directions are being pursued to determine if direct phosphate

H-bonding is important in the duplex structure. Full cartesian coordinate

geometry optimization is being pursued with a tetromer duplex bound to Pt.

Achieving a global minimum is an almost impossible task but a number of local

minimum structures have been examined and those which distort the H-bgnding

between the bases the least were examined for the substituted amines.

Although a phosphate moiety is found to approach closer to ammonia (0»**H of

the order of 3-5A), an H-bond distance of approach has not been found. The

second phase of this calculation is to examine SCF H-binding energies for

Pt(NHo)(R) 2 to phosphate with associated waters in order to examine the

possibilities for water either externally bonded or as a bridged water.

These calculations are still in progress. The results to date do not alter

the earlier conclusion that potency and binding energy are not correlated

if no chemical reaction other than ligand replacement is induced by the

Pt interaction with DNA.

6. Electronic Structure of Phosphates, Phosphoranes , and Their

Analogues

(H. Basch, M. Krauss and W. J. Stevens)

Is the stable five coordinate vanadium complex formed in the binding

of uridine vanadate to ribonuclease an analogue for a five corrdinate phosphate

transition state? By examining the comparative electronic structure and the

proton affinities (PA) the concept of transition state analogues can be made

323
more precise. The relative amount of d orbital contribution and the PA of

different sites will determine whether proton transfer from the protein to

the site as observed for the vanadium complex reflects the phosphorane

situation. At the SCF level there is a substantial difference between the

electronic structure and PA of PO3 and VO3. Electron correlation has only a small effect on PO^ or H2P0I) but the comparable vanadium calculation has not

yet been done.

Whether phosphorothioate anions will interact with proteins at either

the S or 0 site will, in part, be determined by the electrostatic potential

at each site. Although considerable experimental effort has been devoted to

determining bond orders and ionicities for these molecules, the simplest way

to determine the potential is to calculate it from a high quality

wavefunction. Electrostatic potential maps are compared in Fig. 1 for

H2PO14 and H2P03S” in a plane determined by O-P-O or 0-P-S. The outer

potential contour which determines binding behavior is shifted for S relative

to 0 by approximately in proportion to the longer bond in P-S, reflecting the

comparable ionicity of 0 and S. This suggests zwitterionic or H-bonds will

be made initially with S which would be reinforced by the larger

polarizability of S. On the other hand, there is much less difference in the

outer contours of PO^ and P02S~, reflecting the smaller fractional charge

found for S in this case. Optimized geometries and PA's have been determined

for all these species. Calculations have been initiated on the NMR chemical

shifts for 31 p to correlate shifts with electronic structure and

conformation.

li2PO>! ELECTROSTATIC POTENTIAL

SIZE: 38, XC0H=-138, -123,-100.-75,10

H2P03S ELECTROSTATIC POTENTIAL

S I ZE: 30, VCOH= - 1 30, - 113 , - I 90, - 73 . 10

Fig. 4.1 A comparison of the electrostatic potentials of H->P0ij and HoPO^S.

The dashed contours represent potentials of -150 [innermost', -115,

- 1 00, and -50 kcal.

324
7. Rotational Barriers in Formamide and Acetamide

(P. G. Jasien, W. J. Stevens, and M. Krauss)

The energy barrier to rotation about an amide bond is important in

the modeling of protein conformation. There have been a number of ab initio

attempts to calculate the inherent barrier, but a review reveals that the

accuracy was significantly limited by a lack of a complete polarization

basis. The present results indicate that the inclusion of polarization

functions in the basis set leads to a substantial decrease of 5 kcal/mole in

the barrier height at the SC F level. Considering electron correlation and

the zero point energy correction, the in vacuo rotational barriers for

formamide and acetamide are predicted to be 14.2 and 12.5 kcal/mole,

respectively.

8. Future Plans

The major thrust in the biotechnology area is the development of the

reaction field method. The reaction field method will be applied to the

• effect of solvation on the stability of amides, reactions of phosphates and

their analogues, the binding of metals to DNA and protein model compounds,

and the mechanism of reaction of Fe and Mn superoxide dismutase. A continuing effort is needed in evaluating the parameters and assessing the

data (centroids, local polarizabilities, local quadrupoles, ...) required for

the reaction field. The use of both molecular mechanics and statistical

mechanics methods to determine the conformation of the environment region in

the reaction field will be investigated.

B. Quantum Chemistry of Small Molecules

1 . Accurate Calculations on Small Molecules

(W. J. Stevens, P. G. Jasien, and B. Lengsfield)

(a) CrO and CrO

+

Understanding the electronic structure of the transition metal

oxides is a challenge for experimentalists and theoreticians alike. The

multiple open-shell nature of the electronic wavefunction, highly degenerate

constituent atoms, extreme covalent/charge-transfer mixing, and large

spin-orbit splitting make the electronic states difficult to characterize

theoretically and the spectra and thermodynamic behavior difficult to

analyze. The CrO, CrO

+ system is interesting from a theoretical point of

view because there are a number of experimental analyses available including

high-resolution spectroscopy of the ground state, photoelectron spectroscopy

determining the ionization potential, and several estimates of the

dissociation energies. The ground state of CrO is a state with the

dominant valence configuration

325
1 2 2 4 12

0 0 0 TT IT 0 Cr 0 b b a Cr.

The molecule is best described as Cr + 0~. The singly occupied o orbital on chromium is strongly polarized away from both the 0“ and the double occupied

°b bonding orbital. The -tt^ bonding orbital is quite polarized toward oxygen,

and the ir a orbital is only weakly antibonding. Ionization to form the

positive ion will remove an electron from either the singly occupied sigma

orbital or the singly occupied pi orbital. Dyke, et al. (J. Chem. Soc.,

Faraday Trans. 1983, 79 , 1083) have analyzed the photoelectron spectrum of

CrO in terms of a single state of the ion, while our calculations show a

u state only 0.1 eV above the ion ground state. Our calculated

ionization potential of 7.43 eV is in reasonable agreement with the

experimentally deduced value of 7.85 eV, but our ion spectroscopic constants

disagree with the experimental numbers. Our best calculations (singles and

doubles Cl from a multiconfiguration wavefunction ) predict R

0

= 1.64A(^I~),

1.62A(^n) and to e

= 801 cm

-1 (^2

-

), 895 cm

_1 (^H) as opposed to 1 . 7 9 A and 640

cm"”1 quoted by Dyke, et al. Our values for the ground state of CrO of

R

e

= 1.647A and ioe

= 850 cm

-1

agree reasonably well with the values of

R

e

= 1.61 79 A and co e

= 898.50 cm

-1 obtained from the analysis of rotationally

resolved laser-induced fluorescence spectra by Hocking, et al. (Can. J. Phys.

1980, 58 , 516). Since the theoretical calculations for the neutral and ion

states were carried out at the same level of accuracy, we believe that the

analysis of the photoelectron spectrum is in error.

(b) Silicon Carbide, SiC

The silicon carbide molecule, SiC, is of fundamental importance in

astrophysics because of the role it may play in the formation of interstellar

grains. Although the triatomic molecule, SiC 2 , has been observed in the

laboratory and in interstellar space, no observations of the SiC molecule

have been reported. Recently, there have been a number of theoretical

calculations on SiC which predict the infrared and electronic transition

frequencies, but no accurate prediction of the microwave absorption

frequency has been made. Radiotelescope observations of interstellar

spectra are made in 128 MHz spectral windows which require several hours of

data accumulation to develop a reasonable signal-to-noise ratio. At the

absorption frequency of SiC (-18 GHz), the R Q must be known to within ±0.004A

in order to predict the correct window for observation. Such a prediction is

within the capability of modern quantum mechanical calculations.

We have performed singles and doubles Cl calculations from

multi-reference wavef unctions for the ground state of SiC using a very

large Slater-type basis set consisting of s,p,d, and f functions on each

center. In addition to the usual d polarization functions, d and f functions

were added for correlation, and their exponents were optimized in large-scale

Cl calculations. Five points around the bottom of the potential energy curve were calculated and fit to a Morse potential. The internuclear distances for

326
the calculations were chosen to symmetrically surround the minimum and to cover an energy range surrounding the lowest vibrational level. Additional

points were added to ensure that the predicted Morse parameters were not

sensitive to the point distribution. In all cases, the Morse fit reproduced

the calculated data points to within a few wavenumbers. Several curves were generated in this way using a variety of reference wavef unctions and Cl

selection criteria. In the largest calculations the wavefunction consisted

of more than 300,000 configurations. The several largest calculations

produced R

e values that were consistent to within 0.003A and vibrational

frequencies that agreed to within a few wavenumbers.

Spin-orbit coupling splits the ground state of SiC into ft = 2,1, and

0 components. The component is lowest in energy. Using ab initio

effective spin-orbit operators developed in this laboratory, we have

determined that the spin-orbit splitting in SiC is 3^ cm

-1 and nearly

constant across the bottom of the potential curve. Thus, the predicted Rq

value will not be affected by spin-orbit coupling. There is a possibility

that the 3n 2 state could be perturbed by other low-lying ft = 2 electronic

states. In our calculations, the closest perturbing states are 3^ and

both of which ar.e several thousand wavenumbers higher in energy.

The results of this study have been communicated to Dr. Michael

Hollis of NASA, who will compare the predictions to known interstellar

microwave lines. If a sufficiently interesting comparison is found, an application will be made for viewing time at the Kitt Peak observatory.

2. Interaction Energy Curves of RR T , ( R ,

f = He through Xe

(D. D. Konowalow and (Dept. Chem. SUNY Binghamton) M. Krauss)

Application of an ab initio hybrid model of the calculation of the

rare gas dimers has yielded binding energies within 10-20? of experiment for

these molecules. The discrepancy is attributed to the slow convergence in

the attractive dispersion energy with high order multipoles. These

calculations were performed to determine the applicability of the model to

heavier systems to allow calculation of biomolecular models. Very

recently an accurate correlated calculation of the binding energy of HeAr (W.

Meyer et al. , Phys. Rev. A33 , 3807 (1986)) suggested that correlation of the

fragments is important and the hybrid model potential may be questionable.

Correlated atom calculations are now in progress to test this conclusion for

a range of molecules. Since the hybrid model is widely used, it is necessary

to examine the significance of correlation in model systems.

3. Future Plans

Accurate quantum chemistry calculations of model systems will be

carried out to determine the level of accuracy required for predictive value

in energetic conformations and spectroscopic properties. Electron correlation

behavior in model compounds containing transition elements will continue to

be studied by both ab initio and effective operator methods.

327
C. Scattering in the Presence of Radiation

(P. S. Julienne and F. H. Mies)

The general goal of this research is to provide calculations of radiative

cross-sections and fragment state distributions associated with the

collisional broadening and photodissociation of small molecules. We have

developed extensive experience in calculating various nonadiabatic effects in

the conventional weak-field limit, and are expanding our codes to treat the

saturation of continuum transitions in intense, multiphoton fields.

Theoretical input into this program is provided by extensive sets of

computer codes available to the quantum chemistry group. State of the art

calculations of any necessary molecular potentials, couplings and radiative

transition dipoles can be obtained. Our scattering programs have been

expanded to allow for direct radiative interactions among many coupled

channels. Preliminary calculations have been performed to study the pressure

broadening of atomic lineshapes in both weak and strong laser fields. Our

scattering codes presently provide the continuum-continuum scattering matrix

elements needed in lineshape theory, and are being modified to provide the

bound-continuum matrix elements required to describe photodissociation. In

addition to these numerical procedures, the program involves extensive

analysis of many new and exciting theoretical features introduced by very

intense laser fields.

1. Non-adiabatic Theory of Atomic Broadening in Weak Fields

a) Redistribution Calculations for Sr( 1 P'-

1 S) + Ar

(P. S. Julienne and F. H. Mies)

We completed our close-coupled calculations of polarized light

redistribution in the Sr + Ar system. The calculations predict the

polarization ratios of SrC 1 ?) fluorescence following line wing excitation by

either linear or circular polarized light. Ab initio calculations were used

to obtain the ground and excited SrAr molecular potentials, which were adjusted modestly to give improved agreement with experiment. The radiative

scattering theory gives a unified description of the absorption coefficient

and subsequent fluorescence from the small detuning impact limit region to

the far wings. The cross sections for depolarizing collisions of Sr( ] P) * Ar

were also calculated. The calculated absorption coefficient, impact

broadening rate, linear and circular polarization ratios, and depolarization

rate coefficients are for the most part in good agreement with a diverse set

of experimental data.

b) Redistribution Calculations for Na + Rare Gas

(P. S. Julienne and L. Vahala)

We have continued to calculate final state branching ratios for

fine structure states and alignment/orientation for Na( 2

P«- 2 S) He.Ne.Ar

systems, and have obtained good agreement with experimental measurements. In

328
analysing the exact close-coupled data we uncovered a useful spin-uncoupling

approximation of the collision dynamics and its dependence on collision

velocity.

If the separation velocity of two colliding atoms is sufficiently

large, the final state dynamics can be well approximated by the same recoil

limit that has been successfully developed for photofragmentation. Our

calculations show how the recoil limit for fine-structure branching ratios is

approached for both red and blue detuning the separation velocity increases.

The recoil approximation for orientation/alignment only applies for

collisions with small angular momentum (small impact parameter). The recoil

limit applies when the separation time of the fragments is short compared to

the characteristic times of axis rotation and spin-orbit coupling. However,

by comparison to a pure "'p atom we can develop a spin-recoil approximation

which treats the spin projection as fixed in space during the rapid

separation to fragments while accounting for the rotation of electronic

angular momentum projection A with the internuclear axis. Comparison of the

spin-recoil model with exact close coupling results for Na + rare gas shows

the applicability of the approximation.

c) Lorentzian Pressure-Broadened Widths for Na

(P. S. Julienne and L. Vahala)

We have calculated the Lorentzian pressure-broadened widths for

both the D1 and D2 lines of Na broadened by collisions with He, Ne, and Ar. In addition we have performed the first calculation of the so-called asymmetry

parameter which has been widely observed in the impact regions of atomic

lineshapes

The absorption profile within the impact limit for one of the

p isolated fine structure lines may be written as

I(4j)

v

l (A i )/lT

(4j-6j) 2 +v?(0)

where Aj and oj are the respective detunings and shift of the line. The

detuning-dependent quantity vj(Aj) may be shown to have a finite limit as A-j * 0 and exactly equals the usual impact limit broadening coefficient,

including the effects of both elastic and inelastic collisions. The

dependence on detuning give rise to the Lorentzian dispersion asymmetry which

has been observed for Na + rare gas systems. We have calculated the

radiative scattering cross section for detunings near the D1 and D2 lines for

Na broadened by He, Ne, and Ar. The widths and asymmetry parameters are qualitatively in agreement with measured values. Deficiencies in the

existing molecular potentials limit the expected accuracy of the scattering

calculations

329
2. Nonadiabatic Theory of Redistribution in Strong Fields

(a) Collisional Redistribution of Resonant Radiation

(F. H. Mies)

Close-coupling codes developed for scattering in the presence

of radiation fields can be used to calculate the pressure broadening and

collisional depolarization of the Sr resonance transition in both the weak

field and the strong field limit,

Sr^S) + Ar + fiu)L

-» Sr*( 1 P) + Ar Sr^S) + Ar + tuu.

As we increase the Rabi frequency and decrease the detuning a l of

the incident laser three observable properties associated with optical

collision processes are obtained from such calculations, 1) Impact Limit

Lineshapes. As A^ * 0 we can demonstrate that proper pressure broadened half

widths, which include both elastic and inelastic collisional effects, can be

rigorously extracted from close-coupled radiative scattering matrix element.

The first manifestations of a.c. Stark shifts associated with the dressing of

fragments by the radiation field are extracted from the numerical results,

and confirm the anticipated power broadening of the Lorenztian absorption

profile. This suggests that normal perturbation theory as applied to

radiative interactions must be carefully scrutinized. 2) Inelastic

transitions involving dressed atomic states. As 0^ increases and eventually

exceeds A^ the asymptotic Sr atomic states become dressed. Our fully quantal

inelastic cross-sections can be used to calculate population redistri butlon

rates in the presence of intense fields. 3 ) Collisional redistri bution

spectra in saturating fields. In strong fields we obtain the redistri but ion

spectra for in the impact limit and find the typical three-peaked Mollow

lineshape due to fluorescence between dressed atomic states. Both the

half -width and the polarization of the emission peaks are calculated.

(b) Analysis of Multiphoton Lineshape Theory in Intense Fields

(F. H. Mies and A. Ben-Reuven)

The theory of line broadening, collisional redistri bution and

collision-induced multiphoton phenomena is an interdisciplinary area of

research. Particularly when adding the new ingredient of strong laser fields

and the resultant non-linear effects induced by saturation of resonant

transitions, the analysis of such phenomena requires the integration of

several diverse fields of research.

Two complementary theoretical approaches are used to describe these

phenomena. The first is represented by our "optical collision" approach here

at NBS where we calculate the radiative scattering matrix elements for

atom-atom scattering in the presence of intense monochromatic laser fields.

The calculations incorporate many subtle and sophisticated non-adiabatic and

inelastic effects which are often neglected in conventional lineshape theory.

However, these data that we generate must then be incorporated into very

330
subtle and complicated theoretical expressions for the density matrix of the

interacting molecules in the field of the pumping laser fields. Only then do our calculations yield the proper description of the redistributed radiation.

The second theoretical approach, is exemplefied by the unique and

outstanding theoretical approach developed by Professor Ben-Reuven at Tel

Aviv University. The redistribution of radiation is expressed in terms of a tetradic formalism using a Liouvillian analysis of the molecular density

matrix in the presence of collisions. Fortunatley, the formal ingredients of

this sophisticated theory are the very scattering matrix elements that are generated by our optical collision approach.

We have begun a collaboration with Professor Ben-Reuven to explore

the relationship between the tetradic description of redistribution and the

close-coupled theory of scattering in strong multiphoton fields. So far we have succeeded in showing the explicit relationships required to analyze

resonance fluorescence and resonant Raman lineshapes.

3. Future Plans

Our long range plans in the radiative scattering program require

extensive code development combined with a careful theoretical analysis of

strong field effects and multiphoton effects in the presence of collisions.

In the immediate future we intend to complete the calculation of the

pressure-broadening Mollow lineshape for Sr + Ar. At the completion of this

relatively simple, near-resonant one-photon study we intend to explore the

application of our close-coupled codes to multiphoton phenomena in strongly

resonant laser fields with hopes of calculating collisional effects in

four-wave mixing (PIERS-4) in Na. This will be studied in collaboration with

A. Ben-Reuven at Tel Aviv University using his tetradic analysis of

lineshapes

D. Atomic and Molecular Scattering Theory

1 . Half-Collision Amplitudes

a) Analysis of Exact Close-Coupled Codes

(F. H. Mies)

We have previously used a multichannel quantum defect analysis

(MCQDA) of exact close-coupled radiative matrix elements to show that these

can often be factored as follows:

S = N S N

+ fi ff' f * i

i'i

where the ’incoming' half-collision matrix tracks the non-adiabatic

scattering of the incident collision complex, and Nf f

, summarizes the

inelastic behavior of the 'outgoing', radiatively excited collision complex.

331
We have speculated on the unitarity of these matrices which would justify the

persistent use of the pure adiabatic Born-Oppenheimer matrix element o r*\ Sf t » in evaluating total radiative cross-sections for continuum

transitions. Based on a convincing but admittedly indirect numerical

analysis of several previous studies we have been very confident in advancing

the merits of this approximation. We have now modified our exact

close-coupled codes to extract the exact half collision amplitudes without

any commitment to unitarity. This new general capability of obtaining N

+ and

N" directly from close-coupled codes will enjoy a wide range of applicaoiiity

in continuum spectroscopy and allow us to judge the validity of the unitarity

condition.

(b) Multichannel Semiclassical Half Collision Amplitudes

(F. H. Mies and Y. Band)

In addition to solving the close-coupled equations exactly, we have developed a new simplified numerical procedures designed to obtain the

half collision amplitude whenever the non-adiabatic couplings are restricted

to classically accessible regions and the unitarity of N

+ is insured. This is

equivalent to solving a set of coupled semiclassical equations. We begin by

choosing a set of diagonal reference potentials tailored to the nature of the

exact interaction matrix. These are used to generate a set of elastically

scattered WKB reference wavef unctions . Two obvious choices that we have

explored in some detail are either pure diabatic, or pure adiabatic

reference potentials, although in any given situation the 'preferred' choice

is usually self evident. By using a random phase approximation to neglect

quickly oscillating contributions to the close coupled equations we can develop a set of first order differential equations for the half collision

amplitudes which are perfectly unitary, and, in appropriate and well

understood circumstances, reproduce the exact close-coupled amplitudes. This

multichannel semiclassical approximation is presently being applied to a number of interest situations, including multichannel curve crossings, and

asymptotic frame transformation among fine-structure states.

2. Multichannel Photodissociation Amplitudes

(P. S. Julienne)

The expansion of our multichannel close-coupling codes to calculate

photodissociation cross-section is nearly complete. This gives very stable

procedures for evaluating bound-continuum transitions, including all possible

subtleties associated with non-adiabatic effects in molecular dissociation.

A renormalized Numerov algorithm has been incorporated into the codes for the

calculation of the usual continuum-continuum S-matrix elements needed for

collisional problems, but more specifically for calculation of

bound-continuum transition matrix elements needed for photodissociation.

This algorithm is still being tested. In particular the code is designee to

calculate the final state distribution of the photofragments. Ultimately

these exact matrix elements can be compared to the predictions of our half

collision amplitudes based on MCQDA.

332
3. Future Plans

Our first priority is to complete the development of the

non-adiabatic photodissociation codes. The implementation of the

photodissociation (and closely associated predissociation) codes will be

stimulated by forthcoming studies of the Schumann-Runge predissociation of 0

2 in collaboration with L. Vahala at Old Dominion University. The half

collision amplitude studies will be continued and applied to an analysis of

fine-structure distriutions in both continuum-continuum and bound-continuum

transitions. Using our new semiclassical algorithm we intend to examine its

application to polyatomic curve-crossing phenomena in collaboration with Y.

Ban at Ben-Gurion University. In addition, we will continue to pursue our NCQDA studies of molecular dissociation in conjunction with Professor S-h.

Pan from the Chinese Academy of Science in Beijing who will be spending a year with us at NBS. In particular we will analyse the charge transfer

states of alkali-halide molecules.

333
5. PUBLICATIONS

(a) Publications of Past Year

Basch, H., Krauss, M. , and Stevens, W. J., "Cation Binding Effect on H-Bonding,"

J. Am. Chem. Soc. 107 , 7267 (1985).

Based, H,, Krauss, M. , Stevens, W. J. , and Cohen, D., "Electronic and Geometric

Structures of Pt(NH

3 )2+ Pt(NH2 ) 3 Cl2 , Pt(NH 3

) 3 X and Pt(NH3

) 2 XY

(X, Y = H

2 o,OH)," J. Inorg. Chem. 24, 3313 (1985).

Basch, H., Krauss, M. , Stevens, W. J., and Cohen, D., "Binding of Pt(NH

3 )|

+ to Nucleic Acid Bases," J. Inorg. Chem. 25_, 684 ( 1986).

Bodaness, R. S. and King, D. S. , "The Two-Photon Induced Fluorescence of the

Tumor Localizing Photosensitizer Heraatoporphyrin Derivative via

1064nm Photons from a 20ns Q-switched Nd-YAG Laser,” Biochern. and

Biophys. Research Commun. 1 26 , 346 (1985).

Casassa, M. P., Heilweil, E. J., Stephenson, J. C., and Cavanagh, R. R., "TimeResolved Measurements of Vibrational Relaxation at Surfaces," J.

Electron. Spec., _38., 257 (1986).

Casassa, M. P., Heilweil, E. J., Stephenson, J. C. , and Cavanagh, R. R., "TimeResolved Measurements of 0H(v=1) Vibrational Relaxation on SiOp

Surface: Isotope and Temperature Dependence," J. Chem. Phys. , o_4,

2361 (1986).

Casassa, M. P., Stephenson, J. C., and King, D. S., "Vibrational

9 Predissociation of Nitrix Oxide Dimer: Total Energy Distribution in

the Fragments," J. Chem. Phys., 86_, 2333 ( 1986).

Chackerian, C. , Jr., Bus, E. S. , Olson, W. B. , and Guelachvili, G. , "Determination of Aq - Bq of CH^D from Perturbation-Allowed

Transitions," J. Mol. Spectrosc., 117 , 355~360 (1986).

Dang-Nhu, M. and Pine, A. S. , "Intensities des Raies d'Absorption dans la

Bande Chaude + V 1 1 “ V 1 1 de l’Allene," Can. J. Phys. _64_, 289-296

(1986).

G. T., Nelson, D. D., Jr., Peterson, K. I., and Klemperer, W. , "The

Rotational Spectra of NH^-CO and NHn-N 2

", The Journal of Chemical

Physics, 84_, 21472 ( 1986).

G. T., Nelson, D. D., Jr., Gerfen, G. J., and Klemperer, W. , "The

Rotational Spectrum, Barrier to Internal Rotation, and Structure of

NH

3 “N 2 0," The Journal of Chemical Physics, 83., 54442, ( 1985).

G. T. and Coy, S. L. , "Absorber Speed DeDendence of the Coherence

Relaxation Rate of the J = 0-1 Transition of N

2 0," The Jour.na- f Chemical Physics, 83, 5687 (1985).

Fraser

,

Fraser

Fraser

334
Fraser, G. T. , Lovas , F. J. , Suenram, R. D. , Nelson, D. D. , Jr., and

Klemperer, "Rotational Spectrum and Structure of CF^h-NHo," The

Journal of Chemical Physics, 84 , 5983 (1986).

Heilweil, E. J. , Casassa, M. P., Cavanagh, R. R. , and Stephenson, J. C.

,

"Time-Resolved Vibrational Energy Relaxation of Surface Adsorbates,"

J. Vac. Sci. Technol. B3, 1471 (1985).

Heilweil, E. J., Casassa, M. P. Cavanagh, R. R. , and Stephenson, J. C.,

"Vibrational Energy Decay of Surface Adsorbates," Proceedings of

Time-Resolved Vibrational Spectroscopy Conference (Springer-Verlag

Proceedings in Physics, A. Laubereau and M. Stockburger, eds., Vol.

4, pg. 71 , 1985).

Hillman, J. J., Jennings, D. E., Olson, W. B., and Goldman, A., "High

Resolution Infrared Spectrum of Hydrogen Peroxide: The vg Fundamental

Band," J. Mol. Spectrosc., JM7, 46-59 (1986).

Hougen, J. T. , "A Generalized Internal Axis Method for High Barrier Tunneling

Problems, as Applied to the Water Dimer," J. Mol. Spectrosc., 114,

395-426 (1985).

Hougen, J. T., "Symmetry beyond Point Groups in Molecular Spectroscopy," J.

Phys. Chem. 90, 562-568 (1986).

Howard, B. J. and Pine, A. S. , "Rotational Predissociation and Libration in

the Infrared Spectrum of Ar-HCl," Chem. Phys. Lett. 112, 1-8 (1986).

Jacox, M. E. , "Comparsion of the Ground-State Vibrational Fundamentals of

Diatomic Molecules in the Gas Phase and in Inert Solid Matrices," J.

Mol. Spectrosc., 113, 286 (1985). •

Jacox, M. E. , "Reaction of F Atoms with the Methyl Haildes. Vibrational

Spectra of CH^XF and of H 2 CX--HF Trapped in Solid Argon," J. Chem.

Phys. 83, 3255 (1985).

Jasien, P. G. and Stevens, W. J. , "Ab Initio Study of the Hydrogen Bonding

Interactions of Formamide with Water and Methanol," J. Chem. Phys.

84, 3271 (1986).

Jasien, P. G. and Stevens, W. J., "Calculated Proton Affinities for Some

Molecules Containing Group VIA Atoms," J. Chem. Phys. _83, 2984

(1985)

Jennings, D. E., Weber, A., and Brault, J. W. , "Raman Spectroscopy of Gases

with a Fourier Transform Spectrometer : The Spectrum of D

2 ," Appl.

Opt. 25_, 284 ( 1986).

Julienne, P. S. and Mies, F. H., "Analytic Multichannel Theory of Molecular

Dissociation," in Electron and Atomic Collisions , ed. D. C. Lorents,

W. E. Meyerhof, and J. R. Petersen (North Holland, Amsterdam, 1986),

p. 725.

335
Karpas, Z., Stevens, W. J., Buckley, T. J. f and Metz, R., ’’Proton Affinity

and Gas-phase Ion Chemistry of Methyl Isocyanate, Methyl

Isothiocyanate, and Methyl Thiocyanate," J. Phys. Chem. 89, 5274

(1985).

Krauss, M. , Stevens, W. J., and Basch, H., "Relativistic Effective Potential

SCF Calculations of AgH and AuH," J. Comp. Chem. 6_, 287 (1985).

Lovas, F. Jo, "Recommended Rest Frequencies for Observed Intersellar

Molecular Microwave Transitions - 1985 Revision," J. Phys. Chem. Ref.

Data, J_5, 25 1 “303 ( 1986).

Maki, A. G. , Wells, J. S., and Hinz, A., "Heterodyne Frequency Measurements

on the 12°0-00°0 Band of OCS," Int. Journal of Infrared and

Millimeter Waves, J_, 909-91 7 (1986).

Mantell, D. A., Cavanagh, R. R. , and King, D. S. , "Internal States

IDistributions of NO Thermally Desorbed from Pt (111): Dependence on Coverage and Co-Adsorbed CO," J. Chem. Phys. _84, 51 31 (1986).

Mialocq, J.-C. and Stephenson, J. C. , "Picosecond Laser Study of the

Collisionless Photodissociation of Dimethylnitramine at 266 nm,"

Chem. Phys. Lett. 123, 390 (1986).

Mialocq, J.-C. and Stephenson, J. C., "Picosecond Laser Induced Fluorescence

Study of the Collisionless Photodissociation of Nitrocompounds at 266

nm," Chem. Phys (1986).

Miller, K. J., Taylor, E. R., Basch, H., Krauss, M. , and Stevens, W. J., "A

Theoretical Model for the Binding of Cis-Pt(NH^)| + to DNA,” J. Bio. Struct. Dyn&m. 2_, 1157 ( 1985).

Nelson, D. D. , Jr., Fraser, G. T. , and Klemperer, W. , "Ammonia Dimer: A Suprising Structure," The Journal of Chemical Physics, .83., 6201

(1985)

Ohashi, N., Lafferty, W. J., and Olson, W. B., "Fourier Transform Spectrum of

the Torsional Band of Hydrazine," J. Mol. Spectrosc., 117 , 119-133

( 1986).

Perry, J. W. , Woodward, A. M. , and Stephenson, J. C. , "Picosecond Coherent

Anti-Stokes Raman Scattering (CARS) Study of Vibrational Dephasing of

Carbon Disulfide and Benzene in Solution," SPIE Proceedings 620 , (1986).

Pine, A. S. and Howard, B. J., "Hydrogen-Bond Energies of the HF and HC1

Dimers from Absolute Infrared Intensities," J. Chem. Phys. 8^ , 590-596 (1986).

Rosenkrantz, M. E. and Krauss, M. , ''Damped Dispersion Interaction Energie:

for He-H 2

, Ne-H 2 , and Ar -H 2 , " Phys. Rev. A32, 1402 0985).

336
Suenram, R. D., Lovas, F. J., and Pickett, H. M. , "The Microwave Spectrum and

Molecular Conformation of Peroxynitric Acid (H00N0

2 )," J. Mol.

Spectrosc., 116, 406-421 (1986).

Suenram, R. D., Lovas, F. J., and Pickett, H. M. , "Fluoromethanol : Synthesis,

Microwave Spectrum and Dipole Moment," J. Mol. Spectrosc. 119,

(1986).

Thompson, G. A., Maki, A. G. , and Weber, A., "Infrared Tunaole Diode Laser

Spectroscopy of the Av = 2 Band of 'Li”'^l, J. of Mol. Spectrosc.

118, 540-543 (1986).

Thompson, G. A., Maki, A. G. , and Weber, A., "The Infrared Spectrum of GeO,"

J. Mol. Spectrosc., 116, 136-142 (1986).

Thompson, G. A., Maki, A. G. , and Weber, A., "Infrared Spectrum of Lil," J.

Mol. Spectrosc., 118, (1986).

Weber, A. (ed.), "Technical Activities 1985 - Molecular Spectroscopy

Division," N3SIR 86-3313 (1986).

Wofford, B. A., Bevan, J. W. , Olson, W. B., and Lafferty, W. J.,

"Rovibrational Analysis of Vo HCN—-HF Using Fourier Transform

Spectroscopy," J. Mol. Spectrosc., _83_, 6188-61 92 ( 1985).

Wofford, B. A., Bevan, J. W. , Olson, W. B., and Lafferty, W. J.,

"Rovibrational Analysis and Vibrational Predissociation in the v

2 Band of HCN Dimer," J. Chem. Phys. _85, 105-108 (1986).

Wofford, B. A., Jackson, M. W. , Bevan, J. W. , Olson, W. B., and Lafferty, W.

J., "Rovibrational Analysis of an Intermolecular Hydrogen-bonded

Vibration: The Band of HCN HF," J. Chem. Phys. 84_, 6115-6118

(1986).

Vahala, L. L., Julienne, P. S., and Havey, M. D., "Nonadiabatic Theory of

Fine Structure Branching Cross-Sections for NaHe, NaNe, and NaAr

Optical Collisions," Phys. Rev. A 34, 1856 (1986).

337
(b) Publications in Progress

Basch, H., Krauss, M„ , and Stevens, W. J., "Cation Binding Effect on Imidazole Tautomerism, Intern. J. Quant. Chem. (in press).

Bodaness, R. S., Heller, D. F., Krasinski, J., and King, D. S., "Two-photon

Laser-Induced Fluorescence of the Tumor Localizing Photosensitizer

Hematoporphyrin Derivative: Resonance Enchanged 750nm Two-photon

Excitation into the Near UV-Soret Band," J. Biol. Chem. (in press).

Burgess, D.,Jr., King, D. S., and Cavanagh, R. R., "Kinetics and Dynamics of the

Ammonia/Nitric Oxide Coadsorbate System on Pt(111)," in preparation

for submission to Surface Science.

Burgess, D. , Jr., Mantell, D. A., Cavanagh, R. R. , and King, D. S. , "Dynamics

of the Laser-induced Thermal Desorption of Nitric Oxide from a Platinum Foil," J. Chem. Phys. (in press).

Burkholder, J. B., Hammer, P. D., Howard, C. J., Maki, A. G. , Thompson, G. A., and Chackerian, C. , Jr., "Infrared Frequency and Intensity

Measurements of the CIO Radical," (manuscript in preparation) .

Casassa, M. P., Stephenson, J. C. , and King, D. S. , "Vibrational

Predissociation of the Nitric Oxide Dimer," Faraday Discuss. Chem.

Soc. 82_, (1 986) (in press).

Casassa, M. P., Stephenson, J. C., and King, D. S., "Picosecond Measurements

of the Dissociation Rates of the Nitric Oxide Dimer v^v-1) and

vjj(v=1) Levels," J. Chem. Phys. (submitted).

Fraser, G. T. , and Pine, A. S. , "Van der Waals Potentials from the Infrared

Spectra of Rare Gas-HF Complexes," The Journal of Chemical Physics,

( in press)

Fraser, G. T., Suenram, R. D., and Lovas , F. J., "Nearly Free Internal

Rotation in Ar-CH^Cl," The Journal of Chemical Physics (in press).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R., and Stephenson, J. C.

,

"Population Lifetimes of 0H(v=1) and OD(v-l) Stretching Vibrations of

Alcohols and Silanols in Dilute Solution," J. Chem. Phys., (in

press )

Heilweil, E. J., "Vibrational Population Lifetimes of OH(v-l) in Natural

Crystalline Micas" Chem. Phys. Letters (in press).

Hinz, A., Wells, J. S. , and Maki, A. G. , "Heterodyne Frequency Measurements

on the Nitric Oxide Fundamental Band," J. Mol. Spectrosc.

(submitted) .

Hinz, A., Wells, J. S. , and Maki, A. G. , "Heterodyne Measurements of Hot

Bands and Isotopic Transitions of N

2

O Near 7.3um," Zeitschnft fur

Physik D, (submitted).

338
Hougen, J. T., "Hydrogen Migration Tunneling Effects in the Rotational and

Vibrational Spectrum of Protonated Acetylene C-pH^ »

J • Mol.

Spectrosc. (submitted).

Jackson, M. W. , Wofford, B. A., Sevan, J. W. , Olson, W. B., and Lafferty, W.

J., "Infrared Spectrum of the Overtone Band 2v^0 in the Hydrogen

Bonded Complex HCN-HF," J. Chem. Phys. (in press).

Jackson, M. W. , Wofford, B. A., Bevan, J. W. , Olson, W. B., and Lafferty, W.

J., "Rovibrational Analysis of the C-H stretching Band and its

Overtone in the Hydrogen-bonded Heterodimer HCN HF," J. Chem. Phys.

( in press)

Jacox, M. E., "Comparison of the Electronic Energy Levels of Diatomic

Molecules in the Gas Phase and in Inert Solid Matrices," J. Mol.

Struct . ( in press )

Jasien, P. G. , Stevens, W. J., and Krauss, M. , "Ab Initio Calculations of the

Rotational Barriers in Formamide and Acetamide: The Effects of

Polarization Functions and Correlation," J. Mol. Struct. Theochem.

( in press )

Jasien, P. G. and Stevens, W. J. , "Theoretical Studies of Potential Gas-phase

Charge Transfer Complexes: NH^ + HX (X = Cl, Br , I)," Chem. Phys.

Letters ( in press )

Jennings, D. E., Weber, A., and Brault, J. W. , "FTS-Raman Flame Spectroscopy

of High-J Lines in H

2 and D

2

," (submitted).

Julienne, P. S. and Mies, F. H, "Nonadiabatic Theory of Atomic Line

Broadening: Redistribution Calculations for Sr('P •*- f S) + Ar," Phys.

Rev. A (in press).

Julienne, P. S. and Vahala , L. L., "Close Coupled Theory of Fine Structure

Transitions in Collisional Redistribution," in Spectral Lineshapes , Vol. 4, ed., by R. Exton (in press).

Lafferty, W. J. and Olson, W. B., "The High Resolution Infrared Spectra of

the x>2 and Bands of H0C1," J. Mol. Spectrosc. (in press).

Lafferty, W. J., Suenram, R. D. , and Lovas , F. J., "The Microwave Spectra of

the (HF)

2

, (DF) 2, HFDF and DFHF Hydrogen Bonded Complexes," J. Mol.

Spectrosc. (in press).

Lindsay, D. M. , Thompson, G. A., and Wang, Y. , "ESR Spectra of Cuo( 2 A

1 ) in an

N

2 Matrix, J. Phys. Chem., (in press).

Lovas, F. J., Suenram, R. D. , Ross, S., and Klobukowski, M. , "Rotational

Structural Ab Initio and Semirigid Bender Analysis of the Millimeter

Wave Spectrum of H

2 C0-HF," J. Mol. Spectrosc. (in press).

Lovas, F. J. and Suenram, R. D., "Design and Operation of a Pulsed Beam

Fourier Transform Microwave Spectrometer , Measurements on OCS and

Rare Gas-OCS Complexes," J. Chem. Phys. (in press).

339
Maki, A. G. , "High Resolution Measurements of the v

2 Band of HNO, and the

Band of trans-HONO," (submitted).

Mies, F. H., Julienne, P. S., Band, Y. B., and Singer, S. J., "A Converged

Analysis of Radiative Matrix Elements," J. Phys. B., (in press).

Monten, K. M. , Walmskay, C. M. , Henkel, C. , Wilson, T. L., Snyder, L. E.,

Hollis, J. M. , and Lovas, F. J, "Torsionally Excited Methanol in Hot

Molecular Cloud Cores," Astron. Astrophys. (in press).

Nelson, D. D. , Jr., Fraser, G. T., Peterson, K. I., Zhao, K. , Klemperer, W.,

Lovas, F. J., and Suenram, R. D., "The Microwave Spectrum of the K«0

States of Ar-NH^," The Journal of Chemical Physics (submitted).

Ohashi, N. and Hougen, J. T., "The Torsional-Wagging Tunneling Problem and

the Torsional-Wagging-Rotational Problem in Methylamine , " J. Mol.

Spectrosc. (in press).

Olson, W. B., Hunt, R. A., Maki, A. G. , and Brault , J. W. , "Hydrogen

Peroxide: Rotational Constants of the Ground State and the Lowest

Torsional Component of the First Excited Torsional State,"

( submitted)

Pine, A. S. and Looney, J. P., "N 2

~ and Air-Broadening in the Fundamental

Bands of HF and HC1," J. Mol. Spectrosc. (in press).

Schaeffer, R. D., Lovejoy, R. W.. Olson, W. B., and Tarrago^. G. , "High

Resolution Spectrum of 2 °SiH ?D from 1450 to 1710 cm

-1 ," (submitted).

Suenram, R. D. and Lovas, F. J., "The Microwave Spectrum and .Structure of the

Argon --- Acrylonitrile van der Waals Complex," (submitted).

Thompson, G. A., Olson, W. B., Maki, A. G. , and Weber, A., "Fourier Transform

Infrared Spectrum of the Fundamental Band of LiCl at 830°C,"

( submitted)

Wofford, B. A., Bevan, J. W. , Olson, W. B., and Lafferty, W. J.,

"Rovibrational Analysis of the vc Vibrational Band in the HCN-HF

Hydrogen Bonded Cluster," (submitted).

340
6. TALKS

Casassa, M. P., "Picosecond Measurements of Vibrational Relaxation of

Chemisorbed Molecules," Laser Users Group Seminar, NBS, February 1986.

Casassa, M. P., "Time- and State-Resolved Studies of van der Waals Molecule

Predissociation," Gordon Conference, August 1986.

Casassa, M. P., "Picosecond Measurements of Vibrational Predissociation of van der Waals Dimers," Symposium on Clusters and Cluster Ions, Baltimore,

MD, September 1986.

Casassa, M. P., "Picosecond Studies of van der Waals Molecule Vibrational

Predissociation," Surface Science Lunch Bunch Seminar, NBS, September 1986.

Casassa, M. P., "Picosecond Studies of Vibrational Predissociation in van der

Waals Molecules," Symposium on State-to-state Chemistry, ACS National

Meeting, Anaheim, CA, September 1986.

Fraser, G. TV, "van der Waals Potentials from the Infrared Spectra of Rare

Gas-HF Complexes," 41 st Symposium on Molecular Spectroscopy, Columbus,

OH, June 1986.

Fraser, G. T., "Rotational Spectrum, Internal Rotation, and Structure of

Ar-CHoCl," 41 st Symposium on Molecular Spectroscopy, Columbus, OH, June

1986.

Fraser, G. T., "van der Waals Potentials from the Infrared Spectra of

Rare-Gas-HF Complexes," 41 st Symposium on Molecular Spectroscopy,

Columbus, OH, June 1986.

Fraser, G. T., "Infrared and Microwave Spectroscopy of Weakly Bound

Complexes," 20th Mid-Altantic Regional Meeting of the American Chemical

Society, Symposium on Clusters and Clusters Ions, Baltimore, MD,

September 1986.

Fraser, G. T., "Nearly Free Internal Rotation in Ar-CHoCl," NATO-Advanced

Research Workshop on Structure and Dynamcis of Weakly Bound Molecular

Complexes, Maratea, Italy, September 1986.

Fraser, G. T., "Rotational Spectrum and Structure of CFoH-NH^," NATO-Advanced

Research Workshop on Structure and Dynamics of Weakly Bound Molecular

Complexes, Maratea, Italy, September 1986.

Heilweil, E. J. , "Picosecond Vibrational Dynamics of Hydroxyl Groups in

Condensed Phase Systems," National Institutes of Health, January 1986.

Heilweil, E. J., "Picosecond Vibrational Dynamics of Hydroxyl Groups in

Condensed Phase Systems," Chemistry Department, Physical Chemistry

Seminar, University of Illinois, Urbana, IL, February 1986.

341
Heilweil, E. Jo, ’’Population Lifetimes of 0H(v=1) and 0D(v=1) Vibrations in

Alcohols, Silanols and Crystalline Micas," (Jltrafast Phenomena

Conference, Snowmass, CO, June 1986.

Heilweil, E. J., "Picosecond Vibrational Dynamics of Hydroxyl Groups in

Condensed Phase Systems," Gordon Conference on Vibrational Spectroscopy,

Wolfeboro, NH, August 1986.

Hougen, J. T., "Symmetry Beyond Point Groups in Molecular Spectroscopy," Duke

University, Durham, NC, November 1985.

Hougen, J. T., "Hydrogen Migration Tunneling Effects in the Rotational and

Vibrational Spectrum of Protonated Acetylene," University of California

at Irvine, March 1986.

Hougen, J. T., "Overview of Molecular Spectroscopy at NBS," Jet Propulsion

Laboratories, Pasadena, CA, March 1986.

Hougen, J. T., "Hydrogen Migration Tunneling Effects in the Rotational and

Vibrational Spectrum of Protonated Acetylene," NBS, Boulder, CO, March

1986.

Hougen, J. T., "Hydrogen Migration Tunneling Effects in the Rotational and

Vibrational Spectrum of Protonated Acetylene, C

2Ho

+ ," Hist Symposium on Molecular Spectroscopy, Ohio State University, Columbus, OH, June 1986.

Hougen, J. T., "Far-Infrared Spectrum of Methylamine and the Group

Theoretical Treatment of Its Large Amplitude Motions," Hist Symposium on Molecular Spectroscopy, Ohio State University, Columbus, OH, June 1986.

Hougen, J. T. , "Hydrogen Migration Tunneling Effects in the Rotational and

Vibrational Spectrum of Protonated Acetylene, C

2

H

3

+ ," 9th International

Conference on High Resolution Infrared Spectroscopy , Liblice (near

Prague), Czechoslovakia, September 1986.

Hougen, J. T. , "The Role of Tunneling Models in Analyzing High-Resolution

Spectra of Weakly Bound Molecular Complexes," NATO-Advanced Research

Workshop on Structure and Dynamics of Weakly Bound Molecular Complexes,

Maratea, Italy, September 1986.

Jacox, M. E., "Vibrational Spectra of Free Radicals Formed by the Reaction of

F Atoms with Small Molecules," Department of Chemistry, Bryn Mawr

College, Bryn Mawr, PA, November 1985.

Jacox, M. E. , "Vibrational Spectra of Free Radicals Formed by the Reaction of

F Atoms with Small Molecules," AT & T Bell Laborator ies , Murray Hill,

NJ, December 1985.

Jacox, M. E., "Vibrational Spectra of Free Radicals Formed by the Reaction of

F Atoms with Small Molecules," Delaware Valley Section, Society for

Applied Spectroscopy, Philadelphia, PA, February 1986.

Jacox, M. E. , "Vibrational Spectra of Free Radicals Formed by the Reac: .or. F Atoms with Small Molecules," Department of Chemistry, University of

Colorado, Boulder, CO, February 1986.

342
Jacox, M. E., "Matrix Isolation Spectroscopic Studies of the Reaction of F

Atoms with Small Molecules," Symposium on Matrix Isolated Species,

Central Regional American Chemical Society Meeting, Bowling Green, OH,

June 1986.

Jacox, M. E., "Spectroscopy of Free Radicals Formed in the Early Stages of

Nitramine Decomposition," U.S. Army Research Office Workshop on Combustion Probes for the Solid Nitraraines, Combustion Research Facility,

Sandia National Laboratory, Livermore, CA, June 1986.

Jacox, M. E., "Comparison of the Electronic Energy Levels of Diatomic

Molecules in the Gas Phase and in Inert Solid Matrices," Mist Symposium

on Molecular Spectroscopy, Columbus, OH, June 1986.

Jacox, M. E., "The A - X ^l + Near Infrared Absorption Spectrum of HC 2 Isolated in Solid Argon," Mist Symposium on Molecular Spectroscopy,

Columbus, OH, June 1986.

Julienne, P. S., "Close Coupled Theory of Fine Structure Transitions in

Collisional Redistribution," 8th International Conference on Spectral

Line Shapes, College of William and Mary, Williamsburg, VA, June 1986.

Julienne, P. S., "Close Coupled Theory and Analytic Models for Collisional

Redistribution," Department of Atomic Physics, University of Newcastle,

Newcastle-upon-Tyne, England, July 1986.

Julienne, P. S., "Close Coupled Calculations on Laser Assisted Collisions,"

Max Planck Institute for Quantum Optics, Garching, West Germany, July

1986.

Julienne, P. S., "Scattering Theory of Photoassisted Collisions: Application

to Alkali and Alkaline Earth Atoms Colliding with Rare Gas Atoms,"

and "Half Collision Analysis of Photoassisted Collisions: Development

of Physical Insight," Department of Physics, University of

Kaiserslautern, Kaiserslautern, West Germany, August 1986.

Julienne, P. S., "Close Coupling Calculations of Atomic Line Profiles and

Collisional Redistribution for 1 P and 2 P Transitions," Observatoire de

Paris, Meudon, France, September 1986.

King, D. S., "Molecule-Surface Dynamics," Rice University, Department of

Chemistry and Rice Quantum Institute, Rice University, Houston, TX,

November 1985.

King, D. S., "Two-Photon Excitations of the Tumor-Localizing Photosensitizer

HPD," International Laser Science Conference, Dallas, TX, November 1985.

King, D. S., "Dynamics of the Molecular-Surface Interaction," JILA Symposium,

Boulder, CO, March 1986.

343
King, D. S., "Thermal and Laser-Induced Desorption Dynamics," Cornell

University, Department of Chemistry, Cornell University, Ithaca, NY,

March 1986.

King, D. S. , "Dynamics of the Photodissociation of van der Waals Dimers,"

Virginia Commonwealth University, Chemistry Department, Richmond, VA,

March 1986.

King, D. S., "Vibrational Predissociation of NO-containing van der Waals

Dimers," ACS Symposium on Dynamics of Clusters, National Meeting, NY,

April 1986.

King, D. S., "Photodissociation of van der Waals Dimers," Brookhaven National

Laboratory, Chemistry Department, Long Island, NY, April 1986.

King, D. S., "NO/Pt Interactions: Thermal- and Laser-Induced Desorption,"

IBM, Yorktown Heights, NY, April 1986.

King, D. S., "Vibrational Predissociation Dynamics of the Nitric Oxide

Dimer," NBS Staff Research Seminar Series, NBS-Gai thersburg, May 1986.

King, D. S., "Dynamics of the Vibrational Predissociation of the Nitric Oxide

Dimer," Mid-Atlantic Regional Meeting of ACS, Baltimore, MD, September

1986 .

King, D. S., "Vibrational Predissociation Dynamics of van der Waals Dimers,"

Faraday Soc. Disc, on Photodissociation Dynamics, Bristol, England,

September 1986.

King, D. S., "Vibrational Predissociation Dynamics of van der Waals Dimers,"

NATO-Advanced Research Workshop on Structure and Dynamics of Weakly Bound

Molecular Complexes, Maratea, Italy, September 1986.

Krauss, M. , "Pt Binding to DNA," Chemistry Department, Drexel University,

Philadelphia, PA, May 1986.

Krauss, M. , "Pt(NH

2

R )2 Binding to a tetramer Duplex of DNA," Meeting of the

American Society of Biological Chemists, Washington, D.C., June 1986.

Lafferty, W. J., "Sub-Doppler Resolution Infrared Spectroscopy of the Carbon

Dioxide Dimer," Mid-Atlantic Regional Meeting of ACS, Baltimore, MD,

September 1986.

Lovas, F. J., "Microwave Spectrum and Properties of the Methanol-Formamide

Complex," Mid-Atlantic Regional Meeting of ACS, Baltimore, MD, September

1986.

Maki, A. G. , "High Resolution Measurements and Analysis of the v

2

, - 4

. and 2\>g Bands of Nitric Acid," 41st Symposium on Molecular

Spectroscopy, Ohio State University, Columbus, OH, June 1986.

344
Maki, A. G. , "New Infrared Frequency and Intensity Measurements on Chlorine

Monoxide (CIO)," 41st Symposium on Molecular Spectroscopy, Ohio State

University, Columbus, OH, June 1986.

Mies, F. H., "Collisional Redistribution of Intense Laser Radiation,"

Department of Chemistry, Tel Aviv University, Tel Aviv, Israel, February

1986.

Mies, F. H., "Collisional Redistribution of Intense Laser Radiation,"

Department of Chemical Physics, Weizmann Institute, Rohovot, Israel,

February 1986.

Mies, F. H., "Collisional Redistribution of Intense Laser Radiation,"

Department of Physics, Bar Ilan University, Ramat-Gan, Israel, March

1986.

Mies, F. H., "Collisional Redistribution of Intense Laser Radiation,"

Department of Chemistry, Ben Gurion University, Beer Sheva, Israel,

March 1986.

Olson, W. B., "Experimental Values for the Rotational Constants of the OG and

1G Torsional Components of the Vibrational Group State of H

2 02, and the

Matrix Element Coupling Them," 4lst Symposium on Molecular Spectroscopy,

Ohio State University, Columbus, OH, June 1986.

Pine, A. S. , "High-Resolution Infrared Spectroscopy of Hydrogen-Bonded and

van der Waals Complexes," Department of Chemistry, Johns Hopkins

University Baltimore, MD, November 1985.

Pine, A. S., "High-Resolution Spectroscopy of van der Waals and

Hydrogen-Bonded Complexes," NBS Staff Research Seminar, NBS

Gaithersburg, MD, May 1986.

Pine, A. S., "N 2 and Air Broadening in the Fundamental Bands of HF and HC1,"

41 st Symposium on Molecular Spectroscopy, Ohio State University,

Columbus, OH, June 1986.

Pine, A. S., "Vibrational Anomalies and Dynamic Coupling in Hydrogen-Bonded

van der Waals Molecules," NATO- Advanced Research Workshop on Structure

and Dynamics of Weakly Bound Molecular Complexes," Maratea, Italy,

September 1986.

Stephenson, J. C., "Picosecond Studies of Vibrational Energy Transfer:

Surfaces, Solids, and Liquids," AFOSR Contractors Meeting, Dayton, OH,

November 1985.

Stephenson, J. C. , "Picosecond Studies of Vibrational Energy Transfer:

Surfaces, Solids, and Liquids," Department of Chemistry, University of

Pittsburgh, PA, March 1986.

Stephenson, J. C., "Picosecond Studies of Vibrational Energy Transfer:

Surfaces, Solids, and Liquids," Department of Chemistry, Cornell

University, April 1986.

345
Stephenson, J. C., "Picosecond Studies of Vibrational Energy Transfer:

Surfaces, Solids, and Liquids," Department of Chemistry, U. C. Berkeley,

Berkeley, CA, June 1986.

Stephenson, J. C. , "Picosecond Studies of Vibrational Energy Transfer:

Surfaces, Solids, and Liquids," International Quantum Electrons

Conference, San Francisco, CA, June 1986.

Suenram, R. D., "Rotational Spectra and Structural Determinations of Several

van der Waals Complexes," Rice University, Department of Chemistry

Colloquium, Houston, TX, March 1986.

Suenram, R. D., "Rotational Spectra and Structural Determinations of Several

van der Waals Complexes," 11th Annual Austin Symposium on Molecular

Structure, Austin, TX, March 1986.

Suenram, R. D., "Rotational Spectrum of the Hydrogen Bonded Formamide-Water

Complex," Mid-Atlantic Regional Meeting of ACS, Baltimore, MD, September

1986.

Suenram, R. D., "Structures of the Ar •• • Acrylonitrile and Ar • • *Formamide

van der Waals Complexes," NATO-Advanced Research Workshop on Structure

and Dynamcis of Weakly Bound Molecular Complexes, Maratea, Italy,

September 1986.

Suenram, R. D., "Rotational Spectrum of the Hydrogen Bonded Formamide-Water

and Formamide-Methanol Complexes," NATO-Advanced Research Workshop on Structure and Dynamics of Weakly Bound Molecular Complexes, Maratea,

Italy, September 1986.

Thompson, G. A., "Infrared Spectroscopy of High Temperature Diatomics,"

Rome Air Develpment Center, Griff isse Air Force Base, NY, May 1986.

Thompson, G. A., "High Temperature Spectroscopy of Alkali Halides and

Hydrides at High Temperature," Advanced Fuel Research, Inc., East

Hartford, CT, May 1986.

Thompson, G. A., "Infrared Spectroscopy of High Temperature Diatomics,"

Photometries, Inc., Boston, MA, May 1986.

Thompson, G. A., "High Resolution Infrared Spectroscopy of LiCl at 800°C," *41 st

Symposium on Molecular Spectroscopy, Ohio State University, Columbus, OH,

June 1986.

Weber, A., "Research in High Resolution Molecular Spectroscopy at NBS,"

ENEA, Centre Ricerche Energie Frascati, Frascati, Rome, Italy,

September 1986.

Weber, A., "Research in High Resolution Molecular Spectroscopy at NBS,"

Physics Deparment, University of Florence, Florence, Italy, September

1986.

Weber, A., "Research at NBS in High Resolution Spectroscopy of W Bound

Molecular Complexes," Physics Department, University of Giessen, Giessen,

Germany, October 1986.

346
7. MOLECULAR SPECTROSCOPY DIVISION SEMINARS

Balasubramanian, K. , Department of Chemistry, Arizona State University,

Tempe, NJ, "Electronic Structure of Moelcules Containing Heavy Atoms"

May 1986.

Ben-Reuven, A., School of Chemistry, Tel-Aviv University, Tel-Aviv, Israel,

"New Challenges in the Study of Spectral Line Shapes," September 1986.

Bevan, J., Chemistry Department, Texas A&M University, College Station, TX,

"Dynamical Behavior in Linear Hydrogen-Bonded Interactions," November

1985.

Beveridge, D., Department of Chemistry, Hunter College, New York, NY,

"Aqueous Hydration of Biological Molecules: Free Energy Simulations,"

February 1986.

Clough, S. A., Air Force Geophysics Laboratory, Hanscom AFB, MA, "Line Shapes

and Molecular Collisional Broadenings with Applications to Atmospheric

Problems," February 1986.

Cook, M., Naval Research Laboratory, "Electronic Structure of the

MoFeoSi|(SH)g^

- Ion: A Model for the Nitrogenase Active Site,"

October 1985.

DeFrees, D., Molecular Research Institute, San Jose, CA, "Theoretical Studies

of Interstellar Chemistry," November 1985.

Fink, W. H., Chemistry Department, National Science Foundation, Washington,

D.C., "Influence of External Potentials of H-Bonding," December 1985.

Graner , G. , Universite de Paris-Sud, Orsay, France, "Recent Work in Molecular

Spectroscopy at Laboratoire d* Infrarouge, " June 1986.

Harris, D., Chemistry Department, University of California, Santa Barbara,

CA, "Spectroscopy and Structure of MgOH: A Quasi-Linear Molecule,"

December 1985.

Harrison, J., Chemistry Department, Michigan State University, East Lansing,

MI, "Electronic and Geometric Structure of Transition Metal-Containing

Cations," August 1986.

Herman, R., Department of Physics, Penn State University, PA, "Velocitychanging Effects on Collisional Lineshapes," May 1986.

Kok, R., University of Georgia, Athens, GA, "Molecular Mechanics and Ab

Initio Calculations on Some Organic and Organo-metallic Compounds,"

October 1985.

Konowalow, D. D., Ballistics Research Laboratory, Aberdeen, MD, "High Spin

States of He

2 ," July 1986.

347
Lester, V.

,

Department of Chemistry, University of California, Berkeley, CA,

’'Quantum Monte Carlo of Electronic Structure," August 1986.

Lisy, J., Chemistry Department, University of Illinois, IL, "Vibrational

Predissociation Spectroscopy of Molecular Clusters," March 1986.

Malvezzi, M. , Gordon McKay Laboratory, Harvard University, MA, "Picosecond

Laser Excitation, Melting, and Vaporization of Solid Surfaces,"

April 1986.

Mautner, M. , Chemical Kinetics Division, NBS, Gaithersburg, MD, "Cluster

Ions and The Ionic Hydrogen-Bond, " January 1986.

Mialocq, J.-C., Centre d’Etudes Nucleaires de Saclay, Department de

Physico-Chimie , France, "Ultrafast Molecular Dynamics Studied with

Picosecond Lasers," June 1986.

Miller, A. E. S., Department of Chemistry, Bryn Mawr College, Bryn Mawr, PA,

"Electronic Structure of Transition-Metal Hydrides," March 1986.

Mollendal, H., Universiteteti Oslo, Oslo, Norway, "Microwave Spectra of

1,4 defluoro -2-butyne and Several Molecules with Intra-molecular

Hydrogen Bonds," March 1986.

Osman, R., Department of Physiology and Biophysics, Mt. Sinai School of

Medicine, New York, NY, "A New Mechanism of Action of Superoxide

Dismutase," November 1985.

Rappe, A. K. , Department of Chemistry, Colorado State University, CO,

"Studies on 2^ + 2^ Reactions: Allowed Reactions Involving Transition

Metal Complexes," October 1985.

Rosenkrantz, M. , Ballistic Research Laboratory, Aberdeen, MD, "Application of

Quantum Chemistry to Molecules of Atmospheric Interest," October 1935.

Sandroff, C. , AT & T Bell Communications, "Layered Semiconductor Colloids and

Their Uses: Interfacial Science, Cluster Chemistry and New Solid

Materials," December 1985.

Saykally, R., Chemistry Department, University of California, Berkeley, CA,

"Laser Spectroscopy of Molecular Ions and van der Waals Molecules,"

May 1986.

Schrotter, H.-W. , Sekton Physik, Universitat Mtlnchen, West Germany, "High

Resolution CARS and Inverse Raman Spectroscopy," August 1986.

Scoles, G. , Department of Chemistry, University of Waterloo, Waterloo,

Canada, "Infrared Laser Molecular Beam Spectroscopy of Molecule-Noble

Gas Clusters," April 1986.

348
Shapiro, M. , Chemical Pnysics Department, Weizmann Institute of Science,

Rehovot, Israel, "Coherent Control of Unimolecular Reactions," January

1986.

Shuker, R., Physics Department, Ben Gurion University of the Negev, Beer

Shene, Israel, "Laser Induced Cherenkov and Non-linear Effects in Sodium

Vapor," June 1986.

Smalley, R., Chemistry Department, Rice University, Houston, TX, "New Result

with Supersonic Cluster Beams," November 1985.

Sutter, D. H., Institut fUr Physikalische Chemie, Universitat Kiel, Kiel,

Olshausenstrasse , Germany, "Microwave Zeeman and Fourier Transform

Studies at Kiel," February 1986.

Toennies, J. P., Max-Planck-Institut fur Stromungesforchung , Gottingen,

West Germany, "State Resolved Molecular Beam Scattering Experiments on Atom-molecule Inelastic Collisions," March 1986.

Vidal, C. R., Institut ftir Extraterrestrische Physik, Max-Planck-Institut

filr Physik und Astrophysik, Bayern, West Germany, "Laser Intracavity

Absorption," April 1986.

Watts, R. 0., The Australian National University, Canberra, Australia,

"Molecular Structure and Dynamics from Molecular Beam Experiments,

April 1986.

349
8. TECHNICAL AND PROFESSIONAL COMMITTEE

PARTICIPATION AND LEADERSHIP

Hougen, J. T.

Member, Editorial Advisory Board, Journal of Molecular Spectroscopy.

Member of the subcommittee on Notations and Conventions for Molecular

Spectroscopy for the "IUPAC" Commission on Molecular Structure and

Spectroscopy.

Jacox, M. E.

Member, Editorial Advisory Board, Review of Chemical Intermediates.

Member of a National Science Foundation panel for the review of

proposals for Engineering Research Equipment Grants and Research

Initiation Grants.

Member, Admissions Committee, NBS Chapter, Sigma XI.

King, D. S.

Member, DOE University Research Instrumentation Grant Award Review

Panel.

Lovas ,* F. J.

Member, International Astronomical Union Commission I^J: Fundamental

Spectroscopic Data.

Maki, A. G.

Member, Editorial Advisory Board, Journal of Molecular Spectroscopy.

Weber, A.

Editoral Advisory Board, Journal of Raman Spectroscopy.

Chairman, Williams-Wright Awards Symposium, Coblentz Society, March

1 986.

Member, Program Committee, 10th International Conference on Raman

Spectroscopy, 1986.

Chairman, Welsh Symposium on High Resolution Spectroscopy , I0t:i

International Conference on Raman Spectroscopy, University of Oregon,

September 1986.

Director and Chairman, Organizing Committee, NATO Advanced Resear

Workshop on "Structure and Dynamics of Weakly Bound Molecular

Complexes .

350
Editorial Advisory Board, Journal of Physical and Chemical Reference

Data.

Member, Program Committee, International Conference on Infrared and

Fourier Transform Spectroscopy, Washington, 1989.

351
9. PROFESSIONAL INTERACTIONS, CONSULTING

AND ADVISORY SERVICES

Casassa, M. P.

Collaborated with Dr. R. R. Cavanagh, Surface Science Division, cn picosecond infrared laser studies of vibrational relaxation of adsorbed

molecules

Consulted with Dr. K. C. Janda, University of Pittsburgh, on studies of

the photodissociation of van der Waals molecules.

Heilweil, E. J.

Collaborated with Dr. C. Sandroff, AT&T Bell Communications

Laboratories, on Picosecond Streak Camera Studies of Colloidal LeadHalide Semiconductor Luminescence.

Collaborated with Professor R. M. Hochstrasser , University of

Pennsylvania, on transient grating phenomena in molecular solutions.

Jacox, M. E.

Collaborated with Dr. J. Hudgens, Chemical Kinetics Division, NBS, on the assignment and normal coordinate analysis for Rydberg state

of CH 20H.

Consulted with Dr. P. Thaddeus, Institute for Space Studies, on the

spectroscopy of CoH2

, HCCNH .

Collaborated with Dr. R. F. Curl, Department of Chemistry, Rice

University, on near infrared absorption spectrum of HC P .

Consulted with Dr. G. Herzberg, National Research Council of Canada, on infrared spectra of trihalides and trihalide and anions.

Collaborated with Dr. J. Wormhoudt, Aerodyne Research, Inc., on infrarea

spectra of SiH 2 and SiH^.

Consulted with Dr. K. Kawaguchi, Institute for Molecular Science,

Okazaki, Japan, on infrared spectrum of BH^.

Julienne, P. S.

Consulted with Dr. L.Vahala, Old Dominion University, Norfold, V A, on calculation of collisionally broadened line profiles and collisiona.

redistribution of light for Na + He. Ne. Ar systems.

352
Collaborated with Dr. J. Weiner, University of Maryland, on theory of

photoassociation collisions of supercold atoms.

Collaborated with Dr. R. Bieniek, University of Missouri at Rolla, on application of the Lewis-Cooper model to the collisional

redistribution of light for Sr + Ar.

Consulted with Dr. K. Burnett, Imperial College, London, England, on the

development of close coupled and semiclassical theories for collisional

redistribution of light.

Consulted with Dr. H. Hotop, University of Kaiserslautern, West Germany, on the development of close coupled theory and half collision analysis of

collision of oriented or aligned atoms.

King, D. S.

Collaborated with Dr. R. Bodanness, NIH, on the role of biphotonic

processes in the photo-activated generation of singlet oxygen.

Consulted with Dr. D. F. Heller, Allied Chemical Corp., on uses

of Alexandrile laser in biophysics.

Collaborated with Dr. R. R. Cavanagh and Dr. W. Gadzuk, on experimental

and theoretical aspects of molecular dynamics of the gas-surface

interface.

Krauss, M.

Collaborated with Dr. K. J. Miller, Department of Chemistry, Rensselaer

Polytechnic Institute, Troy, NY, on Pt binding to DNA.

Collaborated with Dr. H. Basch, Bar Ilan University, Israel, on molecular

orbital calculations of biomolecules.

Collaborated with Dr. R. Osman, Mt. Sinai Medical School, NY, on mechanisms of metalloenzymes

Lafferty, W. J.

Collaborated with Dr. J. P. Sattler, Harry Diamond Laboratory, on optically pumped far infrared laser line assignments.

Collaborated with Professor N. Craig, Oberline College, on high

resolution infrared studies of fluoroethylenes.

Collaboration with Drs. S. A. Clough and M. Hoke, Air Force Geophysics

Laboratory, in the study of collisional interference on the spectrum of

co 2

.

353
Lovas, F. J.

Collaborated with Professor L. E. Snyder, University of Illinois, and

Dr. J. M. Hollis, NASA/Goddard Space Flight Center, on interstellar

molecular searches.

Collaborated with Drs. C. W. Gillies and J. Zozom, Department of

Chemistry, Rensselaer Polytechnic Institute, Troy, NY, on microwave

spectral studies.

Maki, A. G.

Collaborated with Dr. A. Goldman, University of Denver, on studies

of Nitric Acid spectra.

Collaborated with Dr. A. Fayt, Universite Catholique de Louvain, Belgium,

on the analysis of the v

2 and v

4 bands of HNO 3 and on Lamb-dip

measurements of laser-Stark spectra.

Collaborated with Dr. J. Wells, Time and Frequency Division, NBS-Boulder

on the frequency measurements an analysis of N

2 o and NO absorption

lines using heterodyne techniques.

Collaborated with Dr. C. Chackerian, NASA Ames Research Center, Moffett,

CA, on the use of the Herman-Wallis effect to measure the intensity of

the CIO fundamental band.

Pine, A. S.

Collaborated with Drs. R. M. Herman and J. P. L.ooney, Department of

Physics, Penn State University, University Park, PA, .on line broadening

mechanisms in HF and HC1.

Collaborated with Dr. A. G. Robiette, Oxford University Computing

Service, Oxford, England, on the analysis of the local mode spectrum of

the overtones of germane.

Collaborated with Dr. B. J. Howard, Physical Chemistry Laboratory, Oxford

University, Oxford, England, on the analysis of the spectra of the rare gas-hydrogen chloride van der Waals complexes.

Collaborated with Dr. L. L. Strow, Department of Physics, Unviersity of

Maryland, Baltimore, MD, on line coupling and rotational collapse of

Q-branches of N

2 0.

Stephenson, J. C.

Collaborated with Dr. J.-C. Mialocq, Centre d'Etndes Nucleaires de

Saclay, France, on picosecond laser photolysis of nitro compounds.

Stevens, W. J.

Collaborated with Dr. M. Dupuis, IBM Corporation, on quantum chemistry

calculations for large molecules.

354
Collaborated with Dr. R. Osman, Mt. Sinai Medical School, on quantum

chemistry modeling of mechanisms of raetallo-enzymes.

Collaborated with Dr. D. Beveridge, Wesleyan University, on Monte Carlo

simulation of the aqueous solvation of biomolecules.

Consulted with Dr. H. Basch, Bar Ilan University, Israel, on reaction

field Hamiltonians for molecular calculations.

Consulted with Dr. B. Lengsfield, Ballistics Research Laboratory, on accurate calculations of structures and properties of small molecules.

Collaborated with Dr. W. Fink, University of California at Davis, on frozen fragment calculations of molecular structures and interactions.

Suenram, R. D.

Collaborated with Professor L. E. Snyder, University of Illinois, on radio astronomy searches for interstellar molecules.

Collaborated with Dr. H. M. Pickett, Jet Propulsion Laboratory, on

H00NC>2 and CH 2 FOH rotational spectra.

Consulted with Professor C. W. Gillies, Rensselaer Polytechnic Institute,

on construction of pulsed Fourier transform microwave spectrometer

Consulted with Dr. D. D. Nelson and Professor W. Klemperer, Harvard

University, on Ar^-NH^, and NH^-'NHq van der Waals complexes.

Consulted with Professor R. L. Kuczkowski and Dr. K. W. Hillig, II,

University of Michigan, on construction of pulsed Fourier transform

microwave spectrometer

Consulted with Professor S. G. Kukolich, University of Arizona, on construction of pulsed Fourier transform microwave spectrometer

Collaborated with Professor S. Ross, University of Alberta, on data

fitting for H

2 C0‘**HF hydrogen bonded species.

Collaborated with Professor R. K. Bohn, University of Connetticut, on assistance in the high resolution rotational assignment of several

molecular species.

Collaborated with Dr. R. Ruoff and Professor H. S. Gutowsky, University

of Illinois, on the measurement of dipole moment of the HCN trimer.

Weber, A.

Collaborated with Dr. J. W. Brault , National Solar Observatory, Tucson,

AZ, on Raman Spectroscopy of gases with Fourier transform techniques.

Collaborated with Dr. K. Narahari Rao, Ohio State University, Columbus,

OH, on discussions of the organization of the 1986 Columbus Symposium.

355
Collaborated with Drs. P. Esherick and L. Rahn, Sandia National

Laboratories , Professor B. P. Stoicheff, University of Toronto, Professor

H. W. Schrotter, University of Munich, Professor W. Kiefer, University

of Graz, Dr. G. Rasasco, Temperature and Pressure Division, NBS,

and Dr. J. Nibler, Chemistry Department, Oregon State University, on the

planning for the 10th International Conference on Raman Spectroscopy held

in Eugene, OR, September 1986.

Collaborated with Dr. D. E. Jennings, NASA/Goddard Space Flight Center,

Greenbelt, MD, on Raman spectroscopy of gases with Fourier transform

techniques

Collaborated with Drs. W. C. Harris, National Science Foundation and

I. W. Levin, National Institutes of Health on the planning for the 7th

International Conference on Fourier Transform Spectroscopy, to be held in

Washington 1989.

Consulted with Professor K. Miller, Rensselaer Polytechnic Institute, on advice on vibrational spectra of hydrocarbons.

Consulted with Dr. W, H. Weber, Ford Motor Company, on advice on the

calibration of spectrometers.

356
10. VISITING SCIENTISTS

The Molecular Spectroscopy Division has been host in the past year to the

following scientists who have worked with N3S scientists on problems of

mutual interest.

Adams, George, A., Ballistics Research Laboratory, works with M. Krauss on electronic structure codes for the chemistry and spectroscopy of

. large molecules

Basch, Harold, Bar Ilan University, Israel, is engaged in research on metal

interactions with biomolecules. He works with M. Krauss.

Bodaness, Robert S., National Institutes of Health, works with D. S. King

on laser photosensitization processes in biological samples.

Craig, N., Oberlin College, works with W. J. Lafferty on the Fourier

transform Infrared spectrum of 1 , 2-dif luorethylene

Fink, W. H., National Science Foundation, works with W. J. Stevens on the

development of model potentials and their application to large

molecules

Gillies, C. W. , Chemistry Department, Rensselaer Polytechnic Institute, works

with F. J. Lovas and R. D. Suenram on pulsed beam Fourier transform

microwave spectroscopy of hydrogen bonded molecules.

Hollis, Jan Michael, NASA/Goddard Space Flight Center, works with F. J. Lovas

and R. Suenram on software development for automated microwave

spectrometer and collaborates on astronomical studies.

Jennings, Donald E. , NASA/Goddard Space Flight Center, works with A. Weber

on a project to do Raman spectroscopy of gases with the Fourier

transform spectrometer of the National Solar Observatory (Kitt Peak)

Konowalow, Daniel D. , Professor at SUNY-Binghamton , New York, works with M.

Krauss on studies of electronic structure of alkali and alkaline

earth molecules.

Lengsfield, Byron H., Ballistic Research Laboratory, works with M. Krauss

on electronic structure codes for the chemistry and spectroscopy of

large molecules.

Ohashi, Nobukimi, Kanazawa University, Physics Department, Japan, works with

J. T. Hougen, W. J. Lafferty, and W. B. Olson on high resolution

infrared spectroscopy and theory of methylamine.

Osman, R., Mt. Sinai School cf Medicine, New York, works with W. J. Stevens

on the application of ab initio quantum chemistry to biochemical

modeling.

357
Sattler, Joseph L. , Harry Diamond Laboratories, U.S. Army, collaborates with

W. J. Lafferty and A. Maki on precise line frequency measurements

in the infrared.

Vahala, Linda L. , Physics Department, Old Dominion University, Norfolk, VA,

works with P. S. Julienne on the theory of molecular line broadening

and final state branching ratios for the resonance transitions of

alkali atoms perturbed by rare gas collision partnes.

Zozom, Jennifer, Chemistry Department, Rensselaer Polytechnic Institute works

with Drs. F. J. Lovas and R. D. Suenram on pulsed beam Fourier

transform microwave spectroscopy of hydrogen bonded molecules.

358
NBS-114A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET fSee instructions) NBSIR 86-3470 OCTOBER 1986

4. TITLE AND SUBTITLE

Technical Activities 1986

Center for Chemical Physics

5. AUTHOR(S)

Pierre Ausloos

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract^Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State, ZIP)

10. SUPPLEMENTARY NOTES

I

I Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bliography or literature survey, mention it here)

This report summarizes research projects, measurement method development,

testing and data evaluation activities carried out during Fiscal Year 1986

in the NBS Center for Chemical Physics. These activities fall in the areas

of surface science, chemical kinetics, chemical thermodynamics and

molecular spectroscopy.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key

Chemical kinetics; chemical physics; molecular spectroscopy; surface

thermodynamics

words by semicolon s) science

;

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

[j£j Unlimited

1

1 For Official Distribution. Do Not Release to NTIS 366

| | Order From Suoerintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. 15. Price

rX] Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $28.95

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