U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

NBSIR 85-3257

Technical

Activities 1985

Genter for

Chemical

Physics

Pierre J. Ausloos, Director

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory Center for Chemical Physics

Gaithersburg, MD 20899

December 1985

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, 1984 to September

30, 1985. 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 fifty 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 standard 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 20899. Telephone extensions are listed in the table at

the end of the report ( 301 -921 -EXT)

.

i
TABLE OF CONTENTS

Page

SURFACE SCIENCE - DIVISION 5^1

1 . INTRODUCTION . 1

2. SURFACE STANDARDS PROGRAM 4

Reference Data ; 4 Reference Materials 15

Review Articles and Books . 20

Standards - Committee Activities 29

3. SURFACE MEASUREMENT PROGRAM 35

Reaction Kinetics Over Single Crystal Catalysts 35

Molecular Structure and Reactivity on Surfaces 37

Neutron Scattering Studies of Reactions on Catalysts 40

Surface Characterization Using Synchrotron Radiation 42

Dynamic Effects Associated with Core-Level Ionization 49

Production and Characterization of Ultrasmooth Surfaces 51

Laser Diagnostics of Surface Dynamics 52

Spin Polarization in Secondary-Electron Cascades 56

Theory of Dynamical Molecular Processes at Surfaces 58

4. SURFACE COMPETENCE PROGRAM 64

Novel Two-Dimensional Materials 64

State Characterization of Species Ejected from Surfaces 74

5. PUBLICATIONS 79

6. TALKS 90

7. SURFACE SCIENCE DIVISION SEMINARS 98

8. TECHNICAL AND PROFESSIONAL COMMITTEE PARTICIPATION AND LEADERSHIP 101

9. PROFESSIONAL INTERACTIONS, CONSULTING, AND ADVISORY SERVICES ... 103

10. VISITING SCIENTISTS 110

ii
Page

CHEMICAL KINETICS - DIVISION 542

1. INTRODUCTION ................... 113

2. Data Centers ........ 117

Introduction 117

Chemical Kinetics Data Center 117

Ion Kinetics and Energetics Data Center ...... 121

3. KINETICS OF NEUTRAL SPECIES ........ ...... 123

Introduction ........... 123

Gas Phase Kinetics 124

Condensed Phase Kinetics ......... 137

4. ION KINETICS 145

Introduction .................... . . 145

Gas Phase Ion Kinetics 146

Condensed Phase Ion Kinetics . 150

5. PUBLICATIONS ...... ............ 156

6. TALKS 165

7. CHEMICAL KINETICS DIVISION SEMINARS . 169

8. TECHNICAL AND PROFESSIONAL COMMITTEE PARTICIPATION AND LEADERSHIP 170

9. PROFESSIONAL INTERACTIONS, CONSULTING AND ADVISORY SERVICES ... 172

10. VISITING SCIENTISTS ................ 176

CHEMICAL THERMODYNAMICS - DIVISION 543

1. INTRODUCTION 179

2. BIOTHERMODYNAMICS AND MOLECULAR STRUCTURE 185

Thermodynamics of Enzyme Catalyzed Reactions 195

Differential Scanning Calorimetry 188

Spectroscopy of Phase Transitions in Biomolecules 191

Biomolecular Structure Studies . 192

iii
Page

CHEMICAL THERMODYNAMICS - DIVISION 543 (Cont'd)

3. CHEMICAL THERMODYNAMIC MEASUREMENTS ............... 201

Large Sample Combustion Calorimetry ............... 201

Certification of Combustion Calorimetry Reference Materials . . . 205

Estimation and Calorimetry on Organic Phosphorus Compounds .... 208

Bomb Calorimeteric Measurements of 2-Deoxy-D-Ribose 209

Drop Calorimetry of Non-Reacting Ssytems Below 2800K 210

Weak Interactions in Model Enzyme-Substrate Systems 212

4. CHEMICAL THERMODYNAMIC DATA ACTIVITIES .............. 215

Thermochemical Data Evaluation for Inorganic Systems 216

Organic Thermochemistry 218

Biochemical Thermochemistry 218

Thermodynamics of Electrolyte Solutions 220

Methods for the Correlation of Properties of Solutions 221

Data Base Development -- General 221

Data Base Development — Properties of Electrolyte Solutions . . . 222

Accessions, Information, and Support . . 223

Automation Activities 223

Plans 225

5. PUBLICATIONS 227

6. TALKS 232

7. CHEMICAL THERMODYNAMICS DIVISION SEMINARS 236

8. TECHNICAL AND PROFESSIONAL COMMITTEE PARTICIPATION AND LEADERSHIP 237

9. PROFESSIONAL INTERACTIONS, CONSULTING AND ADVISORY SERVICES ... 239

10. VISITING SCIENTISTS 244

IV
Page

MOLECULAR SPECTROSCOPY - DIVISION 545

1 . INTRODUCTION 247

2. HIGH RESOLUTION SPECTROSCOPY 251

Introduction 251

Calibration and Data Center Activities 252

Spectroscopy for Environmental Studies 256

Spectroscopy of Hydrogen-bonded and van der Waals Complexes . . . 263

General Spectroscopy and Theory 274

Future Plans 285

3. LASER PHOTOCHEMISTRY 288

Introduction . 288

Condensed Phase Energy Transfer 288

Desorption of Molecules from Surfaces 301

Dynamics of van der Waals Molecules 303

Matrix Isolation Spectroscopy . 305

Future Plans 308

4. QUANTUM CHEMISTRY 315

Introduction 315

Electronic Structure 315

Scattering

Multiphoton Effects in Resonance Fluorescence Spectra 326

Future Plans 327

5. PUBLICATIONS . 328

6. TALKS 33 1*

7. MOLECULAR SPECTROSCOPY DIVISION SEMINARS 340

8. TECHNICAL AND PROFESSIONAL COMMITTEE PARTICIPATION AND LEADERSHIP 342

9. TECHNICAL INTERACTIONS, CONSULTING AND ADVISORY SERVICES .... 343

10. VISITING SCIENTISTS 347

PERSONNEL LISTING, CENTER FOR CHEMICAL PHYSICS 350

v

SURFACE SCIENCE DIVISION

C. J. Powell, Chief

SUMMARY OF ACTIVITIES

Fiscal Year 1985

1 . INTRODUCTION

A. Background

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

science and its applications. At the national and local meetings of many

professional societies, there are typically multiple sessions of papers

concerned with the physical and chemical properties of surfaces.

Similarly, many current professional journals and books are devoted in

whole or in part to similar reports of recent advances in this field.

These advances result from investigations of basic properties (such as composition, atomic structure, electronic structure) of surfaces and the

dependence of many complex surface processes (such as molecular sticking,

dissociation, diffusion, reaction, and desorption) on the basic properties

and other variables relevant to catalysis, corrosion, thin-film systems,

microelectronics, computer elements, and communications applications.

Investigations of this type range from fundamental studies, at an atomic

and molecular level, on clean single-crystal surfaces to similar studies

on appropriately modified surfaces or structures and lead not only to the

development of surface science but also to new materials, devices, and

processes. Similar investigations, principally measurements of surface

composition and of other needed properties, are frequently made of a large

variety of materials (e.g., metals, polymers, semiconductors, oxides,

glasses, etc.) after fabrication and at various time during their service

life for quality control, process optimization, and failure analysis. The

growth of surface science and its multidisciplinary impact on many

important technologies have been documented in a recent article by H. D. Hagstrum [ Frontiers in Science and Technology , W. H. Freeman and Co., New

York (1 983) , pp. 113-134].

A large number of techniques are utilized for surface character i za- tion. A choice of one or 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 very few standard

procedures and limited reference data and reference materials. A variety

of techniques is employed for the determination of surface atomic

1
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, there is a need for relevant procedures,

tests to establish measurement reliability, and 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

.

B. Goal, Objectives and Division Program

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

existing surf ace-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

(4) 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 NBS

task titled "Development of Measurement Methods for Surface Properties"

(Task 15502). 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 areas

is reported in Sections 2 and 3. respectively. This work is supported by

2
NBS resources (including some funds transferred through the Office of

Standard Reference Data) and by contracts with two Federal agencies

(Department of Energy and Office of Naval Research).

Objective (4) is met through the Surface Competence Program (Task

26117). This task was established in October, 1984 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 4.

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 surface-characterization 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 NBS

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 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 thirteen 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 hold 1- to 2-year appointments; four Postdoctoral

Research Associates worked in the Division during FY 1985.

3
2 . SURFACE STANDARDS PROGRAM

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

J. Fine, Y. Hashiguchi, R. D. Kelley, C. J. Powell

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

activities that are directed to improving the quality of surfacecharacterization measurements through: (1) development of needed reference

data and standard reference materials; (2) leadership in standardscommittee 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 depth-profile 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 sputter-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,

A r, Kr, Xe , 0

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 developed this

past year to handle the specific needs of the data compilation. The

structure developed allows easy data entry into one of these data bases;
information can then be transferred to the second data base for rapid

access and searching. Additional software has been written to sort and

tabulate the searched data in a format suitable for publication.

Sputtering yield papers are being compiled; data has been abstracted

and entered into the data-base system. Initial tests indicate that the

system is operating properly. Work also is progressing on our on-line

abstract searching capability so that we can collect and enter additional

references and data directly from the computer search into our data base.

In the coming year we intend to complete the data searching and data

entry, to evaluate the data set, and to compile sputtering-yield data of

interest to the surface-analysis and sputter-depth-profiling community on elemental targets.

2. Characterization of the Imaging Properties of a Double-Pass

Cyclindrical-Mirror Analyzer

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

Knowledge of the specimen area being analyzed is important in

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

photoelectron spectroscopy (XPS) , particularly when inhomogeneous

specimens are being examined and experimental conditions are being varied.

We have characterized the imaging properties of a commercial double-pass

cylindrical-mirror analyzer (CMA) used for AES and XPS with extensions of

a method developed elsewhere. These extensions have yielded more

quantitative analyzer characterization than was possible previously. This

work was motivated also by the need to evaluate the analyzer imaging

properties on the binding-energy measurements described in Section 2. A.

5

below.

The electron beam from the coaxial electron gun of the CMA was rastered across a test surface and the intensity of elastically scattered

electrons detected by the analyzer was stored in a computer as a function

of beam position on the specimen and other experimental parameters. The

intensity data could be later plotted to give "three-dimensional" images

that showed clearly the imaging properties of the CMA. Elastic-peak

images have been obtained for a typical specimen orientation (in our case

at an angle of 60° to the CMA axis) and for typical measurement conditions

(electron energies of 100, 500, and 1000 eV ; analyzer pass energies of 25,

50, and 100 eV ; selection of small or large apertures intended for AES or XPS measurements, respectively; and for selected analysis energies ranging

between 1.5 eV above the incident energy and up to 5 eV below the

incident energy). We have investigated how the images were modified as the

specimen was translated along the CMA axis about its optimum position.

Finally, we have obtained absorbed-current images to ensure that the test

specimen was sufficiently smooth to prevent significant artifacts occurring

in the elastic-peak images.

5
Figure 1 shows examples of elastic-peak images recorded with the

specimen at its optimum position and with use of the AES aperture. Figure

1(a) shows images at a fixed pass energy of 50 eV and for incident

energies of 100, 500, and 1000 eV ; Figure 1(b) shows images for an incident

energy of 500 eV and pass energies of 25, 50, and 100 eV. It is clear

that the specimen area contributing to the detected signal is changing as these operating parameters are varied.

Comparisons have been made of observed image widths for particular

operating conditions with those expected from a simple analysis.

Semi-quantitative agreement has been obtained although there are differences in trends (as a function of electron energy or analyzer pass

energy) that can be associated with non-uniformities of grids on the

inner-cylinder apertures, with lack of sphericity of the retarding grids,

and with simplifications of the analysis. Asymmetries in the measured

images, for example at high retardation ratios or when the specimen is

moved from its optimum position, are due to specific imperfections in our instrument

.

Substantial changes are seen in the elastic-peak image shapes as the

specimen is translated along the analyzer axis to simulate accidental

misalignments. Similar changes are obtained in the image shapes as an offset voltage is applied to the electron gun so that the analyzer detects

electrons on the high-energy side of the elastic peak or electrons that

have been inelastically scattered in the specimen. The latter changes can

be qualitatively interpreted in terms of the known coupling between

detected signal and source position, angle of emission, and electron

energy. These results indicate that sharp peaks in an energy distribution

come from a smaller specimen area than for broad peaks or for

inelastically scattered electrons.

We have also measured changes in the posiiton of the elastic peak as the incident beam is deflected to representative points on the specimen in

the field of view of the analyzer. Changes of up to ±0.15 eV in peak

position were found and these were not symmetrical about the vertical as would be expected for an ideal instrument.

It is planned to draft a Recommended Practice for Characteri zation of

the Imaging Properties of Electron Energy Analyzers for ASTM Committee

E-42 on Surface Analysis based on the above methods.

3. Energy Dependence of Electron Attention Lengths

(C. J. Powell)

The attenuation length (AL) of low-energy electrons in solids

is an important parameter in surface analysis by Auger-electron

spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). The AL

determines the surface sensitivity of AES and XPS (and other

electron-spectroscopic techniques of surface characterization) and is

required for quantitative surface analysis by AES and XPS. Accurate AL

6
Fig. 1 Elastic-peak images recorded with a double-pass cyl indri cal-mirror

analyzer, the AES aperture, and a test specimen at its optimum

position. Left: Images recorded with an analyzer pass energy of

50 eV and incident energies of 100 eV (top), 500 eV (center), and

1000 eV (bottom). Right: Images recorded with an incident energy

of 500 eV and analyzer pass energies of 25 eV (top), 50 eV

(center, and 100 eV (bottom). The horizontal (bottom left to

right) distance scanned by the electron beam on the specimen is 13 mm and the vertical distance is 15 mm.

7
measurements are difficult in the electron energy range of practical

interest but relative AL measurements are useful since they give the AL

energy-dependence which is needed in one method of quantitative analysis.

The Bethe theory of inelastic electron scattering in matter has been

very successful and it was thought useful to test whether it was valid

also for AL data in solids. According to the Bethe theory, AL values X would be given the by formula, X = AE/bln(cE/AE) , where E is the electron

energy, AE the most probable excitation energy for the material, A a term

containing material and other constants, and b and c parameters of order

unity

.

AL measurements for Al, Au, Si, Ge, AI 2 O

3

, SiC> 2 , NaF, NaCl , and KI

have been successfully fitted to the Bethe formula for E typically between

100 and 1500 eV. The quality of these fits was generally superior and the

electron energy range greater than for earlier fits to an empirical

formula. It was found, however, that the parameter b was higher and the

parameter c much lower than the values expected from theory. These

deviations are similar to those found in other tests of the Bethe theory

where the electron energies were not high enough for the parameter values

to reach their asymptotic values. Nevertheless, it is useful empirically

that the Bethe equation adequately describe those AL data which exist for

a representative group of materials over a substantial energy range.

Although the derived values of the parameters are material-dependent, good

estimates of the ratios of ALs at different electron energies can be

obtained from the Bethe equation using the average value of c = 0.4 and

the average value of AE = 20 eV.

A separate investigation has shown that electron inelastic mean free

paths (IMFPs) can be calculated from experimental dielectric data. IMFPs

calculated for eight materials agreed reasonably (within 50$) with

available AL measurements (which had been obtained with a model in which

elastic electron scattering was assumed to be insignificant). Since it is

difficult to measure ALs with accuracies much better than about 50$, it is

useful to obtain IMFP data from another base of experimental data. It is

planned to extend these calculations using optical data for additional

materials

.

4. Atomic Layei—by-Layer Analysis of the Source of Angular

Anisotropies in XPS and AES

(W. F. Egelhof f , Jr.)

Attenuation lengths of low-energy electrons in solids, important

for quantitative surface analysis by Auger-electron spectroscopy (AES) and

x-ray photoelectron spectroscopy (XPS) , have been frequently measured from

the characteristic decay or growth of an AES and XPS signal as a film of

increasing thickness is deposited on a substrate. A fundamental

complication for such measurements is the enhancement of an AES or XPS peak

intensity along crystal axes in single-crystal samples. These

enhancements along nearest-neighbor directions are due to forward

8
scattering of the emitted electrons by lattice atoms. An example of the

angular anisotropy is shown in Figure 2(a) for epitaxial Cu layers on Ni(IOO)

.

In order to deepen the understanding of the depth dependence of this

forward-scattering phenomenon, single-scattering electron-diffraction

calculations have been performed in collaboration with Dr. R. A. Armstrong

of the National Research Council, Ottawa. Figure 2(b) shows an example of

these calculations for conditions appropriate to the data in Figure 2(a).

The comparison between the calculations and the data reveal several

important points.

(1) Since all observed peaks are accounted for in the calculations,

single-scattering events must be the dominant mechanism for the observed

peaks

.

(2) The observed thickness at which each of the four peaks first

appears is in accordance with predictions of the calculations. This

result confirms the original interpretation, namely that the intensity of

the peaks is due mainly to constructive interference in the forward

scattering direction by nearest-neighbor and next-nearest-neighbor atoms

in the lattice.

(3) The calculated enhancement in the peak intensities continues to

grow for Cu thicknesses greater than 3 ML whereas in the data there is very

little increase beyond a thickness of 3-3 ML. (Compare, for example, the

peak at 45° in Figures. 2(a) and (b).) This comparison reveals an important

result. The first (single) scattering event enhances the intensity along

a nearest-neighbor direction (e.g. at 45° in Figure 2(c)) but subsequent

(multiple) scattering events wash out this enhancement. The

single-scattering calculations thus predict a continued growth in the

peaks which is not observed experimentally. As a consequence, the

measured peaks are due more to short-range order, or nearest-neighbor

axes, than originally thought.

This combined theoretical and experimental analysis has deepened the

understanding of the phenomena involved in electron attenuation-length

measurements with single-crystal materials. Such measurements will have to

be made in the future for specific angles of electron emission.

5. Measurement of Core-Level Binding Energies

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

Accurate reference values of the binding energies of core-level

electrons are needed for the commonly used technique of x-ray

photoelectron spectroscopy (XPS) and for other surface-characterization

methods. These values are needed for the calibration of instrumental

energy scales. For this application, data are required for a limited

number of pure materials that adequately cover the range of common measurements

.

9
EPITAXIAL Cu ON Ni(IOO)

Fig. 2

0

° <100>

. (a) Measured intensities of the x-ray- induced Cu L^VV Auger

intensity as a function of polar angle of emission for various

thicknesses (in monolayers) of Cu on Ni(100). (b) Corresponding

calculated intensities. (c) Schematic illustration of the

surface profile.

10
We have made measurements earlier of the core-level binding energies

by XPS for the principal peaks of Ni, Cu, Ag, and Au. The accuracy of

these measurement, however, was limited severely by voltage drifts in our

XPS system. To improve the accuracy and precision of the measurements, we

have installed programmable power supplies and digital multimeters for the

control and measurement of the voltages applied to the cylindrical-mirror

analyzer. The experimental measurements are under computer control.

Programs have been written to set and step the analyzer voltage suppliers

and to read the multimeters. Least-squares peak-fitting routines have

been evaluated for determining peak positions. These tests have shown

that fits using a quadratic or a quartic to the top 20-50% of a peak are

about equally satisfactory.

Stability checks have been made to assess the short-term (several

hours) and long-term (ca. 1 month) stability of the upgraded system. The

short-term reproducibility in the location of peaks is now about 4 meV and

is limited by the counting statistics of typical scans. The long-term

stability is approximately 10 meV and is within the instrumental

specifications for electronic drift.

A certified calibration of the voltage-measuring instruments is

scheduled to be made shortly. We will then make new high-accuracy

measurements of the Ni, Cu, Ag, and Au XPS peaks and compare these with

recent independent measurements at the U.K. National Physical Laboratory

(NPL) . We will initially use a beam of elastically scattered electrons

from a gun with a thermionic cathode as an energy reference, as we have

in our preliminary measurements. We will then use a gun with a field-emission cathode to compare results from the two types of electron

sources and to resolve an apparent discrepancy in a recent measurement of

the Au ^fy /2 binding energy made using a field-emission reference source. After completion of these XPS binding-energy measurements, we will make

similar measurements of the kinetic energies of Auger electrons from Cu,

Ag, and Au and compare these results with similar measurements now in

progress at NPL.

6. 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 NBS Office

of Standard Reference Data to prepare compilations and evaluations of

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

Auger electrons for a wide range of elements and compounds. In

particular, data are being compiled of the "chemical shifts" that can 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. Dr. Wagner has currently generated over 10500

data entries in his files from 600 papers and the compilation is
approximately half-completed. During the past year, progress has been

significantly delayed by illness but it is expected that the project

should be completed next year. The reference data will be included in a report for the Journal of Physical and Chemical Reference Data.

7. Algorithm for Fitting Sputter-Depth-Profiles at Interfaces

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

The determination of interface widths from sputter-depth-profiles is

presently accomplished by means of graphical methods. Since the shapes of

such interface profiles are generally not symmetric and since there is no accepted method of measuring interface widths, accurate width

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 = [A + a (T-T

q ) ]/ ( 1 + e + [B + b(T-T 0 )]/(1 + e

1

)

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

as a function of 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 of 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 been written which fits the

measured Auger spectral intensities to the above equation within

measurement error. All currently used measures of the interface width are proportional to D. The statistics associated with the least squares fit

allow confidence limits to be placed on the measured widths of interface

regions and on the widths of surface layers of dissimilar materials.

8. Needs for Reference Data

The growth of surface science and its applications has led to

needs for expanded reference data. These needs can be summarized in the

following three categories.

12
(a) Surface Analysis

Four techniques are now in common use for surface analysis:

Auger-electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS),

secondary-ion mass spectroscopy (SIMS), and ion-scattering spectroscopy

(ISS). With each technique, there is need for the following reference

data:

evaluation of spectra from pure elements for common

conditions of measurement

evaluation of chemical or matrix effects on spectra

benchmark data for the calibration of the energy and

intensity scales of instruments

reference data on line positions in compounds

reference data for key parameters in quantitative analysis

(e.g., ionization cross sections (AES, XPS), ion scattering

cross sections (ISS), electron inelastic mean free paths

and attenuation lengths (AES, XPS), electron backscattering

(AES), ion neutralization cross sections (SIMS, ISS), and

multiple ionization (SIMS)

algorithms for data analysis (e.g., determination of

background due to multiple scattering (AES, XPS, ISS) and

fragments (SIMS, ISS), deconvolution to obtain source lineshape (AES, XPS, ISS), inelastic scattering (AES, XPS),

and double scattering (ISS))

data for ion sputtering yields in elements, alloys, and

compounds as a function of ion type, ion energy, and

bombardment geometry

data for radiation damage rates during analysis, including

cross sections for desorption from surfaces and

decomposition of surface layers.

(b) Surface Science

Many techniques are in common use for the determination of

surface properties and processes. Data are needed in the following areas:

reference data on vibrational energies and intensities for

molecular species on surfaces (as measured by electron

energy-loss spectroscopy, infrared spectroscopy, Raman

scattering, neutron inelastic scattering)

13
reference data for determination of surface structures by

low-energy electron diffraction and other techniques (e.g.,

library of basic data, algorithms to compute surface

structure

)

reference data for absolute determination of surface

coverages (atoms/cm^) on surfaces of different structure and

atomic composition

reference data for surface processes (kinetic data for

catalytic and surface reactions, desorption, diffusion,

segregation)

Ion-surface interactions are of importance in sputtering

and ion scattering spectroscopy. Reference data are needed

to characterize the electron and photon spectroscopy of

scattered and sputtered ions, as well as of excited neutral

species leaving the surface.

(c) Interface Science

There is rapid development now of techniques that can be

used for the _in situ characterization of solid-solid, solid-gas, and

solid-liquid interfaces. A variety of techniques (e.g., Rutherford

backscattering spectroscopy, infrared spectroscopy, Raman spectroscopy,

extended x-ray absorption fine structure, neutron inelastic scattering,

particle- induced x-ray emission) are being utilized and reference data and

algorithms will be required for their effective application.

The Division is providing reference data to meet some of the

above-mentioned needs through the projects described in this Section and

through the publication of the review articles listed in Section 2.C.

Other current Division projects, not described in detail in this report,

are:

comparison of core-level excitation energies by different

spectroscopic techniques

calculation of electron inelastic mean free paths from

experimental optical data

measurement of electron attenuation lengths in condensed

molecular films

The Division will coordinate its efforts with the data activities that

have been initiated recently through the Surface Chemical Analysis

activity of the Versailles Project on Advanced Materials and Standards

(VAMAS) , as described in Section 2.D.2. There will also be coordination

with the NBS Office of Standard Reference Data and the Standard Reference

Data Subcommittee of ASTM Committee E-42 on Surface Analysis.
B. Reference Materials

1 . Development and Production of Standard Reference Materials for

Sputter-Depth Profiling

(J. Fine)

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 E-42 on Surface Analysis were done using Auger-electron spectroscopy, x-ray

fluorescence, secondary- ion mass spectroscopy, 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.

The preliminary analyses obtained on the nickel-chromium multilayered

thin-film structures indicate that this material should be of considerable

benefit as a depth-profiling SRM. Work on its characterization and

calibration has now been completed. We have determined the uniformity and

periodicity of the thin-film layers, absolute film thicknesses, sputtered

interface depth resolution, and structural stability. Measurement methods

used to characterize this Ni-Cr SRM include N(E) Auger sputter profiling,

Rutherford backscattering spectroscopy (RBS), and neutron activation

analysis (NAA). These measurements have resulted in the following

certified values for this Ni/Cr structure that has recently been issued as NBS Standard Reference Material 2135.

(a) Total Cr and total Ni thicknesses

The total thickness of the five Cr layers and the total

thickness of the four Ni layers were determined by NAA using a gravimetri cally calibrated reference and are given below.

Element Total Thickness Uncertainty

Cr 191 yg/cm2 ± 8 yg/cm 2 Ni 235 yg/cm 2 ± 9 yg/cm 2

15
The uncertainty stated is based on our best judgement of all factors

involved and corresponds to about two standard deviations of the average.

(b) Individual layer uniformity and Ni+Cr bilayer uniformity

(periodicity)

.

Layer thickness uniformity was determined by measuring the

ion bombardment time required to sputter-remove a single layer. This time

was obtained by monitoring the surface composition by Auger spectroscopy

during sputter erosion. The uniformity of Ni+Cr bilayer removal also was determined in a similar way.

Type of Layer

Relative Layer

thickness

uncertainty*

Number of profile

me as ur ements

(9 layers each)

Single Cr layer

Single Ni layer

Bilayer of Ni and Cr

±4.856

±4.656

± 3-056

6

6

6

*This uncertainty is two relative standard deviations,

(c) Individual layer thicknesses

The average thickness for a single layer of a given element

was obtained from the total layer thickness for that element and the

number of layers present. The relative uncertainty of this average layer

thickness was determined by combining the uncertainties in the total

thickness and in the single layer uniformity for that element.

Element

Cr

Ni

*This uncertainty is

Single layer

thickness

38.2 ug/cm2

58.8 ug/cm 2

standard deviations

Relative layer

thickness

uncertainty*

±2.3 mg/ cm 2 ±3.5 ug/cm 2

The following additional information has been provided about SRM

2135; this information is uncertified.

(a) Layer thicknesses in units of length

The certified layer thicknesses could be converted into

units of length (nm) if the densities of the layers were known. As these

densities are not known, an approximate thickness in nm can be derived by

using the known bulk densities for Cr (7.19 g cm’^) and Ni (8.9 g cm 3);

the values so obtained are 53 nm for Cr and 66 nm for Ni.

16
(b) Layer thickness and uniformity

Measurements of SRM 2135 using RBS give information on the

single-layer thickness and uniformity of each of the Cr and Ni layers.

RBS measurements of the single-layer uniformity confirm the uncertainties

obtained from the sputter removal times for single layers. Layer

thickness measurements obtained by RBS depend on the value of the stopping

power used to calculate thickness. A 5 to 10$ uncertainty in thickness

can result from the uncertainty in currently available stopping-power data

and can limit the accuracy of this technique. Single-layer thickness

determined by RBS confirm the values certified, providing that a 5 to 1 0$

uncertainty is assumed in the RBS measurements. The RBS result obtained

for the average thickness of a single Cr layer is 8.5$ smaller than its

certified value, while the RBS single Ni value is 5.4$ smaller than that

certified

.

(c) Relative sputtering rates and yields of Ni and Cr using

argon ion bombardment

Ion Energy

(keV)

1.0

2.0

3.0

4.5

Ni/Cr Rate

1 .03

1 .07

1 .09

1 .09

Ni/Cr Yield

1.12

1.17

1 .20

1 .20

Rate is expressed in units of length/time.

Yield is given as number of atoms sputtered per incident ion.

Future work includes characterizing and certifying additional Ni/Cr

structures similar to SRM 2135 as well as a "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 Cr 2 0^.

2. Quantitative Sputter Depth Profiling of Interfaces

(J. Fine, Y. Hashiguchi)

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

interfaces is at present difficult to achieve with sputter-depth-prof il ing

techniques. This is due, to a large extent, to a lack of understanding

of bombardment conditions (i.e., ion beam energy, species, angle of

incidence, current density, and sputtered depth). A careful evaluation

of such factors which affect interface resolution is not available for any

given interface system. A consistent set of such 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-profile analysis took place and would be of value in

determining optimum sputter-profile conditions.

17
Our development of the Ni-Cr thin-film depth-profile SRM 2135 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

measurements of the interface depth resolution for the Ni-Cr material.

In collaboration with Dr. P. A. Lindfors of the Perkin Elmer

Corporation, Physical Electronics Division and Dr. D. F. Mitchell of the

National Research Council of Canada, Ottawa, we have examined the

dependence of Ni-Cr interface broadening an ion beam energy, ion current

density, and angle of incidence, all as a function of sputtered depth.

Our results indicate that much narrower interfaces are observed when

profiling with low-energy ions; for example, the interface widths with 1 keV argon ion bombardment at a particular ion-beam angle of incidence are about half those for 3 keV bombardment. We also find that narrower

interfaces can be obtained by bombarding at more oblique (grazing) angles.

Our narrowest interfaces (- 5 nm) resulted when the ion beam was incident

at 70° with respect to the surface normal.

Preliminary measurements of interface-width dependence on ion-beam

current density indicate this this parameter may affect interface

resolution. We plan to explore this dependence by examining the

relationship between ion current density and ion energy.

3. Needs for Reference Materials

The following needs for additional reference materials have been

identified

.

(a) Depth-Profiling SRM's

Surface analysis is frequently combined with ion sputtering

to measure composition versus depth and to investigate solid-solid

interfaces. It is believed that sputter-depth-profiling applications will

continue to grow and, with the development of new techniques for deposition

of materials (e.g., molecular-beam epitaxy), the development of better

depth-profiling techniques, and demands for better accuracy, use of new materials, and desire for sharper interfaces, there will be an increased

demand for suitable SRM's to ensure the reliability of the relevant

measurement system.

NBS has recently developed a multi-layer periodically-modulated SRM

consisting of alternate layers of Ni and Cr (Section 2.B.1). Similar

structures consisting of Ni/Ag and Cr/Cr2 0o have been fabricated but

remain to be characterized. We have also fabricated films of Ta2

0c; on Ta

and these also have to be characterized.

18
There are needs for similar SRM's involving other types of materials

in high-technology industries, for example, Si02 on Si, epitaxial

modulated- thickness films of GaAs/GaAiAs , thin layers of metals on semiconductors (Schottky barriers), and polymer films on metal substrates.

(b) Calibration of Surface Analysis Instruments

There is a growing need for the characterization and

calibration of surface-analysis instrumentation, particularly since the newer computer-controlled instruments require greater system stability and

reproducibility than before. Until recently, most surface analyses have

been qualitative but there is increasing demand for quantitative analyses

of defined accuracy. These developments require SRM's for instrument

calibration (e.g., of the instrument transmission functions for

Auger-electron spectrometers (AES) and x-ray photoelectron spectrometers

( XPS ) and for the determination of instrument performance (e.g., the

detection of trace constituents).

Pure elemental and multicomponent materials can be utilized for

calibration of the energy and intensity scales (and instrument

transmission functions) of AES and XPS instruments. A suite of pure

elements (e.g., Cu, Ag, and Au) could be used for both purposes. Liquid

alloys (e.g., Ga-Sn or Ga-In) can be cleaned readily to generate

two-component surfaces of known composition for checks of instruments and

algorithms for analyses. Multicomponent materials with known quantities of

trace elements are needed for determining the ability of an instrument to

detect trace species. Suitable materials could include ion-implanted

impurities in silicon (with a specified depth distribution and maximum

concentration) and multi-component liquid alloys (with homogeneous

compositions or with segregation of trace species at the surface).

(c) Surface Science

There is a need for SRM's that would lead, with the user following a prescription, to surfaces of known composition (e.g., to known

coverage of a chemisorbed layer of molecules on a metal substrate or to a monatomic layer of a metal on a substrate). A single-crystal SRM (e.g.,

Ni) could be cleaned and exposed to different gases (e.g., 0

2 , N2

, H2 , CO,

H

2 S) to establish known surface coverages of such gases. Such an SRM would

enable calibration of AES and XPS equipment now used for measurements of

surface coverages. Another use of the SRM could be through the deposition

of several monolayers of a metal (e.g., Ag) , again after cleaning, with

appropriate thermal treatment to remove all but a monolayer of the

deposit. This process could also be used for the calibration of AES and

XPS equipment used for investigations of novel properties of ultrathin

metal films.

The Division will coordinate its activities to produce and

characterize SRM's with related efforts that have been initiated in other

countries through the Community Bureau of Reference of the Commission of

the European Communities and, more recently, the Surface Chemical Analysis

19
activity of the Versailles Project on Advanced Materials and Standards

(VAMAS), as described in Section 2.D.2. Plans for producing additional

SRM’s at NBS will also depend on sales of SRM 2135 (Section 2.B.1) and the

results of a needs survey of the ASTM Committee E-42 on Surface Analysis.

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 24 review articles recently.

The titles and abstracts of review articles published since 1984 are listed below:

(a) "Instrumentation for Photon Stimulated Desorption,"

R. Stockbauer, Nucl . Instr. Meth. 222 , 284 (1984).

Photon stimulated desorption (PSD) refers to the ejection

of ions, atoms or molecular fragments from a surface initiated by the

absorption of single photons; to date, most studies have concentrated on detection of ions. The properties of PSD which make it attractive as a surface characterization tool are its extreme surface sensitivity, the

ions being ejected only from the topmost layer and the rapidity with which

the ions are ejected. Since the desorption is fast (-10

-1 s), with

respect to molecular vibrations (~10

-1 ^ s), the ion trajectory reflects

the initial bonding geometry of the particle to the surface.

To study the ion desorption process, one would like to know the mass,

kinetic energy distribution, angular distribution and the yield

(desorption rate vs. photon energy) of the desorbing ions. Time-of-flight

(TOF) analyzers are used where the time between the light pulses from the

synchrotron light source is on the same order as the flight time of the

ion from the surface to the detector. One can measure easily ion mass and

yield but not kinetic energy or angular distributions with this class of

analyzer. Electrostatic deflection analyzers are used to measure ion

yields and kinetic energy distributions and, in some instruments, ion

angular distributions. In general, they are useful where the time

structure of the synchrotron light is too short to allow TOF analysis.

Optical methods have recently been applied to the detection of excited

states of neutral Li seen in PSD of LiF.

20
(b) "Inelastic Scattering of Electrons in Solids," C. J. Powell, in Electron Beam Interactions with Solids for

Microscopy , Microanalysis , and Microlithography , D. F. Kyser, H. Niedrig, D. E. Newbury and R. Shimizu, eds. (SEM

Inc., Chicago), 19-31 (1984).

The principal mechanisms and available data for the

inelastic scattering of electrons in solids are reviewed. The processes

relevant for electron-probe microanalysis, electron

energy-loss-spectroscopy , Auger-electron spectroscopy, and x-ray

photoelectron spectroscopy are described and examples of relevant electron

energy-loss data are shown. The discussion is based on the dielectric

description of inelastic scattering and treats processes important in the

excitation of both core electrons and valence electrons. Information is

given on the cross sections for ionization of core levels, inelastic mean

free paths of Auger electrons and photoelectrons in solids, and radiation

damage.

(c) "Non-adiabatic Effects in Elementary Surface Reactions:

State-to-State Molecular Beam Experiments as a Probe," J. W. Gadzuk, in Many-Body Phenomena at Surfaces , D. Langreth

and H. Suhl , eds. (Academic Press, N.Y.), 517 (1984).

A theory of elementary chemical reactions at solid surfaces

is described in terms of surface-induced diabatic transitions between

"reactant" and "product" potential curves, it is then shown how the

internal vibrational state distribution of a diatomic molecule scattered

from a surface could provide unique dynamical information required as input

to the diabatic transition theory.

(d) Early Applications of Vacuum, from Aristotle to Langmuir,"

T. E. Madey, J. Vac. Sci. Tech. A2, 110 (1984).

Highlights of the development of vacuum science and

technology from ancient times to the early twentieth century are reviewed.

The view of the Greek philosophers that vacuum was an impossibility

hampered understanding of the basic principles of vacuum until the mid

17th century. Verifiable vacua were first produced in Italy by Berti and

Toricelli; von Guericke's dramatic experiments vividly demonstrated

atmospheric pressure. Piston-like "air pumps" were widely used in England

and the European continent through the 18th and early 19th centuries to

produce and characterize the properties of vacuum (lack of sound

transmission, inability to support life, gas discharges, etc.). The

Industrial Revolution was made possible through the genius of Newcomen,

who designed huge atmospheric engines (based on condensation of steam to

form a vacuum beneath a piston, which was then driven by the pressure of

the atmosphere). A system of "atmospheric railways" propelled by vacuum

pistons was built in England in the mid 19th century. Serious scientific

developments of the 19th century which necessitated vacuum included

Crooke's and Faraday's gaseous discharge measurements, the first

sputtering experiments by Grove, and isolation of the rare gases by

21
Ramsey, the standards work of Miller, the discovery of the electron by

Thomson and of X-rays by ROntgen. The development of the incandescent

light by Edison provided a background for the remarkable achievements of

Langmuir in vacuum and surface science at the dawn of the 20th century.

An appendix is included which lists museums containing vacuum-related

exhibits

.

(e) "Laser Studies of Surface Chemical Reactions," R. R. Cavanagh and D. S. King, Chemistry and Physics of Solid

Surfaces V , Springer-Verlag Series in Chemical Physics 35,

141 (1984).

A review of laser studies of surface chemical dynamics with

emphasis on thermal desorption processes is presented. The correlation of

gas-phase and liquid-molecular dynamics with analogous surface processes

is demonstrated with primary emphasis on experimental techniques for

monitoring relevant quantum state populations. Recent results for the

desorption of NO from Ru(001) and NO from oxidized Ru crystals are compared in terms of rotational populations, and velocity and angular flux

distributions.

(f) "Characterization of Surfaces Using Electron and Photon

Stimulated Desorption," T. E. Madey, D. E. Ramaker, and R. Stockbauer, Ann. Rev. Phys. Chem. 35, 215 (1984).

We review various mechanisms of electron- and photonstimulated desorption of ions and neutrals from surfaces. Examples

include desorption from ionic surfaces, from covalent adsorbates on metal

surfaces, and from layers of physically adsorbed atoms. The use of the

electron stimulated desorption ion angular distribution (ESDIAD) method

for determining local structures of surface molecules is described.

(g) "Inelastic Mean Free Paths and Attenuation Lengths of

Low-Energy Electrons in Solids," C. J. Powell, Scanning

Electron Microscopy/1984, IV, 1649 (1984).

A review is given of calculations of inelastic mean free

paths and measurements of attenuation lengths of low-energy electrons in

solids. The emphasis of the review is on the systematics of the

dependence of these quantities on material and electron energy.

Calculations of inelastic mean free paths from experimental dielectric

data indicate that different dependences on electron energy occur in

different materials and that deviations from simple theoretical or empirical expressions are to be expected.

(h) "On Vibrational Lineshapes of Adsorbed Molecules", J. W.

Gadzuk and A. C. Luntz, Surf. Science 144, 429 (1984).

The possible information content in lineshapes observed in

vibrational spectroscopy of molecules adsorbed on surface is considered by

drawing analogies with similar situations in other spectroscopic areas

22
where the systematics are more completely understood. When possible,

simple physical models are introduced which illustrate the points to be

stressed. Particular emphasis is placed on the relative roles of T-|

(dissipative decay) vs. T

2

' (pure dephasing) processes in determining

linewidths, on the roles of substrate electron-hole pairs, phonons, and

photons in T

1 processes, and possible ways to establish which broadening

mechanism is operative in a given situation. A particular kind of

dephasing that is important for vibrational lineshapes in molecular

crystals, so called exchange-coupling, is suggested as playing a significant role for molecular adsorbates as well. Some recent

experimental studies are analyzed in the light of concepts introduced in

this paper.

(i) "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 of small molecules from single-crystal metal surfaces.

(j ) "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.1985), 465 (1985).

We review experimental techniques and applications of

electron stimulated desorption (ESD) and photon stimulated desorption

OPSD) 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.

(k) "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.

23
(l) "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) for 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, 1984.

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 (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 state require:

(a) a base of principles, definitions of terms, and suitable equations,

(b) reference procedures for the measurement of intensities and spectral

features, (c) procedures and data for instrument calibrations, (d)

reference data for material parameters such as elemental sensitivity

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 the 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.

(m) "Surface Harpooning", J. W. Gadzuk, Comments on Atomic an Molecular Physics, 1_6, 219 ( 1985).

The principles involved in charge transfer/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 experience harpooning

while scattering from a surface are considered.

24
(n) "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

.

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).

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

25
theoretical background is presented at a level readily accessible to the

general reader. Particular attention is paid to relative merits of the

two basically different conceptual frameworks for interpreting core-level

binding-energy shifts, the ini tial-state--f inal-state approach and the

equivalent-core-Born-Haber-cycle approach

.

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

Chemistry", T. E. Madey, C. Benndorf , N. D. Shinn, Z. Miskovic, and J. Vukanic, Proceedings of DIET-II

Symposium (Desorption Induced by Electronic Transitions),

in Springer Series in Chemical Physics.

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 O (i.e., H2 O 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

.

(e) "Excitation Mechanisms in Vibrational Spectroscopy of

Molecules on Surfaces", J. W. Gadzuk, in V ibrational

Spectroscopy of Molecules on Surfaces , J. T. Yates, Jr.,

and T. E. Madey, eds., Vol. 4 of Methods of Surface

Characterization (Plenum, NY).

An introduction to the theoretical basis of vibrational

excitation mechanisms and processes relevant to vibrational spectroscopy

of adsorbed molecules is presented.

(f) "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. M of Methods of Surface Characterization

(Plenum, NY)

.

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-fl ight 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.

26
(g) "Recent Developments in Quantitative Surface Analysis by

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

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

.

(h) "Surface Chemical Analysis - Report on the VAMAS Project,"

C. J. Powell and M. P. Seah, Surf. Interface Anal.

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

.

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

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

Spectroscopy

.

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 issues

of energy decay (T-| ) vs. pure dephasing (

T

2

’ ) overtones, and non-linear

dynamics as they apply to lineshape analysis.

27
(j) "Field Emission Microscopy - Trends and Perspectives," A.

J. Melmed, 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.

3. Books

(C. J. Powell, T. E. Madey)

While there are many books and review articles on different

aspects of surface science and its applications, there is a dearth of

information on how to make reliable surf ace-characteri zation 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 the operation of a commonly used surface-characterization equipment is described. Arrangements have been made with a commercial publisher to produce 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 at the

University of Pittsburgh) constitute an editorial board that will oversee

the production. A series of four volumes in currently planned which will

describe the principles, techniques, and methods considered important for

surface characterization. It is intended to describe how important

surface-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 pedagogical or tutorial.

Volumes 1 and 2 of the book series will describe the techniques and

methods for electron spectroscopy and ion spectroscopy, respectively,

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

concerned largely with techniques for which commercial instrumentation is

available. It is hoped that writing for both volumes will be completed

shortly

.

Volume 3 will describe techniques for specimen handling and depth

profiling. For specimen handling and treatment, this volume will provide

a compilation of methods that have proven useful. This volume will also

address 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. Preparation of this volume should

be completed in 1986.

28
Volume 4 will bring 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. The current state-of-the-art of each technique will be

described as will the relative capabilities. An important component of

the volume will be the summary of the relevant theory. This volume is

essentially complete.

D. Standards-Commi ttee Activities

Three staff members of the 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 Advanced Materials and Standards. 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.

1. ASTM Committee E-42 on Surface Analysis

(C. J. Powell, J. Fine)

The ASTM Committee E-42 on Surface Analysis, founded in 1976, now has some 120 members; in addition, a large 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.

Committee activities of the past year have included development of

the following documentary standards (which are at varying stages of

approval )

- Additional definitions of terms for AES, XPS, SIMS, and Energetic

Ion Analysis

Guide to Depth Profiling in Auger Electron Spectroscopy

- Guide for Specimen Handling in AES and XPS

- Practice for Reporting Spectra in XPS

Method for Calculating Data-Gathering Speed in XPS

Guide to Steady-State Charge-Ref erencing Techniques in XPS

- Practice for Reporting Sputter Depth Profile Data in SIMS

(secondary- ion mass spectroscopy)

Guide to Determine the Depth Resolution in SIMS

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

29
The Standard Reference Data Subcommittee is conducting a survey of

needs for reference data and of format requirements. A survey of the E-42

membership is being made to determine needs for new types of reference

materials. Finally, a report has been submitted for publication recently

of an ISS round robin involving comparisons of peak-position and

peak-width measurements on a Cu-Ag-Au ternary alloy using seven

cyl indri cal-mirror analyzers from the same manufacturer. This round robin

showed that much of the spread in reported peak positions was associated with incorrect positioning of the specimen with respect to the

analyzer

.

The Committee has sponsored two symposia each year, one at the annual

Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy in

the spring and the other at the National Symposium of the American Vacuum

Society (AVS) in the fall. Papers presented at these symposia are published. After 1985, arrangements for the AVS Symposium will be made by

the recently formed AVS Applied Surface Science Division. A workshop is

held at each meeting to discuss particular measurement problems. At the

1984 AVS Symposium the topic was "Data Reduction for Quantification in

Surface Analysis", and the topic at the 1985 Pittsburgh Conference was "Solving Industrial Problems with Surface Analysis".

The Committee is planning to prepare a booklet of E-42 surface

analysis standards which will 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.

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

2. Surface Chemical Analysis Working 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, Federal Republic

of Germany, France, Italy, Japan, United Kingdom, 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 has established

Working Groups in areas such as photovoltaic solar energy, food

technology, advanced robotics, biotechnology, high speed trains, remote

sensing from space, and advanced materials and standards. A summary of

developments resulting from the Versailles Agreement was published as a News and Comment article recently in Science 228 , 827 (1985).

The Versailles Project on Advanced Materials and Standards (VAMAS)

consists of a Steering Committee with respresentati ves from the seven

nations above and the CEC. The overall aim of the project is to encourage

international trade. This objective will result from international

30
agreement on codes of practice and performance standards and from

multilateral research aimed at providing the scientific and technological

base necessary to achieve agreement on standards. The project is

essentially a scheme for stimulating the introduction of advanced

materials into high technology products and engineering structures. The

ubiquity of surface analysis through all sectors of high-technology

industry has been demonstrated in recent surveys, and a proposal to

establish a Surface Chemical Analysis (SCA) Working Party won early

approval from the VAMAS Steering Committee. This SCA Working Party is now one of nine such groups that have been approved.

The main objective of the SCA working party is to produce, by

coordinated effort, the reference procedures, data, and materials necessary

to establish 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.

National representatives to the SCA Working Party have been appointed

with C. J. Powell as Chairman for a three-year period. The 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 established and as other techniques come into greater

use, it is expected that the project will broaden.

Qualitative and quantitative surface analyses require consideration

of the following three items:

(i) the physical principles of the measurement method;

(ii) the behavior of the measuring instrument; and

(iii) the interpretation and expression of the final result.

The basic principles of the physics of the various techniques and the

selected analytical methods are vital since they lead to the working

formulae which are used for quantitative analysis. Agreement must be

obtained on these formulae and their regimes of applicability when working

to certain accuracies for particular types of specimens and for particular

techniques and methods. These formulae involve the measurement of

intensities by the instrument which are then related to the composition at

the surface by functions of the specimen material and the particular

measurement process and by functions of the measuring instrument.

Tabulations are needed of particular materials properties relevant to the

various techniques and information is needed on instrument properties.

Additionally, surface analyses can give chemical-state information, the

interpretation of which requires a similar hierarchy of understanding,

data, and reference procedures. The analyst therefore requires:

(1) an agreed base of principles, definitions of terms, and equations

to relate the techniques and procedures to the measurement;

31
(2) reference procedures specifying how to measure intensities and

spectral features;

(3) reference procedures, reference data, and reference materials for

calibrating instruments, determining instrument functions, and

inter-relating instruments of different designs;

(4) reference data of elemental sensitivity factors, matrix terms,

information depths, libraries of chemical-state spectra,

information on ion-sputtering rates, radation damage, etc.; and

(5) standard methods of specifying an analysis.

Details of specific needs for AES, XPS, SIMS, and SDP have been

identified

.

Suitable infrastructures 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 and cooperate in VAMAS SCA projects. Standards

already developed by the E-42 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 NBS

and other U.S. laboratories also contribute to the VAMAS SCA activity.

Since January, 1985, a large number of technical projects have been

started in the VAMAS states, many largely as a result of the VAMAS

initiative. These projects are largely national activities, as is to be

expected since it is necessary that national needs, opportunities, and

priorities be established prior to the development of more extensive

bi-national or multi-national projects. The first meeting of the national

representatives to the VAMAS SCA Working Party took place in October, 1985

during a conference in The Netherlands. A number of cooperative projects

were discussed and it was agreed that the following should be implemented.

(a) Development of thin oxide films as reference materials. It

is planned to produce thin films of transition-metal oxides

(Fe^^, NiO, and C^O^) with thicknesses of about 25 nm on metal substrates in Canada. Films of similar thickness of

Si02 on silicon will be produced in Italy. These films

will be characterized by sputter-depth profiling at a number of laboratories in Canada and Italy. The ion

sputtering yields of these oxide films under common conditions of sputter-depth profiling will be compared with

similar measurements on existing Ta2 0^ and Ni/Cr reference

materials at NPL and NBS.

(b) Development of calibration data for the energy scales of

Auger-electron spectrometers. Current projects exist at

both NBS and NPL for the independent measurement of the

kinetic energies of the principal Auger-electron

transitions of copper, silver, and gold to be used as

32
calibration data in the energy range 50-2000 eV. After

intercomparison, the calibration data will be utilized in

an interlaboratory comparison of Auger-electron

measurements to be organized by NPL.

(c) Procedures for quantitative x-ray photoelectron

spectroscopy (XPS). It is planned to investigate at NBS

the suitability of recently fabricated Ta2 05 films on silicon and, if necessary, the oxide films prepared in

project (a) as test materials for an interlaboratory

comparison of angle-dependent XPS measurements. If these

films can be cleaned adequately with minimal ion

sputtering, NBS will organize the comparison of XPS

measurements to give information on film thickness and film

stoichiometry

.

Two additional cooperative projects were discussed and it is likely

that these will be initiated following the preparation of more definite

plans. The first such project is the development of alumina reference

materials with known concentrations of oxygen vacancies. These materials

will be used as reference materials for problems in materials science such

as wetting, adhesion, and electrical breakdown as well as for

determining conditions for radiation damage. The second project is the

development of reference procedures for high-resolution scanning

Auger-electron microscopy so that the effects of topography, specimen

crystallinity, and angle of emission can be minimized.

Plans are being developed for two workshops on surface chemical

analysis for which VAMAS will be a co-sponsor. The first workshop is

planned for October 2U, 1986 at NBS and will precede the Tenth

International Vacuum Congress and Sixth International Conference on Solid

Surfaces to be held in Baltimore, October 27—3 1 $ 1986. The second

workshop is planned for November 17, 1986 at NPL and will precede the

fourth Conference on Quantitative Surface Analysis at NPL on November

18-20, 1986. These workshops will publicize VAMAS activities, disseminate

results of recent work on quantitative surface analysis, and promote the

development of new cooperative VAMAS projects. Specific attention will be

given at both workshops to needs for reference data, needs for reference

materials, methods of instrument calibration, and analytical methodology.

The VAMAS Surface Chemical Analysis 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

33
of documentary standards for instrument operation and calibration; and

(4) the development of recommended procedures for data acquisition, data

reduction, and expression of final results.

3. ASTM Committee D-32 on Catalysts

(R. A. Haines and R. D. Kelley)

The activities of the ASTM Committee D-32 on Catalysts are concerned with the physical and chemical properties of commercial

catalysts and with developing suitable procedures for catalytic activity

measurements. The membership of the Committee numbers approximately 130.

Semi-annual meetings are attended by between 60-90 percent of the

membership which includes a significant international component. In the

past year, the expansion of Committee activities has continued. These

activities involve four sub-committees: Physical/Chemical Properties - 6

task groups; Physical/Mechanical Properties - 6 task groups; Chemical

Analysis - 2 task groups; Catalytic Properties - 5 task groups. In

general, this expansion 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, and of multi-element chemical analysis by atomic absorption.

The Subcommittee on Chemical Analysis is chaired by R. D. Kelley.

This Sub-Committee is involved in finishing the test method

for analysis of platinum in fresh reforming catalysts. A "final" round

robin is presently under way. The effort to analyze palladium in

catalysts has progressed to the round robin stage. Standardization of

x-ray fluorescence analytical procedures and of procedures for the

chemical analysis of spent catalysts are being discussed. In the basemetals task group, the primary emphasis is on the development of a satisfactory test method for determining several base metals by optical

atomic spectroscopy.

The NBS Office of Standard Reference Materials (OSRM) will soon distribute special reference materials for catalysts. As a member of

D-32, Dr. Ruth Haines, Deputy Director of the Center for Chemical Physics,

is preparing the documentation required for NBS acceptance of materials

used by D -32 in various round robin tests. Five years ago the Committee

recognized the need to preserve the catalysts, catalyst carriers and feed

stock used in their round robins. D -32 sought a private sector

distributor but none was found. The OSRM can distribute the materials at

cost but NBS will not certify them. Initially, samples will be available

for physical properties such as surface area and particle size

distribution; mechanical properties such as crush strength; chemical

analysis of supported metals; and reactivity via gas oil conversion

microactivity tests. A series of zeolites will also be available for

which diffraction intensity, unit cell dimensions and zeolite areas have

been determined. All the materials should be available within the next

six months. We can then judge the desirability of producing more

standards based on the extent to which these samples are requested.

34
3. SURFACE MEASUREMENTS PROGRAM

C. Benndorf, D. R. Burgess, Jr., R. R. Cavanagh, A. Flodstrom,

J. W. Gadzuk, S. M. Girvin, T. J. Jach, R. D. Kelley, R. L. Kurtz,

T. E. Madey, D. E. Ramaker, N. D. Shinn, R. Stockbauer, P. D. Szuromi

,

T J. Udovic, M. J. Wax

The Division undertakes a number of projects directed to the improved

physical and chemical characterization of surfaces and surface processes.

These projects meet Division objectives through the development of new

measurement techniques, improvement of existing techniques, development of

theories of the measurement process, applications to important scientific

and national problems, development of measurement procedures, tests of the

measurement system, development of new concepts, and provision of needed

data.

A. Reaction Kinetics at High Pressures over Single Crystal Catalysts

(P. D. Szuromi, M. J. Wax, T. J. Udovic, R. D. Kelley, T. E. Madey)

The overall objective of this research is 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. The work is supported, in

part, by the Division of Basic Energy Science 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 S and the promoter effect of Pt thin films on the W substrates.

1. Ethane Hydrogenolysi s Catalyzed by W(100)

Although W is not ordinarily considered a good catalyst, we have

found that the W(100) surface is very effective in catalyzing ethane

hydrogenolysis (p - 100 Torr, 550 < T < 620 K) . A carbidic overlayer

forms rapidly in the early stages of reaction; this surface carbide is the

"true" catalyst for the hydrogenolysis which proceeds with an activation energy of 27 kcal/mole. This is different from the activation

energy for catalytic methanation over W(100), 14 kcal/mole, suggesting

that methanation and hydrogenation do not share a rate-limiting step.

2. Thin Pt Films as Model Alkane Hydrogenolysis Catalysts

Vapor deposition of Pt onto a W(100) substrate in ultrahigh

vacuum has been used to prepare model supported Pt catalysts which are free of extraneous promoters and poisons. Various Pt loadings (from

fractional monolayer to multilayer) have been achieved reproducibly

.

35
Although pure Pt is less active than W for ethane hydrogenolysi s , the

fractional monolayer Pt films catalyze hydrogenolysis at a rate

significantly greater than the ini tially-clean W(100) surface.

3. Effect of S on Catalytic Methanation

The effect of adsorbed sulfur on the rate of catalytic

methanation over a W ( 1 10) crystal has been studied as a function of sulfur

coverage and crystal temperature. As in the case of the initially clean,

non-sulfur-covered surface, carbidic carbon is formed during the course of

the reaction. In Figure 3, the relative rate of reaction as a function of

1.0

0.8

<D

<TJ 0

c

0 0.6

•*— o

(0a) C

C

|

0.4

TOa> cc 0.2

0.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Sulfur Coverage

Fig. 3 . Relative Reaction Rate for Catalytic Methanation over W ( 1 10) as a function of sulfur coverage (in fractions of a monolayer).

Similar data for a Ni(100) are shown for comparison.

i

<\

IV

IX

I 1

o

A

\

o

x

750 K

700 K

600 K

Reaction Temperatures

P u = 100 Torr

CO

1 Torr

Inhibition of Methanation

over W (110) by Adsorbed

Sulfur

x Similar Data for Ni (100)

600 K = 96 Torr

P C0 = 24 Torr

S

- X- Xsulfur coverage (as determined by Auger-electron spectroscopy) is plotted

for several reaction temperatures (together with similar data for Ni(100).

The Arrhenius energy of reaction, 56 kcal/mole, does not change

substantially with sulfur coverage, as can be inferred from the similar

inhibition of the rate of reaction for each temperature at a given

coverage. Although the inhibition at low sulfur coverages is not as

36
dramatic as that seen previously for this reaction over nickel surfaces,

the overall rate of reaction does drop about an order of magnitude at high

coverages of sulfur.

We plan next year to complete both the methanation studies of W ( 1 10)

and the effect of Pt films on hydrogenolysis. The role of Pt films in the

thickness range 1-2 monolayers on W(100) will be characterized for the

hydrogenolysis reaction.

We plan also to initiate a new project to study partial oxidation

catalysts. This important class of reactions has received little

attention from surface scientists, and we propose to probe the mechanism

of the catalytic oxidation of propylene to acrolein over Cu2

0:

h

2 c = ch-ch 3

+ o2

Cu

|° h2 c = ch-c^;°

Initially, the dehydrogenation of alcohols will be examined on a pure

copper crystal. These reactions will be examined using apparatus which

combines both a high-pressure reactor (2 atmospheres) with an ultrahigh

vacuum surface analysis chamber; the surface over which the catalytic

reactions occur will be probed both before and after reaction. Several

aspects of the oxidation reaction are not well understood: the effect of

the surface geometry of the oxide; the electronic state of the catalyst,

both the oxidation state of copper and the surface valence band structure;

the influence of electronegative species (S, Se , halogens) as promoters;

and the Arrhenius parameters for the overall rate of reaction. These

questions can be addressed by employing: single-crystal oxide surfaces to

control geometric effects; post-reaction analysis by electron

spectroscopies (AES, XPS and UPS); preparation of clean surfaces in

ultrahigh vacuum and of promoted samples of known surface concentration;

and measurement of rate data over a wide range of temperatures, pressures

and reactant ratios.

B. Molecular Structure and Reactivity on Surfaces as Studied Using

ESDIAD and HREELS

(T. E. Madey, N. D. Shinn, and C. Benndorf)

A major challenge in surface science continues to be the

determination of the structures of molecules on surfaces, particularly in

the absence of long-range 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

high resolution electron energy loss spectroscopy (HREELS). These

techniques, both singly and in combination, are powerful tools for surface

structural characterization.

The present thrusts of this project are (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^ , H2 0) on

37
surfaces, and (b) to determine the structures of those molecules on initially-clean surfaces, particularly in controversial cases. The work

has been supported in part by the Division of Basic Energy Sciences of the

Department of Energy.

During the last year, progress has been made in the following areas.

1. Evidence for Reorientation of CO when co-adsorbed with K on

Ru(001

)

We have used ESDIAD to address a current controversy concerning

the influence of K on the structure of adsorbed CO: does CO "stand up" or "lie down" adjacent to K on Ru(001)? In the absence of K, CO is bonded

with its molecular axis perpendicular to Ru(001) at all coverages. Upon

coadsorption with low coverages of K, ESDIAD measurements provide evidence

for a strong local interaction between CO and K, which appears to result

in a reorientation of the CO to an "inclined" or lying-down bonding

configuration. Moreover, complementary thermal desorption and low-energy

electron diffraction measurements suggest the formation of ordered surface

species having K

x (C0)2X stoichiometry. The question of CO bonding

geometry is a major area of current interest in the surface science

community, and the present measurements and models provide new insights

into the CO + K surface chemistry.

2. Structure and Reactivity of NH^ on Clean and Modified Fe(100)

Iron is an excellent catalyst in NH^ synthesis, and adsorbed K

is known to "promote" the reaction by increasing the rate. In an attempt

to understand at the molecular level how K influences the bonding geometry

of NH^ to Fe, we used ESDIAD to examine the structure and reactivity of NH^

on clean Fe(100), and on K-dosed Fe(100). On clean Fe(100), adsorption of

NH^ occurs at step sites up to 0(NH^) - 0.02. For higher coverages, up to

saturation of the first layer (9(NHn) - 0.3^) , ESDIAD is dominated by a "halo" H

+ pattern indicating that NH^ is bonded via the N atom and the H

atoms (with no azimuthal ordering) are pointed away from the surface. The

ESDIAD data correlate well with thermal desorption data, where different

binding states due to fractional monolayer, second layer, and multilayer

adsorption are observed. Only a small fraction (0 < 0.02) of NHo

dissociates upon heating. When NH^ is coadsorbed with K, the ESDIAD and

thermal desorption data indicate an interaction in which the NH^ molecular

axis is tilted and the binding energy to the substrate is decreased. In

contrast, the interaction between NH^ and 0 does not lead to structural

changes or azimuthal ordering of NH^ as reported previously on Ru(0001)

and N i ( 1 1 1 ) surfaces. This indicates that the NH^ - 0 distance is not

optimal for attractive hydrogen bonding.

3- Structure of the Surface Hydration Shell of Bromide on Ag(110)

Surface science has been a valuable source of inspiration to

electrochemists in recent years, particularly in studies of the

interaction of water and other electrolytes with clean, well-characterized

38
electrode surfaces. In one such study, we have attempted to synthesize an electrochemical double layer in vacuum by examining the interaction of H

2 o and bromine on an Ag (110) surface using ESDIAD , LEED (low-energy electron

diffraction) and TDS (thermal desorption spectroscopy). Water adsorbed on

clean Ag ( 1 1 0 ) formed a disordered, hydrogen-bonded overlayer. In the

presence of adsorbed bromine, the adsorbed water was characterized by a higher binding energy and pronounced orientational order. The mixed

adlayers resulting from this surface hydration of bromide also exhibited

long range order. The surface hydration number (nH20 / Br ) was two for 0Br < 0.25, and decreased to a few tenths at the Br saturation coverage, 0g r

= 0.75. The present results have important implications for experiments

in which investigators attempt to transfer electrodes from solution to a vacuum environment: neither water on the clean surface nor the hydration

water remain adsorbed in vacuum at room temperature, and would be lost in

a transfer experiment.

4. CO Chemisorption on Cr(110): Evidence f or a Precursor to

Dissociation

HREELS and ESDIAD studies of the chemisorption of CO on Cr(110)

have provided fascinating insights into the structure and kinetics of

molecular dissociation on a metal surface. At 120 K, two molecular

binding modes of CO are sequentially populated. The first, a-iCO, is a novel binding mode for a clean metal surface in which the molecules are bound with the C-0 axis nearly parallel to the Cr(110) surface. Annealing

experiments demonstrate that the binding mode is the precursor to

dissociation on Cr(110) . At higher CO coverages, 0 . 25<©Cq<0 . 35, the a-jCO

overlayer is disordered by the addition of the second binding mode, a

2 C0.

The a

2 C0 species are terminally bound molecules adsorbed at a- top and

bridge sites and aligned approximately perpendicular to the surface.

Annealing studies of CO or 0/C0 adlayers provide evidence for a surface

reaction in addition to direct dissociation at about 170 K. In contrast,

adsorption at 300 K leads to direct dissociative chemisorption with no detectable intermediate molecular adsorbate. The implications of these

results to catalytic reactions of CO have been considered and comparisons

to CO adsorption on clean and "promoted" transition metal been made.

We plan next year to extend the ESDIAD method to the detection of

negative ions; all ESDIAD measurements to date have involved positive

ions. We believe that these challenging measurements will provide new insights into the structure and surface chemistry of a class of molecules

(particularly those containing halogens and other electronegative

groups) for which studies have not been possible previously. A new digital

video system will be constructed for these measurements. This system will

be used to acquire and process data for ion current versus emission angle.

We expect that the digital system will be more sensitive and give more accurate information than the currently used analog system. A later phase

of this work will involve characterization of similar molecules using

39
HREELS and synchrotron methods. The new measurements will be an exciting

complement to our present studies of the influence of surface additives on

the structure and chemistry of adsorbed species.

We will use ESDIAD and HREELS to address a fundamental question in

hyrocarbon surface chemistry, namely, the structure of C

2 H2 on a Cu(110)

surface. Different models have been proposed involving rehybridized

carbon species with the C-C bond vector either parallel or perpendicular

to the Cu atom rows. ESDIAD may be able to provide a unique insight into

the local bonding geometry of this site.

Despite the extensive interest in the chemistry of H

2 0 on transition

metal surfaces, there are no definitive spectroscopic studies of the

adsorption and decomposition of H

2 0 in the temperature range 77-300K on

any metal having a high heat of M-0 bond formation where dissociation is

likely to occur. We propose to study in detail the structure and kinetics

of H

2 o adsorption and decomposition on C r ( 1 10) using ESDIAD and HREELS;

the goal will be to identify the fundamental steps in this important

surface reaction.

We will continue to probe the role of both electropositive and

electronegative additives on the structure and chemistry of small adsorbed

molecules. Of particular interest are the major differences in the

"activity" of oxygen in promoting hydrogen abstraction on different

surfaces

.

C. Inelastic Neutron Scattering Studies of Adsorption and Reaction

on Catalysts

(R. D. Kelley, R. R. Cavanagh, M. J. Wax, T. J. Udovic)

Inelastic incoherent neutron scattering (IINS) studies of

adsorbates on catalyst surfaces are providing new insights into the

vibrational spectroscopy of hydrogen and hydrogen-containing species

adsorbed at the surfaces of high-area catalysts. NBS is ideally suited

for these studies, having a unique combination of neutron physicists and

surface chemists with an interest in catalysis. During the last year,

advances have been made in characterization of both metal and zeolite

catalysts using IINS at the NBS Reactor in collaboration with Dr. J. J. Rush of the Reactor Radiation Division. The work has been supported in

part by the Division of Basic Energy Sciences of the Department of Energy.

1. Interaction of Vibrating H atoms on Pt particles

The dynamical interactions between vibrating hydrogen atoms on the surface of small Pt particles (Pt black) have been studied using IINS

together with isotopic dilution (comparing pure H

acl3 with H a(j S

+ Dads ).

The data revealed direct information on the bonding state and dynamical

non-bonded (as opposed to chemical) interactions of these species. Shifts

and broadening of hydrogen vibrational features were accounted for in terms

of mode dispersion due to strong H-H coupling.

40
2. Hydrogen Adsorption and Interaction with Oxygen on Pt

IINS was utilized to probe the nature of adsorbed hydrogen and

its interaction with oxygen on platinum black. The vibrational spectra of

adsorbed hydrogen at 80 K were found to be in agreement with the results of

other reported IINS studies. The interaction of oxygen with adsorbed

hydrogen provided vibrational spectra corroborating the existence of at

least two distinct hydrogen-adsorption sites. In addition, hydrogen and

oxygen adsorption on the platinum black blank both yielded spectral

information concerning the chemical state of the platinum surface.

Comparison of the present IINS data to published electron energy-loss

spectroscopy results suggests that oxygen reacted with hydrogen over platinum black to product adsorbed hydroxyl (OH) species.

3. Neutron Scattering Study of Zeolite Rho

Incoherent inelastic neutron scattering has been used to examine

the bonding of framework hydrogen to the faujasite zeolite rho in

collaboration with Drs. G. D. Stucky, L. Abrams, and D. R. Corbin of

Dupont. Vibrational spectra obtained from 1 60 to 1 600 cm

-1

are consistent

with the existence of planar, symmetric A10(H)Si units in the acid form of

rho at room temperature. As the zeolite undergoes a slight change in

structure on heating, an accompanying transfer of hydrogen atoms occurs to some new bonding site of unknown nature which is characterized by an unusually large- amplitude , low-energy vibration. Quasielastic neutron

scattering data have allowed an upper limit (4x10“° cm2 s

-

”

1 at 673 K) to

be set for the rate of diffusion of hydrogen on the framework of partially

dehydroxylated rho, a result consistent with diffusion measurements by

macroscopic methods.

We plan next year to extend the applications of IINS to the

characterization of adsorbates on the internal and external surfaces of

zeolite catalysts. The new measurements will build upon our recent

studies of the bonding and of diffusion rates of framework hydrogen of

zeolite rho, and will include both adsorbate structures and diffusive

motion of adsorbates in various zeolites. One example will be the

dynamics of NH? interactions in zeolite rho. Quasielastic neutron

scattering will complement the IINS measurements, and will be used to

derive the rates and nature of diffusional motion.

We will use IINS to probe the interactions of hydrogen on and in Pd

black. The main effort will be devoted to cleaning and characteri zing the

sample before hydrogen adsorption, followed by a study of both surface and

bulk hydrogen in Pd. This effort is expected to answer long-standing

questions regarding the communication between surface and bulk species.

There have been few studies of adsorption and reactions on supported

catalysts using IINS. Our studies to date have involved the adsorption of

H

2 and small hydrocarbons on unsupported metals (Ni,Pt). We plan to extend

these studies to supported metal catalysts for which there is a vast

literature concerning preparation, cleaning, adsorption and reaction. In

41
collaboration with workers experienced in noble-metal catalyst

preparation, we will choose, prepare and initiate neutron-scattering

studies on prototype catalysts.

D. Surface Characterization Using Synchrotron Radiation

(R. Stockbauer, R. L. Kurtz, N. D. Shinn, D. E. Ramaker

,

A. Flodstrom, and 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 from 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

.

Accomplishments during the past year were in six areas:

(1) electronic structure of molecules adsorbed on surfaces; (2) electronstimulated desorption (ESD) and PSD of oxide surfaces; (3) instrumentation

of a new beamline at the NBS synchrotron radiation facility SURF-II;

(4) construction of a new display analyzer; (5) progress at the Brookhaven

National Synchrotron Light Source (NSLS); and (6) theory of stimulated

desorption.

1. Electronic Structure of Molecules Adsorbed on Surfaces:

Relation to Geometric Structure

Synchrotron photoemission studies of the bonding of CO to the

Cr(110) surface at low temperatures have identified differences in the

electronic structure of the molecularly adsorbed CO that are correlated to

the molecular binding configuration. At low coverages (0 < 0.25), only

the o^CO binding state is populated; in this binding state the molecules

are "lying down" on the metal surface. Ultraviolet photoemission measurements reveal a unique Cr:C0 4 a bonding interaction; this result is

evidence for Or: CO bonding substantially different from the conventional

Blyholder model of synergistic CO 5a-* metal charge donation and metal •* CO

In backdonation. In contrast, the terminally-bonded a2 C0 binding mode, seen at high surface coverage (0 > 0.25), is well described by this

conventional model.

Figure 4 illustrates typical UPS data obtained at 40 eV photon energy

in an experimental configuration which is most sensitive to photoelectron

detection along the [110] surface normal direction. A spectrum for the

clean C r ( 1 10) surface, Figure 4(a), can be compared to those with only CO

adsorbed, Figure 4(b), and with both a-, CO and a2 C0 adsorbed at high

coverage, Figure 4(c). The spectral differences associated with the two

42
Cr( 1 10)/CO UPS data

ELECTRON BINDING ENERGY (eV)

Fig. 4. Ultraviolet photoemission spectroscopy (UPS) data for CO on a Cr(110) surface; evidence for two different bonding configurations

are presented. Curve (a) is the clean surface spectrum and curve

(b) corresponds to the a-j state of CO (the "lying-down" mode).

Curve (c) is the spectrum which includes the a^ state of CO (the

"standing-up" mode)

.

binding modes are unmistakable; a weak a-| CO 4 0 peak at 11.6 eV binding

energy is seen in Figure 4(b) whereas an intense o^CO 4a peak at 10.8 eV is

observed in Figure 4(c). Both the binding energy and intensity differences

are strong evidence for the radically different CO binding geometries and

resulting bonding variations.

Angular and photon-energy dependent data provide additional support

for the CO-binding mode models developed from our previous HREELS/ESDIAD

studies (Section 3*B.4). Further studies probing the dissociation of

adsorbed CO and C0:02 interactions on C r ( 1 10) have been performed. As

first seen in the earlier vibrational studies, adsorbate interactions

between co-adsorbed CO and oxygen result in the reorientation of the

lying-down carbon monoxide to a terminally- bonded configuration; this

mode conversion is manifested in the UPS data by the expected changes in

the CO 4a region of the spectra.
Preliminary data have been obtained for molecular nitrogen, an isoelectronic non-polar analog to CO, adsorbed on the Cr(110) surface.

These results will be combined with subsequent vibrational data to

determine whether a molecular "lying down" N

2 (ads) species, analogous to

a-] CO, is present.

2. Electron and Photon-Stimulated Desorption of Ions from Oxide

Surfaces

As part of our continuing effort to understand the mechanisms

involved in stimulated desorption of ions from surfaces, we have made

measurements on single- crystal oxides that have forced a re-evaluation of

currently accepted theories. Much of the previous work in stimulated

desorption involves correlation of photon energies for producing

desorption with photon spectroscopic data for atomic excitations. Such

work originally gave rise to fundamentally new ideas about the types of

atomic transitions that could produce desorbing ions. These mechanisms,

however, are incomplete in several aspects and in particular they neglect

the influence of local bonding geometries and surface structure. The

experimental program presently underway is aimed at studying the influence

of surface structure and is giving rise to a broader understanding of the

mechanisms underlying the desorption process.

The surfaces studied to date include the (001) and (110) surfaces of

Ti02

. This material is particularly important since it is the model

system for the Knotek-Feibelman (KF) mechanism of desorption. This model

describes the inter-atomic Auger process that can occur in a maximal-valent material such as Ti02 when a core hole is produced in the

cation by electron or photon impact. This hole is unstable and can decay

by an inter-atomic Auger process involving charge transfer from the 0

2-

ligands. This results in a positively charged 0-ligand which then desorbs

due to the strongly repulsive Madelung potential. This model predicts

that excitation of the Ti 3p level should produce desorption. It also

predicts that any population of Ti 3d-electron states (i.e. no longer a maximal-valent surface) should strongly reduce the probability of the

inter-atomic decay, favoring an intra-atomic decay. This would result in

a much reduced ion yield.

Figure 5(b) shows the oxygen ion yield versus incident photon energy

from a 700°C annealed Ti02 (001) surface; this is a maximal- valent surface.

At the excitation energy of the Ti 3p level, 38 eV, there is an onset in

the ion yield. It peaks at 47 eV and decays rapidly, following the decay

of the excitation probability of the Ti 3p level. In Figure 5(a), we show

the 0 eV constant-final-state spectrum, essentially the photoabsorption

spectrum of this surface. By comparison of this and other

electron-excitation spectra with the ion emission spectra, we hope to

unravel the specifics of the electronic excitations that product

desorption. Thus, in agreement with the predictions of the KF mechanism,

we observe desorption due to the excitation of the Ti 3p level. This

agreement ends, however, when we compare the magnitudes of these yield

curves for the different surfaces studied.
Desorption from Ti0 2 (001)

Fig. 5. Photon-stimulated desorption (PSD) of oxygen ions from an anneale

TiC>2 (001) surface showing the role of core-hole excitations, (a)

0 eV constant-final-state intensity (proportional to

photoabsorption cross section) versus photon energy, (b) ion

yield versus photon energy.

The unexpected behavior that we have observed occurs when surface

species are intentionally made non-maximal-valent (Ti 3d-electron states

now populated) by the introduction of defects (by 500 eV Ar

+ -ion

bombardment); the magnitude of the ion yield does not always decrease as the KF mechanism would predict. It has been observed that the ion yield

can even increase with such treatment, the opposite of the behavior that

would be predicted by the KF mechanism. The source of this conflict can

be resolved, however, when one considers the influence of surface

structure and the local site geometries on the process.

It is known that surface geometric structure is drastically modified

by A r -ion bombardment; however, the details of the atomic r earrangements

that the bombardment produces are not known. In order to compare the ion

emission from surfaces with different geometries, we have resorted to

45
studying two different surfaces of Ti02 , namely the (001) and the (110).

The (001) surface is known to facet on annealing to (011) planes while the

(110) surface is flat. The electron stimulated desorption ion angular

distributions (ESDIAD) that we observe from the (001) surface are consistent with such a faceting; we observe emission from the faces and

the edges of facets. The ESDIAD patterns from the (110) surface, on the

other hand, give only a normal emission spot. Comparison of the

magnitudes of the ion yields from these surfaces, however, indicates that

increased ligand coordination of the Ti cations (such as is expected to be

the case for a flat surface) produces decreased probability of ion

desorption. The origin of this decreased probability could be an enhanced

reneutralization probability or a decrease in the probability of initial

excitation. There is also the possibility that surface dynamics may

strongly influence the ion escape by lattice polarization and recapture.

Our interest in the relative influences of these additional processes in

desorption is to understand not only the initial excitation but also the

decay of this excitation and the subsequent surface dynamics that lead to

ion and neutral desorption.

In order to better understand the structure of complicated surfaces

such as those of Ti02 , a graphics package has been written in FORTRAN that

allows the display of ball-model crystal surfaces. This routine allows

one to define a basis for a lattice, create a bulk crystal of specified

size, and cut planes through this crystal to expose arbitrary surfaces.

These surfaces can be rotated to be viewed from any perspective and

surface vacancies can be introduced interactively. One such crystal ball

model is shown in Figure 6 where the facet believed to be formed on

Ti02 (001) after annealing to 700°C is shown. This modeling of surface

structures will be associated with planned molecular dynamics calculations

to be done in conjunction with our experimental efforts; we hope to better

understand the variety of processes that influence desorption. Such

calculations could allow us to predict site-specific desorption

probabilities and to model desorption trajectories (perhaps even predict

ESDIAD patterns). It is expected that such a feedback between calculation

and experiment will also result in a better understanding of the structure

of both perfect and defective surfaces.

During the next year, we plan to continue to study the mechanisms of

ion desorption from solid oxide surfaces with both experimental studies

and model calculations. Oxides have been shown to be unique systems that

allow investigation of the relation between desorption mechanisms and the

electronic and geometric structure. We will investigate further

desorption from various surfaces of Ti02

. The recent studies of

desorption from the (001) and the (110) surfaces of Ti02 have promoted

interest in the comparative study of T i02 (011) and Ti 2 0^ (1012). Their

similar surface geometric structures should permit isolation of the

influence of their different electronic structures on the core-hole decay

processes that lead to desorption. In addition, we intend to investigate

the influence of the local-site environment in ion desorption from other

surface such as Mg0(100) and faceted MgO.

46
Fig. 6. Computer-generated model of faceted Ti02 (001) surface.

We plan to make a molecular-dynamics calculation of the lattice

response to a desorption process. An investigation will first be made of

the often complicated geometric structure of oxide surfaces using software

that can produce ball-model drawings of idealized surfaces. This software

will be combined with the molecular-dynamics calculation in which the

initial excitation and decay are assumed to occur rapidly; the subsequent

charge reversal of a ligand then results in the motion of both the ligand

and the rest of the lattice. The calculation should reveal information

about the specifics of the sites that result in desorption and their

angular distributions.

3. New Beam Line at SURF-II

The Surface Science Division has established a new beam line at

the NBS synchrotron light source SURF-II. This will replace the existing

beam line which we have used for the past 5 years. The heart of the new

beam line is a toroidal grating monochromator designed by us to deliver

high photon flux to investigate ion emission from surfaces with low ion

yield. The monochromator has been calibrated and characterized and

delivers IxlO 10 photons per second per milliamp of ring current at a wavelength resolution of 4 A. With SURF-II routinely operating in the

47
100 mA range, we will have -1

0

1 ^ photons per second on the sample at the same resolution. The useful energy range is from 1 7 to 90 eV. A new

laminar grating is being manufactured which will decrease the amount of

second order light being transmitted, and a second new grating will extend

the range of the monochromator to 180 eV.

4. Construction of Angle-Resolving Display Analyzer

A new ell ipsoi dal-mirror angle-resolving electron- and

ion-energy analyzer is nearing completion. This outstanding instrument

was designed at NBS (based on an instrument constructed at IBM by D. Eastman) and is being constructed here. It is ideally suited for

angle- resolved PSD, and will be the only such analyzer in North America

used for the measurements. Details and scientific plans are given in

Section 4.B.3.

5. Experiments at the Brookhaven National Synchrotron Light Source

A major effort during the last several years has been the

initiation of an NBS-Naval Research Laboratory collaboration to establish

four beamlines at the Brookhaven National Synchrotron Light Source (NSLS).

We are providing surface science instrumentation to be used on one of the

beamlines at the x-ray ring. The planned experiments have been delayed

due to machine problems but these now appear to be largely overcome.

Our planned research will be an extension of the experiments

performed at the NBS SURF-II facility (see above) to the higher-photon

energies and more intense light available at the NSLS. Light from a unique, extended- range monochromator (5-5000 eV) will be used to study

surface electronic structure and surface bonding of molecules.

Experimental probes will include photoemission spectroscopy, surface

extended x-ray absorption fine structure, and photon-stimulated

desorption.

The main experimental chamber has been installed at NSLS and a sample

preparation chamber has been acquired. The first experiments using the

limited range of the monochromator presently available (20-200 eV) will

involve measurements of electron attenuation lengths as a function of

electron kinetic energy for condensed thin films of molecular solids. The

synchrotron- based method for these measurements was developed and tested

at SURF-II. These measurements will provide benchmark data for electron

transport through organic materials in an energy range near the minimum

value of the attenuation length. When the monochromator energy range is

extended to -1000 eV, we will undertake detailed studies of the roles of

both core-level and valence excitation in the photon-stimulated desorption

of ions from covalently bonded molecules on surface.

48
6. Theory of Stimulated Desorption

Work continued on the elucidation of the mechanisms that can

give rise to electron- and photon-stimulated desorption of ions from

adsorbates on surfaces as well as from single crystals. During this year,

attention was given to the role of secondary electrons in photonstimulated desorption and the extent to which these effects distort the

ion yield spectra. Our studies suggest that these effects are not as dramatic as indicated in the literature. Work was also begun on understanding the mechanisms for negative-ion desorption from surfaces under

electron bombardment and the role these mechanisms may play in negativeion ESDIAD. Our understanding of the role of secondary electrons and the

mechanisms for negative-ion desorption are important for planned future

experiments (Section 3«B).

E. Dynamical Effects Associated with Core-Level Ionization

(T. J. Jach)

The NBS Quantum Metrology Group under the direction of Dr. R. D. Deslattes is developing an experiment to study electronic effects

associated with core-level ionization in atoms, molecules, and at

surfaces. Specific effects to be 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

assigned to work half-time on this project.

During the past year, experimental work involving synchrotron

radiation was pursued with two particular goals in mind. First, the

long-awaited routine operation of the x-ray ring of the Brookhaven

National Synchrotron Light Source (NSLS) became a reality. We aligned and

corrected problems in our tunable focussed soft x-ray beamline (X-24A) to

the point where it is the most intense source of photons in the 2-7 keV

photons available in the world (-10*11 photons/sec at 3 keV with <0.4 eV

resolution). Second, we initiated experiments to study multi-electron

core-level excitations in atoms and at surfaces.

1. NSLS X-24A Soft X-Ray Beamline (800 eV-7 keV)

The development of the NSLS X-24A beamline at Brookhaven

officially came to fruition in September with the production of a stable,

focussed, tunable x-ray beam in the energy range 2-7 keV. Using a nickel-coated aluminum collecting mirror (which also acts as a low-pass

filter), a double-crystal monochromator, and a nickel-coated focussing

mirror, we obtained a focussed spot 2 mm high by 1 mm wide with the flux

mentioned above. The entire system is in ultra-high vacuum (uhv) with no windows whatsoever (it is contiguous with the main ring vacuum) and

operates stably and comfortably at the highest intensity conditions

reached by the x-ray ring so far (125 mA stored current at 2.5 GeV) . The

system is entirely computer controlled. The flux at this time exceeds all

other tuned sources including the LBL/Exxon 54-pole wiggler at the Stanford

49
Synchrotron Research Laboratory over the energy range described above.

Although an active program of experiments has already begun, we are actively soliciting other potential users.

2. Photon-Excited Multi-Electron Core-Level Excitations Using

Synchrotron Radiation

We have begun a series of experiments aimed at the better

understanding of multi-electron excitations which are photoexcited . Such

effects as the threshold behavior of x-ray resonant Raman fluorescence,

the energy shift due to post-collisional interactions, and the couplings

between different decay channels from multi-electron excited states are

all topics of importance in a number of surface spectroscopies. In

collaboration with the NBS Quantum Metrology Group, we have initiated a three-step program: first, to observe x-ray fluorescence and

Auger-electron decay in monatomic gases; second, to observe these decays

in multi-atom gases; and finally, to observe the decays from solid

surfaces of transition metals. All of these measurements are to be made

as a function of photon energy in the vicinity of the threshold energies

for core-level ionization. Data such as line widths, energy shifts, and

threshold behavior will be used to understand multi-electron excited

states and the dynamics of the decay process.

During the past year we have taken preliminary data on two systems.

We observed K-shell x-ray fluorescence from argon gas using a windowed gas

cell and a uhv bent-crystal (Si) x-ray spectrometer. This work was the

first experiment on the x-24A beamline at NSLS described above. The

incorporation of ion chambers into the gas cell allowed us to tune

precisely the incident beam energy anywhere in the vicinity of the argon

K-edge (including the 4p "white line") and permitted precise tuning of

both the input and output photons.

The second system used an argon gas jet in vacuum and a cyl indrical-mirror electron energy analyzer to observe K-shell

photoemission and KVV Auger-electron decay. This system was put into

operation on the 54-pole wiggler beam line at the Stanford Synchrotron

Research Laboratory. The wiggler was operated as an indulator for the

first time and once again ion chambers monitoring absorption of the photons

in argon gas were used to tune the incident beam.

Both experimental systems yielded spectra with count rates lower than

expected. The coming year will be devoted to system modifications which

are intended to give higher count rates and eliminate other problems which

showed up in the first runs. The same systems will, of course, be used to

take data on monatomic and more complex gases.

A surface-science chamber which has been designed to perform uhv

studies on the x-24a beamline or elsewhere is presently being constructed.

It will permit us to perform the second phase of the multi-electron

excitation work using thin films and single crystals of transition metals.

The lower energy limit of this beamline (-800 eV) was intentionally chosen

50
to allow study of the L- shell excitations in nickel and copper. We have

previously studied the Auger-electron spectra of these metals with

near- threshold electron excitation and believe that experiments with

near- threshold photon excitation will help resolve uncertainties in

interpretation. We expect to measure x-ray fluorescence, photoemission,

and Auger-electron spectra in the new experiments. Our new chamber will

incorporate a precision goniometer, allowing added surface sensitivity to

be obtained by orienting the sample at glancing incidence.

F. Production and Characterization of Ultrasmooth Surfaces

(T. J. Jach)

Previous surface science experiments have indicated a need 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 defect-free

substrates and thin films such as in the semiconductor industry where

device widths of 100A 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 OA

or better for a variety of materials.

Reflection electron microscopy (REM) has been used to measure the

roughness of metal surfaces. In collaboration with Drs. G. Hembree of

the NBS Mechanical Production Metrology Division and L. B. Holdeman of

Comsat, a series of thin gold films were deposited on float glass

substrates at a range of temperatures between 30°C to M30°C. We have been

able to photograph structure on the film surfaces with a resolution of

about 10A. The study indicated that gold films deposited at room temperature are far rougher (100A rms or greater) than previously

thought; other standard techniques such as stylus or scanning electron

microscopy photos failed to reveal this roughness. REM should be capable

of directly detecting step dislocations or other such features on gold

films down to a height of one atom; such a resolution is almost as good as scanning tunneling microscopy. The methods are complementary, however,

since REM is better at looking at large areas rather than small ones. We

have also determined that the roughness is due to initial surface

nucleation and whisker growth which varies in a complex way with

temperature

.

During the following year, we will be extending the reflection

electron microscopy technique to examine GaAs substrates as well as continuing work on the gold films. We hope that the success we have had

in characterizing gold films can be used to determine the polishing and

etching methods that produce the smoothest GaAs substrates.

51
G. 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 techniques. A variety of laser-based techniques,

however, have recently demonstrated their utility in probing such

molecular dynamics in both the gaseous and liquid states. In this

program, the focus is on exploiting similar laser-based techniques for

addressing the issues of energy transfer at surfaces. The program

utilizes both the temporal and spectral characteristics available in

state-of-the-art lasers. Strong collaborations with Drs. M. P. Casassa,

E. J. Heilweil, D. S. King, D. A. Mantell 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 the Dynamics of Thermal

Desorption

Thermally activated desorption remains a key step in a wide

variety of reactions at surfaces. While it is frequently assumed that the

desorbed species can be accurately viewed as being in equilibrium with the

surface, there have been no direct tests of this assumption. For instance

the potential for developing surface chemistries which exploit

non-equilibrium reactions of excited-state species will depend on the

efficiency of the accommodation process.

We have studied the thermal desorption of NO from P t ( 1 1 1 ) using

laser-excited fluorescence. The rotational- state distribution have been

examined as a function of NO coverage (0 = 0.1 to 1.0 of saturation) and

we have found that the internal energy of the desorbed NO can be described

by a Boltzmann distribution with T

int = (0.95 ± 0.05) T surf (see Figure 7)

We have also examined the influence of coadsorbed CO. While the

adsorption sequence can change the desorption rate of the NO, resulting in

temperatures for the maximum desorption rate being lowered by 25$, the

internal energy is still found to be distributed in a Boltzmann manner,

with T

int = T surf . Additional experiments to probe the extent of

rotational alignment of the desorbed NO have indicated that there is no preferred spatial orientation of the rotational angular momentum.

Experiments to measure the kinetic energy in individual rotational states

are presently in progress. It is anticipated that the degree of accommo- dation found for the NO /P t (111) system will make it an excellent

"benchmark" in future studies of rapid desorption processes (see Sections

2 and 4 below). Future plans include the extension of the NO /P t ( 1 1 1 ) measurements to the N 0/P t ( 1 10) system in order to probe the influence of

competition from step-induced NO dissociation with the molecular NO

desorption channel. This work is supported in part by the Department of

Energy

.

52
Fig. 7. Rotational temperature of NO thermally desorbed from Pt(lll),

determined by laser-excited fluorescence, as a function of surface

temperature

.

2. Laser-Induced Desorption

Lasers have recently become popular tools for inducing

desorption from surfaces. The majority of the work in this area has

focused on the removal of near-monolayer quantities of adsorbed species

within the region illuminated by the laser. From the gas-phase species

which are generated, one can identify and measure concentration gradients

of adsorbates and probe adsorbate diffusion by monitoring the relaxation

of the laser- induced concentration gradient. We have recently begun a series of experiments aimed at using laser-excited fluorescence to measure

the internal-energy distribution as a result of desorption induced by a laser pulse.

In the past year we have been able to assemble a vacuum system for

these studies. It is anticipated that this system will permit us to use laser-excited fluorescence and multi-photon ionization as state- specif ic

probes of the laser-induced desorption process. We have already successfully used a quadrupole mass spectrometer to probe the desorption of rh , CO, and NO from a polycrystalline platinum foil upon irradiation with the

second harmonic from a frequency-doubled NdYAG laser. The laser53
desorption yield has been monitored both as a function of the surfacetemperature rise (laser pulse energy) and as a function of surface

coverage. In all cases, the desorption yield was non-linear in laser

intensity and there was a minimum energy density below which no detectable

desorption was observed. Furthermore, this threshold decreased with

increasing coverage, consistent with the shift to lower temperatures

observed in standard thermal desorption experiments.

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. At this time we are examining the utility of blackbody radiation

as a signature of the extent and the reproducibility of laser-surface

heating. It is anticipated that state-specific detection will be

incorporated into this experiment in the coming year in order to determine

the degree to which laser heating is manifest in the internal and

translational energies of the desorbed molecules. This work is supported in

part by the Department of Energy.

3. Time resolved 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.

Following our report last year of the first measurements of

vibrational relaxation on surfaces (OH on colloidal Si02) , the technique

has been extended to self-supporting pressed discs of the same material.

A longer T

^ time for population decay was observed (220 ± 20 ps) than in

any of the measurements where a solvent was also present. Chemical

treatment of the Si02 surfaces has generated BOH, NH2 , and OCH^ adsorbates

which have been probed. The temperature dependence of the vibrational

relaxation rate for both OH and 0D on Si02 has been measured and each is

found to fit a multiphonon model for the thermally-enhanced relaxation

(see Figure 8). These experiments provide a first test of the pathways

involved in vibrational relaxation at surfaces. They also demonstrate

that over the temperature range employed by most industrial reactors, the

relaxation mechanisms on this model catalytic support can be generally

accounted for by a simple multiphonon model of the relaxation process.

Additional work has extended the technique to relaxation measurements of

the OH groups on the zeolite ZSM-5 and of both OH groups and free carriers

on ZnO.

54
Fig. 8. Vibrational relaxation rates (1/T-|) for OH and OD as a function of

temperature. For each isotope, the rates have been normalized to

the rates observed at room temperature. The solid curves represent the temperature dependence of the relaxation rate

predicted by a multiphonon relaxation model, where n is the number

of phonons involved in the relaxation process.

Future work is planned on a range of zeolites in an effort to measure

the differences between the vibrational relaxation rates for OH groups

bound at silica sites as compared to alumina sites. It has long been

postulated that these two sites have distinctly different catalytic

activity and thus it is reasonable to expect that they will have

distinctly different vibrational relaxation rates. By comparing a range

of samples with known catalytic activity, it will be possible to ascertain

the degree of correlation between the observed relaxation rates and the

catalytic activity. We also anticipate that the existing laser system can

be extended into the absorption range of the adsorbed carbon monoxide

fundamental. With this advance in picosecond laser technology, we will be

able to explore the T-j times for CO bound to small supported

transition-metal particles. This project is supported in part by the Air

Force Office of Scientific Research.

55
4. High-Resolution Infrared Reflection-Absorption Spectroscopy and

Picosecond/Femtosecond Measurements

To date, we have been able to contribute to a more detailed

picture of the relevant steps in energy transfer at surfaces. While there

remains a great deal still to be done with the techniques which we have

developed, it is becoming clear that several major advances will be

required before direct measurements of vibrational relaxation at wellcharacterized single-crystal surfaces will be possible. The four major

technical issues which must be addressed are: i) Extension of the tuning

range down to 5 pm in order to probe oscillators with large absorption

cross sections such as CO and NO. ii) Increased time resolution to the

range of < 2 ps in order to follow the faster relaxation rates

anticipated for systems which can couple to electron-hole pairs, iii) A high- resolution (=0.1 cm

-1

) reflection-absorption spectrometer to measure

the shape, cross section, and spectral position of the infrared absorption

feature, iv) An optical detection scheme with increased dynamic range in

order to measure changes on the order of 1 part in 10^ in the two

polarization components in an individual laser shot.

Each of the four technical issues mentioned above would have a substantial impact on the existing program, i.e. new adsorbates could be

studied, faster processes could be followed, damage which accompanies

laser-induced heating could be characterized, and smaller population

changes could be seen. However, if all four objectives can be achieved,

it will then be possible to measure vibrational relaxation rates at the

surfaces of single-crystal metal surfaces. Our efforts to date in the

four areas can be summarized as follows: i) We are currently exploring

several methods for extending the tuning range available to the present

laser system. We have generated = 1 of the required tunable infrared

energy in the 5ym region by mixing the output of the existing optical

parametric amplifier. A dye laser based on the Nd + ^ YAG is being

constructed to permit difference-frequency generation in LilO^. ii) A shorter duration (= 2 ps FWHM) synchronously-pumped tunable dye laser is

being amplified in order to generate sufficiently intense pulses for

mixing in nonlinear crystals, iii) The feasibility of a high-resolution

(= 0.1 cm

-1 resolution) infrared ref lection- absorption spectrometer based

on a 20 ns Nd + ^YAG pumped difference-frequency generator is being

explored, iv) In collaboration with Dr. A. Luntz of IBM, optical

detection techniques with improved dynamic range (yet suitable for use in

pulsed-laser experiments) are being explored.

H. Spin Polarization in Secondary-Electron Cascades in Ferromagnets

(S. M. Girvin)

Recent experimental progress in the production and detection of

spin-polarized, low-energy electrons is opening up new avenues of research

in the study of both bulk and surface magnetism. One of the key

requirements for a proper interpretation of many experimental measurements

is an understanding of inelastic scattering and the production of secondary

56
electrons. In collaboration with Drs. D. R. Penn and S. P. Apell of the

NBS Electron Physics Group, a theory has been developed of spin

polarization in secondary-electron cascades in f erromagnets . We have

found that measurement of the secondary polarization versus kinetic energy

provides useful information about the inelastic scattering which cannot

be obtained from traditional measurements of secondary intensity versus

kinetic energy. In particular, we have found that the ratio of

majority- to minority-spin inelastic lifetimes at an energy E is well

approximated by the simple relation

T t (E)/t + (E)

T~Pr 1 +P(E)

1+P B 1 ~P ( E)

where P(E) is the measured secondary-electron polarization at energy E and

P B is the bulk polarization.

The lifetime ratios deduced from experimental measurements on N i and

Fe are shown in Figure 9. The rise in the ratio at low energies is due to

the ability of minority electrons to scatter into the empty minority

d-band states which arise form the bulk magnetization.

These results will prove useful in interpretation of photoemission

and inverse-photoemission spectra and of polarized low-energy electron

diffraction data. They also provide a testing ground for microscopic

theories of inelastic and exchange scattering in f erromagnets

.

l-~"

Fig. 9. Ratio of spin-up to spin-down lifetimes as a function of energy

for Ni and Fe.

57
I. 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 microscope atomic-scale properties of

individual entities as well as from larger-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.

A large-scale theoretical effort has been underway aimed at the

modeling of reaction dynamics at metallic surfaces and at interfaces of

electro-chemical signficance. Major focus in the past has been on the

role of internal degrees of freedom (vibrational, rotational, and

electronic) of molecules in determining energy flow and redistribution

occurring in elementary molecular processes at surfaces.

Work has remained focused on the role of 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 (developed in collaboration with Dr. S. Holloway

of Liverpool University) for obtaining classical trajectories of a diatomic molecular beam incident upon a surface and in which chargetransf er/curve-crossing events take place.

In collaboration with Dr. Holloway and Ms. M. Karikorpi of Liverpool

University, calculations have been made of the multi-dimensional

Landau-Zener probabilities for a two-state molecule/ surf ace scattering

event. We have obtained the correct branching ratios between scattered

vibrationally-hot neutral molecules and negative-molecular ions. This is

believed to be the first molecular-scattering calculation involving a physical surface which properly includes non-adiabatic coupling between

electronic states of the molecule.

Computer codes have been constructed to calculate the classical

trajectories of molecules over arbitrary potential-energy surfaces (PES)

with emphasis again on those PES which include a curve crossing/ seam. The

example shown in Figure 10 represents a vibrationally cold l£ molecule, with

its molecular axis p in an orientation parallel to the physical surface,

normally incident upon the surface with center-of-mass translational

58
energy * leV. Near the surface, I 2

~ can form and this is characterized by an intra-molecular potential with large equilibrium separation and also by

stronger bonding to the surface. The grill work structure at the top of

Figure 10 is the PES. Contours of constant potential have been projected

IODINE

Fig. 10. A proposed potential energy surface (top) for an iodine molecule

incident upon a physical surface in which dissociative adsorption

is possible in the potential well at the surface for the

molecule-surface separation z * 1A along the intra-molecular

coordinate p. Contour plot (bottom) of the PES in the (p,z)

plane and a trajectory for a scattering event in which

translational- to-vibrational energy redistribution occurs.

onto the (p,z) plane (bottom of Figure 10) where the trajectory is also

shown. Note that the incident molecule becomes trapped for several

oscillations as a negative-molecular ion before scattering, in this case

with - 0.7 eV translational energy. Amongst other things, we have

calculated the probability for dissociative scattering as a function of

incident kinetic energy, treating parametrically the well depth of the

I 2 /surface bond (the depth of the far left potential vs. z curve in

Figure 10). Results are shown in Figure 11 together with experimental

observations of Kolodney and Amirav. The significant point here is that,

in both our theory and in the experiments, the dissociative scattering

probability

59
o

Fig. 11. Normalized probability for dissociative scattering of I 2 from a surface as a function of the kinetic energy of the incident I 2 molecular beam, treating the adsorption energy of I 2

~ (in eV)

parametrically . The points are reported results of Kolodney and

Amiray for I 2 scattering from a MgO surface.

rises from zero at threshold to a saturation value over a kinetic energy

range of - ^-6 eV. On the basis of the similarity between experiment and

theory, it is believed that the charge-transf er mechanism is important in

molecule- surf ace interactions.

We have developed further the " traj ectori zed wave-packet theory"

reported last year to a point where it now satisfies microscopic

reversi bil i ty and energy conservation (significant and ubiquitous flaws in

most previous " imposed-trajectory" theories). At the request of the editor

of "Comments on Atomic and Molecular Physics", a review article on "Surface Harpooning" was written. The principles of chargetransf er/cur ve-cr ossing collisions were sequentially developed for

atom-atom, atom-molecule, atom-surface, and finally molecule-surface

collisions. By working up in order of complexity, it was easy to see how one could use and adapt the results obtained in less complex collisional

events

.

Considerable progress has been made in the area of surface

vibrational spectroscopy, at least in part because of the intimate

connection between atom trajectories and vibrational spectra. A major

60
review article was written on "Excitation Mechanisms in Vibrational

Spectroscopy of Molecules on Surfaces" in which the physics of the

excitation process involved in the five most prevalent experimental

techniques was developed from a single, unified point of view.

Further work on shape- resonances in electron scattering from molecules

demonstrated how a shape-resonance/temporary-negative-molecular ion,

created in an electron energy-loss experiment, not only leads to overtone

enhancement in the intra-molecular excitations but also for any modes

which have a component normal to the surface.

Finally, vibrational lineshapes and spectra of adsorbed molecules

have been studied in terms of the quasi-periodic trajectories over multi-dimensional PES. This is a particularly 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

I C ID ) - i-iiE <l/

2

Y(t)

iwt

dt

where y(t) is the oscillator displacement as a function of time after

initial excitation. As an example, the trajectory of an initially excited

"harmonic" oscillator in the y direction (Y^ n =0.1, X^ n

= 0.01), which is

anharmonically coupled to an x-oscillator with half the frequency is shown

in the top of Figure 12. A number of well-defined y oscillations occur prior to a swing into the large- amplitude low-frequency oscillator and

then return to y. This is a characteristic Fermi resonance and the

vibrational spectrum shown in the bottom left of Figure 1 2 is a typical

slightly-split doublet (Aw/w-O.I here). Increasing the initial

displacement, hence anharmonicity , leads to a breakdown of

quasiperiodicity. Thus chaotic motion prevails, as indicated in the

spectrum shown in the bottom right of Figure 12 (Y in = 0.13, X in = 0.01).

The main peak is very much reduced in height, broadened, and an erratic

background appears. We are applying this methodology for determining

vibrational spectra to current problems of active interest in the surface

vibrational- spectroscopy communi ty

.

We plan to continue work in the area of surface reaction dynamics

with near-term emphasis on the determination of self-consistent reaction

traj ectori es , 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.

61
X10" 1

40 . i f—

I

i\ ^ ,

iJO.) 149. 3 V90.:

Fig. 12. Initial trajectory (top) for an excited oscillator oriented along

the Y axis but anharmonically coupled to an X-oriented oscillator

with half the frequency. Also shown are constant

potential-energy contours. Vibrational spectra (bottom), I(w) vs

a) (arbitrary units), accompanying such an excitation for initial

excitation below (left) and above (right) the chaotic threshold.

Note the scale change between the two spectra.

62
In addition, analysis will be made, whenever possible, of novel

experimental results. Current interest includes laser-assisted surface

processes and state- to-state analysis, high- resolution surface vibrational

spectroscopy, neutron spectroscopy of metal hydrides, and other

experimental probes of non-adiabatic effects.

63
4. SURFACE COMPETENCE PROGRAM

W. F. Egelhoff, Jr., J. Fine, S. M. Girvin, T. J. Jach

R. Klein, T. E. Madey, A. J. Melmed, 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 (NBS Task 26117) 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. Each program component consists of several technical projects; seme of these projects are extensions of activities in the Division that

had existed prior to the start of this Competence Program while others

have been launched this year. The principal objectives of each program

component are described in the following two main Sections together with

reports of the 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 twodimensional 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

64
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 four project areas. First, we are planning

to develop the techniques needed to synthesize, by alternating monolayer

deposition, a new class of materials: non-equilibrium ordered alloys.

The structural properties of these materials as grown and during 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. Third, we will apply modern many-body

theoretical techniques to the study of the quantum Hall effect, magnetism,

and other electronic properties of layered structures. Finally, we are planning to develop techniques for the study of the growth and morphology

of modulated structures using glancing-incidence diffraction of x-rays

from a synchrotron source and other extensions of modern surface methods.

1. Surface and Interface Chemical Physics of Ultrathin Films

(W. F. Egelhof f , Jr.)

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 that 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 reported last year on the discovery of a new aspect of x-ray

photoelectron spectroscopy (XPS) and Auger-electron spectroscopy (AES) and

have termed it the "searchlight effect". The searchlight effect is

manifested in single-crystal samples by enhanced XPS and AES peak

intensities along nearest-neighbor and next-nearest-neighbor directions in

the lattice.

The searchlight effect is a powerful, new probe of short-range order

and is ideally suited for studying a variety of problems associated with

ultrathin films, surfaces, and interfaces. We now have the opportunity to

perform real-time studies of surface morphological and compositional

dynamics such as clustering of overlayers, surface segregation, and

surface alloying or interdiffusion at interfaces. Although these

65
phenomena are interesting in their own right, we are planning to

investigate them in association with our current primary objective of

synthesizing a new class of materials, non-equil ibrium ordered alloys, by

epitaxial growth of alternating metal monolayers. This work has the

potential for opening up a whole 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.

We are in the process of improving our XPS instrument to carry out

the work just described. Changes in electron optics and detection will

provide substantially better operating characteristics. These changes

will, in part, permit application of the XPS searchlight effect to higher

electron energies than the conventional XPS range where it should have

increased diagnostic power. We are also designing a system of

ultrahigh- vacuum ovens to provide the sources with constant metal vapor

flux that are needed to grow high-quality films with alternating

monolayers by molecular-beam epitaxy.

The source of the angular anisotropies of electron emission in XPS

and AES that give rise to the searchlight effect have been investigated

using single- scattering calculations. These calculations, performed for

copper films as a function of thickness, demonstrate that the enhancements

are associated with forward scattering by nearest- neighbor and

next-nearest-neighbor atoms in the lattice. The searchlight effect can thus be used with confidence as a structural probe. The effect, however,

is a serious complication in the conventional method of measuring (and

using) electron attenuation lengths with single- crystal specimens.

Further details of this analysis are given in Section 2. A. 4.

Work has continued on the development of the equivalent-core approximation (ECA) as an interpretati ve tool for analyzing core-level

binding-energy shifts. Figure 13(a) shows how the Ni 2p^/2 core-level

shift induced by the adsorption of CO is governed by total-energy

considerations that can readily be understood with the ECA. In the final

state, a fully-screened core hole on Ni becomes (by the ECA) the chemical

equivalent of Cu. We consider the difference between final states with

clean or CO-covered Cu , as in Figure 13(a). Since there is a choice in

the final state between CO on a Ni atom and CO on the Cu atom, we can immediately use the greater Ni-CO bond strength to predict that the final

state leaving Cu clean will have the lower total energy. The Ni 2p^/2

core-level binding energy is just the energy to get from the initial state

to the indicated final states. We therefore deduce that the clean Ni must

exhibit the smaller binding energy and the CO-induced shift must be to

larger binding energy. Figure 13(b) shows the use of the ECA in

66
a)

TOTAL EXERGY RULE QOVERMNG

SURFACE CORE-LEVEL SHFTS

b) HEAT OF Cu SURFACE SEGREGATION

wrm ADSORBED CO

total anargy

\

853.01 aV

lowac total aoargy / • -w

O =NI

852 34 eV /

IMT1AL STATE

FINAL STATES

NK 100)

Fig. 13. (a) Illustration of how total energy considerations govern the

CO

- induced surface core-level shift in Ni(100). (b) Illustration

of how the bulk-to-surface core-level shift can predict the heat

of CU surface segregation to a surface site with adsorbed CO.

determining from the bulk-to-surface Ni 2p^/2 core-level shift that Cu

segregation to a CO-covered surface site is an endothermic process by 0.2*1

eV (5.5 kcal/mole). This result is in sharp contrast to the case of Cu

segregation to a clean Ni surface which is 0.43 eV (10 kcal/mole)

exothermic. The adsorption of CO will therefore drive Cu into bulk Ni.

Finally, a major invited article titled "Core-Level Binding-Energy

Shifts at Surfaces and in Solids" has been completed for Surface Science

Reports. This review article will, as it appears, be approximately 200

pages long and contain over a thousand references. The article consists

of a review of the theoretical principles of core-level shifts and a selection of the most illustrative, experimental case studies. The

theoretical principles section is written with the experimentalist in mind

and explains the essential concepts such as core eigenvalues, initialstate contributions, total energy differences, charge-transf er screening,

and polarization and dielectric screening without resorting to the usual,

opaque mathematics. Particular attention is paid to the principles of the

reference-level problem since many important fine points have often been

glossed over in previous descriptions. The section on experimental case

studies contains selected results which illustrate, in the most clear-cut

manner possible, the basic mechanisms governing core-level shifts. The

topics include atomic coordination number, charge transfer, Madelung

potentials, cluster size, surface work function, image-charge and chargetransfer screening, band bending, and sample charging. In this section,

particular attention is paid to the relative merits of the two basic

conceptual frameworks for interpreting core-level shifts, the equivalentcore-energy-cycle framework and the initial-state—final-state framework.

67
2. Microcomposi tion and Microstructure of Thin Films

(A. J. Melmed and R. Klein)

This effort is directed to the measurement of microcomposition

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 atonic 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-f ormation process parameters.

During this reporting period, the unique capability of FIM to

characterize the microstructure of novel materials was demonstrated. One of

the recently discovered class of rapidly solidifed aluminum-based alloys,

which appeared by electron diffraction in the transmission electron

microscope (TEM) to have icosahedral long-range order and no translational

symmetry, was made available to us. A considerable amount of theoretical

work has been done to explain and predict the relevant atomic structure.

Thus far, several theoretical models have predicted correctly most of the

observed diffraction features, but no complete description of atomic

positions has been given. The alloy, approximately Al^Mn, was provided to

us in the form of pieces of very brittle ribbon, a few millimeters on a side and some 0.040-0.050 mm thick, and presented some complications in

specimen preparation. However, we succeeded in obtaining reproducible FIM

images which clearly showed that the material has a phase in real space

with structure consistent with icosohedral long-range order; that is,

appropriate two-, three- and five-fold symmetries are present, over a lateral distance of about 200 nm, and no translational symmetry is

evident. Also, we found no evidence for multiple twinning, the major

counter- viewpoint to the acceptance of real icosohedral symmetry. In

those regards, the FIM results clearly agree with the TEM results.

Additionally, the FIM images showed that the microstructur e is replete with

micro-defects. Atomic dissection of the material by field evaporation

clearly showed that these features prevailed through a depth of at least

300 nm. Further microscopy remains to be done in an effort to determine

the details of atomic packing in this complex material.

The construction of our energy-corrected atom-probe (ECAP) , which

will be used for determining composition profiles through thin layers and

layer/ substrate interfaces, has been recently completed. All features of

the ECAP have been tested and found to function qualitatively as expected.

Initial quantitative evaluation has indicated that the mass resolution is

better than anticipated in the lower-resolution Section of the ECAP; that

is, M/AM appears to be at least - 250 and possibly is as high as 500

(compared to an expected value of about 150). Quantitative evaluation of

the high-resolution Section has been thwarted so far by a mechanical

misalignment introduced during the ECAP fabrication.

68
We have found it increasingly useful to combine our atom-probe

analyses with the imaging capability of TEM (in collaboration with

colleagues in the NBS Metallurgy Division). The atom-probe-FIM—TEM

combination is extremely powerful in providing microscopy with a wider

range of contrast and magnification than available to the separate

techniques. For this purpose, we have developed a specimen holder which

allows us to shuttle specimens between the atom-probe FIM and the TEM.

Using this extended capability, we have begun microcomposition and

mi cr ostructure analyses of nickel-based superalloys (of interest as turbine- blade materials) and of a newly developed class of Al-Li-Cu

alloys

.

During the next year, it is planned to complete the quantitative

evaluation of the ECAP and to bring the associated electronics to a convenient working arrangement. Presently, the ECAP is operated using the

timing electronics of the general-purpose atom-probe FIM developed earlier

which is awkward for the user. A more appropriate system is partially

developed

.

Further microscopy and possibly atom-probe analysis of the

icosohedral-symmetry alloys and related materials are planned. Atom- probe

analyses of nickel-based and aluminum- based alloys will also be done. It

is hoped that an ultra- high- vacuum FIM can be assembled specifically for

in situ thin-layer deposition and microstructure characterization.

After full evaluation of the ECAP performance, a program of

depth-probe analyses of thin-layer/substrate combinations will be

undertaken. Metal/metal systems prepared by alternate-layer vapor

deposition will be investigated in order to characterize the interfacial

composition and to determine the extent of intermixing. Appropriate

choices of elemental metals and preparation parameters will be made in

concert with other related experiments (e.g., Section 4.A.1 above).

3. Theory of the Quantum Hall Effect

(S. M. Girvin)

Artificial semiconductor superlattices (heterostructur es or multi-quantum wells) consisting of alternating atomically smooth layers of

GaAs and GaAlAs are among the most novel and successful two-dimensional

materials. By suitable doping one can create at the GaAs-GaAlAs interface

a two-dimensional electron gas which exhibits many interesting effects.

One of the most remarkable phenomena which has been observed in the

GaAs-GaAlAs system is the quantum Hall effect. At very high magnetic

fields (-10 T) and low temperature (< 4 K) , the Hall resistance of the

two-dimensional electron gas takes on universal quantized values of the

form h/e^i where h is Planck’s constant and e is the elementary charge.

The quantum number i is an integer or simple rational fraction. Associated with this quantization is the existence of persistent nearly

69
dissipationless currents similar to those occurring in superconductors and

superfluids. These unexpected findings have stimulated considerable

experimental and theoretical work at many laboratories.

In collaboration with Drs. A. H. MacDonald (National Research

Council, Ottawa) and P. M. Platzman (AT&T, Bell Laboratories, Murray Hill)

a "magneto-roton" theory has been developed of the collective excitations

in these fractional quantum-number states. This theory is closely

analogous to the Feynman theory of superfluid helium and provides new

insight into the physics underlying the persistence of currents.

The collective modes at long wavelength are predicted to be phonons

(density waves) and magneto- rot ons analogous to the roton excitations in

superfluid helium. The predicted mode spectrum is shown in Figure 14.

Independent numerical calculations on model systems by Dr. F. D. M.

Haldane of AT&T Bell Laboratories have shown that this magneto-roton

theory is remarkably accurate. Figure 14 illustrates the good agreement

between the predicted mode energy and Haldane's numerical results. One of

the advantages of our theory is its analytic simplicity which allows one for the first time to compute quite easily experimentally relevant and

Fig. 14. Collective excitation energy A versus wave vector f or v * 1/3,

1/5, and 1/7. The solid lines are analytic results of the

magneto-roton theory. The circles and triangles are from

numerical calculations for v - 1/3 on small spherical and

hexagonal systems by Haldane and Rezayi. Arrows indicate

position of reciprocal lattice vectors of the Wigner crystal at

the appropriate densities.

70
previously inaccessible quantities such as the dielectric response.

Experimental attempts to observe the predicted magneto-roton excitations

via the dielectric response are currently under way in two separate groups

at AT&T Bell Laboratories.

This magneto-roton theory nicely complements earlier work we have

done on the Wigner crystallization transition. As the magnetic field is

increased, the magneto-roton mode goes "soft" at the wave vector

corresponding to the Wigner-crystal reciprocal-lattice vector. The

critical field at which the magneto-roton softening makes the liquid state

unstable agrees quite well with our previous predictions for the field at

which the Wigner crystal becomes stable. Hence the combination of these

two theories gives us a much deeper and more complete understanding of the

liquid-solid transition in this system.

Future work in this area will address questions of the finitetemperature statistical mechanics of the quantum Hall effect and the

effects of disorder. Another project which will take place in the coming

year is the organization of a quantum Hall effect lecture series at the

University of Maryland. In collaboration with Professor R. E. Prange,

plans are being made to edit and publish the lecture notes of the invited

speakers as a Springer-Verlag book. This book is intended to be a tutorial introduction to this rapidly expanding field for both

experimentalists and theorists.

Another area of planned future work concerns the field of metallic

superlattices. Dr. Michael DeWeert will be joining the Division as an NRC

postdoctoral fellow. His area of expertise is superconductivity,

proximity effects, and related phenomena in metallic superlattices. Close

interaction is expected with the superlattice experiments in the Division

and with the proximity effect work in the NBS Temperature and Pressure

Division.

4. Dynamical Diffraction of X-Rays from Crystal Surfaces at

Glancing Incidence

(T. J. Jach)

The structure and registry of adsorbed atoms with respect to the

underlying crystal lattice remains one of the major concerns of surface

science. Diffraction techniques such as low-energy electron diffraction

provide some of this information, but some foreknowledge of potential

sites of the atom and extensive calculation are usually required. We

have developed a new technique using the dynamical diffraction of x-rays

in a glancing-incidence geometry to provide the same type of information.

The technique is surface sensitive but could be employed at interfaces as well

.

Although the theory for dynamical x-ray diffraction has been

developed previously, it had not been tested experimentally since the

necessary experiments require an intense source of monochromatized x-rays

(e.g., from a synchrotron source), a well-collimated beam, and a specimen

71
crystal with a smooth, defect- free surface. In collaboration with Drs. P. Cowan and S. Brennan of the NBS Quantum Metrology Group and Drs. M.

Bedzyk and G. Materlik of the Deutsches Elektronen Synchrotron (DESY)

at Hamburg, an experiment was conducted last fall at DESY to test the

theory. We observed surface diffraction from Ge(220) planes normal to

the (111) surface at 8 keV with angles of incidence as low as 1 milliradian. X-ray beam collimation at the Bragg angle was about 5

microradians (Figure 15). This extreme collimation, possible only on a synchrotron light source, allowed us to obtain data which turned out to

fit the theory very well.

0

Nal 8PECULAR BEAM

Fig. 15. Experimental set-up for grazing- incidence x-ray diffraction.

During the past year we have done considerable data analysis which

gave us a great deal of insight into surface dynamical diffraction theory.

Because we are able to diffract an x-ray beam from a crystal at incidence

angles less than the critical angle for total reflection (- H milliradians) , the x-rays inside the crystal are only evanescent

(exponentially-decaying) waves. There are two waves, however, and their

linear combination at the crystal surface forms an x-ray standing wave.

72
Slight changes in the angle of incidence or deviations from the Bragg

angle translate this standing wave back and forth on the surface,

selectively exciting surface atoms whose fluorescence was observed. The

interference process which makes this possible is illustrated in Fig.

16(a) where the specularly reflected beam is shown to have either a strong

absorption or a maximum at the Bragg condition depending on the angle of

Incidence

.

Fig. 16 Intensities of (a) specular beam and (b ) diffracted beam as a function of deviation from the ideal Bragg angle Og for various

fixed angles of incidence <j>. Curves 2, 3, and 5 are experimental

results and curves 1, 4, and 6 are results from dynamical

diffraction theory. The measurements and calculations are for

three angles of incidence: <j> = 4.74 milliradians , less than the

critical angle for total reflection (curves 1 and 2); <f> = 5.55

milliradians, at the critical angle (curves 3 and 4); and <j> = 6.35 milliradians, greater than the critical angle (curves 5 and

6 ).

73
These initial experiments were carried out in helium at atmospheric

pressure and we are building a chamber to continue the work in ultra-high

vacuum. We intend to measure position-dependent fluorescence,

photoemission, and Auger-electron decay from surface atoms. To this end, we have already built a new bent-crystal ultrahigh vacuum (uhv) x-ray

spectrometer. The principal task during the coming year will be to design

and build a uhv crystal goniometer which will be accurate to a few seconds

of arc. The equipment is designed to be used on our new focussed x-ray

beam line, X-24A, at the Brookhaven National Synchrotron Light Source.

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

.

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 collisonal interaction.

We are combining ultrahigh-vacuum surf ace- sci ence techniques with

state-of-the-art laser spectroscopy in several experiments involving

electron- stimulated desorption (ESD), photon- 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-spectroscopi c 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

74
neutral species desorbed from surfaces by electron or photon excitation

will be detected and characterized. 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 neutral 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-G and 3.1.

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 of specific

atomic collisions that take place in condensed materials.

In recent experiments in which aluminum or silicon targets were bombarded by argon ions, we have shown that the Auger decay of

collisonally 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 iasev' techniques; (2) monitoring the Auger- electron de-exc i tation 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 and Ions

In collaboration with Drs. L. J. Moore (NBS Inorganic

Analytical Research Division) and T. B. Lucatorto (NBS Radiation Physics

Division) , a new series of experiments has been planned and designed to

determine the kinetic energy distributions of specific sputtered atoms

(ions) and their states of excitation. Resonance multiphoton

75
laser-ionization schemes have been developed to detect sputtered atoms in

specific excited states and time- of- flight techniques will be used to

measure their kinetic energy distributions. Pulse timing and gating

sequences have been designed and estimates made of signal intensity

indicate that such measurements are feasible. A new apparatus has been

designed for this experiment and consists of an ultrahigh vacuum chamber

(that allows ion-beam- angle- dependent measurements to be made) connected to

a time-of- flight analyzer. This chamber, which is under construction,

will be coupled to two ultraviolet pulsed-laser systems. We plan to

investigate atoms (ions) sputtered from surfaces of magnesium, aluminum,

and silicon and to determine their charge state, excitation state, and

kinetic energy distributions.

(b) Auger-Electron De-Excitation of Sputtered Atoms

In collaboration with Drs. C. Le Gressus and J. P. Durand

(Centre d' etudes Nucleaires de Saclay, France), a new 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 Auger-electron emission intensity as a function of

rotation 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). 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.

(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).

76
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. The few

measurements made to date have concentrated on desorption from poorly

characterized surfaces, or radi ation- 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

f ractional- 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. A later stage

of the measurements will 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/WO00)) is based on previous related experiments and the

theoretical interest in these conditions.

2. 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.

The construction of a new angle- resolving , display-type ion and

electron energy analyzer is nearing completion. This instrument is based

on the IBM design of Dr. D. Eastman. After completion of the analyzer and

assembly, the analyzer will undergo 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 will be developed

during this initial testing. This same software will be used to process

similar two-dimensional data from a video system to be installed for our ESDIAD 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 H

2 0 on N i ( 1 1 1

)

, 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

.

77
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 co-adsorbates?

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 surfaces. Desorption

thresholds and energy dependences will be correlated with angle- resolved

electron spectroscopic measurements (ultraviolet photoelectron

spectroscopy, constant-initial-state, constant-final-state measurements).

These measurements will be the first detailed, angle- resolved mechanistic

studies of photon-induced bond-breaking processes at surfaces.

78
5. PUBLICATIONS

(a) Publications of Past Year

Armstrong, R. A. and Egelhoff, Jr., W. F., "An Analysis of Angular Dependent

XPS Peak Intensities," Surf. Sci. 154, L225 (1985).

Bange, K., Madey, T. E. and Sass, J. K., "The Adsorption of Oxygen on

Ag ( 110): A New View of Structure and Bonding," Chem. Phys. Lett. 1 1

3

> 56 (1985).

Bange, K., Madey, T. E. and Sass, J. K. , "Characterization of OH(ad)

Formation by Reaction Between H

2o and 0(ad) on Ag(110) f " Surf. Sci.

152/153 , 550 (1985).

Bertel, E., Ramaker, D. E., Kurtz, R. L., Stockbauer, R. and Madey, T. E.,

"Photon Stimulated Desorption of H

+ Ions From OH on Ti and Cr

Comparison with Bulk Solid H

20," Phys. Rev. B Rapid Commun. 3J_, 6840

(1985).

Bertel, E., Stockbauer, R., Kurtz, R. L. t Madey, T. E. and Ramaker, D. E.,

"The Decay Channels of the 3p Resonance in the 3d Transition Metals and

Their Relevance to the Mechanisms of Electron and Photon Stimulated Ion

Desorption," Surf. Sci. 1 52, 776 (1985).

Bertel, E., Stockbauer, R., Kurtz, R. L., Madey, T. E. and Ramaker, D. E.,

"3p- Core Hole State Sensitivity in Ion Desorption from Oxidized Cr," in

Desorption Induced by Electronic Transitions, II , eds. W. Brenig and D.

Menzel, Springer Series in Surface Sciences, Vol. 4 (Springer-Verlag,

Heidelberg), 84 (1985).

Bertel, E., Stockbauer, R., Kurtz, R. L., Ramaker, D. E. and Madey, T. E.

,

"Resonant Photoemission and the Mechanism of Photon Stimulated Ion

Desorption in a Transition Metal Oxide," Phys. Rev. B 31 , 5580 (1985).

Bozso, F., Yates, Jr., J. T., Arias, J., Metiu, H. and Martin, R. M. , "A

Surface Penning Ionization Study of the CO/N i ( 1 1 1 ) System," J. Chem.

Phys. 78, 4256 (1983).

Butler, J. J., Holland, D. M. P., Parr, A. C. and Stockbauer, R., "A

Threshold Photoelectron-Photoion Coincidence Spectrometr ic Study of

Dimethylether (CHoOCHO," Int. J. Mass. Spectro. Ion. Phys. 58, 1 (1984).

3

Casassa, M. P., Heilweil, E. J., Stephenson, J. C. and Cavanagh, R. R.,

"Time-Resolved Measurements of Vibrational Relaxation of Molecules on Surfaces: Hydroxyl Groups on Silica Surfaces," J. Vac. Sci. Tech. A3,

1655 (1985).

Cavanagh, R. R. and King, D. S., "Laser Studies of Surface Chemical

Reactions," in Chemistry and Physics of Solid Surfaces V , Springer

Series in Chemical Physics 35 (Spr inger- Verlag , New York) , 141 (1984).

79
Ceyer, S., Melmed, A. J., Carroll, J. J. and Graham, W. R., "On the Atomic

Structure and Optical Constants of (001) Tantalum," Surf. Sci. 144, L444

(1984).

Ceyer, S. and Yates, Jr., J. T., "Ammonia Adsorption on the Ag (311) Surface,"

Surf. Sci. 155, 584 (1985).

Ceyer, S. and Yates, Jr., J. T., "Orientation of CHoNC Adsorbed on Ag (311 )

,

J. Phys. Chem. 89, 3842 (1985).

Ciszewski, A. and Melmed, A. J., "Epitaxial Growth and Some Properties of

Samarium Crystals on Tungsten," J. de Physique _45_, C9 (1984).

Ciszewski, A. and Melmed, A. J., "Epitaxial Crystal Growth of Gadolinium on Tungsten," Surf. Sci. 145, L471 (1984).

Ciszewski, A. and Melmed, A. J., "Surface Self-Diffusion of Dysprosium and

Gadolinium," Surf. Sci. 1 45, L509 (1984).

Ciszewski, A. and Melmed, A. J., "Epitaxial Crystal Growth of HCP Metals on

BCC Metals: Dysprosium on Tungsten," J. Crystal Growth _6£, 253 (1984).

Cox, D. F. , Semancik, S. and Szuromi, P. D., "The Interaction of Water Vapor

with Tin Oxide," Proceedings of the International Conference on Solid-State Sensors and Actuators-Transducers , Boston, MA, 385,

(1985).

Doering, D. L. and Semancik, S., "Orientational Ordering in a Strongly

Chemisorbed System: Na on Ru(001)," Phys. Rev. Lett. _53, 66 (1984).

Egelhoff, Jr., W. F., "A Core-Level Binding- Energy Shift Analysis of CO, H,

and 0 Adsorption on Cu-Ni Surfaces," J. Vac. Sci. Tech. _A3, 1305

(1985).

Egelhoff, Jr. W. F., "A New Tool for Studying Epitaxy and Interfaces: The

XPS Searchlight Effect," J. Vac. Sci. Tech. A_3, 151 1 (1985).

Egelhoff, Jr., W. F., "Angle Resolved XPS of the Epitaxial Growth of Cu on

Ni(1 10) ," in The Structure of Surfaces , M. A. Van Hove and S. T. Tong,

eds., (Springer, Berlin), 199 (1985).

Egelhoff, Jr., W. F., "The XPS Searchlight Effect: A New Analytical Tool for

Layered Structures, Epitaxy, and Interfaces," in Layered Structures,

Epitaxy and Interfaces , MRS Proceedings, Vol. 37, J. M. Gibson, ed.

(Materials Research Society, PA), 443 (1985).

Fine, J., Lindfors, P. A. Gorman, M. E., Gerlach, R. L., Navinsek, B.,

Mitchell, D. F. and Chambers, G. P., "Interface Depth Resolution of

Auger Sputter Profiled Ni/Cr Interfaces: Dependence on Ion Bombardment

Parameters," J. Vac. Sci. Tech. A3, 1413 (1985).

Fine, J. and Navinsek, B., "Characterization of NBS Standard Reference

Material 2135 for Sputter Depth Profile Analysis," J. Vac. Sci. Tech.

A3, 1408 (1985).

80
Gadzuk, J. W. , "Surface Harpooning," Comments on Atomic and Molecular

Physics, J_6_, 219 (1985).

Gadzuk, J. W. , "Resonance Vibrational Excitation in Electron-Energy Loss

Spectroscopy of Adsorbed Molecules," Phys. Rev. B 31 » 6789 (1985).

Gadzuk, J. W. and Holloway, S., "On the Dissociation of Diatomic Molecules at

Metal Surfaces," Chem. Phys. Lett. 114 , 31 -4 (1985).

Gadzuk, J. W. and Luntz, A. C., "On Vibrational Lineshapes of Adsorbed

Molecules," Surf. Sci. 1 44 , 429 (1 984).

Gadzuk, J. W. and Nrirskov, J. K., "Vibrational Excitation, Harpooning and

Sticking in Molecule-Surface Collisions," J. Chem. Phys. 8J_, 2828

(1984).

Girvin, S. M. , MacDonald, A. H. and Platzman, P. M. , "Collective Excitation

Gap in the Quantum Hall Effect," Phys. Rev. Lett. 54 , 581 (1985).

Click, A. J. and Bryant, G. W. , "Effect of Anisotropy on the Optical

Absorption Spectrum of Polyacetylene," Phys. Rev. B. _28_, 4295 (1983).

Goodman, D. W. and Yates, Jr., J. T. , "CO Isotopic Mixing Measurements in

Nickel: Evidence for Irreversibility of CO Dissociation," J. Catalysis

82, 255 (1983).

Heilweil, E. J., Casassa, M. P. Cavanagh, R. R. and Stephenson, J. C.

,

"Vibrational Energy Relaxation of Adsorbates on Surfaces," in Ultras nort

Pulse Spectroscopy and Applications, SPIE Vol. 533 (Society of

Photo-Optical Instrumentation Engineers, WA) , 15 (1985).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R., and Stephenon, J. C.,

"Picosecond Vibrational Energy Relaxation of Surface Hydroxyl Groups on Colloidal Silica," J. Chem. Phys. _81_, 2856 (1984).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R. and Stephenson, J. C.,

"Temperature Dependence of the Vibrational Population Lifetime of

0H( v=1 ) in Fused Silica," Chem. Phys. lett. 117, 185 (1985).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R. and Stephenson, J. C.,

"Vibrational Deactivation of Surface OH Chemisorbed on Si0 2

: Solvent

Effects," J. Chem. Phys. 82, 5216 (1985).

Heinonen, 0., Taylor, P. L. and Girvin, S. M. , "Electron-Phonon Interactions

and the Breakdown of the Dissipationless Quantum Hall Effect," Phys.

Rev. B. 30, 3016 (1984).

Holloway, S. and Gadzuk, J. W. , "Energy Redistribution and Dissociation in

Molecule-Surface Collisions Involving Charge Transfer/Surface Hopping,"

Surf. Sci. 152, 838 (1985).

Holloway, S. and Gadzuk, J. W. , "Charge Transfer, Vibrational Excitation, ani

Dissociative Adsorption in Molecular-Surface Collisions: Classical

Trajectory Theory," J. Chem. Phys. 82, 5203 (1985).

81
Kelley, R. D., Cavanagh, R. R. f Rush, J. J. and Madey, T. E., "Neutron

Spectroscopic Studies of the Adsorption and Decomposition of C

2H 2 and

C

2H 4 on Raney Nickel," Surf. Sci. 155 , 480 (1985).

King, D. S., Mantell, D. A. and Cavanagh, R. R., "NO Thermally Desorbed From

a Saturation Coverage on Pt (111): Internal State Distributions," J.

Chem. Phys. 82, 1046 (1985).

Kurtz, R. L., Stockbauer, R. and Madey, T. E., "Site Specificity in Stimulated

Desorption from TiO ?J " in Desorption Induced by Electronic

Transitions II , eds. W. Brenig'and D. Menzel, Springer Series in Surface

Sciences, Vol. 4 (Springer-Verlag, Heidelberg), 89 (1985).

Landman, U., Kleiman, G. G. , Cleveland, C. L., Kuster, E., Barnett, R. N.,

and Gadzuk, J. W. , "Hindered and Modulated Rotations of Adsorbed

Diatomic Molecules: States and Spectra," Phys. Rev. B. _29_, 431 3 (1984).

Madey, T. E., "The Uses and Limitations of ESDIAD for Determining the

Structure of Surface Molecules," in The Structure of Surfaces , Springer

Series in Surface Science 2, eds. M. A. Van Hove and S. Y. Tong

(Springer-Verlag, New York), 264 (1985).

Madey, T. E. and Benndorf, C., "Influence of Surface Additives (Na and 0) on

the Adsorption and Structure of NH^ on Ni(110)," Surf. Sci. 152/153, 587

(1985).

Madey, T. E., Benndorf, C., Shinn, N. D., Miskovic, Z. and Vukanic, J.,

"Recent Advances using ESDIAD: Applications to Surface Chemistry," in

Desorption Induced by Electronic Transitions II, eds. W. Brenig and D.

Menzel, Springer Series in Surface Sciences, Vol. 4 (Springer-Verlag,

Heidelberg), 104 (1985).

Madey, T. E., Ramaker, D. E. and Stockbauer, R., "Characterization of

Surfaces Using Electron and Photon Stimulated Desorption," Ann. Rev.

Phys. Chem. _35, 215 (1984).

Madey, T. E. and Stockbauer, R., "Experimental Methods in Electron and Photon

Stimulated Desorption," in Methods of Experimental Physics , Vol. 22,

Solid State Physics: Surfaces , R. L. Park and M. G. Lagally, eds.

(Academic Press, N.Y.), 465 (1985).

Matthew, J. A. D., "Comparison of Vibrational Broadening in Auger and

Photoelectron Spectroscopy," Phys. Rev. B 29., 30 3 1 ( 1984).

Matthew, J. A. D., "Auger Spectroscopy of Solid Surfaces: Electron Versus

Ion Excitation," Phys. Scripts. T 6_, 79 (1983).

Melmed, A. J. and Carroll, J. J., "An Approach to Realism in Field Ion

Microscopy via Zone Electropolishing," J. Vac. Sci. Tech. _A2, 1388

(1984).

Melmed, A. J., Maurice, V., Frank, 0. and Block, J. H., "Rare-Earth Crystal

Growth from the Vapor: Eu/Re and Eu/W," J. de Physique 45, C9 (1984).

82
Melmed , A. J., Twigg, M. E., Klein, R., Kaufman, M. J. and Fraser, H. L.

,

"The Complementary Use of Atom Probe Field Ion Microscopy and Analytical

Transmission Electron Microscopy for the Study of a Ni-Base Superalloy ,

J. de Physique _4^, C9 (1984).

Navinsek , B., Panjan, P., Zabkar, A. and Fine, J., "A Comparison of Sputtered

Ni/Cr Interface Depth Resolution as Obtained by the Quartz Crystal

Microbalance Mass-Loss Method and Auger Spectroscopy," J. Vac. Sci.

Tech. A3, 671 (1985).

NCSbl, C., Benndorf , C. and Madey, T. E., "H 2o Adsorption on Ni ( 1 1 0 )

Evidence for Oriented Water Dimers," Surf. Sci. 157, 29 (1985).

Penn, D. R., Apell, S. P. and Girvin, S. M., "Theory of Spin-Polarized

Secondary Electrons in Transition Metals," Phys. Rev. Lett. _55_, 518

(1985).

Powell, C. J., "Inelastic Mean Free Paths and Attenuation Length of

Low-Energy Electrons in Solids," Scanning Electron Microscopy/ 1 984,

1649 (1984).

Powell, C. J., "Energy and Material Dependence of the Inelastic Mean Free

Path of Low-Energy Electrons in Solids," J. Vac. Sci. Tech. _A3, 1388

(1985).

Powell, C. J., "Innershell Ionization Cross Sections," in Electron Impact

Ionization, edited by T. D. Mark and G. H. Dunn (Springer-Verlag,

New York), 198 (1985).

Powell, C. J. (editor), "Technical Activites 1984 - Surface Science Division,"

NBSIR 84-2994 (1985).

Rendell, R. W. and Girvin, S. M. , "Quantum Hall Effect: Role of Inversion

Layer Geometry and Random Impurity Potential" in Precision Measurements

and Fundamental Constants II , eds. B. N. Taylor and W. D. Phillips,

National Bureau of Standards Spec. Publ. 61 7, 557 (1984).

Schmidt-May, J., Senf, F., Voss, J., Kunz, C, Flodstrdm, A., Nyholm, R.

and Stockbauer, R., "Resonant Photoemission and PSD of Rare Earth

Oxides," Desorption Induced by Electronic Transitions II , eds. W. Brenig

and D. Menzel, Springer Series in Surface Sciences (Springer-Verlag,

Heidelberg), 94 (1985).

Seah, M. P. and Powell, C. J., "The Coordinated Development of Standards for

Surface Chemical Analysis," NBSIR 85-3120 (1985).

Shinn, N. D. and Madey, T. E., "Unusual C-0 Bond Weakening on a Clean Metal

Surface: CO on Cr(110)," Phys. Rev. Lett. _53, 2481 ( 1984).

Shinn, N. D. and Madey, T. E., "Oxygen-Induced CO Reorientation on Cr(110),"

J. Vac. Sci. Tech. A3, 1673 (1985).

Twigg, M. E., "The Effect of Bremsstrahlung-Produced Fluorescence in X-Ray

Microanalysis in the Analytical Transmission Electron Microscope," J.

Electron Microsc. 1 34, 2 (1984).

83
Twigg, M. E., Melmed, A. J., Klein, R. f Kaufman, M. J. and Fraser, H. L., "A

Microanalytical Study of Secondary Precipitation in RSR143 using Atom

Probe Field Ion Microscopy and Analytical Transmission Electron

Microscopy," Superalloys 631 (1984).

Udovic, T. J., Kelley, R. D. and Madey, T. E., "The Methanation Activity of

W(110)," Surf. Sci. 150, L71 (1985).

Yates, Jr., J. T., "The Thermal Desorption of Adsorbed Species," 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).

Yates, Jr., J. T. and Haller, G. L., "The Interaction of Physisorbed Species

with Chemisorbed Species as Studied by Infrared Spectroscopy," J. Phys.

Chem. 88,4660 (1984).

84
(b) Publications in Progress

Bange, K. , Madey, T. E. and Sass, J. K. , "The Structure of the Surface

Hydration Shell of Bromide on Ag(110)," Surf. Sci. (in press).

Brennan, S. t 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. Instr. and Meth.

(in press).

Casassa, M. P., Heilweil, E. J., Stephenson, J. C. and Cavanagh, R. R.,

"Time-Resolved Measurements of Vibrational Relaxation at Surfaces," J.

Elect. Spectroscopy (in press).

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. U of Methods of Surface

Characterization , Plenum Press Publishing Co., New York, (in press).

Cowan, P. L., Brennan, S., Deslattes, R. D., Henius, A., Jach, T. and

Kessler, E. G. , "A High Energy Resolution X-Ray Spectroscopy Synchrotron

Radiation Beamline for the Energy Range 800 eV to 5000 eV," Nucl. Inst,

and Meth. (accepted).

Cowan, P. L., Brennan, S., Jach, T. , Bedzyk, M. and Materlik, G.

,

"Observations of the Diffraction of Evanescent X-Rays at a Crystal

Surface," Phys. Rev. Lett, (submitted).

Cox, D. F., Semancik, S. and Szuromi , P. D., "Summary Abstract: Structural

and Electronic Properties of Clean and Water-Dosed Sn0 2 (110)," J. Vac.

Sci. Tech, (submitted).

Egelhoff, Jr., W. F., "Core-Level Binding-Energy Shifts in Solids at

Surfaces," Surf. Sci. Reports (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).

Erickson, N. E. and Powell, C. J., "Characterization of the Imaging

Properties of a Double-Pass Cylindrical-Mirror Analyzer," Surf.

Interface Anal, (submitted).

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, (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.

^ of Methods of Surface Characterization , Plenum Press Publishing Co.,

New York ( in press )

.

85
Gadzuk, J. W. and Holloway, S., ’’Charge Transfer and Vibrational Excitation

in Molecule-Surface Collisions: Trajectorized Quantum Theory,” Physica

Scripta (in press).

Gadzuk, J. W. and Holloway, S., ’’Collision Induced Dissociation of Diatomic

Molecules on Surfaces: A Charge Transfer Mechanism,” J. Chem. Phys. (in

press)

.

Gadzuk, J. W. , "Dynamics of Molecular Processes at Surfaces: Vibrational

Lineshapes and Spectra,” J. Elect. Spectroscopy (in press).

Girvin, S. M. , MacDonald, A. H. and Platzman, P. M. , "Fractional Quantum Hall

Effect Superfluidity, Magneto-Rotons , and Fractionally Charged

Vortices," J. of Mag. & Mag. Mat. (in press).

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 (submitted)

.

Karikorpi, M. , Holloway, S. and Gadzuk, J. W. , "A Classical Trajectory

Surface Hopping Approach to Non- Adiabatic Molecule-Surface Processes,”

J. Elect. Spectroscopy (in press).

King, D. S. and Cavanagh, R. R., "Final-State Resolved Studies of

Molecule-Surface Interactions,” New Laser and Optical Investigations of

Chemistry and Structures at Interfaces , Verlag-Chemie (in press).

Kurtz, R. L., "The Influence of Surface Structure on Ion Emission from Ti02,”

J. Vac. Sci. Tech. A (submitted).

Kurtz, R. L., Stockbauer, R. and Madey, T. E., "Angular Distributions of Ions

Desorbing from Ti0

2

,» Nucl. Instr. & Meth. B. (submitted).

Kurtz, R. L., Usuki, N., Stockbauer, R. and Madey, T. E., "Measurements of

Electron Attenuation Lengths in Condensed Molecular Solids," J. Elect.

Spect. Rel. Phn. (submitted).

Madey, T. E., "Mechanisms and Applications of Electron Stimulated Desorption

in Surface Science," Vacuum (in press).

Madey, T. E. and Benndorf, C., "Evidence for Molecualar Orientations in

Coadsorption of CO and K on Ru(001)," Surf. Sci. (in press).

Mantell, D. A., Cavanagh, R. R. and King, D. S., "Internal States

Distributions of NO Thermally Desorbed from P t ( 1 1 1 ) : Dependence on Coverage and Co-adsorbed CO," J. Chem. Phys. (submitted).

MacDonald, A. H. and Girvin, S. M., "Collective Excitations of Fractional

Hall States in Higher Landau Levels," Phys. Rev. B. Rapid Commun.

(submitted)

MacDonald, A. H. and Girvin, S. M. , "Quasi-Particle States and the Fractional

Quantum Hall Effect," Phys. Rev. Lett, (submitted).

86
MacDonald, A. H., Liu, K. L. and Girvin, S. M. , "Disorder and the Fractional

Quantum Hall Effect: Activation Energies and the Collapse of the Gap,"

Phys. Rev. B. (submitted).

MacDonald, A. H., 0j i , H. C. A. and Girvin, S. M. , "Magnetoplasmon

Excitations from Partially Filled Landau Levels," Phys. Rev. Lett,

(submitted)

.

MiSkovic, Z., Vukanid, J. and Madey, T. E., "Calculations of

Reneutralization Effects in ESDIAD," Surf. Sci. (submitted).

Penn, D. R., Apell, S. P. and Girvin, S. M. , "Spin Polarization of Secondary

Electrons in Transition Metals: Theory," Phys. Rev. B (submitted).

Platzman, P. M. , Girvin, S. M. and MacDonald, A. H., "Conductivity in the

Fractionally Quantized Hall Effect," Phys. Rev. Lett, (submitted).

Powell, C. J., "Calculations of Electron Inelastic Mean Free Paths from

Experimental Optical Data," Surf. Interface Anal, (in press).

Powell, C. J., "The Energy Dependence of Electron Attenuation Lengths,"

Surf. Interface Anal, (in press).

Powell, C. J., "Recent Developments in Quantitative Surface Analysis by

Electron Spectroscopy," J. Vac. Sci. Tech, (submitted).

Powell, C. J. and Seah, M. P., "Surface Chemical Analysis-Report on the VAMAS

Project," Surf. Interface Anal, (submitted).

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. Chera. Phys. (in press).

Shinn, N. D., "Synchrotron Photoemission Evidence for 'Lying-Down' CO on Cr(110)," J. Vac. Sci. Tech, (submitted).

Shinn, N. D. and Madey, T. E. , "CO Chemisorption on Cr (110): Evidence for a Precursor to Dissociation," J. Chem. Phys. (in press).

Shinn, N. D. and Madey, T. E., "Observation of a Metal: CO 4o Bonding

Interaction for Chemisorbed CO on Cr(110)," Phys. Rev. B (submitted).

Shinn, N. D. and Madey, T. E., "Chemisorption and Dissociation of 0-, on

Cr (110): An EELS/ESDIAD Study," Nucl. Instr. & Meth. B. (in press).

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. B. (submitted).

Twigg, M. E., Melmed, A. J., Klein, R., Kaufman, M. J. and Fraser, H. L. , " A Microanalytical Study of Secondary Precipitation in a Nickel-Base

Superalloy with use of Atom Probe Field Ion Microscopy and Analytical

Electron Microscopy," Proc. Fifth Int. Symposium on Superalloys (in

press )

.

8?
Wang, F. W. , Lowry, R. E. and Cavanagh, R. R., "Picosecond Excimer

Fluorescence Spectroscopy: Applications to Local Motions of Polymers

and Polymerization Monitoring, " Polymer (submitted).

Wax, M. J., Cavanagh, R. R., Rush, J. R., Stucky, G. D., Abrams, L. and

Corbin, D. R., "A Neutron Scattering Study of Zeolite Rho," J. Phys.

Chem. (submitted).

Wax, M. J., Kelley, R. D. and Madey, T. E., "Ethane Hydrogenolysis Catalyzed

by W(110)," J. Catalysis, (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).

88
c) Recent Publications of New Staff Members (Burgess and Szuromi

)

Burgess, Jr., D. R., Hussla, I., Stair, P. C., Viswanthan, R., and Weitz, E.,

"Pulsed Laser-Induced Thermal Desorption from Surfaces: Instrumentation

and Procuedures ," Rev. Sci. Instrum. _55, 1771 (198-4).

Szuromi, P. D., Engstrom, J. R. and Weinberg, W. H., "The Reaction of

Saturated and Unsaturated Hydrocarbons with the (110)— (1x2) and (111)

Surfaces of Iridium," J. Chem. Phys. _80_, 508 (1 984).

Szuromi, P. D., Engstrom, J. R. and Weinberg, W. H., "Adsorption and Reaction

of N-Alkanes on the Pt ( 1 1 0)-( 1 x2) Surface," J. Phys. Chem. _89, 2497

(1985).

Szuromi, P. D. and Weinberg, W. H., "The Adsorption and Reaction of Normal

Alkanes on the the Ir( 1 1 0)-( 1 x2) Surface," Surf. Sci. 1 49, 226 (1985).

89
6 TALKS

Cavanagh, R. R., "Energy Transfer at Surfaces: Pump-Probe Measurements of

Vibrational Relaxation," Department of Chemistry, California Institute

of Technology, Pasadena, CA, November 26, 1984.

Cavanagh, R. R., "Energy Transfer at Surfaces: Pump-Probe Measurements of

Vibrational Relaxation," Department of Chemistry, University of Irvine,

Irvine, CA, November 27, 1984.

Cavanagh, R. R., "Laser Diagnostics of Gas/Surface Interactions," American

Institute of Chemical Engineers, San Francisco, CA, November 28, 1984.

Cavanagh, R. R., "Energy Transfer at Surfaces: Pump-Probe Measurements of

Vibrational Relaxation," Department of Chemical Physics, IBM, San Jose,

CA, November 29, 1984.

Cavanagh, R. R., "Picosecond Pump-Probe Measurements of Vibrational

Relaxation at Surfaces," Department of Chemistry, Rutgers University,

Piscataway, NJ, April 1, 1985.

Cavanagh, R. R., "Energy Transfer at Surfaces: Laser Based Measurements,"

Local Section of American Vacuum Society, University of Minnesota,

Minneapolis, MN, May 16, 1985.

Cavanagh, R. R., "Energy Transfer at Surfaces: Laser Based Measurements,"

Physical Chemistry Department, General Motors Company, Detroit, MI, May

24, 1985.

Cavanagh, R. R., "Nitric Oxide Thermally Desorbed from Pt (111): A

Microscopic Test of Transition State Theory," Physical Electronics

Conference, University of Wisconsin, Milwaukee, WI , June 17, 1985.

Cavanagh, R. R., "Hydrogen on Small Metal Particles: Structure and Dynamics

from Neutron Scattering," Gordon Research Conference on Metal Hydrides,

Tilton, NH, July 15, 1985.

Cavanagh, R. R., "Vibrational Relaxation at Surfaces: Time Resolved Results,"

Gordon Research Conference on the Dynamics of Gas-Surface Interactions,

New London, NH, July 29, 1985.

Cavanagh, R. R., "Picosecond Pump Measurements of Vibrational Relaxation at

Surfaces," Vibrations at Surfaces IV Conference, Bowness-on-Windermere

,

England, September 17, 1985.

Cavanagh, R. R., "Inelastic Incoherent Neutron Scattering: Vibrational

Spectroscopy of Hydrogen on Platinum Black," Vibrations at Surfaces IV

Conference, Bowness-on-Windermere , England, September 18, 1985.

Egelhoff, W. F., Jr., "X-Ray Photoelectron Forward Scattering: A New Tool for

Studying Epitaxy and Interfaces," Materials Research Society Meeting,

Boston, MA, November 29, 1984.

90
Egelhoff, W. F., Jr., "Heats of Adsorption of H and 0 on Cu-Ni Alloy Surfaces

from XPS Data," 31st National Symposium of the American Vacuum Society,

Reno, NV, December 5, 1984.

Egelhoff, W. F., Jr., "Role of Forward Scattering in Angular Dependent XPS,"

31st National Symposium of the American Vacuum Society, Reno, NV,

December 5, 1984.

Egelhoff, W. F., Jr., "New Applications for Angle Resolved XPS," American

Vacuum Society Chapter Meeting, Tampa, FL, February 6, 1985.

Egelhoff, W. F. Jr., "The XPS Searchlight Effect: A New Analytical Tool for

Layered Structure, Epitaxy and Interfaces," American Physical Society

Meeting, Baltimore Convention Center, Baltimore, MD, March 25, 1985.

Egelhoff, W. F. Jr., "A Core-Level Binding-Energy Shift Analysis of CO, H,

and 0 Adsorption on Cu-Ni Surfaces," American Physical Society Meeting,

Baltimore, MD, March 28, 1985.

Egelhoff, W. F., Jr., "Forward Scattering in XPS: A Structural Tool for

Surfaces, Interfaces and Epitaxy," Chemistry Department, University of

California, Berkeley, CA, April 25, 1985.

Egelhoff, W. F., Jr., "Forward Scattering in XPS: A Structural Tool for

Surfaces, Interfaces and Epitaxy," Applied Physics Department, Stanford

University, Stanford, CA, April 26, 1985.

Erickson, N. E., "Characterization of the Imaging Properties of a Double-Pass

Cylindrical-Mirror Analyzer," 6th Symposium on Applied Surface Analysis,

University of Maryland, College Park, MD, May 15, 1985.

Fine, J., "Ion-Beam Mixing and Radiation-Induced Segregation During Sputter

Profiling of Nickel/Silver Interfaces," Condensed Matter and Radiation

Sciences Division Seminar, Naval Research Laboratory, Washington, D.C.,

November 1, 1984.

Fine, J., "Characterization of NBS Standard Reference Material 2135 for

Sputter Depth Profile Analysis," 31st National Symposium of the American

Vacuum Society, Reno, NV, December 4, 1984.

Fine, J., "A Comparison of Sputtered Ni/Cr Interface Depth Resolution as Obtained by the Quartz Crystal Microbalance Mass-Loss Method and Auger

Spectroscopy," 31st National Symposium of the American Vacuum Society,

Reno, NV, December 5, 1984.

Fine, J., "Interface Depth Resolution of Auger Sputter Profiled Ni/Cr

Interfaces: Dependence on Ion Beam Parameters," 31st National Symposium

of the American Vacuum Society, Reno, NV, December 7, 1984.

Fine, J., "Sputter Profile Shapes and Widths of Ni/Cr Interfaces: Their

Dependence on Ion Bombardment Parameters," Seventh International

Conference on Ion Beam Analysis, Hahn Meitner Institute, Berlin, W.

Germany, July 9, 1985.

91
Gadzuk, J. W. , "Molecular Scattering, Energy Redistribution, and Dissociative

Adsorption at Surfaces," Surface Science Seminar, Imperial College,

London, England, September 24, 1984.

Gadzuk, J. W. , "Intra-Molecular Wavepacket Dynamics in Molecule-Surface

Scattering," Workshop on Interactions of Molecular Beams with Solid

Surfaces, St. John's College, Cambridge, England, September 27, 1984.

Gadzuk, J. W. , "Vibrational Lineshapes of Adsorbed Molecules," Department of

Physical Chemistry Seminar, University of Liverpool, Liverpool, England,

October 1 ,

1 984.

Gadzuk, J. W. , "Dynamic Effects in Electronic Excitation and Molecular

Scattering from Surfaces," Department de Medecine Nucleaire and

Radiobiologie, Centre Hospitalie-Universitarire , Sherbrooke, Quebec,

Canada, January 21, 1985.

Gadzuk, J. W. , "Recent Advances in Vibrational Spectroscopy at Surfaces,"

Department de Medecine Nucleaire and Radiobiologie, Centre

Hosptialie-Universitaire , Sherbrooke, Quebec, Canada, January 22, 1985.

Gadzuk, J. W. , "Molecular Dynamics at Surfaces: Harpooning, Vibrational

Excitation, and Dissociative Adsorption," Physics Department Colloquium,

University of Waterloo, Waterloo, Ontario, Canada, January 25, 1985.

Gadzuk, J. W., "Dissociation Dynamics in Molecule-Surface Collisions,"

American Physical Society Meeting, Baltimore Convention Center,

Baltimore, MD, March 25, 1985.

Gadzuk, J. W. , "Collision Induced Dissociation of Diatomic Molecules on Surfaces," Physical Electronics Conference, University of Wisconsin,

Milwaukee, WI , June 17, 1985.

Gadzuk, J. W. , "A Classical Trajectory Surface Hopping Approach to

Non- Adiabatic Processes Occurring During Diatom-Surface Scattering,"

1985 Conf. on the Dynamics of Molecular Collisions, Snowbird Resort,

Snowbird, UT, July 16, 1985.

Gadzuk, J. W. , "A Trajectorized Quantum Model for Surface Harpooning

Processes Occurring in Diatom-Surface Scattering," 1985 Conf. on the

Dynamics of Molecular Collisions, Snowbird Resort, Snowbird, UT, July

17, 1985.

Gadzuk, J. W. , "The Vibrational Lineshapes of Adsorbed Molecules," Vibrations

at Surfaces IV Conference, Bowness-on-Windermere , England, September 17,

1985.

Girvin, S. M. , "Collective Excitation Gap in the Fractional Quantum Hall

Effect," AT&T Bell Laboratory, Murray Hill, NJ, October 31, 1984.

Girvin, S. M., "The Quantum Hall Effect," Solid State Theory Seminar, Oak

Ridge National Laboratory, Oak Ridge, TN, November 2, 1984.

92
Girvin, S. M. , "Rotons in Superfluid Helium and the Fractional Quantum Hall

Effect," Center for Basic Standards Colloquium, National Bureau of

Standards, Gaithersburg, MD, January 9, 1985.

Girvin, S. M., "Introduction to the Quantum Hall Effect," James Franck

Institute Colloquium, University of Chicago, Chicago, IL, January 15,

1985.

Girvin, S. M. , "Rotons in Superfluid Helium and the Fractional Quantum Hall

Effect," Department of Physics, University of Chicago, Chicago, IL,

January 16, 1985.

Girvin, S. M. , "The Quantum Hall Effect," Department of Physics, Catholic

University, Washington, D.C., February 21, 1985.

Girvin, S. M. , "Rotons in Superfluid Helium and the Fractional Quantum Hall

Effect," Physics Department, Princeton University, Princeton, NJ, March

6, 1985.

Girvin, S. M. , "Rotons and Vortices in Superfluid Helium and the Fractional

Quantum Hall Effect," Physics Department, University of Maryland,

College Park, MD, March 11, 1985.

Girvin, S. M., "Collective Excitation Gap in the Fractional Quantum Hall

Effect," American Physical Society Meeting, Baltimore Convention Center

Baltimore, MD, March 26, 1985.

Girvin, S. M. , "Rotons and Vortices in Superfluid Helium and the Fractional

Quantum Hall Effect," Physics Department, SUNY, Stony Brook, NY, April

26, 1985.

Girvin, S. M. , "Rotons and Vortices in Superfluid Helium and the Fractional

Quantum Hall Effect," Physics Department, University of Minnesota,

Minneapolis, MN, May 6, 1985.

Girvin, S. M. , "Introduction to the Quantum Hall Effect with Applications to

GaAs Heterostructures," Center for Microelectronics and Information

Science, University of Minnesota, Minneapolis, MN, May 7, 1985.

Girvin, S. M. , "Rotons, Vortices and Superfluidity in the Fractional Quantum

Hall Effect," Institute of Theoretical Physics, University of

California, Santa Barbara, CA, June 4, 1985.

Girvin, S. M. , "Introduction to the Quantum Hall Effect," Department of

Materials Science, Harry Diamond Laboratories, Adelphi , MD, August 12,

1985.

Girvin, S. M. , "Fractional Quantum Hall Effect: Superfluidity,

Magneto-Rotons and Fractionally Charged Vortices," International

Conference on Magnetism and Magnetic Materials, San Francisco, CA,

August 30, 1985.

Girvin, S. M. , "Introduction to the Quantum Hall Effect," Physics Department,

Texas A&M University, September 26, 1985.

93
Jach, T., "Observations of Dynamical X-Ray Diffraction from a Crystal Surface

at Glancing Incidence," American Physical Society, Baltimore Convention

Center, Baltimore, MD, March 26, 1985.

Jach, T., "Dynamical X-Ray Diffraction at Glancing Incidence: A New Tool for

Surface Science," Physical Electronics Conference, University of

Wisconsin, Milwaukee, Wi , June 18, 1985.

Kelley, R. D., "Catalytic Activity of Single Crystal Tungsten and Tungsten

Carbide Surfaces," Symposium on Advances in Catalytic Chemistry III",

Hotel Utah, Salt Lake City, UT, May 22, 1985.

Kurtz, R. L., "Site Specificity in Stimulated Desorption from Ti0

2

," 2nd

International Workshop on Desorption Induced by Electronic Transitions,

Elmau, Germany, October 15, 1984.

Kurtz, R. L. , "Surface Studies of the Oxides of Titanium: Electronic

Structure, Chemisorption, and Desorption from Ti^^ and Ti02," IBM

Thomas J. Watson Research Laboratories, Yorktown Heights, NY, November

8, 1984.

Kurtz, R. L., "Surface Studies of the Oxides of Titanium: Electronic

Structure, Chemisorption and Desorption from TijO? and Ti0 2

," Applied

Physics Division, Harry Diamond Laboratories, Adelphi , MD, November 20,

1984.

Kurtz, R. L., "Site Specificity in Stimulated Desorption from Ti0 2

," 31st

National Symposium of the American Vacuum Society, MGM Grand Hotel,

Reno, NV, December 6, 1984.

Kurtz, R. L., "Influence of Local Environment in Stimulated Desorption from

Ti0 2

," American Physical Society, Baltimore Convention Center, Baltimore,

MD, March 27, 1985.

Kurtz, R. L. , "Application of Surface Analytical Techniques to the

Characterization of Adsorption and Desorption from Solids," Physics

Department Colloquium, Brandeis University, Waltham, MA, April 30,

1985.

Kurtz, R. L., "Surface Science Applications of Residual Gas Analyzers,"

Residual Gas Analyzer Calibration Workshop, National Bureau of

Standards, Gaithersburg, MD, May 7, 1985.

Madey, T. E., "Uses and Limitations of ESDIAD for Determining the Structures

of Surfaces Molecules," 2nd International Workshop on Desorption Induced

by Electronic Transitions, Garmisch, W. Germany, October 16, 1984.

Madey, T. E. , "Desorption Induced by Electronic Transitions," Pittsburgh

Surface Science Center Symposium, University of Pittsburgh, Pittsburgh,

PA, October 30, 1984.

Madey, T. E., "Use of ESDIAD in Surface Chemistry," Department of Chemistry,

Iowa State University, Ames, IA, November 27, 1984.

9^
Madey, T. E. , "Mechanisms and Applications of Electron and Photon Stimulated

Desorption," 1985 Symposium on Surface Science (3S'85)»

Bundessportschule Obertraun, Obertraun, Austria, January 29, 1985.

Madey, T. E. , "Early Applications of Vacuum, From Aristotle to Langmuir,"

National Bureau of Standards Colloquium, Gaithersburg, MD, February 8,

1985.

Madey, T. E. , "The Structures of Molecules on Surfaces as Determined Using

Electron Stimulated Desorption," Department of Chemistry, University of

Montreal, Montreal, Canada, February 27, 1985.

Madey, T. E., "The Structures of Molecules on Surfaces as Determined Using

Electron Stimulated Desorption," Department of Chemistry, Howard

University, March 8, 1985.

Madey, T. E. , "Characterization of Surfaces Using Electron Stimulated

Desorption," Ceremonial Symposium Honoring the Retirement of Homer

Hagstrum, AT&T Bell Laboratories, Murray Hill, NJ, March 22, 1985.

Madey, T. E. , "Evidence for Molecular Reorientations in Coadsorption of CO

and K on Ru(001)," American Physical Society, Baltimore Convention

Center, Baltimore, MD, March 28, 1985.

Madey, T. E. , "Adsorption and Orientation of NH^ on Clean and Modified

Fe(1 00)," 7th European Conference on Surface Science, Aix-en-Provence,

France, April 3, 1985.

Madey, T. E. , "Mechanisms and Applications of Electron Stimulated

Desorption," Department of Physics, Vanderbilt University, Nashville,

TN, April 26, 1985.

Madey, T. E., "Electron and Photon Stimulated Desorption of Adsorbed Metals:

An Overview," Department of Physics, Vanderbilt University, Nashville,

TN, June 21 , 1985.

Madey, T. E., "The Structure and Chemistry of H

20 on Silver Surfaces,"

Department of Chemistry, Iowa State University, Ames, IA, June 26,

1985.

Madey, T. E., "Influence of Surface Additive Atoms on the Structure and

Chemistry of H

20 on Ag(110)," American Chemical Society Meeting,

Americana Congress Hotel, Chicago, IL, September 9, 1985.

Melmed, A. J., "Long-Range Orientational Order and Icosahedral Symmetry in a Metallic Phase Observed by Field Ion Microscopy," American Physical

Society, Baltimore Convention Center, Baltimore, MD, March 28, 1985.

Melmed, A. J., "Field Emission Microscopy-Trends and Perspectives," 3rd

International Field Emission Symposium, Wheeling, W.Va., July 17, 1985.

Melmed, A. J., "Field Emission Microscopy- Trends and Perspectives," Seventh

International Summer Institute in Surface Science, University of

Wisconsin, Milwaukee, WI , July 23, 1985.

96
Powell, C. J., "Energy and Material Dependence of the Inelastic Mean Free

Path of Low-Energy Electrons in Solids," 31st National Symposium of the

American Vacuum Society, MGM Grand Hotel, Reno, NV, December 6, 1984.

Powell, Co J., "Physics —What Physicists Do," Career Awareness Day, Walt

Whitman High School, Bethesda, MD, December 10, 1984.

Powell, C. J., "Techniques for Surface Analysis," Analytical Topical Group of

the New York Section of the American Chemical Society, New York, NY,

April 4, 1985.

Powell, C. J., "Developments in Quantitative Surface Analysis by Electron

Spectroscopy," Eastern Electron Spectroscopy Society Mtg. , General

Electric R&D Center, Schenectady, NY, June 7, 1985.

Powell, C. J., "Chemical Bonding Studies at the Solid/Gas Interface with

Techniques Using Detected Electrons," Fifth Internat. Conf. on Surface

and Colloid Science and 59th Colloid and Surface Science Symposium,

Clarkson University, Potsdam, NY, June 25, 1985.

Shinn, N. D., "Oxygen-Induced CO Reorientation on Cr(110)," 31st National

Symposium of the American Vacuum Society, MGM Grand Hotel, Reno, NV,

December 7, 1984.

Shinn, N. D., "Chemisorption on Cr (110): Uncommon Results for 0

2 and CO,"

Surface Physics Group, Sandia National Laboratory, Livermore, CA,

December 10, 1984.

Shinn, N. D., "Recent Results and Realistic Goals of Silicon-Fluorine

Chemisorption Studies," Surface Physics Group, Hughes Research

Laboratory, Malibu, CA, December 12, 1984.

Shinn, N. D., "Novel Op and CO Chemisorption on Cr (110) as Revealed by

Stimulated Desorption and Surface Spectroscopies," Los Alamos National

Laboratory, Los Alamos, NM, March 12, 1985.

Shinn, N. D., "CO Chemistry on the Cr(110) Surface: Insights from Unexpected

Results," Sandia National Laboratory, Albuquerque, NM, March 14, 1985.

Shinn, N. D., "A Molecular Precursor to CO Dissociation on Cr(110): The a-jCO

Binding Mode," Americal Physical Society Meeting, Baltimore Convention

Center, Baltimore, MD, March 27, 1985.

Shinn, N. D., "Synchrotron Photoemission Study of Chemisorbed a-jCO and a2C0 on Cr(110)," Physical Electronics Conference, University of Wisconsin,

Milwaukee, WI , June 17, 1985.

Shinn, N. D., "C0:0 2 Interactions on Cr (110): Insights into Surface

Poisoning by Electronegative Adatoms," Department of Physics, Cornell

University, Ithaca, NY, August 14, 1985.

Stockbauer, R., "Photon and Electron Stimulated Desorption of Ions from

Surfaces: Mechanisms and Applications," Physics Department Colloquium,

University of Nebraska, Lincoln, NE, April 4, 1985.

95
Stockbauer, R., "Photon and Electron Stimulated Desorption of Ions from

Surfaces: Mechanisms and Applications," Rice University, Houston, TX,

June 1985.

Stockbauer, R., "The Use of Synchrotron Radiation to Measure Electron

Attenuation Lengths in Condensed Molecular Solids," Synchrotron

Radiation Instrumentation Conference, Stanford University Conference

Center, Stanford, CA, August 1, 1985.

Szuromi , P. D., "UHV Studies of Alkane Activation on Iridium and Platinum

Surfaces," Department of Physics and Astronomy, University of Maryland,

College Park, MD, February 1, 1985.

Szuromi, P. D., "Site Specificity of Dissociative Alkane Adsorption on Platinum and Iridium Surfaces," Physical Electronics Conference,

University of Wisconsin, Milwaukee, WI , June 18, 1985.

Szuromi, P. D., "The Effect of Adsorbed Sulfur on the Hydrogenation of of CO over W ( 1 1 0

) " American Chemical Society Meeting, Americana Congress

Hotel, Chicago, IL, September 10, 1985.

Szuromi, P. D., "Comparative Studies of Alkane Activation by Low Index

Surfaces of Platinum and Iridium," American Chemical Society, Americana

Congress Hotel, Chicago, IL, September 10, 1985.

Twigg, M. E., "An Atom Probe Study of Superalloy Microstructure," 5th Annual

Symposium on Superalloys, Seven Springs Mountain Resort, Champion, PA,

October 9, 1984.

Wax, M. J., "Neutron Scattering Studies of Zeolite Rho," 189th National

Meeting of the American Chemical Society, Miami Beach Convention Center,

Miami, FL, April 29, 1985.

Wax, M. J., "Thin Platinum Films as Model Alkane Reforming Catalysts," 189th

National Meeting of the American Chemical Society, Eden Roc Hotel,

Miami, FL, May 2, 1985.

Wax, M. J., "Thin Platinum Films as Model Alkane Reforming Catalysts,"

Symposium on Applied Surface Analysis, University of Maryland, College

Park, MD, May 16, 1985.

Wax, M. J., "Reforming Reactions of Ultrathin Film Model Catalysts," American

Chemical Society, Chicago, IL, September 10, 1985.

97
7. SEMINARS

Bennett, J. M. , Naval Weapons Center, China Lake, CA, "Optical Evaluation

Techniques for Films and Surfaces," November 21, 1984.

Bishop, H. E., Materials Development Division, AERE Harwell, England,

"Electron Channeling Effects in Auger Electron Spectroscopy and

Secondary Electron Emission," September 26, 1985.

Cavanagh, R. R., National Bureau of Standards, Gaithersburg, MD, "Temporal

and Spectral Probes of Surfaces Processes: New Opportunities with Laser

Diagnostics," May 21, 1985.

Egelhoff, W. F., Jr., National Bureau of Standards, Gaithersburg, MD, "The

XPS Searchlight Effect: A New Analytical Tool for Layered Structures,

Epitaxy, and Interfaces," February 11, 1985.

Einstein, T. , University of Maryland, College Park, MD, "How and Why to Study

Critical Properties of Surfaces and Adsorbates," October 11, 1984.

Ekardt, W., Fritz Haber Institute, Berlin, W. Germany, "Size Dependent

Photoabsorption and Photoemission From Small Metal Particles," April 18,

1985.

FlodstrCm, A., Lund University, Lund, Sweden, "Angle Resolved Photoemission

Studies of Semiconductor Surfaces: Mostly Silicon and Germanium," June

13, 1985.

Freeman, R., AT&T Bell Laboratories, Murray Hill, NJ, "Picosecond Time

Resolved Photoemission from Surfaces of Semiconductors," (cosponsored

with NBS Radiation Physics Division) January 31, 1985.

Gurney, B. A., Cornell University, Ithaca, NY, "Adsorption and Desorption of

CO on Ni(1 10) ," December 17, 1985.

Heiland, W. , Vanderbilt University, Nashville, TN, "Polarized Light Emission

from Grazing Incidence He + Ni ( 1 1 1 ) Interactions," September 18, 1985.

Hicks, R., WR Grace & Company, Columbia, MD, "The Effects of Metal-Support

Interactions on Palladium: Methanol Synthesis Catalysts," April 25,

1985.

Israelachvili , J. N., Australian National University, Canberra, Australia,

"Forces Between Surfaces," (cosponsored with NBS Inorganic Materials and

Thermophysics Divisions) July 1, 1985.

Johnson, A. L. , University of California, Berkeley, CA, "Orientation of

Molecules by NEXAFS (Near Edge X-Ray Absorption Fine Structure)," April 12,

1 985.

Karikorpi, M. , University of Liverpool, Liverpool, England, "Interaction of

H

2 with Metal Surfaces: Dynamics," July 10, 1985.

98
Klein, R., National Bureau of Standards, Gaithersburg, MD, "Weighty

Considerations on the Micro-Mass- Analysis of Alloys with the Atom

Probe," April 19, 1985.

Kurtz, R. L., National Bureau of Standards, Gaithersburg, MD, "Implications

of Recent Results on Photon-Stimulated Desorption," November 15, 1984.

McKay, J. M. , Yale University, New Haven, CT, "Electronic Structure of

NiO-CO, 0

2 , and HpO Surface Interactions," June 12, 1985.

Myers, H. P., Chambers University of Technology, Goteborg, Sweden, "Mixed

Valence in Sm Overlayers on Al(001) and Cu(001) Surfaces," January 14,

1985.

Paal, Z., Hungarian Academy of Sciences, Budapest, Hungary, "Activity,

Surface Structure and Composition of Pt-Black," September 19, 1984.

Pearlstine, K., Harvard University, Cambridge, MA, "Hydrocarbon Chemistry on Modified Tungsten Surfaces: C-H and C-C Bond Activation," March 4,

1985.

Renouprez, A., Institut de Recherches sur la Catalyse, Villeurbanne Cedex,

France, "EXAFS Study of the Structure of Pd Microaggregates. A

Combined EXAFS and Neutron Study of Hydride Formation," July 23

1985.

Rys, F. , Fritz Haber Institute, Berlin, W. Germany, "Surface Roughening and

Small-Particle Faceting-With Epitaxial Overtones," April 2, 1985.

Sass, J., Fritz Haber Institute, Berlin, W. Germany, "Surface Science Model

Studies of the Electrochemical Interface," January 17, 1985.

Sawatzky, G. , University of Groningen, Groningen, The Netherlands, "The

Electronic Structure, Bandgap, and Spectroscopic Properties of Transition

Metal Compounds," (cosponsored with Electron Physics Group) August 20,

1985.

Schwalke, U., California Institute of Technology, Pasadena, CA, "Vibrational

Spectra of Chemisorbed N0 2 and Condensed N 20ij on the Ru(001) Surface,"

July 26, 1985.

Seah, M., National Physical Laboratory, Teddington, Middlesex, England,

"Electron Spectrometer Intensity Transmission Functions for ESCA,"

November 29, 1984.

Steigerwald, D., Carnegie-Mellon University, Pittsburgh, PA, "Surface

Segregation in NiAu Alloys," March 20, 1985.

Stockbauer, R., National Bureau of Standards, Gaithersburg, MD, "Studies of

Electron Transport and Radiation Damage in Condensed Molecular Films

Using Synchrotron Radiation," February 14, 1985.

Strasser, G. , University of Maine, Orono, ME, "Nitrogen Adsorption on Fe ( 1 1 1

)

from the Extrinic Precursor to Atomic Nitrogen," September 16, 1985.

99
Szuromi, P. D. f National Bureau of Standards, Gaithersburg, MD, "Alkane

Activation of Low Index Surfaces of Iridium and Platinum: Comparative

Studies," March 13, 1985.

Szymonski, M., Jagellonian University, Krakow, Poland, "Electron Stimulated

Desorption of Neutrals from Alkali Halide Surfaces," January 16, 1985.

Tomanek, D., Free University of Berlin, Berlin, Germany, "Calculation of

Potential Energy Surfaces for CO and N

2 Dissociation on Transition

Metals," May 28, 1985.

Trenary, M., University of Illinois, Chicago, IL, "Infrared

Ref lection- Absorption Spectroscopy of CO on Clean and Sulfided Ni(111),"

November 28, 1984.

Yarmoff, J., University of California, Los Angeles, CA, "Low Energy Ion

Backscattering Spectroscopies Applied to the Determination of Surface

Structure," March 20, 1985.

100
8. TECHNICAL AND PROFESSIONAL COMMITTEE

PARTICIPATION AND LEADERSHIP

Cavanagh, R. R.

Surface Science Division Safety Officer

Treasurer, General Committee of the Physical Electronics Conference

(from 7/85)

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

Member, Program Committee, 11th Conference on Atomic Collisions in

Solids, Washington, D.C., August, 1985.

Gadzuk, J. W.

Treasurer, General Committee of the Physical Electronics Conference

(through 6/85)

Member, Editorial Advisory Board, "Progress in Surface Science"

Kelley, R. D.

Chairman, Subcommittee D-32.03 on Chemical Analysis of ASTM Committee

D-32 on Catalysts

Madey, T. E. Member, Executive Committee of the Governing Board of the American

Institute of Physics (through 3/85); member of AIP Committee on Corporate Associates, and member of AIP Subcommittee on Electronic

Publishing

U.S. Representative to Surface Science Division of the International

Union of Vacuum Science, Technique and Applications (IUVSTA) and

Secretary of Committee

Member, International Advisory Committee, Second International Conference

on the Structure of Surfaces, Amsterdam, The Netherlands, June, 1987

Program Chairman, International Vacuum Congress and International

Conference on Solid Surfaces, Baltimore, MD, October, 1986

Member, Organizing Committee, 11th Conference on Atomic Collisions in

Solids, Washington, D.C., August, 1985

Member, International Advisory Committee, Second Workshop on Desorption

Induced by Electronic Transitions, Garmisch, W. Germany, October, 1984

Member, Program Advisory Commitee for the Synchrotron Radiation Center

of the University of Wisconsin, Madison, Wisconsin

101
Member, Advisory Committee for Laboratory of Surface Science and

Technology at the University of Maine, Orono, ME

Member, Davisson-Germer Prize Committee of the American Physical Society

Chairman, Committee for Foreign Interactions, American Vacuum Society

Co-Editor, "History of Vacuum Science and Technology", a monograph to

commemorate the 30th Anniversary of the American Vacuum Society

(published 11/84)

Member, ASTM Committee E-42 on Surface Analysis

Member, Editorial Board, "Methods of Surface Characterization";

co-editor of two volumes in series

Member, Editorial Board, "Journal of Vacuum Science and Technology"

Melmed, A. J. Secretary, Steering Committee, International Field Emission Symposium

Powell, C. J.

Chairman, ASTM Committee E-42 on Surface Analysis

Chairman, Surface Chemical Analysis Working Party, Versailles Project on Advanced Materials and Sandards

Member, Board of Trustees, Gordon Research Conferences; Vice-Chairman of

Board and Chairman of Selection and Scheduling Committee

Chairman, American Vacuum Society Surface Science Division (through

11/84)

Trustee, American Vacuum Society Scholarships and Awards Committee

Instructor, American Vacuum Society Short Course: "Surface Analysis by

Electron Spectroscopy"

Chairman, Study Group to Examine AVS-ASTM E-42 Interactions

Chairman, Local Committee, Meeting of American Physical Society,

Baltimore, MD , March 1985

Member, Editorial Board, "Applications of Surface Science"

Member, Editorial Board, "Surface and Interface Analysis"

Member, Editorial Board, "Methods of Surface Characterization";

co-editor of one volume in series

Stockbauer, R.

Assistant Program Chairman, International Vacuum Congress and

International Conference on Solid Surface, Baltimore, MD, October,

1986 .

102
9. PROFESSIONAL INTERACTIONS, CONSULTING

AND ADVISORY SERVICES

Cavanagh, R.R.

Collaborating with Dr. D. S. King of the NBS Molecular Spectroscopy

Division on state-specific diagnostics of molecular desorption processes

Collaborating with Drs. M. P. Casassa, E. J. Heilweil and J. C.

Stephenson of the NBS Molecular Spectroscopy Division on real time

measurements of vibrational relaxation processes at surfaces

Collaborating (with R. D. Kelley and M. J. Wax) 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 du Pont, and Dr. M. J. Wax 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. Tatarchuk of Auburn University on neutron inelastic scattering measurements from adsorbates on dispersed

ruthenium catalysts

Egelhoff, Jr., W. F.

Collaborating with Dr. R. A. Armstrong of the National Research Council,

Ottawa on a theoretical analysis of the basic physics of the XPS

searchlight effect for the purpose of defining and extending its range

of applicability as an analytical tool for surfaces and interfaces.

Fine, J.

Collaborating 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.

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 Technology.

Collaborating 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.

103
Collaborating with Dr. T. Nevadovic 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. L. J. Moore of the NBS Inorganic Analytical

Research Division and Dr. T. Lucatorto of the NBS Radiation Physics

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 Dr. P. A. Lindfors of the Physical Electronics

Division of Perkin-Elmer Corp. on the interface depth resolution of

sputter-profiled Ni/Cr interfaces.

Collaborating with Drs. C. Le Gressus and J. P. Duraud of the Centre

d’ Etudes Nucleaires de Saclay, France on the collisional 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 Prof. U. Landman of the Georgia Institute of

Technology on theoretical modeling of non-linear and stochastic

molecular processes at surfaces.

Collaborating with Dr. S. Holloway and Ms. M. Karikorpi, 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, California Institute of Technology, on a theory of polarized-metastable-helium de-excitation spectroscopy at

magnetic surfaces and on electron-transf er probabilities.

Invited lecturer and participant at the Fourth Electrochemistry Study

Group, Fritz-Haber-Institute , Berlin, September 22-27, 1985.

Girvin, S. M.

Collaborating with Drs. A. H. McDonald of the National Research Council

of Canada, Ottawa and P. M. Platzman of AT&T Bell Laboratories , Murray

Hill on developing a new theory of collective excitations in the

fractional quantum Hall effect.

104
Collaborating with Dr. M. Jonson of Chalmers University of Technology,

Gothenburg, Sweden on the theory of the thermoelectric effect in

disordered quantum Hall systems.

Collaborating with Drs. D. R. Penn and S. P. Apell of the NBS Radiation

Physics Division on a theory of spin polarization in secondary cascades

in ferromagnets

.

Collaborating with Prof. R. E. Prange of the University of Maryland in

the organization of a lecture series on the quantum Hall effect during

fall, 1985. It is planned to publish the lectures as a book.

Visited the Institute of Theoretical Physics at Santa Barbara during

June 3-8, 1985 at the invitation of Prof. J. R. Schrieffer.

Visited AT&T Bell Laboratories, Murray Hill during July 2-12, 1985 at

the invitation of Dr. D. S. Fisher.

Jach, T. J.

Collaborating with Drs. P. Cowan and S. Brennan of the NBS Quantum

Metrology Group on the development of a beamline at the National

Synchrotron Light Source, Brookhaven and on experiments to study

electronic effects associated with core-level ionization in atoms,

molecules, and solids.

Collaborating with Drs. P. Cowan and S. Brennan of the NBS Quantum

Metrology Group and with Drs. G. Materlik and M. Bedzik of the German

Electron Synchrotron Laboratory DESY, Hamburg on surface and interface

x-ray diffraction experiments at DESY using glancing incidence.

Collaborating with Drs. G. G. Hembree of the NBS Mechanical Production

Metrology Division and L. B. Holdeman of COMSAT on the fabrication and

characterization of ultra-smooth surfaces and thin films.

Collaborating with Dr. P. Cowan of the NBS Quantum Metrology Group on glancing incidence x-ray excitation of surface atoms to measure surface

core-level binding-energy shifts.

Collaborating with Dr. R. Perera of Lawrence Berkeley Laboratory on an experiment to measure Auger-electron spectra of argon for near-threshold

excitation at the Stanford Synchrotron Radiation Laboratory.

Collaborated with Dr. H. Winick of the Stanford Synchrotron Radiation

Laboratory to improve undulator efficiency.

Kelley, R. D.

Collaborating (with R. R. Cavanagh and M. J. Wax) with Drs. T. J.

Udovic and J. J. Rush of the NBS Reactor Division on neutron inelastic

scattering measurements of adsorbates on optically opaque

high-surf ace- 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 70$ part-time basis for a two-year period beginning May, 1985.

105
Kurtz, R. L. Collaborating with Prof. V. E. Henri ch of Yale University on studies of

the chemisorption of molecules of catalytic interest on transition-metal

oxide surfaces.

Collaborating (with R. Stockbauer) with Drs. C. Kunz and J. Schmidt-May

of the German Synchrotron Laboratory DESY, Hamburg and Dr. A. Flodstrdm of Lund University, Sweden in studies of the mechanisms of

the photon-stimulated desorption of ions from surfaces.

Collaborating (with R. Stockbauer) with Dr. A. FlodstrCm of Lund

University, Sweden on experiments at the NBS synchrotron radiation

facility of SURF-II to investigate (1) mechanisms of photon-stimulated

desorption of ions from a non-maximal-valent oxide and (2) angular

distributions (ESDIAD) of ions desorbing from adsorbates on semiconductors

.

Collaborating (with R. Stockbauer) 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 T. E. Madey and R. Stockbauer) with Drs. W. R.

Hunter, J. Rife, and M. Kabler of the Naval Research Laboratory and with

Dr. R. Williams of Wake Forest College 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 R. Stockbauer) with Mr. J. Jimenez of Yale

University, Prof. D. Caldwell of the University of Florida, and Dr.

D. L. Ederer of the NBS Radiation Physics Division on measurements of

the angular distribution of fluorescence from molecules excited by

synchrotron radiation from the NBS SURF-II facility.

Collaborating with Dr. J. Pena of the University of Mexico, Mexico City

on the preparation of TiC^ samples suitable both for photon-stimulated

desorption experiments at NBS and for secondary-ion mass spectroscopy

experiments in Mexico.

Madey, T. E. Collaborating with Drs. I. Terzid, J. Vukanid and Z. MiSkovic of the Boris Kidrid Institute, Belgrade, under the

auspices of the U. S. -Yugoslav Agreement for Cooperation in Science and

Technology, on theoretical and experimental studies of electronstimulated desorption and scattering of alkali ions from surfaces.

106
Collaborating (with R. L. Kurtz and R. Stockbauer) with Drs. W. R.

Hunter, J. Rife and M. Kabler of the Naval Research Laboratory and with

Dr. R. Williams of Wake Forest College 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 Drs. J. Sass and K. Bange of the

Fritz-Haber-Institute , Berlin, and with Dr. E. Stuve of the University

of Washington on fundamental studies of electrochemical phenomena with

emphasis on the interaction between water and surfaces.

Collaborating with Dr. N. Tolk of Vanderbilt University on studies of

electron-stimulated desorption of excited- alkali 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 the Dept, of Chemistry, Iowa

State University in writing a comprehensive review article on the

interaction of water with solid surfaces.

Melmed, A. J.

Collaborating as a co-principal investigator with Prof. W. R. Graham of

the University of Pennsylvania on studies of atomic reconstruction of

metal and semiconductor surfaces.

Collaborating with Dr. W. A. Schmidt and Prof. J. H. 31ock of the

Fritz-Haber-Institute, Berlin on properties of semiconductors in

electric fields and effects due to metallic overlayers.

Collaborating with Dr. B. Rioja of the Aluminum Corporation of America

to determine feasibility of atom-probe analysis of a newly developed

class of Al-Li-Cu alloys.

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 microcomposition 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.

107
Collaborating with Dr. J. W. Cahn of the NBS Institute for Materials

Science and Engineering on investigations of the atomic structure in

rapidly solidified Al-Mn alloy ribbons exhibiting icosahedral long-range

order by electron diffraction.

Consulted with Dr. R. D. Young of the NBS Mechanical Production

Metrology Division and Mr. S. R. Mielczarek of the NBS Radiation Physics

Division on probe preparation techniques for scanning tunneling

microscopy.

Powell, C. J.

Member of Solid State Physics Review Panel for Office of Naval Research.

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.

Stockbauer, R.

Collaborating (with R. L. Kurtz) with Drs. C. Kunz and J.

Schmidt-May of the German Synchrotron Laboratory DESY, Hamburg and Dr.

A. Flodstrdm of Lund University, Sweden in studies of the mechanisms

of the photon-stimulated desorption of ions from surfaces.

Collaborating (with R. L. Kurtz) with Dr. A. Flodstrdm of Lund

University, 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) angular

distributions (ESDIAD) of ions desorbing from adsorbates on semiconductors

.

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 College 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 R. L. Kurtz) with Mr. J. Jimemez of Yale University,

Prof. D. Caldwell of the University of Florida, and Dr. D. L. Ederer of

the NBS Radiation Physics Division on measurements of the angular

distribution of fluorescence from molecules excited by synchrotron

radiation from the NBS SURF-II facility.

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 photoelectronphotoion coincidence techniques.

108
Interacting with Drs. A. C. Parr, H. Hardis, and D. L. Ederer of the N3S

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.

Szurorni, P. Collaborating with Drs. S. Semancik and D. F. Cox of the NBS Chemical

Process Metrology Division in an investigation of the surface properties

of semiconducting oxide surfaces used in gas sensing applications

using ultraviolet photoemission spectroscopy. The interaction of H

2 0

with tin oxide (a widely used sensor material) has been studied.

Udovic, T. J.

Collaborating (with R. R. Cavanagh, R. D. Kelley, and M. J. Wax) with

Dr. J. J. Rush of the NBS Reactor Radiation Division on neutron

inelastic scattering studies of adsorbed molecules on catalyst

materials

.

Collaborating (with R. R. Cavanagh) with Dr. J. J. Rush of the NBS

Reactor Radiation Division and with Dr. B. J. Tatarchuk of Auburn

University on neutron inelastic scattering measurements of the

adsorptive behavior of hydrodesulf erization catalysts.

Wax, M. J.

Collaborated (with R. R. Cavanagh) with Dr. J. J. Rush of the NBS

Reactor Radiation Division and Dr. G. D. Stucky of du Pont on the

application of inelastic incoherent neutron scattering to study

diffusional motion of hydrogen in zeolite rho.

Collaborated (with R. R. Cavanagh, R. D. Kelley, and T. J. Udovic) with

Dr. J. J. Rush of the NBS Reactor Radiation Division on neutron

inelastic scattering studies of adsorbed molecules on catalyst

materials

.

109
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 , is working at NBS for one year beginning August,

1985. He is helping to design, construct and test improvements in the

angle-resolved x-ray photoelectron spectrometer (XPS) consisting of a new electron lens system and a position-sensitive electron detection

system.

Benndorf, C., of the University of Hamburg, W. Germany spent two months at

NBS in early autumn 1984 initiating measurements of the structure and

chemistry of ammonia on both clean and alkali-promoted Fe(1 00).

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.

Clinton, W. L., of the Department of Physics of Georgetown University is

spending five months at NBS beginning September , 1985 to perform

theoretical studies relating to electron- and photon-stimulated

desorption of ions and neutral species from surfaces.

Flodstrdm, A., of Lund University, Sweden worked at NBS between May and

August, 1985. He initiated a study of adsorbate structures on semiconductor surfaces using ESDIAD, participated in photon-stimulated

desorption measurements from non-maximal-valent oxides, and cooperated

in the set up and calibration of a new toroidal grating monochromator at

SURF-II.

Hashiguchi, Y., of the Nippon Steel Corporation, Japan has worked at NBS

since March, 1985 on a one- year assignment. He is studying the

interface-width dependence on ion bombardment parameters as well as collisional excitation and laser ionization of sputtered atoms.

Holloway, S. , of the University of Liverpool visited NBS for two weeks during

the summer of 1985 to work on theoretical modeling of reactive molecular

processes at surfaces.

Jansen, W. R., a graduate student of the Twente University of Enschede, The

Netherlands worked at NBS for three months in the fall of 1985. He

extended the existing computer software for automated XPS measurements

to permit operation in a timesharing mode, completed the interfacing of

the computer to the XPS sweep supply, and extended the data reduction

software.

Jimenez, J., a graduate student of Yale University, used the surface science

beam line at SURF-II for three months during the fall of 1985 to study

the angular distributions of fluorescence from gas-phase molecules.

110
Karikorpi, M., a graduate student of the University of Liverpool visited NBS

for two weeks during the summer of 1985 to work on theoretical

modeling of reactive molecular processes at surfaces.

Hoovers, A. D., a graduate student of the Twente University of Technology,

Enschede, The Netherlands, worked at NBS for three months in the fall of

1984. He wrote the basis system software to automate the angle-resolved

XPS instrument with a minicomputer as well as basic software for data

reduction.

Shinn, N. D., of Sandia National Laboratory, Albuquerque, NM, is spending

four months at NBS during the fall of 1985 studying adsorbed molecules

on metal surfaces using high-resolution electron energy-loss

spectroscopy.

Tanuma, S. , of the Nippon Mining Company is working at NBS on a two-year

assignment beginning August, 1985. He will be participating in

measurements of core-level binding energies by different

electron-spectroscopic methods and in calculations of electron inelastic

mean free paths in solids.

CHEMICAL KINETICS DIVISION

S. E. Stein, Chief

SUMMARY OF ACTIVITIES

Fiscal Year 1985

1 . INTRODUCTION

A. Background

The objective of chemical kinetics is to understand the critical

factors controlling chemical change and reactivity. It seeks to both

interpret chemical change in terms of individual molecular events and

develop quantitative theoretical models for these events. The societal

importance and exciting scientific opportunities in this area are well

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 component of each of the other four priority areas, especially

in the Chemistry Around Us and Chemical Behavior Under Extreme Conditions

areas

.

The breadth and vitality of this area were also evident in the first

International Conference on Chemical Kinetics, held at NBS this summer.

Over 100 poster presentations and 30 invited talks spanned 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. The proceedings of the conference will be published in the

Journal of Physical Chemistry (see Section 2.B for additional details.

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,

113
alongside more established techniques, have brought certain areas of

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 more cohesive as interrelations between formerly divergent areas become

increasingly clear. For instance, unimolecular reaction rate theories

developed for neutral species 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. Just four years ago its

primary emphasis was on gas-p’nase 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 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.

Central to the broadening of the Division’s scope have been two

competency development programs. One, entitled "Transformations of

Complex Organic Compounds", has enabled us to add personnel and equipment

in order to apply the exact principles of small molecule kinetics to

reactions of more complex substances. The second program, "Kinetic

Studies of the Effects of Ionizing Radiation" has enabled the growth of

existing programs on gas-phase ion-molecule chemistry to include more

complex reactions in both the gas phase and solution.

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

1 14
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 ESR 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

.

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

polyaromatic molecules.

Data center activities and associated theoretical studies are at the

heart of the division's activities. 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 evaluation activities often prompt

studies in one of our experimental programs. Moreover, the considerable

breadth of ongoing experimental activities in the division ensures that

insight needed for thorough data evaluation is available.

Over the past year we have made considerable progress in upgrading

our instrumentation. Construction of a substantial portion of a laboratory for detection of transient species by multiphoton ionization

(MPI) is complete. A high resolution "reflection" mass spectrometer is

under construction which will significantly improve the resolution and

sensitivity of these MPI experiments. A custom-designed, modular triple

quadruple mass spectrometer is now operational after some initial

installation problems. We are in the process of adding an excimer

photolysis source and multichannel vacuum UV detection for our flash

photolysis experiments.

This has been an exceptionally productive year. Both the total

number of research publications (58 published, 55 in press or submitted)

and the number per research staff member (3-9, 3*7) are at an all-time

high for our division. Viewed in another way, the net cost per published

paper was $44,000, comparable to that for productive academic institutions

and well below that for research institutes. Moreover, the cost per

publication in terms of NBS base support was only $21,000. 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 our two competence-development initiatives.

115
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 85 we participated in the

following NBS and other agency programs:

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 hazardous 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
2. DATA CENTERS

R. J. Cvetanovic, J. T. Herron, R. F. Hampson, Jr., R. D. Levin,

S. G. Lias, W. Tsang, F. Westley and G. W. Zumwalt

A. Introduction

The Chemical Kinetics Division contains two closely related but

distinct data centers, the Chemical Kinetics Data Center (headed by J. T.

Herron) and the Ion Kinetics and Energetics Data Center (led by S. G.

Lias). They are responsible for providing compilations and evaluations of

numerical data on the kinetics of chemical reactions, and the thermochemical properties of ionic and free radical species. They provide this

information to chemical kineticists and to scientists in other

disciplines, such as the analytical and biological sciences, and to

modelers of very complex chemical systems such as encountered in

combustion and atmospheric chemistry. Although the major sources of

information contained in the existing data bases are experimental studies,

a major goal is the development and application of theoretical methods for

both the analysis and extrapolation of existing experimental data, and the

prediction of the behavior of chemical systems for which there is no data.

Over the past year the Data Centers have pooled resources in the areas of

archival article acquisition, development of publication procedures, and

design and implementation of a Data Base Management System.

B. Chemical Kinetics Data Center

(J. T. Herron, R. F. Hampson, Jr., W. Tsang, F. Westley

G. W. Zumwalt and R. J. Cvetanovic)

There are four primary goals of the Chemical Kinetics Data Center.

(1) To provide compilations, bibliographies and evaluated chemical

kinetics data bases for neutral species in support of science and

technology. (2) To develop new or improved theoretical models for the

prediction of chemical kinetic data. (3) To develop cost effective

methods for the acquisition and evaluation of chemical kinetic data. (4)

To disseminate chemical kinetic data to the scientific and technical

community. This center has served for many years as a national resource

in supplying evaluated chemical kinetic data, data compilations, and

annotated bibliographies covering a broad range of scientifically and

technologically important systems. We have been involved in the chemistry

of stratospheric ozone depletion since it was first recognized as a serious problem, and continue to assist in providing the authoritative

chemical kinetic data base used in modeling stratospheric chemistry. We

provide data compilations and evaluations which address critical problems

in combustion chemistry and allow a more thorough testing of kinetic

theory

.

117
One of our major goals in the area of data evaluation is to provide a definitive set of evaluated rate data for use in combustion modeling. This

activity is supported by the Office of Basic Energy Sciences of DoE. The

first major output of that program, "Chemical Kinetic Data Base for

Methane Combustion", is complete and has been accepted by the Journal of

Physical and Chemical Reference Data for publication. It is available on

a limited basis as an NBS Internal Report (NBSIR 84-2913)- It provides

explicit expressions at 0.1, 1, and 10 atmospheres for the rate constants

for reactions in the fall-off region. It contains data on 235 reactions

with a total of 293 separate entries. This evaluation relies heavily on

the application of transition state and unimolecular reaction rate theory

to fit data measured over a wide range of temperature and pressure. The

theoretical framework indicates that much of the data given in the older

literature is valid and that it is possible to derive rate expressions for

many reactions over the entire range of temperature and pressure

encountered in a practical combustion systems.

This work has been extended to include reactions of CH^OH, CH2OH,

C3H3, n-C3H7» i-C^Hy , t-CijHg, and i — C4 H-j q with species in the methane data

base, among themselves, and in unimolecular reactions. This encompasses a total of 164 new reactions. The evaluated data base now includes 399

reactions which corresponds to about 550 separate elementary reactions

when all reaction channels are accounted for.

In addition to kinetic data, this evaluation provides, whenever

possible, the thermal functions for each species. These are either taken

from existing sources (e.g. JANAF Tables) or are independently derived.

In the coming year the data base will be expanded to include

reactions of atomic oxygen with organic compounds. The number of

reactions involved is several hundred. The total data base will then

consist of over 750 evaluated chemical reactions.

A related project on developing a compilation of experimentally

determined rate constants for combustion reactions continues. Papers for

the period 1977-1982 have been abstracted and all data entered into our HP-1000 computer system. A manuscript version of this compilation is

under preparation and will be submitted for publication in early 1986.

Work has also been finished on abstracting data published in 1983. For

1984, relevant articles have been identified and acquired, and abstracting

initiated. This bibliographic activity is the prelude for the critical

evaluation of combustion data for systems more complex than methane. In

the coming year we expect to have identified and abstracted data from all

articles published through 1985.

An evaluation of stratospheri c reactions of halogen-containing

species was completed as part of the Data Center contribution to the NASA

Panel for Data Evaluation and has been published by the Jet Propulsion

Laboratory. These data were also reviewed and evaluated for the CODATA

Task Group on Chemical Kinetics. The complete report of that task group

118
has now been published in the Journal of Physical and Chemical Reference

Data. This will be the final publication in this series following the

discontinuation by CODATA of this activity. The part of this activity

supported by NASA will continue in the coming year.

A new activity in the area of the chemistry of dielectric breakdown

of SF^ and the broader area of plasma chemistry was initiated this year.

Before the chemical kinetics could be treated, it was necessary to

assemble and evaluate a thermochemical data base for the species of

interest. A manuscript, containing thermochemical data on 38 substances

containing S, F, 0, and H has been prepared. Table 1 is a summary of the

recommended values provided in that work. Chemical kinetic data for the

reactions of SF^, SF5 , and S 2 F 1 g have been reviewed and recommended rate

parameters provided for the relevant elementary reactions based on computer modeling fits of experimental data. This work is included in a manuscript under preparation.

The plasma chemistry program will continue through joint activities

with the Electrosystems Division and JILA on modeling aspects of SF^

breakdown and relaxation. Particular attention will be paid to secondary

reactions involving 0

2 , H2 O and 0 .

The development of a data base management system continues under the

direction of R. J. Cvetanovic . Most work on the identification and

nomenclature of inorganic and organic compounds is complete. Work on the

actual searching routines for chemical reactions is underway and should be

largely complete this coming year. Each component of the system is being

tested on a suitably designed data base.

A major objective in the coming year will be the completion of this

database management system and the conversion of existing data bases into

forms suitable for inclusion in the new system. Progress in developing

software for the new system has reached the point at which search routines

for chemical reactions are being tested and modifications made based on an analysis of the test runs. We will continue to work closely in this

endeavor with the Ion Energetics and the Chemical Thermodynamics Data

Centers. We will also be considering various options concerning the

identification, abstraction, and entry of data into the new system.

The Chemical Kinetics Data Center will expand it’s scope to cover a broader range of gas phase reactions of neutral species. The Director of

the Data Center will become responsible for the identification of articles

to be abstracted from the primary archival literature starting with

papers published since December 31, 1984. Papers related to any aspect of

the reactions of neutral species in the gas phase will be abstracted.

This will include theoretical articles and condensed phase data which are applicable to the gas phase. The major thrusts of the data center in the

coming year will remain that of completing the database management

system, and continuing the evaluation and compilation activity in

combustion chemistry.

119
o o Table 1. AH and S for some S-F-0 Molecules, Radicals, and Related

f 298 298

Compounds 3

Species AH

f298’

kCal S

298 ’ cal Source

F 1 8 .86±0 . 40 37.917 [5]

S 66. 20 ±0.06 40 . 086±0 . 008 [2]

SF 3- 1 ±1 .5 5 3 • 8 ±0 .

2

[3]

sf 2 -70.9±4.0 61 . 57±0 .02 [3]

SF

3

-1 16.7±0.5 68 . 4±1 .0 AHf calculated

S from [2]

from [6],

sf 4 -182.4±5 71 . 6 ±0 .

1

C 3 ] sf

5 -21 8 . 1 ±3 • 2 72.8±2.0 AH f calculated

S from [2]

from [6],

SF 6 -291 . 7 ±0 .

2

69. 7 ±0.1 [3]

s

2 30.71 ±0.07 54 . 506±0 .01

2

[2]

SSF ( — 2±7

)

ssf 2 -71 ±5 69 . 96 ±1 .0 AH f calculated

S from [ 3 ] from [3],

FSSF -6 8 ±5 70 . 26±0 . 02 AHf calculated

S from [ 3 ] from [3],

sfsf

3 -158±6 79 . 8±1 .2 AHf calculated

S from [11]

from [11],

S

2 f6

( -270±1 5

)

s

2 f8

( — 375±1 5

)

s

2 f

9

( — 408±8

)

S

2 F 1 Q -482±6 94 . 9±2 .0 AH f from [21 ]

,

S from [2]

0 59.554±0 .024 38 . 468±0 .005 [2]

FO 26 ±1 0 51 .77±0 .

3

[5]

fo 2 3-0±5 61 .9 [5]

FpO 5 . 86±0 . 38 59-12 ±0 .

1

[5]

OS 1 .2±.3 53-020±0 .01 [2]

OSF (-45±7) (62±2)

osf 2 (-1

1

3±8

)

66.69 ±0 .

1

S from [4]

osf

3 (-1 49 ±

1

0

)

(72±2)

osf

3 osf 4

(-1 36±8) ( 72 ±2 )

( — 2 2 3 ± 1 1 ) 74.726 S from [17]

osf

5

( “237 ±4 ) (70±2)

OpSF p -181 . 3±2 67 . 76±0 .

1

[4]

0pSFs

(

2 3 2 ±4 ) H 52 . 1 03±0 .001 27 • 392±0 . 004 [2]

HF -65.1 4±0.

2

41 .508 [5]

sf

3 (oh)

sf 4 (oh)

(

1 89±8 ) (-21 6±5 )

a All values in parentheses are estimated

120
A highlight of the past year was the holding of the International

Conference on Chemical Kinetics at NBS on June 17-19. This meeting,

organized by the Director of the Data Center, was designed to bring

together a cross section of leading kineticists involved in theoretical

and experimental aspects of gas and condensed phase chemistry of neutral

and ionic species. The meeting was attended by 192 scientists from the

United States, Europe, Canada, South America, Asia and Australia. Funding

for the meeting was obtained from AFOSR, EPA, GRI, NASA, NSF and NBS. The

meeting was highly successful as indicated by the quality of invited and

contributed presentations and the vigor of the discussion periods. It

also illustrated in a very convincing fashion the inseparability of theory

and experiment which has a direct bearing on the evaluation of chemical

kinetic data. A selection of papers from the meeting will be published in

a special issue of the Journal of Physical Chemistry .

C. Ion Kinetics and Energetics Data Center

(S. G. Lias and R. D. Levin)

The goals of the Data Center are to collect and maintain an up-to-date file of experimental data pertaining to the thermochemistry of

ions (ionization potentials, appearance potentials, and equilibrium

constants) 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.

The Data Center is closely associated with the Ion Kinetics Group

which, as described in Section 4., can supply benchmark measurements

of ion thermochemical quantities to aid in data evaluation activities.

(1) Publications during past year:

"Evaluated Gas Phase Basicities and Proton Affinities of

Molecules; Heats of Formation of Protonated Molecules" Sharon G.

Lias, Joel F. Liebman, and Rhoda D. Levin, Journal of Physical

and Chemical Reference Data 13, 695-808 (1984).

This comprehensive review of the field of gas phase proton affinity

measurements included evaluated gas basicities and proton affinities for

784 atomic and molecular species, and an annotated bibliography of

references on gas phase proton affinity determinations. To date, more

than 150 reprints have been sent to requesting laboratories worldwide. An

up-date, including references to 28 relevant papers which appeared since

the compilation went to press, was prepared and distributed with the

requested reprints.

"Absolute Values of Gas Phase Proton Affinities and Basicities

of Molecules: A Comparison Between Theory and Experiment," D.

A. Dixon and S. G. Lias, Molecular Struc ture and Energetics (J.

F. Liebman and A. Greenberg, editors) Verlag: Florida (in

press )

.

121
This invited book chapter grew out of collaborative contacts between

the Data Center and Dr. David A. Dixon of the E. I. DuPont de Nemours

Company. Dr. Dixon carried out a comprehensive evaluation of theoretical

determinations of proton affinities as a result of discussions with Data

Center personnel during the preparation of the compilation on the same

subject. This publication is a preliminary presentation of a larger work

on the evaluation of theoretical proton affinity data.

(2) In preparation:

"Ion Thermochemistry" by S. G. Lias, J. E. Bartmess, J. F. Liebman, J. L. Holmes, and R. D. Levin.

This comprehensive and complete compilation of evaluated heats of

formation of more than 3000 positive and negative ions, to be submitted

for publication in the Journal of Physical and Chemical Reference Data , is

currently being up-dated to include data which have appeared in the

literature since our earlier publication of data archives covering the

years 1971-1981 (R. D. Levin and S. G. Lias, "Ionization Potential and

Appearance Potential Measurements, 1971-1981 "). As a result of this

effort, the publication will be nearly up-to-date at the time of

publication. Most of the recent data have been abstracted; current work

involves entering the new data into the computer and obtaining the

auxiliary thermochemical information and drawings needed for the

publication. The data for the years before 1981 have been evaluated,

entered into the computer data base designed for the project, and computer

printouts of that material have already been exhaustively checked and

proof-read

.

The list of authors of this forthcoming publication includes several

outside collaborators , who bring specialized expertise to the project.

Dr. J. E. Bartmess of the University of Tennesee is an expert on the

thermochemistry of anions, a field in which he has published extensively.

Dr. J. L. Holmes of the University of Ottawa is one of the foremost

leaders in measurements of appearance potentials of ions, and derivation

of thermochemical and structural information on ions from mass spectrometric data; his collaboration on the project was sought after it was learned that he had collected and evaluated a vast archive of data on organic ions containing oxygen and nitrogen for the use of himself and his

students. Dr. Joel F. Liebman of University of Maryland, Baltimore County

is a theoretical organic chemist specializing in bonding theory and the

estimation of thermochemical data; as an integral part of this project, he

has collected a vast archive of heats of formation of organic and

inorganic compounds from the experimental literature, and has estimated

more than a thousand additional heats of formation.

122
3. KINETICS OF NEUTRAL SPECIES

R. Billmers, W. Braun, R. L. Brown, A. Fahr , L. L. Griffith,

J. W. Hudgens, M. J. Kurylo, A. Lauf er , M. Manka, G. Z. Mallard,

R. I. Martinez, P. Ouellette, D. Robaugh , M. D. Scheer , S. E. Stein,

W. Tsang, and J. A. Walker

A. Introduction

This program is concerned with the mechanisms and rates of chemical

transformations at the elementary single step level. We determine

reaction mechanisms, measure rate constants, develop measurement methods

and test theoretical formulations. The activities of the group span all

three phases and include processes involving single atoms as well as large

organic moieties. The concentration on elementary processes leads to a special focus on free radical reactions. Accordingly, we develop methods

for the detection of free radicals and we are concerned with the processes

that lead to their generation and destruction We also study their

reactions with each other, as well as with stable substrates. A

considerable amount of the group's activities is concentrated on the

kinetics of reactants in thermal equilibrium. At the same time our activities include the study of unimolecular kinetics in the fall-off

region and intermolecular energy transfer involving large polyatomic

species. In order to extend the range of our measurements, we are particularly interested in the development and testing of predictive

theory

.

The programmatic aim of the group's activities is the understanding

of chemical change at the elementary single step level. This

"understanding" is made more meaningful by the possibility of using such

data as inputs for computer simulation and all the attendant possibilities

of its use as a substitute for expensive and uncertain physical testing.

With the revolutionary advances in computer technology, there is little

question that this line of research will continue to grow. Programs in

this group are designed to assure the proper exploitation of this emerging

technology by making available the best available input data. Currently,

we are focusing on the areas of stratospheric and high temperature

chemistry. Members of this group interact closely with internal and

external efforts aimed at developing the best possible data base for such

efforts. Indeed, much of the data evaluation effort has been carried out

by group members.

The large amount of other agency support obtained by members of this

group, together with other signs of scientific vigor such as a substantially

larger number of publications per person, makes it clear that the group has

had a very successful year. Finally, we would like to call attention to

the retirement of two of the senior members of this group; James A.

Walker, after Ml years service and Milton D. Scheer with 31 years of

service. We are fortunate in being able to retain their services as contractors and thereby continue to benefit from their many years of

experience

.

123
In the following sections we describe in detail the activities of the

group during the past year. They are divided into studies in the gas

phase (B) and the condensed phase (C).

B. Gas Phase Kinetics.

(A. Fahr , M. J. Kurylo, A. Laufer, G. Mallard, R. I. Martinez,

P. Ouellette, D. Robaugh, S.E. Stein, W. Tsang, J.A. Walker)

1 . Stability and Reactivity of Large Polyatomic Species

This activity is a central part of our competence program,

"Transf ormation of Complex Organics." It seeks to develop a detailed

understanding of the stability and reactivity of large polyatomic

molecules. As a result, the emphasis of the work is on the understanding of mechanisms and the measurement of thermal rate constants.

We are particularly concerned with aromatic systems. The stability

of such systems make them the inevitable end products in hydrocarbon

transformations under high energy conditions. As such they are of

major concern in technological problems such as soot formation and

hazardous waste disposal. Much of the current work is concerned with

pyrolytic reactions. In the future we will be increasingly

concerned with oxidative processes.

(a) Very Low Pressure Pyrolysis Experiments: Phenyl

Radical Reactions With Ethene and Acetylene at High

Temperatures

(G. Mallard, A. Fahr and S. E. Stein)

Phenyl radicals are thought to be important intermediates

in high temperature reactions leading to polycyclic aromatic hydrocarbons.

These radicals and related species have been postulated as intermediates

in benzene polymerization mechanisms and appear to play a role in thermal

reactions of polycyclic aromatic hydrocarbons. They are also likely to be

central in the mechanism for soot production in rich flames. While a large body of data exists for liquid phase reactions, most is at room temperature, and the specific reactions of importance in high temperature

systems have not been studied.

The important reactions, from the point of view of the build up of

polycyclic aromatic hydrocarbons from simple fuel molecules, are the

addition of phenyl radicals to unsaturated bonds. The pyrolysis of any

alkane leads to large quantities of ethene and acetylene at high

temperatures. The reaction of phenyl radicals with these species is thus

likely to dominate the chemistry of molecular build-up beyond the phenyl

radical. The addition to ethene and acetylene, two major species in

pyrolytic reactions, to produce styrene and phenylacetylene are expected

to be critical steps. Rate constants for these steps were measured using

the techniques of very low pressure pyrolysis adapted to the study of

bimolecular reactions.

124
The rate constants for H-atom displacement resulting from phenyl

radical addition to ethene and acetylene were measured relative to the

rate constant for phenyl radical recombination. The ratios found were:

kadd// ( k rec) 10 3-46±.55 (m_1 s

_ 1

) 1/2 at 1066K for C 2 h2 and

103.44±.18 (m-1

s

- 1 ) 1/2 at 1028K for C

2 h4 .

Assuming that the recombination rate constant for phenyl radicals is the same as that for a number of large hydrocarbon radicals ( 10^*5 M^s- *

1 ),

the addition rate constants are found to be

This work was partly supported by NASA.

We are now in the process of studying reactions of phenyl radicals

with benzene and diacetylene, two processes that can directly generate

polyaromatic species.

(b) Single Pulse Shock Tube Studies: Stability of

Nitroaromati cs and the Hydrogen Atom Induced Decomposition

of Toluene and Phenol

(W. Tsang and D. Robaugh)

Our heated single pulse shock tube has been used in studies

of the thermal and chemical stability of aromatic compounds. The

compounds of interest are the nitro- aromatics in the first area (with the

support of the Army Research Office) and the hydrogen-atom-induced

decomposition of toluene and phenol in the latter. We have made a number

of interesting new observations and laid the basis (supported by DoE) for

future research.

In last year’s report we described our initial experiments with

nitrobenzene decomposition. The experimental results are consistent with

a dual thermal decomposition mode; C-N bond cleavage and isomerization to

form the nitrite prior to N-0 bond cleavage. The prime mode for

decomposition of ortho- ni trotoluene , studied this year, is clearly not

through these two processes. On the other hand para-nitrotoluene behaved

like nitrobenzene. Our evidence for this conclusion is the failure in the

decomposition of the ortho compound to recover more than 4 0 % of the

expected yields of toluene and ortho cresol, while for nitrobenzene and

para-nitroltoluene mass balance was obtained. Considerable effort was devoted to deducing the nature of this new process with as yet very little

success. There are a number of processes which we know do not occur;

for example, H0N0 elimination or isomerization and decomposition to form

the alcohol. We are coming to the conclusion that this new pathway does

not involve removal of the nitrogen from the ring. Currently, we are carrying out experiments to check this hypothesis. It is interesting that

in the earlier studies of Fields and Myerson using a flow system, [J. Org.

Ch em . , 33, 4487, 1968] ortho-ni trotoluene also displayed pathological

C 2 H2 at 1066K

C

2

Hi| at 1028K.

125
behavior since it was much less stable than other nitroaromatics and its

decomposition led to large yields of aniline. They attributed this to a surface process. Since surface reactions cannot occur in a shock tube, it

appears that there is a complex molecular rearrangement is occurring in

ortho nitrotoluene decomposition. In the course of carrying out this work

we have also determined the rate of C-N02 bond cleavage for the two

nitrotoluene compounds. For the three nitroaromatic compounds the

relative rates are 3:1 *5:1 for ortho- nitrotoluene: nitrobenzene: paranitrotoluene , respectively. The effect of methyl substitution is, as expected, rather small. This is in contrast to similar experiments at SRI

using laser heating via energy transfer through SFg, where ratios of the

order of 60:10:1 were obtained. This may be due to the extreme

inhomogeneity, both in space and time, of the laser experiments.

Until this year, all our single pulse shock tube work has

concentrated on unimolecular reactions. We have now taken the first steps

toward extending this methodology towards the study of high temperature

bimolecular processes. The first reactions that have been studied are:

H + Toluene —> Benzyl + H

2 H + Toluene —> Benzene + CH^.

These are important reactions in high temperature aromatic chemistry and

accurate determination is made difficult by the two reaction channels.

Our approach has been to use hexamethylethane as the hydrogen atom source

through the reactions,

Hexamethylethane —> 2 t-butyl • t - butyl • —> isobutene + H

In sufficiently large excesses of toluene (>100 to 1) every isobutene

formed releases a hydrogen atom into the system. The ratio of

(isobutene-benzene )/benzene is a direct measure of the relative rate

constant for abstraction and displacement. If we now add into the system

large quantities of methane, the decrease in benzene yield is directly

relateable to the hydrogen abstraction from methane. Since the rate

constant for this process is well established we can then place these

results on an absolute basis. The rate expressions at 950-1 100K for the

two processes are,

k(di splacement ) = 9.0x10^ exp(-2240/T) M

-1

s -1

k (abstraction ) = l.lxlO’ 1 exp(~3900/T) M

- ^s- ^

The abstraction must be exclusively from the benzylic position (the

maximum rate for hydrogen abstraction from the benzene ring is estimated

to be a factor of 30 slower). The activation energy for abstraction

demonstrates that only half of the benzyl resonance energy contributes

toward lowering the reaction barrier. For the displacement reaction the

results indicate that hydrogen addition is little affected by methyl

substitution. A paper on this work has been completed and will be

submitted to the Journal of Physical Chemistry

.

126
With the partial support of the Department of Energy , are now using this

method to study hydrogen atom attack on phenol. Equally exciting is the

prospect of obtaining an entire series of high accuracy relative rate

constants between various pairs of reactants. Thus, as we determined the

rate constants for hydrogen attack on toluene from studies in the presence

of methane, then the addition of ethane in the presence of traces of

he xamethyl ethane in toluene will permit us to determine the rate constant

of hydrogen attack on ethane from ethylene yields as referenced against

the rate for attack on toluene. We believe that we can measure these

relative rates with an accuracy of a f ew percent. It should therefore be

possible to make drastic improvements in the accuracy of kinetic data

obtained at high temperatures

.

(c) Data Evaluation: Stability of the Cyclohexadi enyl Radical

(W. Tsang)

Our interest in the reactions of hydrogen atoms with

unsaturated organics have led to an investigation of the stability of

cyclohexadienyl radicals. Nicovich and Ravishankara (J. Phy

s

. Chem . , 88,

2534, 1984) have recently reported the rate expression

k(C

6 H

? + CgHg + H) = 1.5 x 10 16 exp (-32000/RT ) /

s

This large A-factor is characteristic of bond breaking reactions to form

two radicals and is different from what has been derived for alkyl

radicals decomposing to alkene + H. We have reanalyzed the experimental

data on the basis of a third law approach (i.e., using an estimated value

for the entropy of the cyclohexadienyl radical) . We first demonstrate

that the high A-factor in combination with the well established rate

expression for the reverse process implies an intrinsic entropy for

cyclohexadienyl radical that is much smaller than that for benzene. This

is an unlikely possibility. Assumption of a more reasonable frequency

assignment for cyclohexadienyl using as a basis the assignments for

benzene, 1,4 cyclohexadiene and cyclohexene leads to a new value for the

entropy of cyclohexadienyl. When this is combined with the measured

equilibrium constant (from k

f /kr

= Keq ) at the midpoint of the

experimental determinations, a new heat of formation for cyclohexadienyl

is calculated. Combination of the new thermochemistry with the rate

expression for the reverse addition process leads to

k(C

6 H

? + C

6 H6 + H) = 1.5x10 13 exp (-28000 /RT )/

s

The A-factor on a per hydrogen atom basis is, within experimental

uncertainty, the same as that which we calculated previously for the

decomposition of alkyl radicals, even though the structure of the

molecules are rather different. It demonstrates the localized nature of

the structure of the transition state and the applicability of

group-additivity. In the coming year we intend to apply the same

procedures for analysis of OH radical attack on unsaturated compounds.

127
(d) Oxidation Chemistry

(R.I. Martinez)

The general objective of this program is to elucidate the

specific rates and mechanisms of oxidation reactions involving 0 , 02 , and

0

3

. The research has primarily been focused on the kinetics and

energetics of dioxymethylenes (R'R"C00*) and their isomers. These are the

likely agents responsible for the complex chemistry observed in ozone-alkene

reaction systems, among the most important of all classes of atmospheric

oxidation reactions.

Our observations on the reaction of ozone with Me 2 C=CMe2 were consistent with the following:

O

3 + Me 2 C=CMe2

> Me2 C00* + Me2 C0 (1)

Me2 C00- > Me 2 C0 + 0 (2a)

> {H 2 C=C(Me)00H} > MeC(C)-CH2 0H (2b)

> OH + H

2 C=C(Me)0* (2c)

The occurrence of reaction (2a) provides additional support for our unifying postulate that dioxymethylenes serve as intermediates connecting

three reaction systems:

R ' R"C : + 0

2

( carbene+02

)

0

3 1

Olefins

R ' R"C00

I

products

> R ’ R"C0 + 0

<— (0 + oxoalkane)

Further analysis of the data is in progress.

2. Chemical Dynamics of the Reactions of Small Free Radicals

(A. Fahr, M. J. Kurylo, A. Laufer and P. Ouellete)

The kinetic behavior of small reactive intermediates is crucial

to the understanding of complex chemical transformat ions . Such

information also provides crucial tests of theory. The work in our laboratory during the current year has concentrated on the H 0

2 and

vinylidene radicals. The former is a ubiquitous intermediate in all

oxidative systems. Its self reaction represents a type of complex

elementary tranformation which is a challenge to chemical theory. The

vinylidene radical was discovered at NBS. It is of particular importance

in photolytic systems involving unsaturated organics and as the simplest

128
unsaturated carbene; experimental data on its properties should provide

crucial tests of theory and improve our understanding of more complex

carbenes

.

(a) Reactions Involving Hydroperoxy Radicals

(M. J. Kurylo and P. Ouellete)

This program employs spectroscopic techniques for the

detection and chemical characterization of small gas-phase free radicals.

The reactive behavior of these species has many applications, for example,

stratospheric ozone depletion, hazardous waste incineration, combustion,

and planetary atmospheres.

During the past year, we have focused attention on the measurement of

the rates of reactions involving the hydroperoxy free radical (H02

) . This

species is an important chemical intermediate in both combustion and

atmospheric chemistry and its reactions are characterized by complex

pressure effects. With the partial support of the NASA Upper Atmospheric

Research Program, we have used flash photolysis, kinetic absorption

spectroscopy to study the reactions

00 tc 0 + HO2

+ M * H2 O2

+ O2

+ M (1)

ho2

+ no2+ M + H02 N02

+ M (2)

with M = 0

2 and N 2

. Our results for reaction (1) support the body of

recent laboratory data which indicates the existence of both a bimolecular

and pressure dependent component for k-j . A statistical analysis of the

combined N

2

+ O2 data base permits calculation of a rate constant expression suitable for use in atmospheric modeling. Our experience in the

mathematical analysis of second order decay curves gained in this investigation indicates a high potential for systematic error in such fitting. A

manuscript giving full details about the experiments and the data

reduction has been accepted for publication in the Journal of Physical

Chemistry

.

Experimental conditions suitable for the measurment of k

2 are far

more restrictive than those employed in the study of reaction (1). For

example, contributions to the HOp loss by reaction (1) must be minimized

and any residual effects accounted for. Corrections, however, can be made

utilizing a knowledge of the initial concentration of hydroperoxy radical.

Other interferences due to reaction (3)

H02

+ NO + OH + N02 (3)

can be minimized by restricting the amount of NO formed via N02 photolysis

through use of appropriate flash lamp filtering. The pressure'

dependencies observed for both N

2 and 0

2 can be described by fitting the

data to the formula recommended by Troe and coworkers,

k(M) = + k o>M [M]/kco)}0.6 1/a

1 29
where a - 1 + {log(k 0 ^[M]/ka,)}. Using this analysis there appears to be a slight systematic difference between our results and those of another

recent laboratory investigation. While this difference at 298K is

certainly within the quoted uncertainty limits of both studies, future

experiments should shed more light on its significance. A second

manuscript scheduled to appear in the Journal of Chemical Physics presents

a more detailed discussion of these experiments.

During the forthcoming year, we plan to extend our investigation of

reaction (2) to lower temperature thereby gaining information regarding

the temperature dependence of k2 in the fall-off region. Such information

allows one to calculate much needed thermodynamic parameters for

peroxynitric acid (HO2NO2). In addition, information on the temperature

dependence of k2, particularly in the low pressure region of the fall-off

curve, is of critical importance in assessing the role of this reaction in

stratospheric chemistry.

We intend to continue our investigation of the kinetics of small

oxygen-containing free radicals by initiating measurements on the cross- disproportionation reaction between H02 and CH3O2. During our early work

on the HC>2 self- reaction we were able to calculate, via computer modeling,

the optimal experimental conditions for this investigation. This reaction

is important both in the atmospheric oxidation of methane and other

hydrocarbons and in low temperature combustion systems. From a theoretical standpoint, such results should lend themselves to thorough

analysis in view of the rather good data bases existing for the relevant

self- reactions , HC>2 + HO2 and CH3O2 + CH3O2. Experiments are planned in

which both the HO2 and will be monitored by absorption spectroscopy.

However due to the large differences in the self reaction rates of the two

radicals, such dual measurement will not be possible for all sets of

initial concentrations.

During the past year, we have collaborated with members of the Center

for Analytical Chemistry in designing and fabricating an apparatus for H02 detection by infrared diode laser spectroscopy (including second harmonic

detection). To date, an apparatus has been partially constructed and most

of the needed equipment procured. The diode laser spectrometer is

expected to be available for our extended use this fall. In addition to

focussing on the sensitivity of the infrared detection, we intend to make

measurements on pressure broadening coefficients and the effect of water

solvation on the measured line strengths. Hopefully, this collaboration

will pave the way for future joint projects.
(b) Reactions of Biradicals and Unsaturated Free Radicals

(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 proceses.

Our recent efforts, supported by the NASA Planetary Atmospheres

Program, are directed towards understanding the mechanism of

formation and the chemistry of the vinylidene unsaturated biradical

(H2 CC). This species, the smallest of a large class of unsaturated

biradicals, was initially identified by us on the basis of its

characteri Stic absorption in the vacuum ultraviolet. We have

determined that the particular state of vinylidene under observation is

the lowest lying excited triplet, about 1.7 eV (40kcal/mol) above the

ground singlet state. The particular excited state is metastable with

respect to the ground singlet state as there is a 45 kcal/mol barrier to

its isomerization to acetylene. The intermediate is quite stable requiring

about 10^ collisions to quench.

We have identified triplet vinylidene as an intermediate in the

combination of triplet methylene, and in the photolysis of C

2 H2 , C2H4, and

C

2 H^C 1 . During the past year we have completed a study of the photolysis

of vinyl chloride. The photodecomposition may proceed by several paths:

c

2 h

3 ci — -> H2 c = c ( 3 B2 ) + HC1 (1)

C

2 H2

+ HC1 (2) —> C

2 H

3

+ ul ( P

3 /2 , 1/2

( 3 )

Aside from C

2 H

3 radicals, all decomposition products are readily

discernable from their well-characterized VUV absorption features;

reaction 1 is differentiable from reaction 2 by the temporal profile of

C

2 H2 production even in the presence of the isomerization of H 2 C=C. There

was no evidence for Cl atom production and reaction 3 represents a minor

process in the photodecomposition.

We found the time history of both H

2 C=C( 3 B2

) and HC1 to be identical

which indicates they are both formed by a single process. HC1 , a non- transient product, was determined directly from its absorption at 129 nm

.

At short times, following the incident flash, prior to any significant

coll isionally induced isomerization of the triplet H

2 C=C, the

concentrations of HC1 and H

2 C=C are equal. As a result we have been able

to derive the extinction coefficient for the 134 nm transition in

H

2 C=C( 3 B

2

) = 694 ± 218 cm

-1

atm base e.

131
While the direct observation of vinylidene is of great scientific

interest, the importance of the radical in hydrocarbon chemistry remains

unknown. The determination of the extinction coefficient permits a direct

determination of the quantum yield for triplet vinylidene formation in the

photolysis of C2H2 and C2H4. In fact, H2C=C(^B2) formation represents

major processes in both systems with quantum yields equal to 0.4 and 0.75,

respectively. The photolysis of hydrocarbons control the atmospheres of

the outer planets. Recognition of the important role of H2C=C(^B2)

formation in these processes will have profound effects on models for

these atmospheres.

We are in the process of determining quantitative quenching

parameters of H2C=C(^B2) by A r, N2, H2, CO, and CH4. In an earlier study

it was shown that He quenched the deuterated vinylidene (D2C=C) about 5.5

times slower than the protonated moiety. In the present work we have

utilized that observation to increase the lifetime of the absorbing

species and obtain rate data with greater precision and accuracy over longer times than if H2C=C were the reactive fragment.

The rate constants are the sum of all removal processes, including

chemical interactions. In the case of H

2 and CH4 we were unable to

observe chemical reaction by end-product analysis, i.e., products derived

from C2H3 or CH^ radicals, respectively. The observation agrees with our earlier bond-strength-bond-length theoretical prediction of slow abstraction rate constants. For N2, there was no spectral evidence for HCN

production. Overall rate constants, for the above species, are of the

_ 1 C O _ 1 _ 1 order 10 D cm-1 molecule *s

In the coming year we will continue to investigate excited triplet

vinylidene chemistry. We will search for other sources of the fragment

and such chemical processes uniquely associated with excited triplet

vinylidene. The flash photolysis-kinetic spectroscopy apparatus utilizes

spectral detection technology that is out of date. We will upgrade the

instrumentation with improved detection capability using array detectors.

These offer the ability to record a large number of spectral elements

which maintains the advantage inherent in plate technology, with

photomultiplier sensitivity and speed without loss of spectral resolution.

3 . Methods Development

(W. Braun, M. Hoffbauer, J. W. Hudgens, M. D. Scheer)

New technological developments offer many opportunities for the

characterization of reactive systems and the generation of novel

environments. The thrusts of our work involve the detection of reactive

intermediates through multiphoton ionization and tandem mass spectrometry

and the use of laser heating to study energy exchange effects. In each

cases, a foundation has been laid for exciting future advances.
(a) Multiphoton Ionization Detection of Free Radicals

(J. W. Hudgens, M. Hoffbauer)

Resonance enhanced multiphoton ionization (REMPI) is a new method which probes the spectroscopy and dynamic properties of molecules.

REMPI is a more universal detection method than laser excited fluorescence

(LEF) since it does not require fluorescence from the probed species. As

a result, REMPI will greatly expand the number of different chemical

species that can be detected with lasers. Our efforts have concentrated

upon free radical detection because the most important reactions in

processes such as combustion, catalysis, and reactive etching involve free

radicals. This work has been partially supported by the Army.

Multiphoton ionization works by subjecting molecules to intense

visible or ultraviolet laser light that causes them to absorb photons

until they ionize. Usually the first step features a simultaneous

absorption of two or more photons which promotes the molecules into an excited electronic state. Then, the excited state molecule absorbs an additional photon and ionizes. Since ions are easy to detect, the

technique is very sensitive.

During the past year the first phase of a laboratory for the

detection of transient species was constructed. A significant effort was also expended designing future experimental apparatus. In addition to

these activities, this year's research efforts produced manuscripts

describing REMPI detection of benzyl radicals and SiF radicals.

Our experiments on benzyl radicals yielded the first successful REMPI

detection of an aromatic free radical. Detection of aromatic free

radicals using REMPI spectroscopy is an important goal since improved

aromatic radical detection methods will allow studies that enable a better

understanding of the reaction mechanisms important in the combustion of

aromatic fuels.

In our experiments, benzyl radicals were generated in a flow reactor

by reacting fluorine or chlorine atoms with toluene. The radicals effused

into a mass spectrometer ion source where they were ionized by laser light

tuned between 490-520 nm (Figure 1). The laser generated molecular ions were analyzed and detected by the mass spectrometer. The nature of the

electronic state which facilitated the resonance enhancement was not

ascertained, but resonance enhancement of the multiphoton ionization

cross-section originated either from two photon resonances involving a Rydberg state, from two photon preparation of the 3

2 B

2 state, or from

three photon preparation of a Rydberg state associated with the second

ionization potential. Future work will resolve this issue. Nevertheless,

the detection sensitivity for benzyl radicals appears sufficient for use

in kinetic experiments.

Silicon monofluoride, SiF, is a radical product from reactive etching

of silicon surfaces. Its detection is of interest to the semiconductor

industry. This year we studied its spectroscopy and reported two REMPI

133
LRSER WAVELENGTH (nm)

Fig. 1. The m/z 91 (Benzyl cation) signal observed from the flow reactor

effluent as a function of dye laser wavelength (nm) between

490-525 nm for the reactions: a) F + toluene and b) Cl + toluene.

detection schemes. In both schemes SiF was ionized by absorption of three

photons at wavelengths between 430-492 nm. One scheme involved two photon

resonance enhancement from the C' n. TI., bands. The second scheme used

sequential one-photon steps between (0,0) A A

2

£

+

(1 ,0) C" transitions. 2

Z

+ 2

I

+

-n

1 / 2 and

The works cited above are typical experiments used for the

development of the REMPI radical detection data base. By generating a catalog of REMPI detectable species we can use selective and sensitive

laser techniques to study problems which involve these radicals. We note

that over the past year our earlier work on CH^ and CH 2 0H REMPI

spectroscopy has enabled studies at other laboratories of hydrocarbon

pyrolysis (Exxon), flame processes (NBS) , photolysis (Yale, Cornell), and

surface chemistry (Naval Research Laboratory). We believe the work

described here will provide a similar stimulus.

1 34
This coming year phase two of the apparatus construction program

will be largely completed. A paper describing the spectroscopy of CH2

f,

CH and CF radicals observed during the reaction of F + Ketene will be

published and more detailed assignments of the resonant states of CH 2 OH

radicals will also be submitted. Laboratory work will target the

generating reactions and spectroscopy of phenyl, vinoxy and vinyl

radicals. Laser strategies used to selectively ionize these species may

include two frequency MPI, production of doubly charged ions, and laser

induced charge exchange schemes.

(b) Laser Heating

(W. Braun and M. D. Scheer)

Two separate projects have been pursued over the past year.

These involved the further development of a high temperature furnace to

study high temperature reaction kinetics and the development of a method

to directly measure v-v and v-r, t energy transfer involving high energy

species

.

Many reaction processes either do not occur at low temperature or proceed so slowly that they cannot be conveniently measured. Two

important cases are unimolecular bond scission and rearrangement reactions

that require energies that exceed 50 kcal/mole. Historically, these

reactions have been investigated either in conventional furnaces or in

shock tubes employing chromatographic end-product detection. If a furnace

can be designed such that high temperatures can be achieved for short

residence times, then real-time measurements on stable products or reactive intermediates can isolate individual reaction steps and eliminate

complicating and obscuring secondary reactions. Two papers have been

published that have shown the feasibility of using a continuous wave IR

laser heated reactor for mechanistic and activation energy studies. The

first paper, "The Application of a New High Temperature Reactor to

Unimolecular Decompositions" by M. D. Scheer, W. Braun, and J. R. McNesby

describes the heating of fused silica by the absorption of laser infrared

radiation as the basis for the design of a short residence time-high

temperature reactor. When the laser is focused on the exit orifice of a silica flow tube a dilute mixture of a reactant gas in helium is exposed

to the high orifice temperature for only about 2x10

-^s. During such short

time intervals, secondary decompositions tend to be reduced. This heating

method was applied to the multichannel decomposition of cyclobutanone

.

The formation of propylene by the secondary isomerization of cyclopropane

was suppressed sufficiently and most of what was formed was shown to come

directly from the cyclobutanone in a high activation energy dissociation

channel

.

"A New Comparative Method for the Determination of Activation

Energies", by W. Braun and M. D. Scheer describes the use of the thermal

radiation emitted by the surface of a rapid flow reactor as a reference

standard in a new comparative method for determining chemical activation

energies. The surface temperature, its thermal radiation, and the

products formed in a reactive gas flowing through the reactor are all

135
modulated by the periodic on-off switching of a C02 laser that heats the

reactor surface to incandescence. The activation energy may then be

obtained from the energy of the thermal photons selected for observation

and a comparison of the temperature dependence of the rate of product

formation with that of the spectral radiance of the reactor surface at the

chosen wavelength.

The direct energy transfer measurement consists of exciting

vibrational energy in a molecule such as SFg, siFy or hexaf luorobenzene

.

Using a translational energy monitor one can detect the energy flow from

SFg(v) to SFgCr.t). Similarly using an internal (v) energy monitor such

as toluene one can measure SFg(v) + Tol(v’) —> SFgCv’ 1 ) + TolCv'*’). By

setting up suitable microscopic phenomenological energy transfer

mechanisms (equations) one can relate microscopic energy transfer

parameters to macroscopic energy flow measurements. This in turn, will

allow one to further distinguish the relative importance of v-v vs. v-r,t-v T processes. A publication describing the experimental method and

the theory is presently in preparation.

(c ) MS/MS Tandem Mass Spectrometry

(R.I. Martinez)

The focus of this study is the development of an analytical

methodology to monitor directly in real-time, selected reactive polyatomic

species in complex reacting mixtures. It is supported by the Air Force.

The work will involve structural characterization of any component in a reaction mixture via MS/MS tandem mass spectrometry subsequent to the

species-specific ionization of each component by " soft" 2-color

multiphoton ionization (one wavelength used for up-pumping; a second

wavelength used for ionization near threshold).

During the past year the specially-designed, modular MS/MS system has

undergone extensive testing of all system and subsystem components

(hardware and software). The breakdown of several critical components

caused significant delays, and has necessitated extensive repairs and

modification of the system hardware and software. Nonetheless, we were

able to demonstrate the feasibility of coupling laser ionization to the

MS/MS. Using tunable wavelengths between 277 nm (4.48 eV/photon) and 300

nm (4.13 eV/photon) to photoionize NH, ( IP =10.16 ev), we observed

NH2

+ (IP-11.4 eV; AP[NH^]=15.7 eV) and NH+ (IP-13.1 eV ; AP[NH

3 ]-17. 1 eV).

Moreover , the characterization of critical MS/MS control parameters to

date supports the theoretical basis for the original design criteria, and

suggests minimal f ringing-field effects throughout the MS/MS. Relative to

this, we installed variable rf-amplitude controllers for each quadrupole to

allow independent control of the rf- amplitudes. This enables us to test

theoretical concepts of acceptance/emittance through the tandem

quadru poles

.

136
Work in FY86 will involve the measurement of CID breakdown curves for

selected compounds, and development of 2-color MPI schemes for the same. These will be used in the study of oxidation reactions in flow reactors to

be coupled to the MS/MS.

C. Condensed Phase Kinetics

(R. L. Brown, R. Chen, L. Griffith, S. E. Stein and

V. Senthilnathan)

This program represents one of the main thrusts of our competence

program. We have found that aromatic condensation reactions, like their

logical reverse reactions, ring-opening and desubstitution, are catalyzed

by H-donors. A simple mechanism has been proposed for the former process

and partly validated by experiment. Our work has also led to the first

reported rate constants for a key hydrogen transfer step in liquid

pyrolysis, transfer of an H-atom from a radical to a molecule. Our

theoretical studies of large graphite-like molecules have systematically

applied reliable organic theories to elucidate edge effects. This work

provides details concerning the dominant role of edge structure in

graphite chemistry discovered last year. Experimental studies are supported by the Gas Research Institute, theoretical studies by AFOSR.

1 . Mechanistic Studies of Aromatic Pyrolysis

(R. Chen, V. Senthilnathan, S. E. Stein)

We are examining reactions in organic fluids at high

temperatures with the aim of finding reaction pathways leading to

polymerization and carbonization. We use this information to develop

predictive theory. Over the past year a series of studies of the

condensation of 1 ,

1

1 -binaphthyl to perylene at 400°-560°C have been

completed. This reaction is catalyzed by hydrogen donors and kinetic

studies suggest the following mechanism,

This finding is counter to general experience in the area of carbonization

chemistry where excess hydrogen leads to ring breakup. Rate parameters

derived from these studies promise to provide a new means for obtaining

free radical thermochemistry. We intend to determine the precise mechanism

and rate limiting steps for several related condensation reactions next year.

2. Elementary Kinetic Studies of Polyaromatic Species in Solution

(R. L. Brown, L. Griffith, S. E. Stein)

These experiments are designed to yield rate constants and

thermodynamics of elementary chemical reactions involving polyaromatic

molecules and free radicals. Reactions are studied when they have been

137
identified as key processes in the thermal chemistry of aromatic

substances and their rate constants are not available or reliably

estimable. We have investigated the transfer of hydrogen from

9, 1 O-dihydrophenanthrene to anthracene,

Kinetic studies at 350°C along with thermochemical kinetic analysis and

computer modeling of results were used to derive the following mechanism

and rate constants:

1/ forward Lr reverse

• • M

-

*

1 s

-1

M

-1

s"

1

An + PhH2 - oco % 3.2x10”® 3. OxlO9

AnH PhH

^

AnH2

+ An

- 2AnH 7.8x10" 4

1 .7x10®

AnH + PhH 2

-

«- AnH2

+ PhH 1 .OxlO 2 3.4x10 3

PhH + An - Ph + AnH 2.9x10 3

Especially noteworthy is reaction an exothermic chain propagation step

transferring a 8~H atom from a radical to a molecule. It had been

proposed but never unambiguously observed thermal chemistry prior to this

work

.

In other studies of H-transfer, we determined the rate of a similar,

but thermoneutral reaction,

Assuming an A-factor of 10°*') M~ s~ we obtain an activation energy of 18

kcal mol

-1

for the reaction. This high value is consistent with the lack

of prior kinetic data for these reactions; they are simply too slow to

compete with other paths in most chemical systems. They are effective in our reaction systems because of the high concentrations of reactants and

the lack of facile alternative pathways.

138
and 1 -naphthyl radicals ( @oj ) in high temperature fluids. Preliminary

studies indicate that aryl aldehydes are very effective sources of such

radicals. A mixture of bibenzyl (R-R, a radical initiator), toluene (RH,

a radical trap) and an aldehyde has been found has been found to provide

an excellent means of generating these radicals at 300-400°C via the

following mechanism,

R-R t 2R

ArCHO + R- -*• ArCO + RH

ArCO -»• Ar* + CO

Ar* + RH * ArH + R.

3. ESR Detection of Aromatic Radicals at High Temperatures

(R. L. Brown, M. Manka and S. E. Stein)

These experiments used our unique high temperature flow ESR

instrument to investigate reactions of species large enough for steric

effects to measurably influence their rates. Our goal is to separate the

effects of steric and electronic factors on reaction rates to permit the

development of more reliable predictive theory for large chemical species.

We have determined concentrations of diphenylmethyl radicals (D)

in equilibrium with their dimer, 1, 1

1

, 2, 2 -tetraphenylethane (DD)

between 648 and 683K. Using previously measured rates for dissociation of

DD we derived a rate constant for D recombination of 1.5x10^ M

-1 s-1

at

648K. This is markedly slower (a factor of ca. 6) than benzyl radical

recombination under similar conditions, indicating a steric impediment to

D recombination. An analysis of this data also indicates that the rate of

DD dissociation was accelerated by a factor of ten by release of strain.

This work provides unique quantative data for species just large enough

for strain to exert a measurable but not overwhelming influence on rates.

4. Graphite Properties

(R. L. Brown and S. E. Stein)

In continuation of our work on the properties of very large

polybenzenoid hydrocarbons, we have made a detailed study of the

predictions which Huckel molecular orbital (HMO) theory makes for these

molecules. HMO calculations yield orbital energies and wave functions for

their pi-electrons. We have examined energy level densities, bond orders

,

electron distributions, free valence (a reactivity index), and resonance

energies. Over thirty years ago, Coulson and Taylor [ Proc . Phys . Soc . A65 , 815 (1952)] applied HMO theory to graphite considered as an infinite,

planar polybenzenoid molecule. They calculated the pi-electron energy

per carbon, the density of states in the pi-electron band, and the pi-band

order. We have been able to compare our calculations of these properties

139
for large finite-sized molecules with their limiting values. As in our previous work, four series of molecules, each with a different edge

structure was considered.

The density of pi-states as a function of energy is shown in Figure 2 for a very large molecule having 281 4 carbons and a phenanthrene type

edge. The smooth curve shows the graphite limit calculated by Coulson and

Taylor

.

The orders of the bonds in the center of these molecules is given in

Figure 3 as a function of molecular size (N

c

= number of carbons). They

clearly extrapolate to the graphite limit in each of the different series.

Hess and Schaad [J. Amer . Chem . Soc . 94 , 3068 (1972)] have proposed a definition of resonance energy as the difference between the Huckel

pi-electron energy and that of a particular reference structure which they

define. Figure 4 shows the resonance energies per carbon for each of

these series as a function of molecular size. They all extrapolate to the

graphite limit although the series containing an anthracene type edges

(series 1) experiences a deep minimum in resonance energy at about 400

carbons.

In graphite, the energy of the highest occupied molecular orbital

(HOMO) is at the energy zero. For all of the series, the energies of the

HOMO'S extrapolate to zero. However, as shown in Figure 5, the rate of

approach to this limit varies widely. Molecules with phenanthrene type

edges (series 3) have HOMO levels which are particularly slow to approach

zero. Since the pi-electrons in these top levels are the ones must likely

to be involved in chemical reactions, this suggests the molecules having

edges of the phenanthrene type would be relatively non-reactive until they

reached a very large size.

These differences between the HOMO'S of the different series are also quite evident in their pi-electron distributions. In the more reactive anthracene edge series, electrons in this top level are concentrated around the molecular perimeter while in the phenanthrene edge

series these electrons are distributed more uniformly over the whole

molecule. In the anthrecene edge type, this concentration of electron

density at the edge is not restricted to the top level only but extends

downward some seven or so levels.

In the coming year we plan to consider strain and steric effects

associated with edges and imperfections. Working models for chemical

reactions of graphitic molecules will be devised.
Number

of

Levels/Energy

Interval

Fig. 2. Density of HMO orbital energy levels as a function of energy for

molecule with 28lU carbons and a phenanthrene edge type. The

smooth curve shows the graphite limit.

lUl
Bond

Orders

of

Central

Bonds

0. 540]

0. 535—

Series 1: *

Ser i es 2: +

Series 3:

Series 4: O

O 9

0. 530 —

0. 525—.

+

rj.tr

J I L 1—1 l J L i J—I—

L

i J—J—

L

J—

I

0. 02 0. 04 0. 06 0. OG

N

~1/2

0. 10

Fig. 3. Bond orders of bonds in centers of molecules in different

homologous series as a function of molecular size. Dotted line

shows graphite limit.
Resonance

Energy/E

1

ectron

Fig. U. Resonance energies per carbon as a function of molecular si

Dotted line shows graphite limit.
Fig. 5- Energy of highest occupied molecular orbital as a function

of molecular size.

lUU
4. ION KINETICS

R. E. Huie, R. D. Levin, S. G. Lias, M. Mautner, P. Neta, I, Price

L. W. Sieck, Z. B. Alfassi , N. Altstein, A. Harriman, Z. Karpas

S. Mosseri, J. Rabani and M.-C. Richoux

A. Introduction

The scientific emphasis and focus of the work of the Ion Kinetics

Group is derived largely from the competence-building program, "Kinetic

Studies of the Effects of Ionizing Radiation". The Ion Kinetics Group was organized in 1979 under the direction of Dr. P. Ausloos to fulfill the

requirements of this Competence. Originally called the Ionizing Radiation

Group and assigned to the Chemical Thermodynamics Division, the nucleus of

the group was transferred in 1983 to the Chemical Kinetics Division where

the work on the kinetics of ionic processes became a natural complement to

the existing programs on the kinetics of neutral species. The

pre-existing Chemical Kinetics Division program on Aqueous Chemical

Kinetics was incorporated as an integral part of the Liquid Phase Ion

Kinetics activities. 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 to 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 long range goal of our program "Kinetic Studies of the

Effects of Ionizing Radiation" is to obtain experimental and theoretical

results which contribute to the understanding of the response of matter to

ionizing radiation in sufficient detail for application to radiation

biology, radiation dosimetry and radiation processing.

The approach to the study of radiation effects involves diverse

experimental tasks which examine individual facets of the problem area in

detail. These individual tasks are summarized below:

Kinetics of the Interactions between Ions and Molecules

Fundamental investigations of the chemistry of ions, including

elucidation of reaction rates, mechanisms and thermochemistry

.

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.

145
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 SO^

-

, SO5

-

, and HSO5

-

.

Ion Kinetics and Energetics Data Center

The maintainance of an up-to-date evaluated data base relating

to the thermochemistry of ionization processes and the kinetics

of ionic reactions, and the publication of related

compilations

.

The description of the scientific activities of the Group which

follows will be organized under headings corresponding to the various

activities listed above, although an arbitrary subdivision has been made

between Gas Phase Ion Kinetics and Liquid Phase Ion Kinetics. Data Center

activities are discussed in Section 2.

B. Gas Phase Ion Kinetcs

The program aims at achieving a fundamental understanding of the

unimolecular and bimolecular reactions of ionic species generated by high

energy radiation, and further, at examining the effects of ion-molecule

clustering, i.e., of solvation. Aspects of the program currently

supported by the Department of Energy and the Air Force Office of Scientific Research give particular emphasis to examinations of processes

involving small organic molecules, while experimental work tied in to the

Liquid Phase Ion Kinetics effort (described below) focuses on model

compounds which give information about processes in biochemical systems.

1 . Kinetics of Ion-Molecule Reactions: Thermochemical Kinetics of

Ions (S. G. Lias, M. Mautner, L. W. Sieck and Z. Karpas, in

collaboration with P. Ausloos and T. J. Buckley)

Irradiation at energies above the ionization threshold produces

positive ions which may undergo rapid ion-molecule reactions. This task

involves the elucidation of the bimolecular chemistry of such ions,

including an examination of reaction mechanisms, and measurements of rate

constants and equilibrium constants as a function of temperature. The

latter experiments lead to quantitative information about the

thermochemi stry of proton transfer, charge transfer, and other ionic

reactions. Much of the work ties in directly with the work of the Ion

Kinetics and Energetics Data Center. Accomplishments of the past year are discussed below.
(a) In connection with an extensive evaluation of heats of

formation of ions and of proton affinities of molecules being carried out

this year in the Ion Kinetics and Energetics Data Center, a large number

of proton affinity determinations have been accomplished (through

equilibrium constant determinations or ’’bracketing" experiments) using the

ion cyclotron resonance spectrometer. Species studied include selenium

and tellurium compounds, and isocyanates, thiocyanates, and

isothiocyanates. In a study of proton transfer from halogenated methyl

ions, the first internally-consi stent reliable heats of formation of the

carbenes CF2 , CCI 2 . CFC1, CFH, and CC1H were established.

(b) In exothermic charge transfer reactions of organic ions

with organic molecules the possibility that a collision will be reactive

is usually close to unity. However, charge transfer reactions in

hydrazines have been shown to proceed with efficiencies as low as 0.001 to

0.1. In these reactions, the components undergo large geometry changes

and it appears that these changes lead to significant barriers to reaction,

which become smaller when the reaction is highly exothermic.

Correspondingly, the rate constants increase with exothermici ty . Steric

effects are also observed in that cyclic reactants react faster than

acyclic reactants.

(c) Several studies mapping mechanistic details of ion-molecule

reactions have been completed. It was, for instance, demonstrated that in

the reaction of alkyl ions, RH

+

, with alkylamines, (AH)NH9 , the branching

ratio of the two competing channels,

RH

+ + (AH)NH2

-* (AH)NH

3

+ + R (proton transfer)

RH

+

+ (AH)NH2

-> (RH) ( AH) NH2

+ * (condensation)

remains constant from pressures of 10

-

^ torr to -1 torr, a result which

reflects the probabilities for different alkyl ion-amine configurations in

the ion-molecule collision process. At low pressures it was demonstrated

that the excited condensation ion, (RH)(AH)NH2

+

, dissociates by cleavage

of the weaker of the two N-C bonds to form an alkyl ion-amine complex,

followed by proton transfer _in the complex and dissociation:

(RH)(AH)NH2

+ + [ ( AH+

)

• (RH)NH2

] > [(A) • (RH)NH

3

+ + A + (RH)NH

3

+

In another investigation, it was shown that the reaction of the

parent radical cations of halogen substituted alkanes with the respective

parent molecules to form dialkyl halonium ions:

RX

+

+ RX + RXR

+

+ X

147
proceed through a classical Sj,j 2 mechanism in which the halogen atom in the

product ion originates entirely from the reactant neutral molecule.

Earlier literature results had suggested that in the gas phase, the

reaction proceeded through formation of a complex in which the halogen

atoms were statistically distributed to the products.

(d) In a project sponsored by the Air Force Office of

Scientific Research, the rates and mechanisms of consecutive ion-molecule

reactions in styrene and phenylacetylene have been studied. A

comprehensive examination of the structures and reaction kinetics of

ions is also being completed; it is found that structural assignments made

in previous studies in the literature are in error. The photochemical

dissociation mechanisms of the product condensation ions formed in most of

these systems are currently being investigated using an argon ion laser as well as a xenon arc lamp fitted with interference filters as light

sources

.

2. Solvation Thermodynamics and the Kinetics of Solvated Ions

(M . Mautner, L. W. Sieck)

Ionic species such as those generated in acidic or basic

environmetns 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 environemnt. 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 prediction of 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 H9 o, for example) to determine the

thermochemisry of solvation by an examination of equilibria such as:

A

+

+ M -*• (A

+ -M)

(A

+ *M) + M -> (A+ *M 2

) , etc.

and to study the kinetics and mechanisms of reactions of the solvated

ions

.

Work has been carried out during the past year on the following

problems:

(a) Studies of ionic charge transfer complexes: Ionic states

of aromatic molecules, such as benzene, substituted benzenes, or aniline

and its derivatives are important in the radiation chemistry and

electrochemistry of these compounds as well as in the conductivities of

organic semiconductors. In these phenomena, the positively charged

1 48
radical ions interact with neutral molecules. The interaction can involve

resonance charge transfer , i.e., stabilization of the complex by the

resonance forms

[

B

+

• B] O [ B*

B

+

]

To understand the energetic effects of charge resonance, a study was conducted in collaboration with S. E. -Shall of Georgetown University of

the complexes of the aniline radical cation with aniline derivatives and

with aromatic hydrocarbons, as well as with other polar molecules. These

studies were also complemented by Extended Hiickel Molecular Orbital

calculations. The results lead to the following conclusions: (1) Charge

transfer (CT) resonance is most effective in complexes for which the

ionization potentials of the components are equal. In these cases, charge

transfer contributes 4-6 kcal/mol to the total binding energies of 1 6 - 20 kcal/mol of the complexes. (2) Charge transfer resonance is similar

whether or not the charge on the components is delocalized or partially

localized. (3) The most stable conformations of the complexes have

parallel- plane sandwich type geometries. (4) With highly polar

substituents such as -CN or -NO2 , the complexes rearrange to a linear

geometry which is bonded by electrostatic interactions.

(b) In environments under irradiation, including planetary

atmospheres, carbonium ions such as CH^* or more complex species, such as

t— CjjHg

+ can associate with electron pair donors such as H 2 O and HCN.

These interactions could lead to covalently bonded protonated alcohols

and nitriles:

R

+

+ H

2 0 + R0H2

+

, R

+ + HCN RCNH

+

However, the observed thermochemistry of some of the reactions, especially

the entropy changes, indicates that the products are in some cases not

covalent condensation products, but hydrogen- bonded complexes.

R

+

+ H

2 0 -> [R

+

• H

2 0], R

+

+ HCN + [R

+

• HCN]

Both thermochemical arguments and collisional dissociation spectroscopy

were used to show that the reactions result in the formation of the

hydrogen bonded complexes. This may be important in planetary chemistry,

since cluster formation will be an alternative route to the synthesis of

higher molecular weight products by condensation.

(c) In acidic environments, amines and oxygen compounds are protonated to form the ions, BH

+

. These species are important in a range

of phenomena from organic synthesis to enzyme reactions. The properties

of these ions in water are strongly affected by solvation. To understand

the details of ion solvation, data on ion clustering, which involves the

first solvent shell, were analyzed. The results showed that enthalpies of

hydration can be predicted from the thermochemistry of gas-phase

ion-molecule clustering events. Further, it is possible to use the

clustering data to analyze individual components of the heats of solvation

149
of ions, hydrogen bonding and bulk solvation terms (that is, cavity

forming and dielectric charging terms). These terms show reasonable

variation with the proton affinities and with the size of alkyl

substituents of the ions.

(d) The stabilities of N 0

2 ”-X and CgF^NC^

- ** association ions,

where X was a dipolar protic or aprotic organic solvent, were investigated

by pulsed high pressure mass spectrometry . By comparison, analogous

measurements were made with Cl” for certain model systems. Equilibrium

constants were determined as a function of temperature in order to define

AH and AS values for solvation. Solvation energies were found to vary as N02

- >Cl”>CgH5N02

- for ligands having -OH sites. Association entropies were

found to be constant at -27±2 for cluster ions incorporating N02 “ or CgHc;!^

- and protic ligands, but vary significantly when Cl” is the core

ion. For aprotic ligands, such as X = CH3CN, CH3NO2, (CH3) CO, etc., the

values of AH° and AS° for both N 0

2 ”*X and CgH^J^

- ^ were also found to

exhibit large variations. Predictive correlations of AH° as a function of

gas phase acidity were developed. Differences in the various cluster

stabilities are explicable in terms of the dipole accessibility of X. For

example, the depressed AH° values for CH3CN and CH3NO2 can be interpreted

in terms of the blocking effects of the methyl groups, which shield the

group having most of the dipole moment of the ligand (-C+N, etc.). These

measurements represent the first quantitative data ever gathered for gas

phase association reactions involving complex anions and complex organic

molecules

.

(e) Another study funded by the Dept, of Energy involved

association reactions of SF^” with H2O, low molecular weight alcohols, and

DMSO. AH§ values were found to be quite low, ranging from 10.0 kcal/mol

for SFg-'t-C^HgOH. As with NO?

-

, etc., the binding energies increase with

the acid strength of the ligand. The hydrogen bond strengths are 3 kcal/mol lower than those found for with common ligands, and

essentially identical to, or slightly higher than, those reported

elsewhere for clustering by I”. Association reactions with simple

carboxylic acids could not be investigated due to very efficient F”

transfer reactions yielding F” (Acid)- type ions. An "effective" ionic

radius of - 2.1 A was deduced for SFg

-

. These results provide a new insight into electrical breakdown mechanisms in SFg under conditions where

it is used as a high pressure insulating gas.

C. Liquid Phase Ion Kinetics

1 . Radiation Chemistry of Organic and Biochemical Solutions

(P. Neta, M.-C. Richoux, A. Harriman, M. Mautner, Z. B. Alf assi

,

S. Mosseri, and J. Rabani

)

150
Pulse radiolytic techniques are used to characterize the chemical

properties of short-lived species in irradiated solutions. Particular

attention is given to reactions of reactive transients which have been

implicated as intermediates in radiation- induced and thermal processes 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

of 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 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 the 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 product hydrogen (a fuel) and oxygen by sunlight

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 for oxygen

production. 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. With this approach, a tedious search for

oxygen product under different conditions was unnecesary. After

optimization of the kinetic factors by pulse radiolysis, it was found that

the optimal kinetic conditions also gave the highest oxygen yield.

Last year’s experiments with several zinc porphyrins showed that

although all the porphyrins examined had sufficiently high oxidation

potentials so that their radical cations could oxidize water to oxygen,

their efficiencies were determined to a large extent by the lifetime of

the cations, i.e. kinetic parameters were more important than

thermodynamics. Therefore, a search for porphyrins with longer-lived

radical cations was continued. It was found that at high pH, zinc

p-tetrahydroxyphenylporphyrin formed a very long-lived radical cation, but

that reaction with the RuC^ catalyst for water oxidation was inefficient

because the redox potential of this porphyrin at high pH was too low. An

examination of the oxidation of magnesium tetrasulfonatophenyporphyrin

(MgTPPS) showed the formation of a stable radical cation which was able to

oxidize water to oxygen on RuC^ catalyst only at very high pH values.

Another approach to the problem is to utilize metalloporphyrins in which

the metal is oxidized rather than the ligand. Experiments with

Pbll-porphyrins indicated two stage oxidation to the radical cation and

151
then to the PblV- porphyrin. The latter product was unstable over long

times and its decay was hardly affected by the presence of the Ru0 2

catalyst, i.e. it was not found suitable for efficient oxidation of water.

Preliminary experiments with Mnl I

I -porphyrins showed that the

MnIV-porphyrins produced upon oxidation decay in a pH dependent process

and their decay was accelerated by the addition of Ru02

. The pH profile

of the reaction with the catalyst and oxygen production is currently under

study.

Since the probability of reaction with the catalyst is found to be

greatly dependent on the lifetime of the porphyrin radicals, a systematic

examination of the parameters that affect the lifetimes was initiated. A

study of various metalloporphyrin radical anions indicated dependence of

the lifetime on the electronegativity of the metal, which affects also the

reduction potential of the porphyrin. This was rationalized on the basis

of electron-wi thdrawing by the metal center from the porphyrin ligand

radical anion, which inhibits protonation of this anion in water. The rate

and extent of protonation was found to affect the decay very strongly. A

systematic study on porphyrin radical cations has been initiated.

After completion of the study on the stability of radical cations and

the catalyzed decay of MgTPPS.+ and of the MnIV-porphyrins, the basic

redox chemistry of other metalloporphyrins will be examined, and the

possibility of utilizing them in the photodecomposition of water will be

explored. To further improve the efficiency of reaction of porphyrin

radical cations with catalysts, micelles and polyelectrolytes will be

utilized to extend the lifetimes of the radical cations.

With relation to the use of polyelectrolytes in solar energy

conversion systems, the possibility of using radiation to bind ruthenium

trisbipyridyl covalently to several polyelectrolytes has been explored. It was found that if OH radicals are allowed to react partially with the

Ru(bpy)3 and partially with the polyelectrolyte, the two types of radicals

react to a large extent to form new covalent bonds. The irradiated

polyelectrolyte was indeed found to have the complex bound to it.

(b) The toxicity of halogenated alkanes (such as carbon

tetrachlori de and the anaesthetic agent halothane, CF^CHClBr) is believed

to originate from cytochrome-Pi^g-mediated generation of peroxyl radicals

with subsequent attack on biological targets, especially unsaturated

lipids. The feasibility of this proposed mechanism was demonstrated last

year in this laboratory in a pulse radiolytic study of the reactions of

peroxyl radicals with iron porphyrins and with fatty acids using

Fe^^-deuteroporphyrin as a model for cytochrome P 45 Q. Peroxyl radicals

derived from the halogenated hydrocarbons were found to oxidize the ferric

porphyrin by an electron transfer mechanism to product a Fe^^-porphyrin

pi-radical cation. In the continued investigation of this problem area,

the reaction of peroxyl radicals derived from methanol and isopropanol

with Felll-porphyrins was found from kinetic studies to involve the

formation of an intermediate complex which decomposes to final products in

acid-dependent and acid-independent processes. This may suggest that all

152
reactions of peroxyl radicals with porphyrins involve an intermediate

complex. To further understand the behavior of peroxyl radicals, a kinetic study of their reactions with other porphyrins in a variety of

solvents, and with other organic reactants has been initiated.

(c) A focus of the on-going program of study of intramolecular

electron transfer processes is the investigation of temperature effects on such processes. Studies were carried out on ni troaromatic halides in

which electron attachment on the nitro group is followed by electron

transfer through the molecule leading to halide loss. Earlier work had

demonstrated that the rate of the intramolecular electron transfer depends

on the respective geometries of the nitro and halide functions in the

molecule. Since the dependence of the rate constants on molecular

geometry is governed by energy barriers and entropies of activation, a physical understanding of structural effects can be achieved only if both

of these factors are known, i.e. if the rate constants are known as a function of temperature. Using the temperature-controlled pulse

radiolysis cell, a series of reactions were examined. The results show

that both the energy barriers and the entropies of activation vary

significantly from reaction to reaction. Some specific structural trends

emerge, such as the decrease of reaction probabilities when steric factors

interfere with optimal orientation of the substituents for electron

transfer

.

Other intramolecular interactions examined were those in dimeric

viologens. A series of compounds was synthesized having two identical

violgen groups separated by organic bridges of varying degree of

flexibility. Chemical or radiolytic reduction results in formation of the

viologen radicals which undergo di sproportionation to form the doubly

reduced viologen. In this species, both viologen units are reduced to the

radical and there is a distinct stabilization effect if the molecule can form an intramolecular cofacial dimer. The mono radical could be

stabilized by intramolecular association with the unreduced viologen.

This is achieved by fairly slow conformational rearrangement and it is in

competition with bimolecular electron transfer to the preferred

conformation. All the mono radicals disproportionate and the bimolecular

rate constants have been measured. This study will be extended to mixed

viologen dimers in order to examine the possibility of intramolecular

electron transfer. Similar experiments are planned also with dimeric

porphyrins and mixed porphyrin-viologen dimers. The purpose of this work

is to achieve an understanding of similar natural processes, occuring for

example during photosynthesis, with the hope of synthesizing a model that

will mimic the natural process effectively.

(d) 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

equilibrium constants in the pulse radiolysis of liquids was studied using

the temperature-controlled pulse radiolysis cell. Preliminary results show

that the major differences between molecular electron affinities are due

to enthalpy effects, but in large molecules entropy effects are also

153
significant. This is of interest to biological systems relate! to the

action of quinone containing co-enzymes, which are large molecules and

which participate in biological electron transfer processes.

2. Kinetics and Radiation Chemistry of Aqueous Inorganic Solutions

(R. E. Huie and P. Neta in collaboration with P. A. Ouellette)

The current experimental work in aqueous phase chemical kinetics

is an outgrowth of an effort to understand the mechanism for formation of

acid rain, with particular emphasis on the chemistry of the key

intermediates SO^

-

, SO^

-

, and peroxymonosulfate , HSO^

-

. Work in this

problem area is now being supported by a contract with the EPA. Under

this contract, several free radical reactions involved in the aqueousphase oxidation of (IV) are to be investigated along with reactions of no

3

.

In this work, pulse radiolysis is used as a technique to selectively

generate reactive intermediate species of interest. Stopped flow and

kinetic spectrophotometry experiments are performed to obtain

complementary information on aqueous kinetics.

(a) During the past year, the initial thrust of the

experimental effort to establish the basic reactivity of the radicals SO^

- and SO^

- was completed with the study of the reactions of these radicals

with a series of phenolic compounds. The mutual effect of hydroquinone

and sulfite on each other’s autoxidation has been known for a century. It was apparent very early that this was due to interference with the free

radical chain reactions involved in autoxidation. In order to understand

better the mechanism of the autoxidation of sulfite solutions and the

chemical effects associated with this phenomenon, the rates of the

reactions of SO^

- and S0^~ with hydroquinone and other hydroxyphenols , and

of sulfite with some phenolyl radicals, were determined. The rate

constants for the oxidation of hydroxyphenols by SO^

- were small in

neutral solution, but increased dramatically in basic solution as the

hydroxyphenol was deprotonated . The S0^~ radical reacts with most

hydroxyphenols at moderate rates in neutral solution. Phenoxyl radicals

with high redox potentials (phenol, resorcinol, and chloroglucinol ) were

found to oxidize sulfite in neutral solution.

(b) Few quantitative data exist on the electron transfer

reactions of the radicals N0? , C10 2

, and peroxy radicals, although these

species are of considerable importance in many field of chemistry.

Systematic studies aimed at determining these rate constants have been

initiated. Rate constants for the oxidation of C102

~ an N02

_ by several

organic and inorganic free radicals along with rate constants for several

reactions of C102

, N02, and BrOo have been determined. Also, equilibrium

constants have been determined for the reactions of C102 with aniline at

pH 6.9 and N,N-dimethylaniline at pH 9.6, leading to redox potentials at

these pH's of 1.03 V and 0.87 V for the aromatic amines. From the rate

constants for the reactions of C102 and N02 with f errocyanide , a ratio of

self-exchange rates for these radicals was derived which is consistent

154
with that derived from the rate constants for the oxidation of CIC^

- and

NO?

- by several substi tution- inert transition metal complexes. From the

rate constants for the reactions of these radicals with several organic

compounds, a substantially different value was derived, due to a much

higher apparent self-exchange rate for the NO2 /NO2

- couple.

(c) The NO? radical may be of considerable importance as a radical initiator in the aqueous chemistry of the atmosphere. A study of

the chemistry of this species has been made using the pulse radiolysis of 6

M nitric acid to generate the radical. The rate constants for the

reactions of NO^ with several organic and inorganic reactants have been

determined. It is seen that NO^ is a strong oxidant with a one-electron

oxidation potential greater than 2 V.

(d) The reactions of ferrous ions with peroxymonosulf ate have

been studied using the stopped-flow method using both excess ferrous and

excess peroxymonosulf ate . In both cases, the reaction did not show simple

second-order behavior. At low concentrations, the first-order rate

constant increased noramlly with the concentration of the reagent in excess. As the concentration of this reagent increased further, however,

the first-order rate constant approached a plateau, suggesting that the

reaction involves the initial formation of a complex which dissociates to

the ferric product (and a free radical which rapidly oxidizes a second

ferrous ion). The formation of the complex is the rate-limiting step at

low concentration, while its dissociation is rate-limiting at high

concentration. These data are presently being analyzed in collaboration

with Dr. N. C. Peterson of the Polytechnic Institute of N.Y. to extract

the rate constants for the individual steps.

155
5. PUBLICATIONS

(a) Publications of Past Year

Baral, S., Hambright, P., Harriman, A. and Neta, P., "Radiolytic Studies

of the Redox Reactions and Alkylation of Rhodium Tetrakis

(4-Sulfonatophenyl) Porphyrin in Aqueous Solution", J. Phys. Chem.

,

89, 2037 (1985).

Baral, S., Neta, P. and Hambright, P., "Spectrophotometr ic and Kinetic

Studies of the Radiolytic Reduction of Several Pyr idylporphyrins and

their Metal Complexes", Radiat. Phys. Chem., 24., 245 (1984).

Baulch, D. L., Cox, R. A., Hampson, R. F. , Kerr, J. A., Troe, J. and

Watson, R. T., "Evaluated Kinetic and Photochemical Data for

Atmospheric Chemistry: Supplement II", CODATA Task Group on Chemical

Kinetics, J. Phys. Chem. Ref. Data, _1_3_ (#4), 1259-1 380 (1 984).

Billmers, R., Griffith, L. L. and Stein, S. E., "Hydrogen Transfer Between

Anthracene Molecules", ACS Fuel Div. Preprints, .30.(4), 283 (1 985)

Braun, W. and Scheer, M. D. , "A New Comparative Method for the

Determination of Activation Energies", Chem. Phys. Letters, 118 , 229

(1985)

.

Brown, R. L., "Modeling of Axially Symmetric Flow Reactors", Computers and

Chemistry, 8., 139 (1984).

Buckley, T. J., Sieck, L. W. , Metz, R., Lias, S. G. and Liebman, J. F.,

"Consecutive Ion-Molecule Condensation Reactions and Photodissociation Mechanisms of Condensation Ions in Polyacetylenic Compounds",

Int. J. Mass Spectrom. Ion Phys., 65_,

1 8 1 (1 985).

Carlson, B. W. , Miller, L. L. , Neta, P. and Grodkowski, "Oxidation of NADH

Involving Rate-Limiting One-Electron Transfer", J. Am. Chem. Soc.

,

106, 7233 (1984).

Christensen, P. A., Harriman, A., Porter, G. and Neta, P.,

"Metalloporphyr in and Photochemical Study of the Oxidation of Water

by Zinc Porphyrin tr- Radical Cations", J. Chem. Soc. Faraday Trans. 2,

80, 1451 (1984).

DeMore, W. 3., Golden, D. M. , Hampson, R. F., Howard, C. J., Kurylo,

M. J., Margitan, J. J., Molina, M. J., Ravishankara , A. R. and

Watson, R. T., "Chemical Kinetics and Photochemical Data for Use in

Stratospheric Modeling, "Evaluation No. 7 of the NASA Panel for Data

Evaluation, JPL Publication 85~37, Jet Propulsion Laboratory,

Pasadena, CA, July, 1985.

Duignan, M. T. and Hudgens, J. W. , "Multiphoton

CIO and BrO Radicals", J. Chem. Phys., 82,

Ionization Spectroscopy of

4426 (1985).

Dulcey, C. S. and Hudgens, J. W. , "Detection of

Multiphoton Ionization Spectroscopy", 118,

SiF Radicals by

444 (1985).
Fahr, and Laufer, A. H. f "Photodissociation of Vinyl Chloride: Formation and Kinetics of Vinylidene-H2 cc( 3 B

2

) " , J. Phys. Chem. , 89, 2906

(1985).

Fahr, A. and Laufer, A H., "Extinction Coefficient of H

2 cc(^B2 ) at 137

nm" , J. Chem. Phys., _83_, 908 (1985).

Greenberg, A., Stein, S. E. and Brown, R. L., "Relative Thermochemical

Stabilities and Reactivities of Benzo[a]pyrene and Selected Isomers",

The Science of the Total Environment, _40, 219 (1984).

Grodkowski, J. , Jr., Chambers, J. H. and Neta, P., "Kinetics of Electron

Transfer from Cobalt ( II )-Porphyr ins to Various Metalloporphyr in

TT-Radical Cations in Irradiated Carbon Tetrachloride Solutions", J.

Phys. Chem., 88, 5332 (1984).

Grodkowski, J., Neta, P., Schlesener, C. J. and Kochi, J. K. , "Rates and

Mechanisms of Reduction of Trisphenanthroline-Fe( III ) by Various

Radicals. Effect of Solvent", J. Phys. Chem., j89_, 4373 (1 985).

Gupta, R. P., Larroquette, C. A., Agrawal, K. C., Grodkowski, J. and Neta,

P., "Potential Radiosensitizing Agents. 7. (4(5)-iodo-5(4)-Nitroimidazole Derivatives", J. Med. Chem., _28, 987 (1985).

Harriman, A., Christensen, P. A., Neta, P. and Richoux, M. C.,

"Metalloporphyr in Photosensitized Oxidation of Water", Sci. Papers

Inst. Phys. Chem. Res. (Japan) _78, 1 43 (1984).

Hudgens, J. W. and Dulcey, C. S., "Observation of the 3s 2 A Rydberg States

of Allyl and 2-Methylallyl Radicals with Multiphoton Ionization

Spectroscopy" , J. Phys. Chem., _89_, 1505 (1985).

Huie, R. E. and Neta, P., "The Chemical Behavior of SO^

- and S0^~ Radicals

in Aqueous Solutions", J. Phys. Chem., _88_, 5665 ( 1 984).

Huie, R. E. and Neta, P., "Reaction of the Vanadate Ion with Chlorpromazine and the Chlorpromazine Free Radical with Vanadyl Ion", Inorg.,

Chem., Acta., 93, L27 (1984).

Huie, R. E. and Neta, P., "Oxidation of Ascorbate and a Tocopherol

Analogue by the Sulfite Derived Radicals SO?

- and SO^

-

", Chem. Biol.

Interactions, _53, 233 (1985).

Huie, R. E. and Neta, P., "One-Electron Redox Reactions in Aqueous

Solutions of Sulfite with Hydroquinone and other Hydroxyphenols"

,

J. Phys. Chem., 89, 3918 (1985).

Infante, G. A., Guzman, P., Alvarez, R., Figueroa, A., Correa, J. N.,

Myers, J. A., Lanier, L. J., Williams, T. M. , Burgos, S., Vera, J.

and Neta, P., "Radiosensitization by Derivatives of

Isoindole-4 , 7-dione" , Radiat. Res., _98, 234 (1984).

Laufer, A. H., "Vinylidene (3 b

2 ) - An Active Intermediate in the

Photolysis of Ethylene", J. Photochem. , 27, 267 (1984).

1 57
Lias, S. G. , Liebman, J. F. and Levin, R. D., ’’Evaluated Gas Phase

Basicities and Proton Affinities of Molecules: Heats of Formation of

Protonated Molecules", J. Phys. Chem. Ref. Data, J_3, 695 (1984).

Lias, S. G. , "Thermoneutral Isotope Exchange Reactions in Proton-Bound

Complexes of Water with Organic Molecules: Correlations with

Energetics of Formation of the Corresponding Association Ions", J.

Phys. Chem., 88., 4401 (1984).

Lias, S. G. , Jackson, J.-A.A., Argentar , H. and Liebman, J. F.,

"Substituted N, N-Dialkyl Anilines: Relative Ionization Energies and

Proton Affinities through Determination of Ion-Molecule Reaction

Equilibrium Constants", J. Org. Chem., .50., 333 (1985).

Lias, S. G. and Ausloos, P. J., "Structures of CgHy + Ions Formed in

Unimolecular and Bimolecular Reactions", J. Chem. Phys., _82, 3613

(1985)

.

Meot-Ner (Mautner), M., Nelsen, S. F., Willi, M. F., Frigo, T. B.,

Effects of an Unusually Large Neutral to Radical Ion Geometry Change

Adiabatic Ionization Energies and Proton Affinities of

Alkylhydrazines" , J. Am. Chem. Soc., 106, 7684 (1984).

Meot-Ner (Mautner), M. and Deakyne, C. A., "Unconventional Ionic Hydrogen

Bonds. 1. CH

+ * ,, X. Complexes of Quaternary Ions with n- and

ir-Donors", J. Am. Chem. Soc., 107, 469 (1985).

Meot-Ner (Mautner), M. and Deakyne, C. A., "Unconventional Ionic Hydrogen

Bonds. 2. NH+ •••ir. Complexes of Onium with Olefins and Benzene

Derivatives", J. Am. Chem. Soc. 1 07, 474 (1985).

Meot-Ner (Mautner), M. , Ross, M. M. and Campana, J. E., "Stable Hydrogen

Bonded Isomers of Covalent Ions", J. Am. Chem. Soc., 1 07 , 4835

(1985).

Morehouse, K. M. and Neta, P., "Kinetics of Demetallation of

Manganese( II )-Porphyrins in Aqueous Solutions", J. Phys. Chem., 88 , 3118 (1984).

Neta, P., Dizdaroglu, M. and Simic, M. G. , "Radiolytic Studies of the

Cumyloxyl Radical in Aqueous Solutions", Israel J. Chem., .24., 25

(1984).

Neta, P. and Simic, M. G. , "Free Radical Chemistry of Natural Products",

Proc. IFT Basic Symposium on Chemical Changes in Food Processing, 63

(1984).

Neta, P. and Huie, R. E., "One-Electron Redox Reactions Involving Sulfite

Ions and Aromatic Amines", J. Phys. Chem., .89., 1 783 (1985).

Neta, P. and Harriman, A., "Zinc Porphyrin tt—

R

adical Cations in Aqueous

Solution. Formation, Spectra and Decay Kinetics", J. Chem. Soc.

Faraday Trans. II, 81, 123 (1985).

158
Vita, P., Richoux, M. C. and Harriman, A., "Intramolecular Association of

Covalently-Linked Viologen Radicals", J. Chem. Soc. Faraday Trans.

2, 8j_, 1427 (1985).

Scheer, M. D., "A Kinetic Isotope Effect in the Thermal Dehydration of

Cellobiose", in "Fundamentals of Thermochemical Biomass Conversion",

Elsevier Applied Science Publishers, London and New York, 1985,

pp. 89-95.

Scheer, M. D., Braun, W. and McNesby, J. R., "The Application of a New

High Temperature Reactor to Unimolecular Decomposition", Chem. Phys.

Letters, JM_3 , 407 (1985).

Schwarz, F. P., Okabe, H. and Ausloos, P., "Pulse Radiolysis of

Hexafluorobenzene : Production and Quenching of C^F^+ (B)", Chem. Phys

Lett., 119, 188, (1985).

Schwarz, F. P. and Smith, D., "The Yields of Excited States of Aromatic

Derivatives in the Radiolysis of Hydrocarbon Solutions", Radiat.

Phys. Chem., Vol. 26, No. 3, 257-266, 1985.

Schwarz, F. P., "Positive Charge Transfer in the UV Photolysis and 6 Radiolysis of Trans-Decalin Solutions", Radiat. Phys. Chem., Vol. 2,

No. 3, 401-413, 1985.

Shaub, W. and Tsang, W. , "Overview of Dioxin Formation in Gas and Solid

Phases Under Municipal Incinerator Conditions" in "Chlorinated

Dioxins and Dibenzofurans in the Total Environment" , L. H. Keith, C.

Ruppe and G. Choudhery, ed., Butterworth, London, England, 1985,

p. 469.

Sieck, L. W. and Meot-Ner (Mautner), M. , "Thermal Decomposition of Ions.

1 . Pyrolysis of Protonated Ethers-Activat ion Energies and A Factors"

J. Phys. Chem. 88., 5324 ( 1984).

Sieck, L. W. and Meot-Ner (Mautner), M. , "Thermal Decomposition of Ions.

2. Pyrolysis of Protonated t-Butyl Methylether at the Pressure Limit

Activation Efficiencies for Various Bath Gases", J. Phys. Chem.,

88, 5328 (1984).

Stein, S. E. and Manka, M. , "Disproportionation-Recombination Rate Ratios

of Hydroaromatic Radicals", J. Phys. Chem., _88_, 591 4 ( 1984).

Stein, S. E. , Brown, R. L., Griffith, L. L. and Manka, M. , "Chemical

Fundamentals of Coal Char Formation", ACS Div. Fuel Chem. Preprints,

29(2), 42 (1984).

Stein, S. E., "Free Radicals in Coal Conversion", in "Coal Conversion

Chemistry", R. D. Schlosberg, ed. , Pergamon Press, 1985, pp. 1

3

- 4 4

.

Stein, S. E. and R. L. Brown, "Chemical Theory of Graphite", Carbon, 23 , 105 (1985).

159
Stein, S. E. and Fahr, A., "High Temperature Stabilities of Hydrocarbons”,

J. Phys. Chem., 89, 3714 (1985).

Tsang, W. , "Single Pulse Shock Tube Studies of the Thermal Stability of

Ketones”, Int. J. Chem. Kin., _1_6> 1543, (1984).

Tsang, W. , "The Stability of Alkyl Radicals”, J. Am. Chem. Soc., 107,

2873, (1985).

Tsang, W. and Hampson, R. F., "Chemical Kinetic Data Base for Methane

Combustion”, NBSIR 84-2913, June, 1985

Tsang, W. , Macek, A., Domalski, E., Walker, J. A., Charagundl, S. R.,

Colbert, J. C. , Kirklin, D. R., Ledford, A. E., Dekker, P. H. and

Ryan, R. V., "Combustion Characteristics of Refuse Derived Fuels",

NBSIR, 83-1343, 1985.

Tsang, W. and Walker, J. A., "Chemical Processes During the Starved Air

Incineration of Municipal Solid Waste", NBSIR 84-2938, 1985.

160
(b) Publications in Progress.

^usloos, P. and Lias, S. G. , "On the Mechanism of the Reactions of Alkyl

Ions with Alkylamines: Competing Proton Transfer and Condensation

Reactions", J. Am. Chem. Soc. (in press).

Billmers, R., Griffith, L. L. and Stein, S. E., "Hydrogen Transfer Between

Anthracene Structures", J. Phys. Chem. (in press).

Brault, D. and Neta, P., "Oxidation of Fe^-^-Porphyr ins by Peroxyl

Radicals Derived from 2-Propanol and Methanol - Evidence for Acid

Dependent and Acid Independent Pathways", Chem. Phys. Letters (in

press)

.

Brault, D., Neta, P. and Patterson, L. K. , "The Liquid Peroxidation Model

for Halogenated Hydrocarbon Toxicity. Kinetics of Peroxyl Radical

Processes Involving Fatty Acids and Fe(II)-Porphyrins" , Chem. Biol.

Interact, (in press).

Brown, R. L., "Application of Semi-Empirical SCF-MO Theory to Very Large

Hexagonally Symmetric Benzenoid Polyaromatic Hydrocarbons", NBSIR

( submitted)

.

Christensen, P. A., Harriman, A., Neta, P. and Richoux, M. C.,

"Photooxidation of Water Using Prussian Blue as Catalyst", J. Chem.

Soc. (in press).

Davis, C., Braun, W. , Cvetanovic, R. J. and Tulloch, J., "Studies of

Infrared Laser Heating of Polyatomic Gases by Optical Heterodyne

Techniques", in "Lasers as Reactants and Probes in Chemistry", Howard

University Press, (in press).

Deakyne, C. A., Meot-Ner (Mautner), M. , Campbell, C. L., Hughes, M. G.

,

Murphy, S. P., "The Proton in Multisolvent Clusters. 1. The

Acetonitr ile-Water System", J. Chem. Phys. (in press).

Dixon, D. A. and Lias, S. G. , "Absolute Value of Gas Phase Proton

Affinities and Basicities of Molecules: A Comparison Between Theory

and Experiment", in "Molecular Structure and Energetics", J. F.

Liebman and A. Greenberg, ed. (in press).

El-Shall, M. S. and Meot-Ner (Mautner), M. , "Ionic Charge Transfer

Complexes. 2. Localized Acceptors Delocalized Donors: Complexes of

Aniline with Aromatic Hydrocarbons", J. Am. Chem. Soc. (submitted).

Fahr, A. and Laufer, A. H., "Primary Processes in the Photochemistry of

Simple Hydrocarbons of Planetary Interest", Icarus, (in press).

Frenklach, M. , Clary, D. W. , Gardiner, W. C. and Stein, S. E., "Detailed

Kinetic Modeling of Soot Formation in the Shock Tube Pyrolysis of

Acetylene", Twentieth Symposium (International) on Combustion, Ann

Arbor, MI, 1984, (in press).
Frenklach, M. , Clary, D. W. , Yuan, T., Gardiner, W. C. and Stein, S. E.,

"Shock Tube Pyrolysis of Acetylene: Sensitivity Analysis of the

Reaction Mechanism for Soot Formation", Int. J. Chem. Kinetics (in

press)

.

Herron, J. T., Tsang, W. , Stein, S. E. and Golden, D., "International

Conference on Chemical Kinetics", J. Phys. Chem. (in press).

Hoffbauer, M. A. and Hudgens, J. W. , "Multiphoton Ionization Detection of

Gas Phase Benzyl Radicals", J. Phys. Chem. (in press).

Huie, R. E. and Neta, P., "Kinetics of One-Electron Transfer Reactions

Involving CIO2 and NO 2

" , J. Phys. Chem. (in press).

Huie, R. E., "Chemical Kinetics of Intermediates in the Antoxidation of

SO 2 ", ACS Symposium Series (submitted).

Jackson, W. M. and Okabe, H., "Photodissociation Dynamics of Small

Molecules", Advances in Photochemistry Vol. 1 3 * Wiley, NY, (in

press)

.

Karpas, Z. and Lias, S. G. , "On the Mechanism of the Reactions of Alkyl

Ions with Dialkylhalonium Ions in Alkyl Halides", J. Org. Mass

Spectrom. (submitted).

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. (in press).

Karpas, Z., "The Proton Affinity of H

2 Se, SeCO and H

2 CSe and Reactions of

Positive Ions with H

2 Se", Chem. Phys. Letters (in press).

Karpas, Z. and Jasien, P. G. , "The Proton Affinity Hydro Telluride", Int.

J. Mass Spectrometry and Ion Processes (in press).

Kurylo, M. J., Ouellette, P. A. and Laufer, A. H., "Measurements of the

Pressure Dependence of the HO 2 Radical Self Disproportionation

Reaction 298K" , J. Phys. Chem. (in press).

Kurylo, M. J. and Ouellette, P. A., "The Pressure Dependence of the Rate

Constant for the Reaction H0 2

+ NO 2+ M

* H0 2 N0p + M (M=N 2 * 0 2

) at

298K", J. Phys. Chem. (in press).

Lias, S. G. , Karpas, Z. and Liebman, J. F., "Halomethylenes : Effects of

Halogen Substitution on Absolute Heats of Formation", J. Am. Chem.

Soc. (in press).

Manka, M. J., Brown, R. L. and Stein, S. E., "Flow ESR and Static Studies

of the Decomposition of Phenyl Substituted Ethanes, J. Phys. Chem.

(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. Am. Chem. Soc. (submitted).

162
Meot-Ner (Mautner), M. and Sieck, L. W. , "The Ionic Hydrogen Bond and Ion

Solvation. 4. SH + ***0 and NH+ ***S Bonds. Correlation with Proton

Affinity. Mutual Effects of Weak and Strong Ligands in Mixed

Clusters", J. Phys. Chem. _89_, 1985 (in press).

Meot-Ner (Mautner), M. , "Conventional and Unconventional Ionic Hydrogen

Bonds. Solvation of Protonated Oxygen and Nitrogen Bases", in

"Molecular Structure and Energetics", J. F. Liebman and A. Greenberg,

ed. (in press)

.

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., _89, 1985 (in press).

Mautner, M. , Rumack, D. T. and Nelson, S. F., "Slow Organic Electron

Transfer Reactions", J. Am. Chem. Soc. (submitted).

Meot-Ner (Mautner), M. , Karpas, Z. and Deakyne, C. A., "Ion Chemistry of

Cyanides and Isocyanides. 1. The Carbon Lone Pair as Proton Acceptor:

Proton Affinities of Isocyanides", J. Am. Chem. Soc. (submitted).

Meot-Ner (Mautner), M. and Karpas, Z., "Ion Chemistry of Cyanides and

Isocyanides. 2. Alkilation of HCN and Cyanides by Oxygen and Sulfur

Compounds. Gas-Phase Synthesis and Reactions of Protonated

Isocyanides", J. Phys. Chem. (submitted).

Meot-Ner (Mautner), M. , El-Shall, M. S. and Keoterz, M. , "Ionic Charge

Transfer Complexes. 1 . Partially Localized Acceptors and Donors:

Dimer Cations of Anilines", J. Am. Chem. Soc. (submitted).

Neta, P., "Reactions of Radicals with Biologically Important Molecules",

in "Chemical Kinetics of Small Organic Radicals", the CRC Press Inc.,

Boca Raton, FL (in press).

Neta, P. and Huie, R. E., "Free Radical Chemistry of Sulfite", Environ.

Health Persp. (in press).

Neta, P., Richoux, M. C. and Harriman, A., "One- and Two-Electron

Oxidation of Lead (II) Tetrakis (N-Methylpyr idyl ) Porphyrins in

Aqueous Solution", J. Chem. Soc., Faraday Trans. 2, (in press).

Neta, P., Richoux, M. C., Harriman, A. and Milgrom, L. R., "Resonance

Stabilization of Zinc Porphyrin pi-Radical Cations", J. Chem. Soc.,

Faraday Trans. 2, (in press).

Okabe, H., " Dissociation Energetics of Simple Diazirines by Photon and

Electron Impact in the Chemistry of Diazirines M. T. H. Liu, ed.,

The CRC Press Inc., Boca Raton, FL (in press).

Richoux, M. C., Neta, P., Harriman, A., Baral, S. and Hambright, P., "Oneand Two-Electron Reduction of Metalloporphyr ins . Radiation Chemical,

Photochemical and Electrochemical Studies. Kinetics of the Decay of

ir-Radical Anions", J. Chem. Soc., Faraday Trans. 2 (in press).
Richoux, M. C., Neta, P., Christensen, P. A. and Harriman, A., "Formation

and Decay of Zinc Tetrakis (N-Methyl-3~Pyridyl) Porphine - Radical

Cation in Water", J. Chera. Soc., Faraday Trans. 2 (in press).

Robaugh, D. A. and Stein, S. E., "Stabilities of Highly Stabilized

Radicals", J. Amer. Chem. Soc. (in press).

Robaugh, D. A., Tsang, W. and Fahr , A. and Stein, S. E., "Ethylbenzene

Pyrolysis C-C or C-H Bond Cleavage, Ber . der Bunsen. Gersell. Phys.

Chem. , ( in press)

.

Shaub, W. and Tsang, W. , "Hazardous Waste Aspects of Municipal Solid Waste

Incincerators" , in NBSIR Research in the Character ization of Municipal Solid Waste (in press).

Sieck, L. W. , "Thermochemistry of Solvation of N0

2

~ and CgHN02 ~ by Polar

Molecules in the Vapor Phase. Comparison with Cl

- and Variation with

Ligand Structure", J. Phys. Chem. (in press).

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., 1985 (in press).

Stein, S. E. and Brown, R. L. "Pathways to Graphite: Properties of Very

Large Polybenzoid Hydrocarbons", in "Molecular Structure and

Reactivity", Liebman and Greenberg, ed. , 1985 (in press).

Tsang, W. and Hampson, R. F., "Chemical Kinetics Data Base for Combustion

Modeling", J. Phys. Chem. Ref. Data (submitted).

Tsang, W. , "Stability of Cyclohexadienyl Radical", J. Phys. Chem.

( in press)

.

Tsang, W. , "Thermal Stability of Perf luoromethyl Bromide", J. Phys. Chem.

( in press)

.

Tsang, W. and Shaub, W. , "Tracers for Quality Assurance in Municipal Solid

Waste Incinerator", in NBSIR Research in the Characterization of

Municipal Solid Wastes (in press).

Tsang, W. , Walker, J. A. and Kodres, C. A., "The Character izat ion of

Refuse Derived Fuels Using Thermal Methods of Analyses", in

Energy from Biomass and Wastes IX (in press).

Tsang, W. and Robaugh, D. A., "Single Pulse Shock Tube Studies on the

Stability of Aromatic Compounds" Proceedings of the 15th Int.

Symposium on Shock Waves and Tubes, (in press).

Walker, J. A. and Tsang, W. , "RDF Character ization Using Thermal Method of

Analysis", in NBSIR Research on the Character izat ion of Municipal

Solid Waste (in press).

164
6. TALKS

3rown, R. L., "A Chemical Theory of Graphite", West Virginia University,

Morgantown, WV, April, 1985.

Brown, R. L., "A Chemical Theory of Graphite", Catholic University of

America, Washington, D.C., April, 1985.

Brown, R. L., "A Chemical Theory of Graphite", 17th International Carbon

Conference, Lexington, KY, June, 1985.

Fahr, A., "Rate Constants for Reactions of Phenyl Radicals with

Acetylene, Ethylene and Benzene", 17th International Symposium on

Free Radicals, Granby, CO, August, 1985.

Herron, J. T., "Modeling of Complex Chemical Processes: From Planetary

Atmospheres to Gaseous Dielectrics", Westinghouse Research and

Development Center, Pittsburgh, PA, March, 1985.

Herron, J. T., "The Thermal Decomposition of S

2 f<|q", International

Conference on Chemical Kinetics, NBS, Gaithersburg, MD, June, 1985.

Herron, J. T., "Chemical Processes Following the Dielectric Breakdown of

SF-», Electrosystems Division, NBS, Gaithersburg, MD, August, 1985.

Hudgens, J. W. , "Multiphoton Ionization of Free Radicals", University of

Maryland, Chemistry Department, College Park, MD, December, 1984.

Hudgens, J. W., "Spectroscopy of Free Radicals Using Resonance Enhanced

Multiphoton Ionization", ACS meeting, Chicago, IL, September, 1985.

Hudgens, J. W. , "Multiphoton Ionization of Free Radicals", University of

Illinois, Chemistry Department, Urbana, IL, September, 1985.

Hudgens, J. W. , "Detection of SF Radicals with Multiphoton Ionization

Spectroscopy", 1985 Annual Meeting of the Optical Society,

Washington, D.C., October 1985.

Huie, R. E., "Chemical Kinetics of Intermediates in the Autoxidation of

S0 2

" Symposium on Environmental Effects of Fossil Fuels, 139th

Meeting, ACS, Miami, FL, April, 1985

Huie, R. E. , "Kinetics of One-Electron Transfer Reactions Involving CIOand N0 2 in Aqueous Solutions", International Conference on Chemical

Kinetics, NBS, Gaithersburg, MD, June, 1985.

Kurylo, M. J., "Recent Laboratory Measurements of SC

X Atmospheric

Chemistry: Their Effect on the Atmospheric Modeling Data 3ase", NASA

Panel for Data Evaluation, Washington, D.C., November, 1984.

Kurylo, M. J., "An Assessment of Laboratory Chemical Kinetic Data for

Atmospheric Sulfur Compounds", NASA Panel for Data Evaluation, NCAA,

3oulder, CO, February, 1985.

165
Kurylo, M. J., "Rate Constant Measurements for H0

2 Reactions of Atmosheric

Importance by Kinetic Absorption Spectroscopy", International

Conference on Chemical Kinetics, NBS, Gaithersburg, MD, June, 1985

Kurylo, M. J., "The Pressure Dependence at 298K of the Rate Constants for

the Reactions H0

2

+ HO 2 and HO 2

+ NO 2

+ M" , XII International Conference on Photochemistry, Sophia University, Tokyo, Japan,

August, 1985.

Lias, S. G. , "Reactions of Alkyl Ions with Amines", International

Conference on Chemical Kinetics, NBS, Gaithersburg, MD, June, 1985.

Lias, S. G. , "Mechanisms of Competitive Condensation - Proton Transfer

Reactions", Purdue University, West Lafayette, IN, June, 1985.

Lias, S. G. , "Structures and Reactivities of C^Hc"1" Ions", Seventh East

Coast Symposium on Ion-Molecular Chemistry, University of Delaware,

Newark, DE, October, 1985

Mautner, M. , "Kinetics Controlled Completely by the Reaction Free

Energy: Entropy Effects and Fast Endothermic Reactions", International Conference on Chemical Kinetics, NBS, Gaithersburg, MD,

June, 1985.

Mautner, M. , "Slow Organic Electron Transfer Reactions", International

Conference on Chemical Kinetics, NBS, Gaithersburg, MD, June, 1985.

Mautner M., "Free Energy Surfaces with Multiple Wells", Slow Proton

Transfer Reactions and Entropy Barriers Due to Steric Hindrance",

International Conference on Chemical Kinetics, NBS, Gaithersburg, MD

,

June 1985.

Mautner, M. , "The Filling of Solvent Shells About Ions", 10th

International Mass Spectrometry Conference, London, England,

September, 1985.

Mautner, M. , "Slow Electron Transfer Reactions", 10th International Mass

Spectrometry Conference, London, England, September, 1985.

Neta, P., "Reaction of Peroxyl Radicals with Lipids and Cytochrome P-450:

A Study of Model Compounds by Pulse Radiolysis", NIH, Bethesda, MD,

December, 1984

Meta, P., "Redox Reactions of Porphyrins", Miller Conference on Radiation

Chemistry, Windermere, England, April, 1985.

Neta, P., "Redox Reactions of Metalloporphyr ins Studied by Pulse

Radiolysis. Catalyzed Decay of TT-Radical Cations", Ninth DOE Solar

Photochemistry Research Conference, New Pfaltz, NY, June, 1985.

Neta, P., "Pulse Radiolysis Studies of Porphyrins. Application to Solar

Energy Conversion Systems", Pan-American Chemical Congress, San Juan,

PR, October 1985.

166
Okabe, H., " Photodissociation Dynamics of Simple Molecules-Recent

Developments", Chemical Institute of Canada, Queen’s University.

Kingston, Ontario, Canada, June, 1985.

Okabe, H., "Recent Development on the Studies of the Photochemistry of

Acetylene and Carbondisulf ide" , Institute for Molecular Science,

Okazaki, Japan, August, 1985.

Okabe, H., "Historical Development of Gas Phase Photochemistry", Mie

University, Tsu, Japan, September, 1985.

Sieck, L. W. , "Thermochemistry of Solvation of NO 2

- and CgH^i^

-

t>y Polar

Molecules in the Vapor Phase. Comparison with Cl

-

, and Variation with

Ligand Structure" , International Conference on Chemical Kinetics,

NBS, Gaithersburg, MD, June, 1985.

Stein, S. E., "Thermal Chemistry of Polyaromatic Hydrocarbons" , Louisiana

State University, Department of Chemistry, Baton Rouge, LA, November

1984.

Stein, S. E., "Kinetic and Thermodynamic Property Estimation Schemes",

Fort Detrich, MD, April, 1985.

Stein, S. E., "Hydrogen Transfer Between Polyaromatic Molecules",

International Conference on Chemical Kinetics, NBS, June, 1985.

Stein, S. E., "Hydrogen Transfer Between Polyaromatic Molecules", ACS Fuel

Division Symposium, Chicago, IL, September, 1985.

Tsang, W. , "Single Pulse Shock Tube Experiments on Ignition Behavior",

Workshop on Diagnostic of Ignition Mechanisms, Aberdeen, MD,

November, 1984.

Tsang, W. , "Unimolecular Processes over Extended Temperature and Pressure

Ranges", Technical meeting Eastern Section of the Combustion

Institute, Clearwater Beach, FL, December, 1984.

Tsang, W. , "The Characterization of Refuse Derived Fuels Using Thermal

Methods of Analysis", IGT Symposium, Orlando, FL, January, 1985.

Tsang, W., "Energy from Biomass and Wastes IX", IGT Symposium, Orlando,

FL, January, 1985.

Tsang, W. , "Chemical Kinetic Data Base for Combustion Modeling", Fort

Detrich, MD, April, 1985.

Tsang, W. , "Thermal Stability of Perf luoromethyl Bromide", International

Conference on Chemical Kinetics, NBS, Gaithersburg, MD, June, 1985.

Tsang, W. , "Mechanism and Rate of Hydrogen Atom Attack in Toluene",

International Conference on Chemical Kinetics, NBS, Gai thersburg, MD,

June, 1985.

167
Tsang, W. , "CO as a Monitor for Hazardous Waste Destruction Efficiency in

MSW Combustion", Office of Municipal Waste Research Panel,

Washington, D.C., June, 1985.

Tsang, W. , "Single Pulse Shock Tube Studies on the Stability of Aromatic

Compounds", 15th Symposium on Shock Waves and Tubes, Berkeley, CA,

July, 1985

Tsang, W. , "Shock Tube Studies on the Stability of Aromatic Compounds",

Department of Chemistry, The Catholic University of America,

September, 1985.
7. CHEMICAL KINETICS DIVISION SEMINARS

Koplitz, 3. D., Princeton University, Department of Chemistry, Princeton,

NJ, "Laser-Induced Multiphoton Processes in Aromatic Systems",

October, 1984.

Dean, A. M. , Exxon Research and Engineering Company, Annandale, NJ,

"Kinetics of Rich CH^ Flames", November, 1984.

Klein, D. J., Office of Naval Research, Arlington, VA, "ir-Conjugated

Polymers: Valence-Bond Description, Solitons, etc.", December, 1984.

Harriman, A., The Royal Institute, London, England, "Design of Molecular

Models for Solar Energy Storage", December, 1984.

Senthilnathan, V. P., Ohio State University, Department of Chemistry,

Columbus OH, "Solid State Chemistry and the Kinetics of Carbenes in

Low Temperature Matrices", March, 1985.

Dalai, N., West Virginia University, Department of Chemistry, Morgantown,

WV, "EPR and ENDOR Studies of Pretransitional Cluster Dynamics Near

Ferroelectric Phase", March, 1985.

Greenberg, A., New Jersey Institute of Technology, NJ, "Sources and Fates

of Atmospheric Polycyclic Aromatic Hydrocarbons", March, 1985.

El-Shall, S. S., Georgetown University, Department of Chemistry,

Washington, D.C., "Ionic Charge Transfer Complexes: Charge Localized

and Delocalized Dimer Ions", April, 1985.

Laufer, A. H., Department of Energy, Germantown, MD, "Vinylidene:

Everything You Wanted to Know (More or Less)", April, 1985.

Nelsen, S., University of Wisconsin, Department of Chemistry, Madison, WI,

"Electron Transfer Reactions with Large Geometry Change", May, 1985.

Sangster, D. F., CSIRO, Division of Energy Chemistry, Lucas Heights

Research Laboratory, Australia, "Radiation Chemistry Research in

Australia", June, 1985.

Bartmess, J. E., University of Tennessee, Department of Chemistry,

Knoxville, TN, "Gas Phase Ion Chemistry", July, 1985.

Dheandhanoo, S., York University, Department of Chemistry, Downview,

Ontario, Canada, "Growing Molecules with Ion/Molecule Reactions:

Reactions with Diacetylene", September, 1985.

Kalantar, A. H., University of Alberta, Department of Chemistry, Alberta,

Canada, "Extracting First Order Kinetic Results from Noisy Data",

October, 1985.

169
3. TECHNICAL AND PROFESSIONAL COMMITTEE PARTIPATION AND LEADERSHIP

Brown, R. L.

Member, Organizing Committee of Greater Washington Area EPR

Discussion Group

Hampson, R. F.

Member, NASA Panel for Data Evaluation

Herron, J. T.

Member, ASTM Subcommittee E47.06 on Environmental Fate of Chemical

Substances

Member, ASTM Committee E35 on Pesticides

Chairman, International Conference on Chemical Kinetics, NBS, June,

1985

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.

Neta, P.

Member, International Commission on Radiation Units and Measurements

(Committee on Chemical Dosimetry).

Sieck, L. W.

Lead Panel Member for Small Business Innovative Research Program of

the U.S. Department of Energy.

170
Stein, S. E.

Member, Editorial Advisory Board, International Journal of Chemical

Kinetics

Member, Organizing Committee, International Conference on Chemical

Kinetics, NBS, June, 1985.

Tsang, W.

Member, Organizing Committee, International Conference on Chemical

Kinetics, NBS, June, 1985

171
9. PROFESSIONAL INTERACTIONS, CONSULTING AND ADVISORY SERVICES

Braun, W. , collaborating with A. Laufer of DoE on the design of an improved V.U.V. photolysis - V.U.V. kinetic spectroscopy apparatus.

Brown, R. L., participated in Chemical Research and Development Center

Scientific Conference on Observation and Aerosol Research, Aberdeen,

Maryland.

Hampson, R. F., participated in the NASA Panel for Data Evaluation

meeting, Arlington, VA, 1984.

participated in the NASA Panel for Data Evaluation meeting, Boulder,

CO, 1985.

participated in the International Conference on Atmospheric Ozone,

Les Diablerets, Switzerland, 1985.

Herron, J. T., collaborated with R. VanBrunt of Electrosystems Division

and A. Phelps of JILA on modeling plasma chemistry.

collaborated with J. Sauers, Oak Ridge National Laboratory on chemistry of SFg dielectric breakdown.

chaired the International Conference on Chemical Kinetics, NBS, June,

1985.

participated in DoE, Basic Energy Sciences Meeting, Lake Geneva, WI,

May, 1985 and acted as secretary for the Informal Panel on Chemical

Kinetics

.

Huie, R. E., consulted with Raymond E. Hansen, President, Update

Instrument, Inc., on the determination of thermal excursions during

rapid mixing.

collaborated with C. A. Clarke of South Carolina State University on

the ferric-sulfite reaction.

collaborated with S. Jovanovic of CRR on the oxidation of tryptophon

and related compounds.

Hudgens, J. W. , collaborated with D. Bogan, Catholic University of

America on the reactions of F atoms with ketene.

collaborated with C. Dulcey, Naval Research Laboratory on the MPI of

free radicals.

Kurylo, M. J., collaborating with A. Fried and R. Sans of the Center for

Analytical Chemistry on the detection of HO 2 by dioxide laser

spectroscopy.

collaborated with A. H. Laufer of the Department of Energy on the

study of the pressure dependence of the gas phase disproportionation

of HO

2 radicals.

172
collaborating with A. H. Laufer of the Department of Energy on the

design and fabrication of a laser photolysis ultraviolet absorption

apparatus

.

provided advisory services to the Upper Atmospheric Chemistry

Program of NASA, the Fundamental Interactions Branch of DoE, and the

Atmospheric Chemistry Program of NSF.

consulted with A. Kalantar of the University of Alberta on numerical

integration techniques for kinetic analysis.

Lias, S. G., Drs. John L. Holmes (University of Ottawa), John E. Bartmess

(University of Tennessee), Joel F. Liebman (University of Maryland,

Baltimore, County) and David Dixon (Dupont) are collaborating with

Sharon G. Lias and Rhoda D. Levin on data evaluation projects for the

Ion Kinetics and Energetics Data Center.

Martinez, R. I., provided technical information and consultation

regarding the Martinez-Herron Desulfurization Process (U.S. Patent

No. 4,351,810) to several international corporations.

consulted with H. Niki, Ford Motor Company on the mechanisms of

O^-olefin reaction systems and on the photooxidation of formaldehyde .

consulted with P. Dawson, NRC-Ottawa, on CID dyamics of MS/MS tandem

mass spectrometers.

consulted with Sam Trevino, U.S. Army, on trajectory calculations and

associated kinetics.

consulted with E. K. C. Lee, UC-Irvine, on the mechanism for the

matrix photooxidation of H

2 C0

.

consulted with J. G. Calvert, NCAR, on photooxidation of H

2 CO

.

consulted with S. Dheandhanoo, York University, on synthetic ionmolecule reactions in SIFT apparatus.

consulted with P. S. Berger, President of Teknivent Corporation, on requisite design and operational characteristics for an MS/MS system

controller

.

consulted with J. W. Hellgeth, Virginia Polyteclinic Institute and

State University on FTIR flow-cell interface for HPLC and

supercritical fluids.

Mautner, M. , collaborated with Dr. C. A. Deakyne, College of the Holy

Cross, Worchester, MS on ion clustering energetics.

collaborated with Professor S. Nelsen, Department of Chemistry,

University of Wisconsin, Madison, WI on ion chemistry of hydrazines.

173
collaborated with Professor J. Liebman, Department of Chemistry,

University of Maryland, Baltimore on proton affinities of

heterocyclic compounds.

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, Washington, D.C., on porphyrin reactions.

collaborated with G. Infante, Chemistry Department, Catholic University of Puerto Rico, Ponce, PR, on determination of one-electron

reduction potentials of radiosensitizer drugs by pulse radiolysis.

collaborated with L. Pohl, NIH, on destruction of cytochrome P450 by

free radicals.

Sieck, L. W. , collaborated with the Analytical Mass Spectrometry Group

of the Organic Analysis Division, Center for Analytical Chemistry,

NBS (White, Christensen) concerning adduct ion formation in MS/MS.

collaborated with R. Van Brunt of the Electrosystems Division, NBS

concerning electron transport mechanisms in SFg.

collaborated with S. Nelsen, Department of Chemistry, University of

Wisconsin, Madison, WI , concerning proton affinities of hydrazines.

Stein, S. E., collaborated with A. Greenberg, N. J. Institute of

Technology on reactivities of polyaromatic hydrocarbons

.

collaborated with M. Frenklach, Louisiana State University on soot

formation thermochemistry

.

collaborated with W. R. Moore, West Virginia University on synthesis

of polynuclear aromatic compounds.

served as reviewer for the R. A. Glenn award for the best paper

presented at the fall ACS Meeting Fuel Division Section.

collaborated with K. Kishore, IIS, Bangalore, India, on pyrolysis of

polymers

.

collaborated with N. Trinastic, Boscovic Institute, Yugoslavia, on theory of graphite.

Tsang, W. , collaborated with John Callahan and John Samuels, Edgewood

Arsenal, on the interpretation of kinetic data on the decomposition

of organic phosphorus compounds.

collaborated with D. Chang, Department of Civil Engineering, U.C.,

Davis on the interpretation of results from the combustion of

hazardous wastes.
collaborated with A. Liftshitz, Hebrew University, Jerusalem on shock

tube investigations on the stability of oxygenated hydrocarbons under

an Israeli-American binational foundation grant.

served on ONR panel on priority research directions in physical

chemistry.

collaborating with G. Mallard, Fire Research, on studies on the

stability of aromatic compounds at high temperatures

.
10. VISITING SCIENTISTS

Alfassi, Z., of Ben Gurion University has spent one month 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

.

Chen, R., of West Virginia University has spent six months at NBS as a guest scientist working on free radical chemistry.

Colussi, A., of University of Mar Del Plata has spent two weeks at NBS as

a guest scientist working on high temperature free radical chemistry.

Fahr , A., has spent one year at NBS under a cooperative agreement with

Georgetown University, working on thermolysis of aromatic compounds.

Fujimoto, G. , of University of Maryland has spent six months at NBS as guest scientist working on thermal stability of molecules.

Griffith, L., of West Virginia University has spent six months at NBS as a guest scientist working on liquid phase pyrolysis studies of aromatic

substances

.

Harriman, A., of The Royal Institution, London, has spent three months at

NBS as a guest scientist working on pulse radiolysis.

He, Yu Zhong, of the Institute of Mechanics Academia Sinica, Beijing, has

spent six months at NBS as a guest scientist working on shock tube

studies on thermal stability of molecules.

Hoffbauer, M. , of West Virginia University has spent six months at NBS as

a guest scientist working on chemical processes in molecular beams

using laser techniques.

Kafafi, S., of the University of Cairo has spent six months at NBS as a guest scientist working on polynuclear aromatic hydrocarbons.

Karpas, Z., of the Nuclear Research Center, Negev, Israel, spent a year

at NBS as a guest scientist working on the kinetics of ion-molecular

reactions using the ion resonance spectrometer

.

Laufer, A., of the Department of Energy has spent one day a week at NBS

working on free radical species.

Manka, M., of Catholic University has spent six months at NBS as a guest

scientist working on thermolysis of organic compounds.

Mosseri, S. , of Ben Gurion University of the Negev has spent six months

at NBS as a guest scientist working on pulse radiolysis.

Richoux, M.-C., of The Royal Institution, London, has spent one year at

NBS as a guest scientist working on pulse radiolysis experiments.

176
Robaugh, D., of West Virginia University has spent ten months at N3S as a guest worker working on high temperature shock tube studies of

aromatic pyrolysis.

Rumack, D., of the University of Wisconsin has spent two months at NBS

as a guest scientist working on mass spectrometry of hydrazine

derivatives

.

Senthilnathan , V. f of West Virginia University has spent seven months at

NBS as a guest scientist working on free radical reactions on high

temperature fluids.

Speller, C. , of the University of Paris completed a year at NBS as a guest scientist working on ion chemistry.

Walker, J., of West Virginia University has spent one year at NBS as a guest scientist working on thermal stability of organic compounds.

177

CHEMICAL THERMODYNAMICS DIVISION

Stanley Abramowitz, Chief

SUMMARY OF ACTIVITIES

Fiscal Year 1985

1 . INTRODUCTION

A. Objectives

Chemical Thermodynamics provides measurement techniques, concepts and

data on the energetics and equilibria of chemical processes. Among the uses of chemical thermodynamics are the prediction of equilibria in

chemical reactions, thermodynamic properties of high temperature

refractory materials and gases, activities of aqueous solutions used in

such diverse technologies as power generation, biotechnology and

electrorefining. 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 microjoule to

megajoule 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 particular emphasis is being directed towards

biothermodynamics and biomolecular structure which will yield basic data,

measurement techniques standards and concepts for the emerging

biotechnology industry.

Specific 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 zo attain

enhanced measurement precisions and accuracies.

o Development and certification of Standard Reference Materials.

o Measurement of thermodynamic properties of key chemical species

and processes including phase transitions of biomolecular

species

.

o Development of measurement techniques to characterize the

molecular structure of biopolymers such as proteins and DNA using

the techniques of x-ray and neutron diffraction in order co establish structure function relationships.

o Provision of critically evaluated compilations on the chemical

thermodynamic properties of inorganic and organic compounds.

- - Q
o Development of estimation methods for the prediction of

thermodynamic properties of organic and inorganic species in the

gaseous, liquid, solid and aqueous phases.

o Response to the needs of industry, government and academia for

thermodynamic and related information.

B. Organization and Staff

The Chemical Thermodynamics Division is organized into three major

groups. These groups are:

o Biothermodynamics and Molecular Structure, S. Abramowitz, Group

Leader

o Chemical Thermodynamics Measurements, E. S. Domalski , Group

Leader

o Chemical Thermodynamic Data Centers, D. Garvin, Director, Chemical

Thermodynamics Data Center

The division has 22 full-time staff, 3 part time employees, 4 guest

workers, 4 students, 6 contractors, 1 IPA and 1 consultant. This past

year we have added two new research areas one in Biomolecular Structure,

using the techniques of x-ray and neutron diffraction and one in

Differential Scanning Calorimetry of Biopolymers. A librarian - information specialist has been added to the Chemical Thermodynamics Data

Center. Several guest workers have joined the staff.

We regret to have to report the death, in June 1985, of William H.

Evans. Dr. Evans, a coauthor of NBS Circular 500 and the "NBS Tables of

Chemical Thermodynamic Properties" retired in 1977 but remained a very

active participant in the work of the data center until his death. The

master index to thermodynamic measurements, in design and operation, and

the present form of the Bulletin of Chemical Thermodynamics are monuments

to his skill and perserverence

.

C. Research for NBS Programs

The division participates in the work of two of the NBS programs.

Office of Standard Reference Data

o Evaluation of thermochemical properties of inorganic species.

o Development of a data base management system for chemical

thermodynamics

.

o Development of critically evaluated data and reliable estimation

schemes for organic and biochemical species.

180
Office of Standard Reference Materials

o Certification of heating value, residual moisture, ash and sulfur

content of coals, SRM 2682, 2683, 2684, 2685.

o Certification of synthetic refuse-derived fuel, SRM 1657.

o Certification of an oxygen bomb calorimetry standard ref erence materials, thianthrene, (SRM 1656); nicotinic acid, (SRM 2151); and

urea (SRM 2152)

.

o Research to develop a phosphorous containing organic compound for

an oxygen bomb calorimetry standard.

D. Other Agency Research

The research needs of two federal agencies and one industrial trade

association are being addressed by the Division. The funding agency, NBS

manager/ investigator , and programs are given below.

Funding Agency NBS Program Manager/ Program Title/

Investigator Description

Department of Defense S. Abramowitz High temperature thermo

Air Force Office of

Scientific Research

( AFOSR)

D. A. Ditmars dynamic measurements on ceramics, pure elements

and compounds

Department of Energy D . Garvin Thermodynamic data for

Pittsburgh Energy R. N. Goldberg flue gas clean-up in

Technology Center V. B. Parker fossil fuel technology

(PETC) D. Smith-Magowan

Department of Energy E. S. Domalski Chlorine content of

Energy from Municipal K. L. Churney municipal solid waste;

Waste (EMW) A. E. Ledford Threshold condition for

S. S. Bruce the f ormation/destructT. J. Buckley ion of chlorinated

organic species.

Design Institute for D . Garvin Bibliographies of

Physical Property R. N. Goldberg thermodynamic data on Data (DIPPR) T. L. Jobe, Jr. sour water and various

D. Smith-Magowan salt systems.

U.S. Department of the E. S. Domalski Combustion calorimetry

Army, Aberdeen Proving

Ground

D. R. Kirklin and estimation methods

for organic phosphorus

compounds

.
Solar Energy Research E. S Domalski Revision and up-date of

Institute (SERI) T. L. Jobe, Jr. previous publication on thermodynamic data for

waste incineration.

E. Collaborations within NBS

In addition to the interactions with other NBS programs and federal

agencies, the Division collaborates with other NBS units. Among these

are:

With CCP - joint program with Chemical Kinetics Division on Database Management Systems

- collaboration with Chemical Kinetics and

Molecular Spectroscopy Division on carrying out

and planning a research program in support of the

high temperature technology needs of AFOSR.

- collaboration with Surface Science Division in

developing algorithms for the interpretation of

sputtering depth profiles

With NML - cooperation with Center for Analytical Chemistry in

planning a program initiative for Biotechnology.

- cooperation with Center for Analytical Chemistry

in determining trace organic chlorine

constituents in combustion products

- cooperation with OSRM and OSRD in planning

standards reference materials and evaluated data

needs

- cooperation with Center for Basic Standards on temperature measurements in combustion studies

With IMSE - collaboration in planning and carrying out a research program in support of AFOSR needs in

high temperature technologies

With NEL - collaboration in planning and carrying out a research program in support of AFOSR high

temperature technology needs

Our staff has many interactions with voluntary standards

organizations and international societies such as ASTM, ANSI, ASME,

CODATA, IUPAC, IAEA etc. Staff members hold memberships on diverse

committees ranging from environmental and health concerns to energy

utilization to data base management.

182
The breadth of scientific interest is shown in the discussions of

current projects in the body of this report. While these reports show the

scientific content of the Division's work, they do not show individual

scientific achievements, participation of the staff in NBS programs,

extensive interactions with other federal agencies, standards

organizations and international scientific organizations. Some of the

individual achievements of particular note are given below.

Eugene Domalski gave an invited talk at the 5th International

Symposium on Chlorinated Dioxins and Related Compounds at University

of Bayreuth, Bayreuth, West Germany.

David Garvin gave an invited talk on Recent Evaluations of

Thermochemical Properties of C

-j —

C

5 paraffins at a Symposium on Natural Gas Measurements at the Institute for Gas Technology,

Chicago, 111.

Alex Wlodawer authored a chapter in Neutrons in Biology entitled

"Application of Joint Neutron and X-ray Refinement of the Structure

of Ribonuclease A at 2A Resolution".

William H. Kirchhoff authored a report entitled "A National Program

of Measurement Services and Standards for Biotechnology at the

National Bureau of Standards" for the U.S. Congress.

In FY 85 our program has become less involved in applied programs. We

have been successful in raising funds for more research in

biothermodynamics and biomolecular structure. In particular a laboratory

for molecular structure is being outfitted. A staff member, Alex

Wlodawer, has joined the division together with three guest workers and a NRC postdoctoral fellow. This group is using the techniques of x-ray and

neutron diffraction to obtain structures of proteins, enzymes and DMA

species. A Hart differential scanning calorimeter which has been designed

for biological standards has been installed in a new laboratory. Fred

Schwarz has joined the division and is pursuing a research program using

this instrument. He is collaborating with researchers from NIH and FDA.

In FY 86 we will continue our efforts in the biothermodynamics and

biomolecular structure area. Work will continue in the thermodynamics and

enzyme catalyzed reaction, differential scanning calorimetry of proteins

and other biopolymers, molecular structure determinations of biopolymers

including enzymes, proteins and DNA fragments, critical data evaluation

and development of predictive schemes for organic and biomolecular

species

.

Work will also continue on the determination of enthalpies of

formation of key phosphorous compounds and biomolecular building blocks.

This will be done in a symbiotic manner with cooperation between data and

predictive programs in order to produce reliable predictive schemes.

Benzoic acid will be recertified. Research to characterize t.ne effluents

resulting from the combustion of municipal solid waste will be continued.
Plans for the data activities include an expansion into the area of

thermal functions with an addition to the staff. The additional staff

member, Malcolm Chase of the Dow Chemical Corporation, will afford us a direct link between the high temperature experimental programs in CCP, CCE

and IMSE and data evaluation. Work will continue on CODATA and key values

proj ects

.

184
2. BIOTHERMODYNAMICS AND MOLECULAR STRUCTURE

S. Abramowitz, E. Gajewski, R. N. Goldberg, R. W. Harrison

W. H. Kirchhoff, M. Miller, H. Savage, F. P. Schwarz, D. Steckler,

Y. B. Tewari , I. Weber, A. Wlodawer

A. Thermodynamics of Enzyme Catalyzed Reactions

(E. Gajewski, R. N. Goldberg, D. Steckler and Y. B. Tewari)

Accurate thermodynamic data on biochemical reactions are needed to

facilitate a better understanding of the reactions themselves and for the

optimization of product yields for reactions having industrial

significance. The goal of this effort is to provide reliable

thermodynamic data (equilibrium constants, enthalpies, and heat

capacities) for biochemically and industrially important reactions and the

associated measurement and computational techniques. The accomplishments

of this past year are in several areas: (1) measurements on specific

enzyme-catalyzed reactions, (2) development of chromatographic separation

techniques, (3) studies of the feasibility of isomerization reactions of

carbohydrates which are catalyzed by glucose isomerase, (4) additions to

and refinement of the software used for running calorimetric experiments,

and (5) applications of computational procedures to the treatment of data

involving complex equilibria. The focus of the research has been on item

(1) above with the other items (2-4) being necessary for its proper

accomplishment

.

The specific enzyme-catalyzed reactions which have been investigated

are: (1) The conversion of xylose to xylulose, (2) ribose to ribulose and

to arabinose, (3) aspartic acid to fumaric acid and ammonia, and (4) the

hydrolysis of adenosine 5 ' -triphosphate (ATP) to adenosine 5 ' -diphosphate

(ADP) and inorganic phosphate. Summaries of the results of these

investigations follow.

(a) xylose(aq) = xylulose(aq)

This reaction, an intermediate step in the conversion of biomass

(hemicellulose ) to ethanol, was carried out in aqueous phosphate buffer

over the pH range 6.8 to 7.4 using solubilized glucose isomerase with

MgSOi| as a cofactor. The temperature range over which this reaction was investigated was 298.15 to 342.15 K. A combined analysis of both the HPLC

and microcalorimetric data leads to the following results at 298.15 K for

the conversion process: K = 0.170, AG° = 4.39 ± 0.03 kJ mol

-1

, AH 0 = 16.09 ± 0.67 kJ mol

-1

, and ACp° = 40 ± 23 J mol

-1 k .

185
(b) ribose (aq) = ribulose (aq) = arabinose (aq)

These reactions were carried out in aqueous phosphate buffer

over the pH range 6.8 to 7.4 and over the temperature range 313.15 to

343. 75K using solubilized glucose isomerase with Mg(N0^)2 and MgSOij as cofactors. The equilibrium constants and the standard state Gibbs energy

and enthalpy changes at 298.15 for these equilibria are:

ribose (aq) = ribulose (aq) K = 0.317, AG° = 2 . 8 5 ±0 . 1 4 kJ mol -1

AH 0 = 11 .0±1 .5 kJ mol -1

ribose (aq) = arabinose (aq) K = 4.00, AG° = -3 • 44±0 . 30 kJ mol-1

AH 0 = -9.8 ±3.0 kJ mol -1

ribulose (aq) = arabinose (aq) K = 12.6, AG° = -6.25±0.34 kJ mol -1 AH 0 = -20 .75i3 • 4 kJ mol -1

Qualitative information on the rates of the above reactions was also

obtained. The existence of arabinose as an isomerization product

had not been previously reported in the literature.

(c) L-aspartate

- (aq) = fumarate2- (aq) + NHj^(aq)

The above reaction which is catalyzed by aspartase, was carried

out in aqueous phosphate buffer over the pH range 7.25 to 7.43, the

temperature range 268.15 to 3 1 6 . 1 5K , and at ionic strengths varying form

0.066 to -0.366 mol kg

-1

. The treatment of the experimental data requires

detailed modelling calculations involving not only all of the species

involved in the above process, but also the species formed from malate.

Effects of ionic strength on the activities of all of the species were included in all the equilibrium calculations. The following values were found for the above process at 298. 1 5K and at zero ionic strength: K =

( 1 . 4 8 ±0 . 0 8 ) x 10~3

, A g° = 16.15 ± 0.13 kJ mol -1, AH° = 24.5 ± 1.0 kJ

- 1 - 1 -

1

mol , and ACp° = -147 ± 100 J mol K . Calculations have also been

performed which give values of the apparent equilibrium constant, (E

fumarate) ( E ammonia)/(E L-asparate), as a function of temperature, pH,

and ionic strength. The above value for AG°, when adjusted to an ionic

strength of 0.1 mol kg

-1

, fits well into a thermochemical cycle

calculation recently performed by D. Smith Magowan of the Electrolyte Data

Center. The industrial synthesis of L-aspartic acid uses the above

process

.

(d) H

2 0U) + ATP

4-

(aq) = ADP 3 ~(aq) + HP0 4 2 "(aq) + H

+ (aq)

This reaction is currently the subject of a calorimetric

investigation where the effects of variations of pH, temperature, and

ionic strength on the molar enthalpy of reaction are being determined.

The buffer selected was TRIS/HC1. Thus far, the pH has been varied from

6.4 to 8.8 and the ionic strength from - 0.1 to - 0.6 mol kg 1

. It has

been found that the enthalpy of reaction is a constant over the pH range

8.3 to 8.8 in agreement with the predictions of equilibrium calculations,

186
but that the enthalpy varies by 2.7 kJ mol -1 due to a change of ionic

strength of = 0.5 mol kg-1

. At a pH of 8.5 and an ionic strength of 0.1

mol kg -1

, the tentative value of AHD is 20.5 ± 0.2 kJ mol

-

"

1 . The

understanding of the energetics of this process is of particular

significance due to the ubiquitous nature of ATP in biochemical processes.

Three of the above investigations used HPLC for the quantitative

separation and analysis of the equilibrium reaction mixtures. The ATP

study also used HPLC to establish the purity of the ATP and to confirm the

absence of side reactions. The chromatographic separations were performed

using calcium cation exchange columns. Quantitative separations have also

been obtained for glucose 6-phosphate, fructose 6-phosphate, glucose, and

fructose using a quatermary- ammonium ion-exchange column. These

separations will allow thermodynamic investigations involving the

phosphorylation of glucose and fructose as well as for the isomerization

of glucose 6-phosphate to fructose 6-phosphate.

Preliminary investigations have also been performed on the

isomerization of the hexoses, allose, altrose, galactose, talose, psicose,

sorbose, and tagatose. It has been found that an equilibrium was established between aqueous allose, altrose, and psicose after one week in

the presence of glucose isomerase at 60°C. This reaction has not been

previously reported in the literature. If feasible, a detailed

equilibrium investigation may be undertaken. The other hexoses showed no detectable isomerizations under similar conditions.

High precision microcalorimetry was used in the above investigation

for the direct measurement of the enthalpy changes of the enzyme-catalyzed

reactions (a-d). This past year the software used for the conduct of the

experiments and for the calculation of results from the experiments has

been improved. At present, three microcalorimetric experiments can be

conducted simultaneously with automatic data requisition and convenient

calculation of results. An algorithm has also been developed for the

deconvolution of the experimental thermograms to yield a thermo-kinetic

curve of the process which has occurred in the microcalorimeter

.

Plans for the coming year include completion of the ATP hydrolysis

study, documentation of the microcalorimetric procedures and the computer

software used for data acquisition and calculation and, if possible a study of the equilibrium between allose, altrose and psicose. Trans

aminase reactions of the type

nh

3

+ RC00

- = RCH(NH2 )C00"

will be studied which are relevant to the industrial synthesis of amimo

acids such as phenylalanine and tyrosine. The chromatographic separations

obtained using the quaternary ammonium columns enable the study of the

following fundamental phosphorylation and isomerization reactions:

187
glucose + HPOjj

2-

= glucose 6-phosphate 2-

fructose + HPOjj

2-

= fructose 6-phosphate 2-

and glucose 6-phosphate 2- = fructose 6-phosphate2-

B. Differential Scanning Calorimetry

(F. P. Schwarz and W. H. Kirc’nhoff)

Differential scanning calorimetry provides information on the

thermodynamics of conformational changes occurring in proteins, nucleic

acids and polysaccharides and of phase changes occurring in lipids and

biological membranes. This information is useful in characterizing the

interactions between components of biological systems, such as the

chemical binding between an enzyme and substrate, the structural

properties of biological molecules and the thermal stability of proteins

in solution. There is also a need for temperature and transition enthalpy

standards based on biological systems to calibrate the heat capacity and

temperature measurements of a differential scanning calorimeter in the

temperature range from 0 to 100°C.

1 . Temperature and Enthapy Standards for Differential Scanning

Calorimetry

(F. P. Schwarz)

The di-alkylphosphatidylchol ines are a class of lipids which

undergo sharp phase transitions in aqueous solutions below 100°C. These

species have been proposed as standard reference materials for the

calibration of DSCs. The di-alkylphosphatidylchol ines consist of two long

hydrophobic alkyl chains and a hydrophlic aminoalkylphosphate head group.

When suspended in water these species form bilayers with the polar head

group on the exterior of the bilayer. The bilayers undergo a gel to

liquid crystal phase change in which the alkyl chains change from an all

trans configuration to a mixture of trans and gauche configurations (main

transition) and a smaller, bilayer surface configurational change at a lower temperature (pre-transition) . Specifically, the enthalpies of the

main transitions are on the order of 5-10 kcal/mole and occur at temperatures from 12.6°C ( 1 , 2-dielaidoyl-L-phosphatidylchol ine ) to 65.5°C (1,

2- diarac hi doyl-L- phosphatidylcholine )

.

Suspensions of the phosphatidylcholines in pH=7.0 buffered aqueous

solutions were prepared and stored under a variety of experimental

conditions similar to those found in biological laboratories. It was observed that the main and pre- transi tion enthalpies depended on the

preparation and storage conditions of the suspensions and that under

certain storage conditions additional transitions were observed at lower

temperatures. A phase transition, corresponding to a change in the alkyl

chain packing from orthorhombic to quasihexagonal , was observed at 8°C for

1 ,2-dimyristoyl-L-phosphatidylcholine. This transition only had been

previously observed for 1, 2 dipalmitoyl-L-phosphatidylcholine and 1,2

distearoyl-L-phosphatidylcholine. Despite the variation of the transition

188
enthalpies, in some samples on the order of 20$, the temperature of the

main phase transition remained within 0.05 centigrade degrees for all the

phosphatidylcholines studied. For this class of lipids suspended in

buffered water solutions, the temperature of the main phase transition

could serve as a temperature standard for calibrating the temperature

measurements of DSCs. They would however not be useful for enthalpy

standards

.

Ribonuclease a and Lysozyme exhibit unfolding transitions in the

temperature range of 20°C to 80°C which could be used as enthalpy

standards for the calibration of the transition enthalpy measurements of

the DSC. The enthalpies and temperatures of the unfolding transitions of

these proteins were measured as a function of pH to evaluate their

potential as enthalpy standards. Preliminary results indicate that the

transitions are not fully reversible because of some thermal degradation

above the transition temperature and that the transition enthalpies are dependent on pH. For example the enthalpy of Ribonuclease a increases by

30$ in going from a pH 3-0 to a pH 4.0 buffer solution. The results

however, are reproducible and are not dependent upon storage conditions.

2. The Thermal Stability of Clathrin Structures

(F. P. Schwarz and W. H. Kirchhoff in collaboration with C. Steer

and I. W. Levin of NIH)

The coated vesicles in eukaryotic cells have been implicated in

a variety of shuttling processes within the cell such as the transfer of

proteins and lipids from the cell membrane to the interior of the cell.

The coated vesicles consist of lipid vesicles enclosed in a polyhedral

protein lattice consisting basically, of trimers of 130-kDal clathrin

molecules in association with smaller 35 _ kDal polypeptide units. Under

mild alkaline conditions (pH=8.5) the lattice coating is dissociated from

the coated vesicle and breaks down into units termed triskelions which

consist of the clathrin trimers associated with the smaller polypeptide

units. In weakly acidic solutions (pH=6.5), the triskelions reassemble

into cagelike structures with lattices similar to those of the coated

vesicles. From 15 to 95°C, buffer solutions of the coated vesicles

exhibit one transition at 55.7 + 0.1 °C with an enthalpy of transition of

10.5 + 0.2 j/g and a van* t Hoff enthalpy of 1.79 ± 0.01x10^ j/mole. The

cooperativity of the transition, determined from the ratio of the enthalpy

to the van't Hoff enthalpy (using a molecular weight of 540-kDal for the

clathrin trimer unit), is 3.17 ± 0.06 indicating that three cooperative

regions are participating in the transition. Solutions of the reassembled

cages exhibit two transitions over the same temperature range: at 53.0 ± 0.2°C with a transition enthalpy of 4.6 ± 0.3 j/g and a van't Hoff

enthalpy of 1.20 ± 0.01x10° j/mole and at 56.1 + 0.1 °C with transition

enthalpy of 3-7 ± 0.1 j/g and a van't Hoff enthalpy of 2.81 ± 0.09x10°

j/mole. The cocperativities are 2.1 ±0.1 for the lower temperature

transition and 0.71 ± 0.02 for the higher temperature one. In contrast,

solutions of the triskelions exhibit no transitions over the same temperature range. Infrared spectroscopic studies show that the alpha

helix structure of the triskelions decreases substantially as they

189
reassemble into cages and that the structural properties of the

triskelions in the reassembled cages are very similar to the structural

properties of the triskelions of the coated vesicles. The decrease in the

alpha helix structure would reduce the thermal stability of the triskelion

as is observed in the DCS results.

3. The Thermal Stability of Serum Albumin

(F. D. Schwarz in collaboration with A. Shrake of the FDA)

Serum albumin is the most abundant protein in human plasma,

accounting for 60% of the normal concentration of 42g/l, and it functions

as a transport protein in the blood. Commercial processing of 5% normal

serum albumin solution requires heating the solution at 60°C for 10-11 hr.

Since this temperature is close to the thermal denaturation temperature of

66.8°C, for undefatted serum albumin, small concentrations of

N-acetyltryptophanate and octanoate are added to the solution to increase

the thermal stability of the albumin by complexing with the albumin. For

example, a combination of 4mM N-acetyl-DL-tryptophanate and 4 mM octanoate

increases the denaturation temperature to 75.9°C. The tryptophanate

,

however, can induce photodegradation of the solution since it absorbs room

light. In a previous study, it was observed that 4 mM octanoate alone

increases the thermal stability of the serum albumin to a denaturation

temperature of 75.3°C and that the presence of the thermal stabilizers at

subsaturated concentrations induces a second transition at a higher

temperature (bimodality).

To elucidate the bimodal nature of the denaturation transition and to

identify other thermal stabilizers not susceptible to photodegradation, a study was initiated to determine the effect of different concentrations of

octanoate and other fatty acid anions on the thermal stability of serum

albumin. To date, the thermal stability of solutions of human defatted

serum albumin containing concentrations of butanoate, hexanoate,

heptanoate, octanoate, and decanoate anions has been determined from 30°C to

100°C. For all the solutions studied, the denaturation temperature

increases to a maximum value as the anion concentration is increased and

then levels off with a very slight decrease at very high anion

concentration. This increase is also accompanied by an increase in the

enthalpy of transition to a constant value at high concentrations. The

maximum thermal stability is achieved with 73 mM octanoate where the

denaturation occurs at 87.3°C. The transition bimodality begins to appear

with the octanoate anions and becomes more pronounced with increase in

the anion chain length which also increases the binding affinity between

the anion and the serum albumin. A model has been proposed based on ascribing the bimodality to the presence of two protein species in the

solution and to migration of the anion ligands from the more labile

species to the more stable species as the former unfolds; such migration

would increase the stability of the latter. The model has been successful

in predicting the extent of migration from the magnitudes of the affinity

of the albumin for ligand and from the magnitude of the maximum increase

in thermal stability (the magnitude of the temperature shift). This model

190
is important since the bimodal thermograms exhibited by proteins in the

presence of a substrate in solution may be explained by ligand migration

and not be related to the macromolecular substructure of the protein.

In FY 86 the unfolding transitions of proteins in solution will be

investigated in more detail with regard to their applicability as enthalpy

standards for DSC measurements. The relationship between the enthalpy and

temperature of the transition will be investigated for model systems. The

dependence of both of these parameters on pH will also be determined. The

serum albumin thermal stability study will be extended from fatty acid

chain lengths of 10 carbons to 18 carbons where the bimodality is more

pronounced. The thermal stability of novel DNA oligonucleotides in

solution will also be investigated to determine their equilibrium

conf igurations in solution.

C. Spectroscopic Characterization of Phase Transitions in Biomolecules

(W. H. Kirchhoff)

The two-state model for phase transitions in biomolecules which was developed for Raman Spectroscopy studies of lipid bilayers has been shown

to be generally applicable to other spectroscopies and to other

biomolecular systems. The model derives from the thermodynamic properties

of small systems as described by Hill.

The statistical analysis of phase transition data has been made more

robust through a novel means of dealing with a paucity of data in the

phase transition region. The analytical expression for the two state

model as it applies to spectroscopic data is given in its simplest form by

A

+ _B

1+et+ He-t ( 1 )

where t is the scaled temperature, t = (T-T Q )/D. T 0 is the midpoint of

the transition and D is the width parameter for the transition region. The

parameters T

0 and D are determined by the data falling in the phase

transition region. A statistical method has been developed to estimate

the width of the transition interval which is based on the precision of

the data in the asymptotic limits. The number of data points falling

within this estimate of the transition interval determines the confidence

interval within which T

Q and D can be estimated. Even in situations where

only one or no data fall within the interval, upper bounds can be placed

on the value of D. The program has been extensively documented and is

available for distribution.

The function in equation (1) is known as the logistic function and

has the differential form dy/dx = y ( 1 — y ) . In the differential form, the

logistic function strongly resembles the Gaussian function but with longer

tails. It has been extensively used in statistics because of this

resemblance and because of its greater analytical simplicity in its

cumulative form. The cumulative form, equation 1, is widely encountered in

191
chemistry (autocatalysis, bimolecular reactions, oxidation-reduction

potentials) and the statistical analysis program, with minor modification,

should be applicable to these classes of data as well.

During the next fiscal year, three projects will be undertaken. The

logistic function analysis program will be applied to sputter depth

profiles as a systematic procedure for parameterizing the interface

between dissimilar materials. The analysis will be used in the

certification of standard reference materials being developed in the

Surface Science Division for the characterization of metal interfaces. The

two state model for phase transitions in small systems will be extended to

the numerical analysis of differential scanning calorimetric measurements

with the objective of developing a standardized method of data reduction

and parameter estimation. Finally, an existing molecular dynamics code

(CHARMM or AMBER) will be adapted to run on the new NBS Cyber 205 computer

and will be evaluated for its usefulness to division programs in

biotechnology

.

D. Biomolecular Structure Studies

(A. Wlodawer, R. Harrison, M. Miller, H. Savage, I. Weber)

Introduction

The aim of the Macromolecular Structure Group is to develop an active

program of measurement and analysis of the structures of biologically

important macromolecules. The molecules under study include proteins,

enzymes, enzyme inhibitors, hormones, DNA and also assemblies of molecules

such as proteins complexed with DNA. The biological activity depends on

the structure and dynamics of these macromolecules which are of general

interest in the field of biotechnology. For example, the structure of an enzyme may be altered by the binding of an inhibitor molecule so that the

structure in the presence and absence of the specific inhibitor may be

necessary to understand the function. Enzymatic function may also be

elucidated by analyzing the structure of several mutant proteins.

The principal experimental techniques used by the group are X-ray and

neutron diffraction from single crystals and neutron small angle scattering from solution. We also rely on collaborations with other scientists

who analyze the biological functions of these molecules in vivo and in

vitro. The determination of a macromolecular structure passes through

three major stages. First, single crystals must be grown; then the

structure must be solved by X-ray diffraction; and finally the structure

must be refined at high resolution, including neutron diffraction data if

possible, in order to produce a highly accurate model with all hydrogen

atoms and the surrounding solvent molecules. The experimental program

proceeds through crystallization studies to X-ray and neutron diffraction

measurements. Then the structure must be built and analyzed by computer

graphics system and at that stage extensive computations are required.

The simultaneous determination of biomolecular structures using both X-ray

and neutron diffraction data is unique to the NBS program. Neutron data,

192
unlike X-ray data, allow accurate placement of hydrogen atoms. The

experimental program is augmented by the development of better tools for

each experimental stage. We are developing better computer techniques for

solving macromolecular structures, for analyzing and modeling structures,

and for understanding the dynamics of biological systems.

The projects described below vary in their objectives from attempts

to describe the modes of interaction of proteins and nucleic acids at very

low resolution, to solving the structures of several proteins at

near-atomic resolution and refining structural models at very high

resolution including hydrogen atoms and water molecules. Several

different biological systems are under investigation including proteins

that activate genes; enzymes that have chemotherapeutic activities and a sweet tasting protein. We are also interested in the interactions between

macromolecules and solvent since almost all biologically important

reactions take place in aqueous media.

1. Structural Studies of Three Antitumor Amidohydrolases

(I. Weber, A. Wlodawer and R. Harrison)

Three bacterial amidohydrolases with antitumor properties have

been crystallized: a glutaminase- asparaginase (GAse) from Ac inetob ac ter

glutaminasif icans , a Pseudomonas 7A GAse and a Vibrio Succinogenes

asparaginase (Ase).

The enzymes are tetramers with subunit molecular weights of ca. 34,000 daltons. The Ac inetob acter GAse crystallizes in space group 1222

with one subunit per asymmetric unit. Native data are available to 2 . 9 A.

;

MIR data (3 derivatives, 4.7-4A) permitted the direct phasing of 2617

reflections. Extension of the phases for an additional 4784 reflections

(2.9A) and phase improvement was achieved with two complementary density

modification techniques.

These were (a) the method of B. C. Wang that flattens the solvent

region and improves protein connectivity and (b) 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. It proved

possible to fit a polyalanine chain to the density, although the

connectivity is ambiguous in several places.

The map produced by R. W. Harrison allowed the tracing of a polypeptide chain into parts of the solvent that were masked in the map

computed with the algorithm of B. C. Wang. These coordinates yielded an initial R of .48; R = .34 following refinement. In the absence of a known

amino acid sequence, the amino acid types have been estimated resulting in an improved fit of the model to the electron density. The R factor for

the coordinates with a guessed sequence is now . 30 . The polypeptide chain

folds into two domains. The amino terminal domain consists of a five-stranded 8 - sheet and four a-helices. The second domain is less well

determined

.

193
6A intensity data are presently available for a form of the

homologous Pseudomonas GAase with one tetramer per asymmetric unit; space

group P2-|2-j2-|. The structure was initially solved with rotation and

translation function techniques, using a 3«2A Acinetobacter GAase map as a starting point. The Acinetobacter GAase polyalanine coordinates confirmed

the solution. The 3.2A map also has been used to solve the rotational

problem for the V ibrio Ase. This protein crystallizes in space group

P22-|2

i with a dimer in the asymmetric unit.

2. Structural Studies of Mutations in Catabolite Gene Activator

Protein

(I. Weber)

Catabolite gene activator protein (CAP) regulates transcription

of genes in E. coli. In the presence of allosteric activator, cyclic AMP,

(CAMP). CAP binds to specific DNA sequences at several operons, causing the

stimulation or repression of transcription. The crystal structure of a dimer of CAP with bound CAMP was solved (McKay and Steitz) at Yale

Unversity

.

CAP with an altered amino acid sequence is being investigated by Dr.

Alan Peterkofsky at NIH. Three CAP mutants, crp 91, crp 220 and crp 222,

that function in the absence of CAMP, have been sequenced. The amino acid

changes are: Ala 1 4 1 to Thr in crp 91 ; Thr 127 to lie and Gin 170 to Lys

in Crp 220; and Thr 127 to lie, Gin 170 to Lys and Leu 195 to Arg in crp

222. Crystallization trials have been performed on these three mutants in

order to study the relation of structure to functional changes. Crp 91 forms crystals with CAMP under the same conditions as wild type CAP. Both

crp 91 and crp 222 form crystals with CAMP under different conditions

using polyethylene glycol as precipitant. These 3 crystal forms have

similar unit cell dimensions to the crystals of wild type CAP, so it

should be relatively easy to solve the structures of the mutant proteins.

3. Predicted Structure for Two Domains of the Regulatory Subunit of

CAMP-dependent Protein Kinase

(I. Weber)

The mammalian CAMP dependent protein kinase regulates various

biochemical reactions by phosphorylating enzymes in the presence of CAMP.

The activator, CAMP, is bound in the regulatory subunit. The structure of

the regulatory subunit is not known, however it can be predicted by

analogy with the known structure of catabolite gene activator protein

(CAP) . CAP and protein kinase are both activated by CAMP. The amino acid

sequences have been determined of the regulatory subunits type I and II,

(RI) and (RII). Both sequences are homologous to each other and to the

sequence of catabolite gene activator protein from E.coli. Therefore, the

structure of CAP has been used as a model for the unknown structures of

the two homologous domains of RI and RII. The sequences of RI and RII

have been fitted to the CAP structure using a computer graphics system.

The model structures have similar binding sites for CAMP. The validity of
the model structure will be tested by comparing the predicted CAMP-protein

interactions with those deduced from experimental studies of the binding

of CAMP analogs to RI and RII.

4. Crystallization of the Fragments of Synthetic DNA

(M. Miller, A. Wlodawer)

The structure of a self-complementary synthetic sequence of DNA:

CGCGAATTCGCG has been known for several years as the best example of a B-type double helix. We are interested in obtaining large crystals of this

compound in order to conduct a neutron diffraction study which would

elucidate more details of the structure of associated water. The largest

crystals grown by us so far reach their maximum size of 0.25 mm3 after

about three months and it is necessary to further explore conditions for

making them larger.

A related sequence in which adenine is inserted in position 8

(following the sequence ...ATT...) has also been investigated. This

sequence is expected to form unmatched base pairing, with the additional

residue excluded from the Watson-Crick type double helix (or a loop made

of single chain). While such structures are common in nature, they have

not yet been observed experimentally. This materials crystallizes readily

at room temperature but the crystals are small, often are twinned, and

their diffraction pattern is disordered. Much better crystals can be

grown at 4°C, but they are very unstable during temperature changes and

the availability of a proper cooling device will be necessary before they

can be fully characterized.

5. Structural Studies of a sweet protein, monellin

(M. Miller, A. Wlodawer)

Monellin, a small protein of molecular weight 9000 dal tons, is

the second sweetest substance known. Knowledge of its three-dimensional

structure would be important to further understanding of the mechanisms of

sensory perception and in constructing artificial sweeteners.

Conditions for growth of large crystals of monellin have been

optimized. It is necessary to use a macro-seeding method in order to assure

reproducibility . This is accomplished by nucleating growth with an addition of a partially dissolved, small crystal to the growth medium.

The crystals can reach the final size of about 0.5 mm, but due to their

inability to withstand transfers to other solutions they have to be

crosslinked in 0.01% glutaraldehyde before use.

Two promising heavy atom derivatives of monellin have been found

after extensive search. These two derivatives are made by soaking in

either solution of .25 mM K

2 Pt(CNS )4 for 24 hours or 0.2 mM KAuCl^ for 16

hours. X-ray crystallographic data have been collected from several

native crystals to the resolution of 4A, and three centrosymmetri c zones were measured to 3.6A from a platinum derivative. Work on locating the

heavy atoms using Patterson syntheses is in progress.

1 95
6. Joint Neutron and X-ray Structural Refinement of Porcine Insulin

(A. Wlodawer and H. Savage)

Joint X-ray/neutron refinement of insulin has been performed

using 2.2 A neutron data collected on the BT8 flat cone diffractometer at

the N3S and 1.5A x-ray data provided by Dr. G. Dodson, University of

York, England. Several different models were calculated, using the X-ray

structure as a starting point. The first model was essentially a refinement of the x-ray data alone, lowering the R-factor to 0.148. Next,

24 cycles of joint refinement resulted in a model with R factors of 0.176

and 0.199 respectively for the x-ray and neutron data. The main problem

with this model was posed by the movement of solvent atoms out of x-ray

density, particularly severe for alternately occupied sites closer than

2A. Another model was calculated by fixing solvent positions to the

initial values and allowing only the atomic positions belonging to the

protein to refine. Finally, occupancies of amide hydrogens were refined

using neutron data only in order to study hydrogen exchange in the

crystals. The R factors in the final model were 0.183 (x-ray) and 0.191

(neutron). The bond lengths deviated by 0.02A from their ideal values.

The structure of two insulin molecules present in the asymmetric unit

was compared in order to correlate the differences with the crystal

packing. The two crystallographically distinct molecules differ by the

following RMS deviations: 1 .88A in their positions of all non-hydrogen

atoms and 2.23A for all atoms. This apparent discrepancy is due mostly to

concerted rearrangements in which the individual elements of secondary

structure such as a helices do not vary in an appreciable manner, but

their relative positions are strongly influenced by crystal packing

forces. The overall average temperature factors for the two molecules

were very similar (18.5 A^ and 17. 0A^). However, large local differences

were observed in regions connecting a helices and irregular parts of both

termini of the chain B. A number of hydrogen positions could be found

directly in the neutron density maps, showing that all histidines were fully protonated , and confirming a direct bond between histidine B10 and

zinc, without an intervening hydrogen.

The pattern of protection of amide hydrogens from exchange is

strikingly different in insulin than in any other protein studied so far

- see Figure 1 . The only region of significant protection under

experimental conditions employed by us (over four months soak of crystals

at pH = 6.5) was found in the center of the helical region in the 3 chains

(residues 14-19 in molecule 1 and 12-19 in molecule 2). No significant

protection of amide hydrogens was observed in areas of 3 sheets. Insulin

is comparatively less rigid than proteins such as BPTI and ribonuclease

and thus is more susceptible to processes leading to exchange which is in

good agreement with the available solution exchange data.

Most of the strongly bound solvent appears to occupy similar

positions in the neutron and x-ray 2F

o-F 0 maps, but there were significant

differences in the more disordered regions away from the protein surface.

196
T Q'

Diagram

or

the

hydrogen

bonds

Involving

the

main

chain

atoms

and

the

level

of

protection

of

the

amide

hydrogens

(H

exchanged

for

D):

Black

residues

are

fully

exchanged,

half

black/white

are

parti

illy

exchanged

and

the

white

residues

are

unexchanged.
7. Experimental water structure from hydrate crystals

(H. Savage)

Detailed structural characteri sties of water structure, both

ordered and disordered, have been obtained from a survey of various

geometrical parameters around water molecules in the available neutron

crystal structures which have been published. These included the ice

polymorphs, a large number of small hydrate crystals containing between

one and nine waters per asymmetric unit, and some larger hydrate crystals

(10-20 waters), in which parts of the solvent regions are disordered. The

hydrogen bonding geometries in these structures follow the same trends as those generally observed in known structures, hydrates and non-hydrates. A

majority of the waters have either trigonal or tetrahedral coordination,

but large distortions of the 0-H...0 and 0...0...0 H-bond angles from

their 'expected' linear and tetrahedral values occur.

What is not clearly understood about water structure, is how the

molecules orient themselves and pack together in more disordered phases

such as liquid water. These structural aspects depend critically on the

local short range non-bonded contacts which easily outnumber the more attractive ones around a water molecule by more than 24:4. These include

0...0, H...0, and H...H non-bonded contacts. In the hydrate crystals, the

0...0 non-bonded contacts appear to vary around the water oxygens: - 3 . 5

A

over the lone pair region, -3-3A between the hydrogens and —

3 - 1 A between

the lone pairs and the hydrogens. The remote H2...01 contacts of the

configuration 01 -HI . . .02-H2 , are seen to have minimum contacts of -

3 .IA

between the lone pairs and the hydrogens. The remote H2...01 contacts of

the configuration 01 -HI . . .02-H2 , are seen to have minimum contacts of

-3.0A (0-H distances fixed at 0.8A to represent the hydrogen electron

density). These minimum contacts are maintained around each water

molecule at the expense of distortions in the local H-bond geometries.

Water structure in protein crystals, that have been studied using

neutron and x-ray diffraction, is currently being analyzed. A computer

program is under development which is designed to formulate water network

structures using both the H-bonding and short range non-bonded information

as restraints.

8. Statistical Density Modification as an Approximation to Maximum

Entropy

(R. W. Harrison)

A simple and quick approximation to the maximum entropy

principle can be used in conjunction with phase combination to improve the

quality of electron density maps. The distribution of electron density

values is required to be Gaussian. When the phases are highly incorrect

the distribution is far from Gaussian. A Gaussian distribution

corresponds to the distribution found by maximum entropy with the

constraint of constant scattering power. With this method the observed

electron density values are replaced by values determined by a mapping

198
between a histogram of the observed density and a Gaussian distribution of

the same standard deviation. The mapping is found by requiring that the

integrals of the histogram and the Gaussian be identical. The Fourier

transform is then calculated and phase combination with any isomorphous

replacement data is then used to determine phases for the next cycle.

An electron density map produced by this method was used in solving

the structure of Ac inetobac ter asparaginase in parallel with the method

of 3. C. Wang. The two maps are comparable in the interior of the

protein, but differ considerably on the surface. The map produced by the

Gaussian appears to have more electron density at the protein surface than

the map produced by solvent flattening. The interpretation of the

asparaginase electron density map is described by I. Weber.

9. Structure of DNA Gyrase

(A. Wlodawer, S. Kruger, University of Maryland)

The structure of an enzyme DNA gyrase was investigated by the

technique of small angle neutron scattering (SANS). This enzyme acts as a topoisomerase and catalyzes negative supercoiling of DNA coupled to AT?

hydrolysis, by allowing a double- stranded DNA segment to pass through an enzyme-bridged, transient double-stranded break. DNA gyrase is composed

of two subunits designated A and 3 with molecular mean close to '00,000

daltons each. The active enzyme is an A

2 3£ tetraaer of molecular weight

400,000 daltons.

We have collected SANS data from solutions of each type of subunits,

from the active enzyme and from 1 :1 complexes of gyrase with a cloned

fragment of DNA consisting of about 170 base pairs. All experiments were performed in mixtures of 60$ H2 o buffer/ '40 % glycerol. Molecular weights

of A and 3 subunits obtained in the experiment were 206,000 and 100,000

daltons respectively (estimated error ± 11$) indicating that while 3

subunits make monomeric solutions, A subunits dimerize under the same conditions. Radii of gyration were 43± 3A and 41 ±5 A respectively,

indicating compact molecules. Radii of gyration of the holoenzyme and of

the gyrase - DNA complexes were both about 53A. Molecular weights of the

enzyme and of the complex were measured as 320,000 and 398,000 daltons

respectively. While these numbers are lower than expected, their ratio is

exactly that expected on the basis of known molecular weights. Their low

estimates may be due to errors in the measurements of the concentration of

macromolecules and this problem is being investigated. Further experiments will be performed in deuterated solutions, with the aim of

investigating the arrangement of DNA and protein in the complex.

10. Future Plans

The main thrust in the next year will be to complete the x-ray

data collection facility in order to provide us with in-house capabilities

in that field. We will build, from commercially available parts, a unique

diffractometer equipped with a two-dimensional position sensitive deceoto 0 which will be the best available. It will enable us to collect high

199
resolution x-ray diffraction data in temperatures ranging from -65°C to + 80 °C in a very short time. We shall continue to convert programs to run

on the IBM 4381 and develop programs for the Cyber 205.

We are planning to continue most of the current research programs and

to start several new ones. We hope to complete work on the structure of

Acinetob acter asparaginase and to compute high resolution maps of the

Pseudomonas enyzme. We will attempt to solve the structures of one or more CAP mutants and hope to produce an electron density map of monellin.

We will attempt to crystallize other available proteins and DNA. We hope

to complete the neutron investigation of insulin and to initiate neutron

investigation of Z-DNA and of an enzyme elastase. We will continue

theoretical work on the development of the technique of maximum entropy as applied to electron density maps. Since the currently available flux on

the small- angle neutron scattering instrument at NBS is insufficent to

complete the investigation of DNA gyrase, we will collect necessary data

in Grenoble, France.

200
3. CHEMICAL THERMODYNAMIC MEASUREMENTS

E. S. Doraalski, S. S. Bruce, T. J. Buckley, J. Colbert, H. DeVoe

D. A. Ditmars, D. R. Kirklin, P. Thompson, S. P. Wasik

A. Large Sample Combustion Calorimetry

(E. S. Domalski, D. R. Kirklin, J. C. Colbert, K. L. Churney, A. E. Ledford, S. S. Bruce, and T. J. Buckley)

This research is being perfomred in support of the Research

Conservation Recovery Act. Its purpose is to provide measurement methods,

standards and data for establishing heating values of a variety of

municipal solid wastes and for assessing the environmental impact of using

these waste streams for generating electrical power.

1 . The Calorific Value Problem

Incinerator-boiler systems used to dispose of municipal solid

waste (MSW) are bought and sold on the basis of thermal specifications.

To determine whether a system meets its thermal specifications, the

calorific value of the input waste stream must be known. During FY 1984,

we completed a study showing that, using suitable procedures,

representative gram-size test samples can- be prepared from a 2.5 kg

sampling increment. (The set of such increments is used to characterize

the calorific value of the waste stream fed to an incineration.) These

results settled the dispute among combustion engineers concerning whether

gram-size test samples are too small to characterize a multi-ton pile of

municipal solid waste

A second problem with existing calorific value test methods is that

combustion results are for complete combustion of the organic fraction of

MSW to C0 2 , H

2 0 etc. To apply these results to an incinerator, they must

be corrected for the products of incomplete combustion that occur in

real-world waste to energy systems. Currently no data are available for

validating methods either for the measurement of the degree of incomplete

combustion or the calculation of appropriate calorific corrections. To

rectify this situation, a study of the energy balance for incompleted

combustion was started in FY85. During the first half of the year, eleven

preliminary experiments, with associated apparatus development, were

carried out in the 2.5 kg flow calorimeter. Pellets of pure

(microcrystalline ) cellulose or synthetic ref use-derived-fuel (RDF) were

combusted in 0

2 /N 2 gas mixtures of 100, 50, 35, 21 and 17 mol? 02

. The

synthetic RDF was made from a mixture of cellulose and 20 mass %~ inert

material (silica and alumina). A goal of the study was to determine the

conditions for incomplete combustion of the cellulose, alone or as a component, to gaseous products and a solid char. The char is required to

have a mass sufficient for subsequent elemental and calorific value

analysis. Cellulose was used in order to have a reproducible enthalpy of

201
combustion (i.e. to CC^, H2

O, etc.). The material was burned in pellet

form rather than in loose form to simplify quantitative collection of ash

and char

.

The principal results of the study were:

(a) Appreciable (>40g) char and (usually) no unburned cellulose was produced by combustion of synthetic RDF at 21 mol % oxygen. Part of the

gas supplied to the combustor was preheated (by electrical heating) to

100°C to prevent appreciable amounts of unburned cellulose being present

in the combustion residue (ash). The sample did not completely char at

17 % oxygen and the amount of char formed at 35% or higher oxygen

concentrations was small (<2 g) . The amount of char is evidently

dependent on the inert material particle size. The amount cited above for

21 % oxygen is for 650-800 uM particle size silica. Negligible char (<29)

is formed at 21 % oxygen using a 50yM particle size of inert material

consisting of 50:50 silica and alumina.

(b) Hot gaseous hydrocarbons leaving the combustor were monitored

using a heated sample line (>105°C) and a flame ionization detector.

Provision for correction of the associated heat loss of the calorimeter is

accomplished by a thermocouple to determine the temperature of the sample

gas as it leaves the calorimeter, a flow meter, and calculation of gas

composition obtained by other measurements.

A final series of combustion measurements (ten as of 8/19/85) for

comparison of energy and mass balances at 100, 50, 35, and 21 mole percent

oxygen is in progress.

During FY 1986, we plan to complete the elemental and calorific value

analysis of the ash residue (i.e. char), the calculation, and the

evaluation of the energy balance study.

2. Organo-Chlorine Compounds in MSW

During the past decade, dioxins and difurans have been found in

the ppt to ppb range in the fly ash and flue gas of a number of

incinerators in the U.S. and Europe. The resulting public alarm has

seriously slowed or even stopped construction or operation of many waste

to energy plants. The main methods proposed for reducing the dioxin and

difuran emissions are removal of the responsible components of the waste

and "proper" design and/or operation of the incinerator. Currently, the

quantitative data bearing on these proposals is meager. As of 1984, we were aware of only one study of the chlorine content of the various

components of MSW. No consensus concerning "proper" design and/or

operation of incinerators to reduce dioxin emissions exists because of

lack of data and theory on the formation/destruction of organo-chlorine

appropriate to incinerator combustion conditions. In response to this

situation, the following two studies are being carried out.

202
(a) Chlorine Content of MSW

During the FY 1984, sampling of MSW was carried out at two

sites, each for periods of five days. Five days samples were obtained

from Baltimore County, Maryland, and five days samples from Brooklyn, New

York to provide some idea of differences between MSW from different areas. About 13 _20 kg of refuse was sampled daily from the output of the primary

shredder of the Baltimore County Resource Recovery Facility in

Cockeysville, Maryland. The New York samples were obtained by removing

five to seven increments of MSW on each of five days from the receiving

pit of the Green Point Incinerator in Brooklyn, New York. All samples were

dried and hand sorted into combustible components (paper, hard and soft

plastics, textiles, wood/ vegetable matter, and fines/ sweepings ) and

non-combustible components (glass, metals). Each of the combustible

components was processed to < 2 mm particle size, blended (i.e.,

homogenized) , and sampled for analysis to determine water-soluble chlorine

and total chlorine content. A reconstituted sample of each of the ten

days waste was prepared to determine the chlorine and the total sulfur

content of the original (i.e., unsorted) MSW. Analytical determinations

were completed.

During FY 1985, the results of the study were evaluated and

published. The principal results are as follows:

(1) All combustible components contain chlorine.

(2) The paper and plastic fractions contain the major portion of the

chlorine content.

(3) Most of the water soluble chlorine content is found in the paper

fraction

.

(4) Most of the water insoluble chlorine content is found in the

plastic fraction.

(5) In the MSW from Baltimore County, MD , the total chlorine content

is 0.4555 on a dry basis. About half of the chlorine is from the

paper, one quarter is from the plastics, and the other quarter

is from the remaining components. The mass percent of the paper

and plastics in the original, dry waste stream were about 60$

and 7%, respectively.

(6) In the MSW from Brooklyn, NY, the total chlorine content is

0.89$ on a dry basis. About half is from the plastics, one quarter from the paper, and the other quarter is from the

remaining components. The mass percent of the paper and

plastics in the original, dry waste stream were about 47$ and

11%, respectively.

203
(7) Removal of the plastic fraction from either waste stream reduces

the total chlorine content of the MSW from Baltimore County, MD

,

from 0.45 to 0.3 3% and the waste from Brooklyn, NY, from 0.89 to

0.50?.

During FY 1986, we propose, if time and funding permit us, to

initiate analysis of the sorted components of the above two sources of

waste for the type and amount of chi oro- organics

.

(b) Threshold Conditions for Formation/Destruction of

Organo-chlorine Compounds

A study to determine the threshold conditions for the formation

and/or destruction of organo-chlorine compounds in the combustion of MSW

was initiated at the end of FY 1984. During the FY 1985, equipment

construction and measurement procedure appropriate to this study were

carried out during the course of our study of the energy balance for

incomplete combustion discussed in section 3 • A . 1 . Our purpose is to

determine if we can reproducibly form and/or destroy organo-chlorine

compounds including dioxins in the 2.5 kg capacity flow calorimeter and, if

so, whether the combustion conditions (used in the energy study) can be

sufficiently well characterized to admit application of the results in the

threshold study to incinerator combustion conditions. The following was accomplished:

(1) A gas trap for trapping out gaseous species having dew points

>-10°C and a charcoal scrubber have been installed in the main stream of

the product gas exit line. The trap removes dioxins to the tens of ppt

level or less, and the scrubber finishes the removal of organo-chlorine

compounds before the product gas enters the laboratory exhaust system.

(2) An EPA modified method 5 gas and particulate sampling train for

chlorinated organics was built. The product gases are sampled through a heated (> 105°C) line from the calorimeter combustor. Particulates are trapped on Zitex filters and subsequently gaseous chlorinated organics are adsorbed on XAD-2 resin.

(3) To date, two combustions of synthetic RDF doped with polyvinyl

chloride (PVC) have been run: one 2.5 kg pellet with 1.5 mass % PVC in 35

mol % oxygen and a 3-7 kg pellet with 0.8 mole % PVC in 21 mol % oxygen.

Procedures for extraction of the sampling train filters and the XAD-2

resin and isolation of various polychlorinated dibenzo-p-dioxins and then

chlorinated organic components using chromatographi c means were developed

and carried out by S. Chesler et. al . of the NBS Organic Analytical

Research Division. Qualitative analyses using gas chromatography with an electron capture detector were carried out for the second combustion run. Chlorinated benzenes, (tetra, penta, and ’nexa) , chlorinated phenols (2, 4,

6 trichloro) and strong indications of a number of the polychlorinated

biphenyl cogeners (e.g. PCB 3, 28, 52, 101, 153) were found.

204
(4) Computer control of the gas mixture supplied to the combustor of

the flow calorimeter (air doped with C>2 or N 2 for 50 to 97 mol$ 03 ) was implemented and software was developed to evaluate combustion conditions

as a function of time.

During FY 1986, we plan to complete the preliminary study of the

combustion of pellets of synthetic RDF doped with PVC and with an inorganic chloride (and possibly both). Combustion conditions will be

modified to improve their definition as needed. A final study would be

initiated that would involve variations in MSW composition, including both

synthetic and real world RDF doped with chlorine compounds.

Financial support for this activity comes from the U. S. Department

of Energy, Biofuels and Municipal Waste Technology Division.

B. Certification of Combustion Calorimetry Standard Reference Materials

(J. C. Colbert and D. R. Kirklin)

The precision bomb calorimetry activities include the certification of

primary and secondary calorimetric standards that are used worldwide to

calibrate and check calorimetric and analytical procedures. The primary

calorimetric standard is benzoic acid, which has been available from NBS

since the 1920’s and which remains one of the top selling standard

reference materials (SRM’s). Secondary calorimetric standards are needed for

compounds which contain elements other than carbon, hydrogen and oxygen

and therefore require slightly modified calorimetric procedures to obtain

accurate and meaningful data.

Standard Reference Material certificates were prepared for three

calorimetric standards. Thianthrene was certified as an organic sulfur

standard. Nicotinic acid and urea were certified as low nitrogen and high

nitrogen content organic nitrogen standards. A Synthetic Refuse Derived

Fuel has also been certified. In addition, triphenyl phosphine oxide was studied as a possible organic phosphorous standard.

1. Certification of the Energy of Combustion of Thianthrene

(D. R. Kirklin)

Thianthrene was certified as a test substance for use in

checking calorimetric apparatus, analytical procedures and the calculations utilized in oxygen bomb calorimetry of organic sulfur compounds.

The actual measurements were performed during fiscal year 1984 and the

certificate was prepared during fiscal year 1985. The certified value was -33,480.4 ± 7.4 J/g at 298.15 K.

205
2 . Certification of the Energy of Combustion of Nicotinic Acid and

Urea

(D. R. Kirklin)

During the month of January 1985, measurements were made on SRM

2151 (Nicotinic Acid) and SRM 2152 (Urea) to check the certified energy of

combustion at 25°C. The following values in MJ/kg were obtained.

Nicotinic Acid (SRM 2151) Urea (SRM 2151)

22.183 1 0 .53-4

22.187 10.539

22.188 10.533

Mean: 22.183 10.535

These values were obtained at 28°C and when calculated to 25°C are within the uncertainty limits of the certified energy of combustion

values. The certified values for nicotinic acid and urea are 10.536 ± 0.003 and 22.185 ± 0.005 MJ/kg, respectively.

All of the measurements were made on samples which had been dried to

a constant weight. In addition, the number of grams of water placed in

the bomb was equal to 30 times the volume of the bomb in cubic decimeters

(liters )

.

3. Investigation of Triphenyl Phosphine Oxide as an Organic

Phosphorous Calorimetric Standard

(D. R. Kirklin)

This calorimetric standard is needed to evaluate calorimetric and

analytical procedures utilized in organic phosphorous studies. Triphenyl

phosphine oxide has been suggested as a suitable calorimetric phosphorous

standard because it can readily be obtained in a state of high purity and

is a non-hygroscopic substance that is very stable under ambient

conditions. Triphenyl phosphine oxide should exhibit difficulties

similar to other "unknown" phosphorous compounds and therefore should

allow experimenters to evaluate their procedures. A set of six

measurements yielded a specific energy of combustion of 35,788.15 ± 5.06

J/g with a percent coefficient of variance of 0.007%.

4. Calorimetric Update on SRM Coals 2682, 2683, 2684 and 2685.

(J. C. Colbert)

The annual calorimetric update on SRM Coals 2682, 2683, 2684 and

2685 was performed to determine if there has been any change in the

calorific value of these coals due to sample degradation as a result of

aging and oxidation.

206
Sixteen unopened bottles of the coals were received from the OSRM,

four of each SRM. One measurement was made for calorific value and one

for residual moisture. The original certified value for sulfur and ash

were used in making the calculations since these constituents remain

constant with time. All of the measurements were performed in random

order as established in a sampling procedure and run protocol designed by

R. C. Paule, NML Statistician.

The results were statistically evaluated and as was expected minor

degradation of the calorific values had occurred. The SRM certificate was revised to reflect these changes in the calorific values along with the new uncertainties and were included on the revised certificate of

February, 1985.

The uncertainty includes the observed variability within and between

HHV2 (calorific value-moisture free) measurements , any observed sample

heterogeneities, and an allowance for sample degradation equivalent to one year’s degradation.

5. Certification of Synthetic Refuse-Derived Fuel, SRM 1657.

(J. C. Colbert)

Certification of the Synthetic Refuse-Derived Fuel, SRM 1657, was completed this fiscal year with the certificate issued in March, 1985.

This SRM consists of three components blended to resemble a sample of

ref use-derived fuel. The composition of the SRM is approximately 80 mass

percent microcrystalline cellulose, 15 mass percent silica, and 5 mass

percent alumina.

Measurements have been performed on the bulk and bottled synthetic

RDF. The measurements on the bottled material consisted of moisture, ash

and calorific value. Five batches, each consisting of six samples were measured for moisture and ash. Selected sample bottles of the same material were used for the bomb calorimetric measurements . A total of

fourteen bomb calorimetric measurements were made. Statistically

significant bottle- to- bottl e heterogeneity was observed for the measured

properties. The dry ash value for the bottled material of 20.34$ was appreciably lower than the 20.67$ value observed for the bulk material

that was run in FY 84. In an effort to confirm these values a side-by-side comparison of the bulk and bottled material was made.

Determinations for residual moisture and ash were performed. The results

clearly showed that the 0.33$ difference was statistically significant.

The reason for this difference is not understood but could be attributed

to a small loss of the ash in the bottling procedure. The certificate

values are for the bottled material only and are appropriate since it is

the bottled material which is sold. The certificate value for the dry ash

is 20.34 ± 0.54 mass percent.

207
In FY 86 the enthalpy of combustion of benzoic acid will be

recertified. Benzoic acid is a best seller of the SRM program and

periodically needs to be recertified as stocks run out. Enthalpies of

combustion of oils and coals will also be measured for certification as SRM'S.

C. Estimation Methods and Combustion Calorimetry on Organic Phosphorous

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 for many of these compounds is not feasible

because of their toxicity or their limited availability. The objective of

this project is to develop correlation and estimation schemes which are needed to predict enthalpies of formation at 298 K for compounds having no reported experimental values.

A table of reaction enthalpies at 298 K has been compiled for some

50 organic phosphorous compounds. Group contribution values which follow

the additivity principle have been derived from the evaluated data. An

experimental calorimetric program to determine the thermochemical

properties of key organic phosphorous compounds has been formulated as a result of these correlation and estimation schemes.

The first objective of the experimental program is to establish a calorimetric standard for the combustion of organic phosphorous compounds.

The calorimetric standard is necessary to evaluate calorimetric and

analytical procedures utilized in organic phosphorous studies. Triphenyl

phosphine oxide has been suggested as a suitable calorimetric phosphorous

standard because it can be readily obtained in a high state of purity and

is a non-hygroscopic substance that is very stable under ambient

conditions. Triphenyl phosphine oxide should exhibit difficulties similar

to other "unknown" phosphorous compounds and therefore should allow

experimenters to evaluated their procedures.

Over twenty measurements of the enthalpy of combustion of triphenyl

phosphine oxide were made in the MBS adiabatic rotating bomb calorimeter.

The rotating feature is especially important because one of the major

problems associated with combustion studies of these compounds is the

attainment of a homogeneous bomb solution to ensure that the acids of

phosphorus with large energies of dilution are not formed in various

concentrations in different parts of the bomb. The attainment of complete

combustion was also a major problem. Oxides of phosphorus and their acids

tend to condense on the burning compound causing significant amounts of

carbon residue to remain in the crucible. Another problem encountered was

that many of the usual crucible materials were readily attacked during the

combustion process. Platinium and quartz crucibles were readily attacked.

Gold crucibles showed no signs of attack but sometimes melted when the

combustion reaction proceeded too vigorously. A stoichiometric accounting

of the combustion reaction requires a complete determination of the
substances present in the initial and final states. The combustion

products may contain a mixture of several oxyacids of phosphorus which

must be quantitatively measured. A set of six of the best measurements

yielded a specific energy of combustion of 35 778.15 ± 5.06 J/g with a percent coefficient of variance of 0.007$. However, this value is about

0.03$ below the best value in the literature. We believe that this

discrepancy is due to our inability to quantitatively determine the

amount of carbon residue of the combustion reaction.

Future plans are to run another set of approximately 7 combustion

experiments under conditions which will produce insignificant quantities

of carbon residue and determine the extent of reaction by analyzing the

CO? produced in the combustion of the sample. After establishment of

triphenyl phosphine oxide as a secondary combustion calorimetry standard,

several key organic phosphorous compounds will be investigated. Proposed

compounds are tricyano phosphine and triphenyl phosphine.

Funding for this research comes from the U. S. Army, Chemical

Research and Development Center, Aberdeen, MD

.

D. Bomb Calorimetric Measurements of 2-Deoxy-D-Ribose

(J. C. Colbert and E. S. Domalski)

Combustion bomb calorimetric measurements were completed on a sample

of 2-deoxy-D-ribose in FY 85. The molar enthalpy of combustion at 301.15

K for seven experiments is AqH = -18842.34 J ± 1.20 ( 1 SDM) kj mol

-

'. The

measurements were carried out with the aid of an auxiliary substance,

benzoic acid, which acts as a catalyst in the ignition of the sample.

Initially, measurements were performed by encapsulating the pellets in a small polyethylene bag. The sugar is slightly hygroscopic and the

polyethlene B served to protect the sample from moisture absorption. All

samples were encapsulated in a dry box. This method was abandoned since

there was appreciable scatter in the data that was found to be

attributable to the polyethylene.

The measurements were finally performed using samples that were dried

in a 25°C vacuum oven. Measurements on moisture content made by the Karl

Fischer Method were used to correct the sample mass to a dry basis.

NMR sample characterization techniques indicate that the anomeric

content of the sugar is the 3-pyranose and 5-pyranose form in the amounts

of 65$ and 35$, respectively. This anomeric content is assumed to exist

in the solid as well as in solution, which is the method in which these

NMR measurements were made. Time dependence studies of equilibrated

solutions of the sugar in DMS0-dg, when extrapolated to time-zero, support

this assumptions.

CC>2 analysis was performed on the bomb combustion products to

determine the sample purity. The gaseous products of combustion were released from the bomb and passed through absorption tubes containing
Asearite, magnesium perchlorate and P2 0

5

. The amount of C0 2 was then

determined gravimetrically . The analysis for C0 2 indicates a purity for

2-deoxy-D-ribose of 99.93 ± .03 % (sd).

In FY 86 the enthalpy of combustion of either hexaglycine or hexaalanine will be determined. Both these peptides are straight chain

like molecules. This experiment is being done to establish the feasibility of an "additivity approach" to the estimation of enthalpies of

formation of simple peptides using the enthalpy of formation of the amino

acids residues and an enthalpy of formation of the peptide bond.

E. Drop Calorimetry of Non-Reacting Systems Below 2800K

(D. A. Ditmars)

This activity is a continuation of a calorimetric research

program whose goals are:

1 . to obtain accurate thermodynamic data on non-reacting refractory

materials in either the solid or liquid state up to 2800 K.

2. to measure specific heat at temperatures above 273 K of wellcharacterized materials of the highest attainable purity for which

existing C

Q data are insufficient or in conflict and which are:

(a) critical to energy and space related technology, or (b) especially

suited as models on which to test refined lattice-dynamic calculation of

thermodynamic properties.

3. to produce and support high- temperature calorimetric standard

reference materials (SRM’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 (adiabatic receiving celorimeter). These are being used in research intended to provide calorimetric

measurements at the highest accuracy on materials related to the hightemperature applications mentioned above. Every effort is made to

coordinate this research with that of another NBS facility (very-hightemperature pulse calorimeter) in order to provide the capacity for

210
continuous coverage of high-temperature thermodynamic studies up to 5000 K or above on especially important systems. We have in addition an operative high- temperature discrete-heating adiabatic calorimeter

(300-800 K) and we maintain in reserve a low-temperature (4-300 K)

adiabatic calorimeter for possible future research needs.

In order that NBS thermal data and that of other high-temperature

investigations can be fairly intercompared 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 continued our investigation of boron nitride. This material,

exists in two phases, hexagonal and cubic. The hexagonal phase is a layered structure akin to the graphite structure and is widely used in the

fabrication of components for service at high temperatures in chemically

agressive environments, particularly where high resistance to mechanical

and thermal shock are important. We have prepared a specimen and

commenced relative enthalpy measurements in the range 1200-2800 K.

In fiscal year 1984, our research on pure metals for which the

existing tabulated thermodynamic functions are known to be in error,

included calcium and strontium. A sample of calcium, upon which enthalpy

measurements in the range 273 to 715 K had previously been completed, was submitted for analysis and found to contain in excess of 2 mole percent

CaO. This impurity was qualitatively confirmed in the behavior of the

sample in Thermal Analysis. The sample was re-distilled in the Metallurgy

Department of Iowa State University, thereby reducing the oxygen

concentration by a factor of 10 and the hydrogen concentration by a factor

of 2. A portion of the purified sample was loaded into an adiabatic

low-temperature calorimeter at the U. S. Geological Survey in Reston, V

A

and its heat capacity measured from 4 to 380 K. Another portion was encapsulated and its relative enthalpy measured in the bcc stability

range, 715 to 1112 K. The heat of the fcc-bcc transition at 715 K was also measured for both the original sample and the purified sample.

Preliminary analysis of the heat capacity data confirms that existing C

Q

data compilations for calcium can be in error by as much as 30 percent.'

A specimen of purified strontium was obtained on loan from Prof.

Westrum of the University of Michigan Chemistry Department. There exist

no published high-temperature data on this element. We have measured the

heat capacity of the fee phase up to 812 K, the temperature of the fcc/bcc

transition.

In fiscal year 1986 we plan to complete measurements on BN (hex) and

combine this data with our existing data below 1200K. We plan to commence

a study of pure zirconia, yttria-stabilized zirconia and/or

zirconia/alumina ceramics in order to generate the thermodynamic data

necessary to AFOSR investigators working in the modelling of

21

1
transformation-roughened ceramic systems and in the calculation and

prediction of multi-component ceramic phase diagrams. We plan also as time allows to extend our strontium measurements into the bcc phase above

812 K and to determine the enthalpy change on melting of our pure calcium

sample. A guest worker from Brock University is coming to NBS to measure

the heat capacity of copper up to its melting point. This data is to be

used to verify theoretical models for calculating thermodynamic properties

of bcc metals.

Financial support for this work has come from the U.S. Department of

Defense, Air Force Office of Scientific Research.

F. Weak Interactions in Model Enzyme-Substrate Systems

(P. T. Thompson, R. H. Wood, D. Smith-Magowan , S. P. Wasik, and H.

Devoe

)

Intra- and intermolecular interactions between functional groups and

other moieties of molecules dissolved in an aqueous medium play crucial

roles in a variety of properties and reactions. For example, the tertiary

structure of a globular protein is determined by non-bonded intramolecular

interactions, as well as by hydrogen bonding. The binding of a substrate

molecule to an enzyme also depends on these interactions. The objective

of this research is to measure the Gibbs energy, enthalpy and entropy

components of the interaction of several hydrophobic solutes with a variety of molecules dissolved in water, and to analyze these quantities

in terms of either group-group interactions or solute dimerization. These

data are needed for understanding the physical basis of hydrophobic

effects, for predicting various solubility and binding properties, and for

refining empirical potential functions for the pairwise interaction of

molecular groups immersed in water. The information is of great interest

to technologies which deal with stability and binding effects involving

macromolecules, such as enzyme-substrate specificity, to researchers in

the area of molecular recognition and host/guest chemistry when

hydrophobic groups are involved, and to those who calculate aqueous

properties by Monte Carlo and molecular dynamics computations.

The research underway is based upon measurements of the solubility of

a solid hydrophobic compounds in aqueous solutions containing a second

solute (the cosolute). At a given temperature and pressure, the chemical

potential of the dissolved hydrophobic solute in the saturated solution is

constant regardless of the concentration of the cosolute. Therefore, the

effect on the solubility of changing the cosolute concentration can be

interpreted as an activity coefficient effect; or, alternatively, as a free energy of interaction between the hydrophobic molecule and the

cosolute species. The data (solubility versus molality of cosolute) from

measurements with cosolutes containing different functional groups is

treated by the method of Savage and Wood to provide the free energies of

group-group interactions. The temperature dependence of these free energy

parameters yields the enthalpy and entropy components of the interactions.

212
The aqueous solubilities are measured using a coupled-column liquid

chromatography (CCLC) method developed at NBS. A generator column is

packed with crystals of the solute, or with a chromatographic solid support

coated with the solute. Pure water or an aqueous solution of the cosolute

Is pumped through the column to saturate the solution with the solute.

The solute concentration in the aqueous phase is found by extracting the

solute from a known volume onto an extractor column, and eluting this

solute onto a reverse phase analytical column for determination by HPLC

.

An automated version of the CCLC apparatus has been developed and

used to measure the solubilities of naphthalene and pyrene in aqueous

butanol solutions. The automated system includes control by a microcomputer of temperature, valves, HPLC pumps, and integrator, together

with provision for automatically changing the colsolute solution used as solvent. Recently, this apparatus was moved to a new location and

reassembled. Its performance has been thoroughly evaluated and several

changes expected to improve the precision of the measurements are being

incorporated

.

The solubility of napthalene, pyrene, anthracene, phenanthrene , and

tetracene in the presence of aqueous butanol, cyclohexanol , myoinositol

and mannitol are planned as the next experiments. Later it is expected to

proceed with the solubility of these same solutes with cosolutes

containing aromatic rings with hydroxyl and amine functional groups.

Eventually it is planned to include cosolutes containing aromatic rings

with hydroxyl and amine functional groups. Eventually it is planned to

include cosolutes containing nitrogen heterocyclic rings with amine and

carbonyl groups in order to explore stacking interactions of the type

encountered in aqueous nucleic acid systems.

These results will be analyzed to yield the pairwise Gibbs energy of

the solute-cosolute interactions and further broken down into group-group

interactions according to the Savage-Wood additivity principle [J.

Solution Chem. 5 , 733 (1976)]. This principle assumes that the total

interaction between two solute molecules is the sum of all possible

group-group interactions. From these results it should be possible to

construct a hydrophobicity scale which, being based on actual hydrophobic

interactions would be an improvement over existing scales which have been

calculated from data on the transfer of groups from water to the vapor

phase or to a nonaqueous solvent. These results could also be used to

interpret dimerizations constants of polycyclic aromatic hydrocarbons in

water, e.g. of the type observed for benzene by Tucker and Christian [J.

Phys. Chem. 83, 426 (1979)].

A related but separate project is to calculate aqueous solute-solute

Gibbs energies directly by evaluation of the integrals contained in the

cluster expansion expression for the second virial coefficient of

solute-solute interaction. Results obtained from calculations on a carefully chosen experimental data set including alcohols and polyols has

led to preliminary values of the parameters in the square-well potential

functions of the CH 2 —CH2 , CH2 —OH, and OH--OH interactions. The model is

213
crude and some numerical approximations are necessary, but results obtained

so far indicate that it will be possible to predict aqueous solute-solute

interactions on a theoretically sound, albeit simplified, basis. This work

is in progress, using the new NBS computer facilities, and plans are being

made to extend the results to include polysaccharide interactions and

cyclodextrin-inclusion compound complexes. Because of the known enzymatic

and transporting capabilities of the cyclodextrins in real biological

systems, the latter study would be especially significant and interesting.

21 J4
4. CHEMICAL THERMODYNAMIC DATA ACTIVITIES

D. Garvin, D. Bickham, D. Cockrell, P. Fagan, C. Jackson

T. Jobe, D. Neumann, D. Smith-Magowan

The goal of this work is to provide reliable values of thermochemical

and thermodynamic properties of chemicals, both inorganic and organic.

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 the work: the Chemical Thermodynamics Data Center (CTDC)

and the Electrolyte Data Center (ELDC). Their work is interlinked and is

reported here by topic, not by organization. The work of both data centers

is being extended by extra-mural collaborations.

The data group now consists of three and one-half thermochemists, a computer system manager, two computer programmers, a technical information

specialist and a clerk. In addition four thermochemists do special tasks under

contract

.

The Chemical Thermodynamics Data Center (CTDC) emphasizes evaluation

of data leading to formation properties (enthalpy and Gibbs energy) and

entropy at 298.15 K for as wide a range of chemicals as possible. The

resulting recommendations are published in NBS series, the Journal of

Physical and Chemical Reference Data, Handbooks, publications of CODATA

and ASTM, and by other agencies and professional societies such as the

Design Institute for Physical Properties Data (DIPPR) of the American

Institute of Chemical Engineers. In addition, the Center prepares an annual current awareness index to inorganic thermochemistry and answers

requests for information. This work is based on the Center’s subject index

to the world's literature on chemical thermodynamics and molecular

properties, which is updated each year.

CTDC also manages the computer facilities that also are used by the

Chemical Kinetics and Ion Energetics Data Centers and the Sputtering Data

Project in the Surface Science Division. This work includes day-to-day

operation of a mini-computer system, selection and testing of new hardware

and software, system and applications programming, and training of users.

During FY1985, emphasis has been on (1) collaborative work— the

CODATA Thermodynamic Tables , the CODATA Key Values for Thermodynamics,

and the OECD Nuclear Waste Disposal Study, (2) energy use--flue gas

cleanup for coal fired power plants and data for biomass, (3) information

services, and, (4) development of new automated tools for data evaluation

and data base management.

The demands for thermodynamic data continue to come from all parts of

science and industry. Current requests for information show no pattern other

than interests in specific compounds. Symposia on thermodynamics, however,

indicate general interests in high temperature processing of solids, vapor

transport, mineral assemblages, hydrothermal reactions, and, in the organic

215
chemical area, continued interest in fluid mixtures and vapor pressures. The

geochemists are among the most avid current customers for thermochemical data.

It is noteworthy that all of these applications require thermodynamic data as

a function of temperature, and at times, pressure.

The Electrolyte Data Center (ELDC) provides evaluated data on the

physical and chemical properties of electrolyte solutions to a diverse body

of users in the scientific and technical communities. Data are disseminated

through contributions to scientific publications, information services in

response to telephone and letter inquiries, and and through collaboration

with the NBS Corrosion Data Center.

The ubiquity of technical problems involving electrolyte solutions gives

the Electrolyte Data Center an extremely broad constituency to serve. In the

past, programs have been conducted that addressed needs in such diverse areas

as water pollution, battery design and development, corrosion and deposition

problems in steam power cycles, geochemistry, oceanography, natural gas and

oil exploration and processing, other energy technologies, as well as basic

laboratory study in virtually every physical science discipline. Emerging

technologies such as electronics and biotechnology present challenging new applications as they develop increasingly sophisticated processing and

separation techniques using aqueous fluids of increasing chemical complexity.

The Center conducts research into improved or new methodologies for the

correlation and estimation of solution properties and presents the results of

such research to interested forums.

Effort in FY 1985 was directed to activities that fall in three

categories: (1) Studies of the thermodynamics of aqueous electrolytes, (2)

development of data evaluation methods, and (3) thermochemistry of

biochemical equilibria. These are described later.

A. Thermochemical Data Evaluation for Inorganic Systems

(D. Garvin, V.B. Parker)

The data evaluation effort this year involved participation in

three cooperative international programs. NBS evaluates data, coordinates

work, advises on procedures and provides support services for each.

1 . CODATA Thermodynamic Tables System

A comprehensive set of thermodynamic tables on selected

compounds of calcium has been completed on a collaborative program

sponsored by CODATA (Committee on Data for Science and Technology of the

International Council of Scientific Unions). These tables, prepared as the

first of an international series, include thermal functions,

thermochemistry, an alloy, a fused salt and an aqueous solution system.

Extensively documented, entirely automated, this 200 page book is now being reviewed and prepared for publication late in 1985.

216
The work has been done in five laboratories: NBS, Dow Chemical ( JANAF)

,

AERE Harwell, U.K., ENSEEG, Grenoble, France, and the Akad. Nauk Thermocenter,

Moscow, USSR.

The NBS data centers provided: (1) selected values at 298.15 K for

thermochemical properties of 68 compounds, (2) thermodynamic properties for

the CaC^-^O system, 298.15-373*15 K, (3) 394 evaluations of thermochemical

measurements, (4) quality controls to assure conistency among all tables, and

(5) editorial supervision (with D.D. Wagman, R. L. Nuttall).

2. Key Values for Thermodynamics

The "CODATA Key Values for Thermodynamics" have been completed

and are being edited for publication late in 1985. This final report of a CODATA Task Group has been written by D.D. Wagman, V. A. Medvedev and J.D.

Cox. The report covers 150 substances (53 elements and one or two

compounds of each) that are central to thermodynamic measurements and data

evaluations. These recommendations are backed up by 100 tables of thermal

functions, extensive documentation, a catalog of measurements related to

the thermochemistry of aqueous ions and a 2000 item bibliography. These

reference data are expected to be the standards used throughout chemical

thermodynamics for the next 10 years. NBS data centers have provided

analyses of data, particularly for aqueous species, and editorial

services

.

3. Data for iron compounds and nuclear waste storage systems

Two new thermochemical data projects have been undertaken. One

is the thermochemistry of compounds of iron. The objective is to provide

an up-to-date thermodynamic data base for use in process calculations

involving this economically important element and its compounds. The

evaluation is being done for the CODATA Thermodynamic Tables jointly by

NBS and the USSR Academy of Sciences Thermocenter, Moscow. The scope has

been established and preliminary evaluations have been made on properties

of the element, oxides, chlorides, sulfides and aqueous ions. Data bases

are being exchanged. Ultimately, the work will treat the element, oxide,

halides, sulfides, sulfates, carbonates and silicates. These are the

"basic" compounds upon which the thermochemistry of all other iron

compounds and systems rest. The project also includes thermal functions

for all compounds, and several high temperature systems (Fe-0, Fe-S, Fe-C

and Fe0-Si02

) to be done in other laboratories

.

The second is an evaluation of the thermochemistry of compounds of

strontium that is related to the problem of storage of nuclear wastes. This

is being done as part of a larger project sponsored by the OECD Nuclear

Energy Agency. The NBS role in this work also includes assuring that the

results are compatible with the current evaluations of data being made for

CODATA.

217
B. Organic Thermochemistry

(E.S. Domalski, T. L. Jobe, Jr. with E. Hearing)

Two projects treat very different aspects of organic thermochemistry:

prediction of properties of pure compounds and compilation of data on reusable biomass and industrial products.

1 . Estimation Procedures

"Nearest neighbor group contributions" have been developed for

hydrocarbons in condensed phases. The contributions, orginally developed

by Benson, have also been refined for the gas phase. These group values

can be used to calculate enthalpies of formation, heat capacities and

entropies at 298.15 K. Tests show that the agreement between experimental

and predicted to be within 4 kJ/mole for the enthalpy of formation in

condensed phases and 1 J/mol K for entropy in condensed phases. A

manuscript is in preparation which will be sent to J. Phys . Chem.

Reference Data.

2. Biomass

Thermodynamic data on material relevant to biomass utilization have

been compiled. These include heat capacities, enthalpies of combustion, and some density data. This compilation extends earlier NBS work on incineration

and waste recovery. The entire set will be published in 1986 jointly with the

Solar Energy Research Institute.

C. Biochemical Thermochemistry

(D. Smith-Magowan)

Gibbs energies of formation for 22 species that are metabolized by the

Krebs (or TCA) cycle were evaluated from experimental measurements of

equilibrium constants for 30 enzymatic reactions and Gibbs energy of

formations for 6 species calculated from enthalpies of combustion and Third

law entropies.

The network formed by these reactions was fitted by the CATCH least

squares programs to obtain the best internally consistent set of Gibbs

formation energy values(at 298.15 K, 1 atm pressure and 0.1m ionic strength)

for the 22 species comprising the network. The standard deviation of the

residuals for the reactions was <0.5 kJ while the 95 % confidence intervals

for the resultant formation energies were “1-2 kJ. This is a collaborative

project with S.L. Miller, U. Calif., San Diego.

To our knowledge this is the first network treatment of the data.

The values obtained represent a marked refinement over values compiled by

Burton and Krebs, Wilhoit, Long and Johnson. A schematic diagram of the

network is shown in Figure 2. New NBS measurements (Goldberg, Gajewski,

Tewari, Steckler) on the fumarase to aspartase conversion equilibrium are significantly more consistent with the values predicted by the network

solution than are earlier measurements on this conversion.

218
Acelyl

CoA

219

Expanded

Krebs

cycle

thermodynamic

network:

Each

arrow

represents

a

measured

equilibrium

constant.

The

circled

numbers

refer

to

the

particular

process

as

referenced

in

the

paper

to

be

published.
The importance of the Krebs cycle in the biological production of energy

and its connection with many other metabolic and synthetic pathways ensures a broad-based constituency, among researchers concerned with many aspects of

enzyme activity, that will benefit from this study and the continued

application of the network analysis method.

D. Thermodynamics of Electrolyte Solutions

(D. Smith-Magowan, V. B. Parker, D. Garvin)

The thrust of the electrolyte data evaluation work has been to

correlate properties in the T, P, x surface in a general manner. Calcium

chloride has been the specific example studied.

1. Heat capacities for CaCl 2 as a Function of T and X

An evaluation has been made of the heat capacity of calcium

chloride solutions as a function of temperature and composition. A new numerical algorithm has been used that was developed at the University of

Delaware (and is described below). The correlation covers the temperature

range 273 - 403 K and 0-11 molal, and is believed to be a more accurate

representation of the data than those presented recently by Anathswamy and

Atkinson and by Staples. A larger data set has been used than those used

by the other authors.

2. Activity Coefficients and Enthalpies for CaCl 2 as a Function of

T and X

A self consistent set of activity coefficients, excess enthalpies and excess heat capacities has been prepared for calcium

chloride solutions, 298.15-373-15 K, 0-11 molal. These are based on the

heat capacity correlation, previously evaluated activity coefficients and

a new correlation of enthalpies of dilution. This work is being published

as part of the CODATA Thermodynamic Tables. This work is believed to be

the most self-consistent treatment of these properties throughout the

given temperature and composition ranges.

3. Solubilities

Solubility data for calcium chloride solutions have been

evaluated and recommendations made for the temperature range 223 _530 K.

These data also are being published in the CODATA Tables.

4. Sulfur Dioxide

"Thermodynamics of Solution of S02 (g) in Water and Aqueous

Sulfur Dioxide Solutions", by R.N. Goldberg and V.B. Parker is scheduled

for publication in J. Res. NBS. This updates work reported previously and

include consideration of unpublished measurements by Hepler and

Dobrogowska. The work was supported by NBS OSRD, DoE and DIPPR.

220
E. Development of Methods for the Correlation of Properties of Solutions

(D. Smith-Magowan)

Methods have been developed for testing both strong and weak

electrolytes

.

1. Spline Procedures for the (T,P,X) Surface.

The algorithm developed at the University of Delaware for fitting

Cp, and applied to data on calcium chloride solutions provides a spline fit as

a function of temperature and composition. This gives a model independent

numerical representation of the data. It appears to reproduce the data very

well

.

A major extension has been made of this algorithm to permit spline

fitting of a mixed set of thermodynamic data (heat capacities, enthalpies,

activities and PVT data) in terms of the independent variables T, P and

composition. Tests of this extended algorithm against measurements for

calcium chloride will be performed as soon as data collection is completed.

This testing should start by the close of FY 1985.

2. Treatment of Weak Electrolytes

The article " An Equilibrium Model for the Calculation of Activity

and Osmotic Coefficients in Aqueous Solutions”, by R. N. Goldberg was published in J. Res. NBS, 89, pp 252-263 (1984). The model provides the

capability to calculate activity and osmotic coefficients of the constituents

of multicomponent mixtures in which multiple equilibria are taking place.

F. Data Base Development—General

(V.B. Parker, and with R.L. Nuttall , R.H. Schumm)

A continuing thrust is the preparation of numerical data bases for use in evaluations and to document past work.

1 . Data Bases Developed at NBS

Five numerical data bases have been completed. Two document parts

of the "NBS Tables of Chemical Thermodynamic Properties" , and cover compounds

of rubidium and lithium. One covers sulfur, its hydrides, oxides and oxyacids

and is part of a project to develop data bases for use in flue gas cleanup

studies for coal fired power plants. The fourth is based on the compilation

of data relevant to biomass conversion. The fifth is a detailed listing of some 550 measurements required to define the thermochemical properties of

common aqueous ions. It is being published as part of the "CODATA Key Values

for Thermodynamics". (D. Neumann, D. Bickham, with J.B. Pedley)

221
2 . Data Bases Contributed by Others

Four numerical data bases have been received as parts of

collaborative programs. One hundred tables of thermal functions and a thermochemical data base on iron compounds have been obtained from the USSR

Thermocenter . A thermochemical data base of measurements on iron, cobalt and

nickel chlorides, together with thermal functions has been obtained from Dr.

J.B. Pedley, University of Sussex. All of these are being used in current

evaluations of data for CODATA.

The fourth is a file of evaluated data for enthalpies of formation

for 3000 organic compounds from the University of Sussex data base plus

enthalpies of formation for selected organo-phosphorus compounds evaluated

at NBS.

G. Data Base Development — Properties of Electrolyte Solutions

(D. Smith-Magowan, R.N. Goldberg, V.B. Parker, R.L. Nuttall, J.L. Manley,

D.K. Steckler)

Data bases and bibliographies have been prepared. The data base has

been provided in magnetic tape format together with appropriate software.

1. Activity Coefficient Prediction Program

A data base of the activity coefficients of about 350 electrolytes

was published on magnetic tape for distribution by OSRD . The companion

documentation was published as NBS-Technical Note 1206 "GAMPHI-A Database of

Activity and Osmotic Coeficients for Aqueous Electrolyte Solutions" by R. N. Goldberg, J. L. Manley and R. L. Nuttall. The program was structured to

provide both interactive recall of values for desired compounds at specified

concentrations and direct transfer of values to user programs via supplied

subroutines

.

2. Bibliographies of Industrial Interest

"A Bibliography of sources of Thermodynamic Data for the Systems:

C0 2 +NH3+H2 0, C02 +H2 S+H2 0, H2 S+NH3+H2 0, and C0 2

+ NH3+H2 S+H2 0" by R. N. Goldberg, and D.K. Steckler was issued as NBS Spec. Publ. 699. This work was supported in part by DIPPR whose concern focusses on the chemical processing

of such mixtures as they occur in wastewater streams. Other bibliographies

that were submitted to DIPPR at the end of FY 85 will soon be available for

issuance as NBS documents. During the past year additional material has been

identified that will necessitate minor revision of the monographs prior to

publication

.

222
H. Accessions, Information, and Support

(D. Cockrell, T.L. Jobe, P. Fagan, C. Jackson, with E. Hearing,

W.H. Evans and N. Young)

These are ongoing activities that make possible the systematic

evaluation of data. During the year 3500 articles from the current literature

have been located, abstracted, and entered in our index to thermodynamic

measurements. This work also is the basis for the Inorganic Substances

section of volume 28 of the Bulletin of Chemical Thermodynamics. Emphasis in

the current year has been to streamline day-to-day operations including

making more use of automated retrieval from Chemical Abstracts on Line. In

addition, the use of automated searches and the production of reports from

our files has been significantly expanded and simplified.

I. Automation Activities

(D. Bickham, P. Fagan, D. Neumann)

Four data centers share the use of an HP-1000 mini-computer via

terminals and interfaced personal computers. Principal uses of the

mini-computer are word processing and data manipulation. Calculations and

graphics are a small but growing fraction of the work load. Individual

researchers reduce and model data. Users are supported by the automation

group of the Chemical Thermodynamics Data Center which is responsible for

system maintenance and development.

1 . Computer Upgrade

In FY1985 the mini-computer system received a major upgrade with a faster CPU, larger memory, and a more flexible operating system. Software for

graphics, data management, and communications were purchased and numerical

analysis packages were down-loaded from the NBS central facility. Personal

computer software packages, such as LOTUS 1-2-3 and WORDSTAR, have been put

into use and are being integrated with applications running on the

mini-computer

.

2. Data Communications

Transfers of data and text between personal computers, the N3S main

frame, the NBS typesetting system, the secretarial workstations, and the data

center’s mini-computer are now possible. In addition, computer- to-computer

communications with cooperating researchers outside NBS, have been enhanced

and simplified. Transfers of data to NBS are now being made from JANAF

(Midland, MI), ENSEEG (Grenoble, France), AERE (Harwell, UK), and

Thermodynamic Research Center (College Station, Texas) Transfer on tape

remains the method used for data from the Academy of Sciences Thermocenter

(Moscow, USSR).

223
3. Cooperative Program with the Univ. Sussex.

(with J.B Pedley, A. Pedley)

In a joint effort during the summer of FY85 with J. B. Pedley,

Univ. of Sussex, UK., the data center has imported several of his programs,

converted them for use on the HP-1000, and begun to integrate them with other

modules. These programs consist of the following:

(a) Thermochemical calculations. These consist of a set of

programs for the management, adjustment, and prediction of thermodynamic

data for chemical and physical processes. The system provides for storage

of raw data, reduction of equilibrium data, comparison of measurements

with previous selections, and calculation of tables of thermal functions.

(b) Organic Search and Retrieval System. This program is a data storage and retrieval system based on a new notation for organic

functional groups. With this system thermodynamic data, at present

enthalpies of formation, can be retrieved for compounds having common

substructures. The associated data base is the entire Sussex

Thermochemistry file.

(c) Prediction of Enthalpy of Formation for Organic Species.

This set of programs predicts enthalpies of formation of organic

substances. It is based on a group contribution method that allows some next-nearest-neighbor interactions. An effort is underway to extend this

work to heats of vaporization, heat capacities, and entropies, and to

compare its performance with the prediction scheme developed by E.S.

Domalski at NBS.

4. Information Processing

A number of efforts have been made this year to streamline our day

to day operations and to enhance access to our data base by evaluators. These

efforts consist of:

(a) A bibliographic retrieval system with printed and on-line

documentation which is almost complete. It is under test currently with

40,000 references from CTDC's pre-1969 bibliography (with W.H. Evans).

(b) New programs for processing abstracts which have been

completed, tested and are now in use. With these programs the collection of

abstracts from 1970 to 1985 have been prepared for loading to the CTDC data

base. In addition, these programs have processed the inorganic contribution

to volume 27 and 28 of the Bulletin of Chemical Thermodynamics and have also

been used to reformat the organic contribution from Texas A&M to volume 27 of

BCT

.

(c) The automation of the storage, retrieval, and printing of

tabular thermal function data with a report generator. This system was used

to produce chapters in the "CODATA Thermodynamic Tables" and the "CODATA Key

Values for Thermodynamics". It is expected that in the next year these

224
programs will be integrated with the programs for management of chemical

reaction data obtained from U. of Sussex this year (see above) (with R.J.

Cvetanovic )

.

(d) A further success has been the coordinated planning, and

implementation of a chemical species and chemical reaction retrieval system.

This joint effort with the Chemical Kinetics and Surface Science Divisions

has proceeded to a point where plans are firm and programs for storage and

retrieval have been written and are being tested. In its final form this

system will permit on-line access (at NBS) to evaluated kinetic and

thermodynamic data using a uniform system of programs and utilities based on shared substance, reaction, and bibliographic data bases.

J. Plans for FY 86 include

1. Thermodynamic Data Evaluation.

v Recommended values will be developed for thermochemical properties

of selected compounds of iron (with possible extension to cobalt and nickel)

,

selected compounds of strontium, and for nitrogen-oxygen-sulfur compounds.

These projects are, respectively, in support of the CODATA Thermodynamic

Tables, The NEA Nuclear Waste Study, and the DoE Flue Gas SOx-NOx Removal

Program.

An analysis will be made of data on equilibria in biochemical cycles

closely related to the Krebs cycle, as part of the NBS Biotechnology Program.

A major new project will be the preparation of tables of thermal

functions for use in science and industry. (This will be done by merger of

the JANAF Tables into the NBS thermodynamic data activity.)

A new procedure for analyzing thermophysical and volumetric properties

in terms of a (T, densi ty ,composi tion ) surface for solutions of strong

electrolytes and their mixtures will be tested and applied to CaClp-H 2 0. This

is part of a joint project with the Univ. of Delaware.

Estimation of enthalpies of formation of organic compounds will be

extended to organophosphorus compounds. This is part of a joint project with

the Univ. of Sussex.

2. Data Base Development

Catalogs will be prepared of measurements on thermodynamic

properties of compounds of iron, and strontium, and of N-0-3 compounds.

Previously prepared catalogs of measurements will be prepared for

publication

.

Current articles on thermodynamics and molecular properties (about 3500)

will be selected, abstracted and used in the NBS Thermodynamic Index and the

Bulletin of Chemical Thermodynamics.

225
A heat capacity, enthalpy and molecular properties data base will be

developed from the joint holdings of NBS, JANAF and Univ. of Sussex.

3. Thermodynamics of Aqueous Electrolyte Solutions

The algorithm for fitting properties of electrolyte solutions

versus T, P, and x will be tested against data collected for CaC^. the

results of this study will be prepared for publication. Data for KC1

solutions are being collected since this is the next candidate for treatment

by this method.

A proposal to DIPPR for the development of a microcomputer based

interactive database system for the thermodynamic properties of electrolytes

as functions of temperature and presssure has been accepted and support is

expected to begin with calendar year 86. The proposal calls for

approximately 6 persons months of effort per year for the next three years.

Objectives for the first year include supplementing the existing Gibbs energy

collection and developing software modules for calculating engineering

quantities, estimating methods and diagnostic testing for complexing and ion

association

.

4. Biothermochemical Equilibria.

The network analysis used for the Krebs cycle will be applied to

additional cycles that are connected to the Krebs cycle. The exact choices

have not been made but candidates included the glycolytic pathway,

ATP-citrate lyase sequence, catalyzed amino acid syntheses and others.

5. Automation Activities

The emphasis in FY86 will be to place the joint Kinetics,

Ion-Energetics, Surface Science, Chemical Thermodynamics data base system

into full operation. This will be an on-line system, screen oriented, if

possible, with a common chemical dictionary and bibliographic protocal but

separate kinetics and thermodynamics data files.

Calculational programs for thermodynamic properties will be integrated

with the existing NBS data base. Existing predictive systems such as that

from Sussex will also be incorporated and futher documented to allow greater

access and use.

The management of computer operations for the several data centers using

the mini-computer will continue with programming services, selection of new software and hardware, and integration of micro- and mini-computer

capabilities. An effort will be made to encourage word-processing and small

calculations on the micro's and to encourage shared uses such as data bases,

complex programs, and graphics on the mini-computer.

226
5. PUBLICATIONS

(a) Publications of Past Year

Abramowitz, S. , "Biotechnology and Bioseparations", Proceedings of the

National Science Foundation Workshop, Thermodynamics Needs for the

Decade Ahead: Theory and Experiment. October 28-29, 1983, S.

Sandler, Ed.; Vol . 1 , 55-66 (1985) and Vol.2.

Ammon, H.L., Murphy, K.C., Chandrasekhar K. and Wlodawer, A., "Preliminary

Crystallographic Study of an L-Asparaginase from Vibrio Succinogens, J.

Mol. Biol., 184, 179 (1985).

Borah, B. , Chen, C., Egan, W., Miller, M., Wlodawer, A. and Cohen, J.

,

"Nuclear Magnetic Resonance and Neutron Diffraction Studies of the

Complex of RNase A with Uridine Vanadate, a Transition-State Analog",

Biochemistry, 2_4, 2058 ( 1 985).

Buckley, T.J., Sieck, L.W., Metz, R. and Lias, S.G., "Consecutive

Ion-Molecule Condensation Reactions and Photodissociation Mechanisms of

Condensation Ions in Polyacetylenic Compounds", Int. J. Mass.

Spectrometry and Ion Processes, 65_, 1 81 (1 985).

Busenberg, E., Plummer L.N., Parker, V.B., "The Solubility of Strontianite

(SrCO^) in CO 2 and H 2 O Solutions Between 2 and 92 °C, the Association

Constants of SrHCO^ (aq) and SrCO^ (aq) Between 5 and 80 °C and an Evaluation of the Thermodynamic Properties of Sr^ + (aq) and SrCO^ (cr)

at 25 °C and 1 Atmosphere", Acta Geochimica 48., 2021 ( 1 984).

Churney, K.L., Ledford, Jr., A.E., Bruce, S.S. and Domalski, E.S., " Chlorine

Content of Municipal Solid Waste from Baltimore County, MD and Brooklyn,

NY", NBSIR 85-3213, April (1985).

Colbert, J.C. and Kirklin, D.R., "Determination of Sulfur, Calorific Value,

and Ash Content in NBS Coals Using ASTM Procedures D2015, D 3 1 80 , D3 1 77

,

D3 1 73 , and D3174", Chapter III of NBS Special Publication 260-94, T.E.

Gills, editor; "Standard Reference Materials: Methods and Procedures

Used at the National Bureau of Standards to Certify Sulfur in Coal SRM's

for Sulfur Content, Calorific Value, and Ash Content", December (1984).

Colbert, J.C., "Certificate of Analysis, Standard Reference Material 1657,

Synthetic Refuse Derived Fuel Combustion Calorimetric Standard",

February (1985).

Domalski, E.S., Churney, K.L., Ledford, Jr., A.E., Colbert, J.C., Bruce,

S.S., Buckley, T.J., Paule, R.C. and Reilly, M.L., "Determining the

Calorific Value of Municipal Solid Waste: Experimental Results from a 2.5 Kilogram-Capacity Flow Calorimeter", Proceedings of Energy from

Municipal Waste Research Workshop held in Kissimmee, Florida, February

22-24, 1984, 29-47, ( ANL/CNSV-TM-1 44)

.

Gajewski, E. , "Radiation-Induced Products of Peptides and Their Enzymatic

Digestibility", Dissertation Abstracts International, 4_4, 381 3-3

(1 984).

227
Gajewski, E. , Dizdaroglu, M., Krutzsch, H.C. and Simic, M.G., "OH

Radical-Induced Dimerization and Racemization of Methionine in

Peptides", Int . J. Radiat. Biol., 46_, 47 ( 1 984).

Garvin, D., Domalski, E.S., Wilhoit, R.C., Somayajulu, G.R. and Marsh, K.N.,

"Heating Values of Components of Natural Gas", Proc . Symp. "Natural Gas

Energy Measurements", August 26-28, Chicago, 111., (1985).

Garvin, D., Goldberg, R.N. and Staples, B.R., "Evaluated Data and Data Bases:

Chemical Thermodynamics in the Steam Power Cycle", Proceedings of the

Workshop in Steam Power Cycles Data Requirements, H. White and 0. Jonas,

Editors, February 8-9, 1983, NBSIR 85-3205, July (1985).

Goldberg, R.N., "Compiled Thermodynamic Data Sources for Aqueous and

Biochemical Systems: An Annotated Bibliography (1930 to 1983)", NBS

Special Publication 685, U.S. Government Printing Office, Washington,

DC, (1984).

Goldberg, R.N., Manley, J.L. and Nuttall, R.L., "GAMPHI - A Database of

Activity and Osmotic Coefficients for Aqueous Electrolyte Solutions",

NBS Technical Note 1206, U.S. Government Printing Office, Washington,

DC, (1985).

Goldberg, R.N. and Steckler , D.S., "A Bibliography of Sources of

Thermodynamic Data for the Systems: C0 2

+ NH^ + H 2 0, C0 2

+ H2 S + H2 0,

H2 S + NH

3

+ H2 0, and C0 2

+ NHo + H2 S + H2 0" , NBS Special Publication,

69, U.S. Government Printing Office, Washington, DC, (1985).

Johnson, W.H., "Certificate of Analysis, Standard Reference Material 2154,

Nicotinic Acid Combustion Calorimetric Standard", 1985.

Johnson, W.H., "Certificate of Analysis, Standard Reference Material 2152,

Urea, Combustion Calorimetric Standard", 1985.

Kirchhoff, W.H., "A National Program of Measurement Services and Standards

for Biotechnology at the National Bureau of Standards", National Bureau

of Standards, Planning Report 22, March (1985).

Kirklin, D.R., Decker, P.H. and Domalski, E.S., "Characteri zation of RefuseDerived Fuel at Various Stages of Processing", Resources and

Conservation ]J_* 255 (1985).

Kirklin, D.R. and Domalski, E.S., "Certificate of Analysis, Standard

Reference Material 1656, Thianthrene, Combustion Calorimetric Standard",

January ( 1 985)

.

Owens, J.W., DeVoe, H. , Buckley, T.J. and Wasik, S.P., "An Automated

Coupled-Column Chromatography System for Measuring Aqueous Solubilities

of Hydrophobic Solutes", J. Research NBS 90, 41 (1985).

Simic, M.G., Gajewski, E. and Dizdaroglu, M., "Kinetics and Mechanisms of

Hydroxyl Radical-Induced Crosslinks Between Phenylalanine Peptides",

Radiat. Phys. Chem. 24, 465 (1985).

228
Smith-Magowan, D., "Evaluation of the Applicability of Colloid Studies to

Cobalt-60 Deposition in LWRs", NP-3773 Electric Power Research

Institute, Palo Alto, CA, November (1984).

Smith-Magowan, D., "The Impact of Colloidal Chemistry on Radioactivity

Transport in Nuclear Power Plants", NP-4032 Electric Power Research

Institute, Palo Alto, CA, May (1985).

Steitz, T. A. and Weber, I.T., "Structure of Catabolite Gene Activator

Protein", In 3iological Macromolecules and Assemblies, Vol.2: Nucleic

Acids and Interactive Protein (F. Jurnak and A. McPherson, editors),

John Wiley and Sons, Inc., New York, 289 (1985).

Tewari, Y.B. and Goldberg, R.N., "A Note on the Thermodynamics of the

Conversion of Aqueous Glucose to Fructose", Applied Biochemistry

Biotechnology, 1_1_, 17 (1 985).

Tsang, W., Macek, A., Domalski, E.S., Walker, J.A., Charagundle, S.R.,

Colbert, J.C., Kirklin, D.R., Ledford, Jr., A.E., Decker, P.H. and Ryan,

R.V., "Combustion Characteristics of Refuse Derived Fuel", NBSIR

83-1343, October (1984).

Wasik, S.P., Schwarz, F.P., Tewari, Y.B., Miller, M.M. and Purnell, J.H., "A

Head-Space Method for Measuring Activity Coefficients, Partition

Coefficients and Solubilities of Hydrocarbons in Aqueous Solutions", NBS

J. Res. 89, 273 (1984).

Weber, I.T. and Steitz, T.A., "A Model for the Non-Specific Binding of

Catabolite Gene Activator Protein to DNA", Nucleic Acids Res. 1

2

, 8475 (1984).

Weber, I.T. and Steitz, T.A., "The Crystallization of rec A Protein from

Proteus Mirabilis", NBSIR 85-175, September (1985).

Wlodawer , A., "Structure of Bovine Pancreatic Ribonuclease" , in Biological

Macromolecules and Assemblies, Vol.II: Nucleic Acids and Interactive

Proteins, A. McPherson and F. Jurnak, eds . , John Wiley: New York,

393-439 (1984).

Wlodawer, A. and Sjolin, L. , "Application of Joint Neutron and X-ray

Refinement to the Investigation of the Structure of Ribonuclease A at

2.0 A Resolution", in Neutrons in Biology, B.P. Schoenborn, ed., Plenum

Publishing Corporation, 349-364 (1984).

Wlodawer, A., Walter, J., Huber, R. and Sjolin, L. , "Structure of 3ovine

Pancreatic Trypsin Inhibitor: Results of Joint Neutron and X-ray

Refinement of Crystal Form II", J. Mol. Biol., 180, 301 (1984).

229
(b) Publications in Progress

Ditmars, D.A., "Drop Calorimetry above 300 K" , McGraw-Hill/CINDAS Data Series

on Material Properties, Chap. 13, Compendium of Thermo physical Property

Measurement Methods, Vol . I, Plenum Publishing Corporation, 1985, (in

press )

.

Ditmars, D.A., Plint, 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 , 1985, (in press).

Gajewski, E. , Goldberg, R.N. and Steckler , D.K., "Thermodynamics of the

Conversion of Fumarate to L(-)malate", Biophys. Chem., (in press).

Garvin, D., Staples, B.R. and Jobe, Jr., T.L., "A Bibliography on the

Equilibria in the CuClp-i^O System", Handbook of Aqueous Thermodynamics,

Design Institute for Physical Property Data, (DIPPR), (submitted).

Goldberg, R.N., Gajewski, E. , Steckler D.K. and Tewari, Y.B., "Thermodynamics

of the Conversion of Aqueous L-aspartic Acid to Fumaric Acid and

Ammonia", (submitted).

Goldberg, R.N. and Parker, V.B., "Thermodynamics of Solution of SOp(g) in

Water and of Aqueous Sulfur Dioxide Solutions", J. Res. NBS, (in

press )

.

Jobe, T.L. and Goldberg, R.N., "A Bibliography of Sources of Thermodynamic

Data for Aqueous Phosphoric Acid Solutions", Handbook of Aqueous

Thermodynamics, Design Institute for Physical Property Data, (DIPPR),

(submitted )

.

Jobe, T.L. and Goldberg, R.N., "A Bibliography of Sources of Thermodynamic

Data for Aqueous Zinc Chloride Solutions", Handbook of Aqueous

Thermodynamics, Design Institute for Physical Property Data, (DIPPR),

(submitted )

.

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, (in press).

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 Thiocyante", J. Phys. Chem., (in press).

Kirchhoff, W.H. and Levin, I.W., "Description of the Thermotropic Behavior of

Membrane Bilayers in Terms of Raman Spectral Parameters: A Two-State

Model", (submitted).

Miller, M.M., Wasik, S.P., Guang, G.L., Shiu, W.Y. and MacKay, D.,

"Relationships Between Octanol-Water Partition Coefficients, Aqueous

Solubility and Bioconcentration Factors", (submitted).

230
Neumann, D.B., "Data Base Management Systems, Part I. A Quick Overview",

Proceedings of "Training Course in Accessibility and Dissemination of

Non-Bibliographic Data in Science and Technology", October 1983 , CODATA,

(in press )

.

Neumann, D.B., "Data Base Management Systems, Part II. An Application to

Scientific Technical Data and its Associated Bibliographic Data",

Proceedings of "Training Course in Accessibility and Dissemination of

Non-Bibliographic Data in Science and Technology", October 1983 , CODATA,

( in press )

.

Owens, J.W., Wasik, S.P. and DeVoe, H. , "Aqueous Solubilities and Enthalpies

of Solution of n-Alkylbenzenes" , J. Chem. Eng. Data, (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).

Schwarz, F.P., "Positive Charge Transfer in the UV Photolysis and 6 Radiolysis of Trans-Decalin Solutions", J. Phys . Chem., (in press).

Shukla, R.C., Plint, C.A. and Ditmars, D.A., "Aluminum( II) : Derivation of

C from C

p

and Comparison to C v Calculated from Anharmonic Models",

Int. J. Thermophysics, (in press).

Tewari, Y.B. and Goldberg, R.N., "An Investigation of the Equilibria Between

Aqueous Ribose, Ribulose and Arabinose", Biophys. Chem. (in press).

Tewari, Y.B., Steckler, D.S. and Goldberg, R.N., "Thermodynamics of the

Conversion of Aqueous Xylose to Xylulose", Biophys. Chem. (in press).

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, (in

press )

.

Wlodawer, A., Borkakoti, N. , Moss, D.S. and Hawkin, B. , "Comparison of Two

Independently Refined Models of Ribonuclease A", Acta Cryst., (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", (submitted).

23

'
6. TALKS

Abramowitz, S., "NBS’ Proposed Biotechnology Program", Center for Chemical

Engineering, NBS, Boulder, CO, December 8, 1984.

Abramowitz, S., "NBS' Program in Support of AFOSR's Spacecraft Survivability

Program", Obscuration and Aerosol Research Chemical and Research

Development Center, Aberdeen, MD, June 19, 1985.

Buckley, T. , "Interfacing of Heat Conduction Microcalorimeters to a Microcomputer", IUPAC Thermodynamics Conference, Hamilton, Ontario,

Canada, August 1984.

Buckley, T. , "Consecutive Ion-Molecule Reactions in Diacetylene and Related

Systems", Sixth East Coast Ion Cyclotron Resonance and Ion Molecule

Chemistry Symposium, September 22, 1984.

Buckley, T., "The Gas Phase Ion Chemistry and Proton Affinity of Methyl

Isocyanate, Methyl Isothiocyanate and Methyl Thiocyanate", American

Society for Mass Spectrometry, San Diego, California, May 27, 1985.

Churney, K.L., "Recent Developments in Large Sample Flow Calorimetry", 40th

Annual Calorimetry Conference, Pacific Grove, California, August 29,

1 985.

Colbert, J.C., "Enthalpy of Combustion of 2-Deoxy-D-Ribose" , 40th Annual

Calorimetry Conference, Pacific Grove, California, August 27, 1985.

Ditmars, D.A., "Measured Heat Capacity of fee Strontium", 9th Annual Symposium

on Thermophysical Properties, University of Colorado, Boulder, Colorado,

June 1985.

Ditmars, D.A., "Heat Capacity of fee and bcc Calcium; Derived Thermodynamic

Functions", 40th Annual Calorimetry Conference, Pacific Grove,

California, August 26, 1985.

Domalski , E.S., "Estimation Methods and Combustion Calorimetry for Organic

Phosphorus Compounds", 1984 Scientific Conference on Chemical Defense

Research, U.S. Department of the Army, CRDC, Aberdeen Proving Ground,

Maryland, November 16, 1984.

Domalski, E.S., "The Chlorine Content of Municipal Solid Waste", ASME Dioxin

Committee, United Engineering Center, New York, NY, January 23, 1985.

Domalski, E.S., "Materials and Energy Balances for Chlorine during MSW

Combustion", ASTM Committee E-38 on Resource Recovery Subcommittee

E-38.01 on Energy, Bear Mountain Inn, Bear Mountain, New York, March 25,

1985.

Domalski, E.S., "Materials and Energy Balances for Chlorine during MSW

Combustion", ASME Research Committee cr. Industrial and Municipal Wastes,

Bear Mountain Inn, Bear Mountain, New York, March 26, 1985.
Domaiski, E.S., "Thermodynamic Data Evaluation and Estimation for Organic

Phosphorus Compounds", 40th Annual Calorimetry Conference, Pacific

Grove, California, August 29, 1985.

Domaiski, E.S., "Monitoring the Fate of Chlorine from MSW Sampling through

Combustion", 5th International Symposium of Chlorinated Dioxins and

Related Compounds, University of Bayreuth, Bayreuth, West Germany,

September 17, 1985.

Domaiski, E.S., "The Chlorine Content of MSW", Warren Spring Laboratory,

Stevenage, United Kingdom, September 24, 1985.

Domaiski, E.S., "Recent Studies in the NBS Large Sample Flow Calorimeter

using Oxygen/Nitrogen Mixtures", Warren Spring Laboratory, Stevenage,

United Kingdom, September 24, 1985.

Gajewski, E., "Thermodynamics of the Conversion of Fumarate to L(-)malate",

29th Meeting of the Biophysical Society, Baltimore, Maryland,

February 27, 1 985.

Gajewski, E. , "Thermodynamics of Fumarase and L-aspartase Reactions",

Biotechnology Seminar, National Bureau of Standards, Gaithersburg,

Maryland, September 19, 1985.

Garvin, D., "Heating Values of Components of Natural Gas", Institute of Gas

Technology Symposium, Chicago, Illinois, August 26, 1985.

Garvin, D., "Comprehensive Consistent Thermodynamic Tables", International

Meeting on Phase Equilibrium Data, Paris, France, September 8, 1985.

Goldberg, R.N., "DIPPR Project 811 at the National Bureau of Standards",

Presentation to DIPPR Panel, AIChE Meeting, San Francisco, California,

November 1984.

Goldberg, R.N., "A Computerized Electrolyte Data Base", Conference on Electrolyte Solutions in Science and Engineering; Thermodynamics

Division, National Bureau of Standards, Gaithersburg, Maryland, June 11,

1 985.

Kirchhoff, W.H., "Modeling Phase Transitions in Lipid Bilayers: Fitting

Sigmoidal Curves Without Sufficient Data", Statistical Engineering

Division Seminar Series, National Bureau of Standards, Gaithersburg,

Maryland, October 2, 1 984.

Kirklin, D.R., "Combustion Bomb Calorimetry of Key Organic Phosphorous

Compounds", 40th Annual Calorimetry Conference, Pacific Grove,

California, August 29, 1985.

Neumann, D.B., "The New RTE-A Operating System for the HP-1000 Computer",

Chemical Thermodynamics and Chemical Kinetics Division Seminar, National

Bureau of Standards, Gaithersburg, Maryland, February 24, 1985.

233
Parker, V.B., "Thermodynamics of Solution of S02 (g) in Water and of Aqueous

Sulfur Dioxide Solution", Conference on Electrolyte Solutions in

Science and Engineering, Thermop’nysics Division, National Bureau of

Standards, Gaithersburg, Maryland, June 11, 1985.

Smith-Magowan , D., "Electrolyte Data Center, Where Are You?", Conference on Electrolyte Solutions in Science and Engineering, Thermophysics

Division, National Bureau of Standards, Gaithersburg, Maryland, June 11,

1 985.

Tewari, Y.B., "Thermodynamic Investigations of the Reactions Catalyzed by

Glucose (xylose) Isomerase" , Chemical Thermodynamics Division Seminar,

National Bureau of Standards, Gaithersburg, Maryland, February 26,

1 985.

Tewari, Y.B., "Thermodynamic Investigations of the Reactions Catalyzed by

Glucose (xylose) Isomerase", 7th Symposium on Biotechnology for Fuels

and Chemicals, Gatlinburg, Tennessee, May 15, 1985.

Tewari, Y.B., "Thermodynamic Investigations of the Equilibria Between Aqueous

Ribose, Ribulose and Arabinose", 40th Annual Calorimetry Conference,

Pacific Grove, California, August 29, 1985.

Tewari, Y.B., "Thermodynamics of the Conversion of L-aspartate to Fumarate",

40th Annual Calorimetry Conference, Pacific Grove, California,

August 29, 1985.

Weber, I.T., "Structural Studies of Three Anti-tumor Amidohydrolases"

,

American Crystallographic Association, Stanford California,

August 1 9-23, , 1 985

.

Weber, I.T., "The Analysis of Protein Structure from Crystallographic Data",

Course on Protein Structure and Function, Les Diablerets, Switzerland,

September 30 - October 3, 1985.

Weber, I.T., "The Structure of Catabolite Gene Activator Protein and Its

Complex with DNA" , Course on Protein Structure and Function, Les

Diablerets, Switzerland, September 30 - October 3, 1985.

Wlodawer, A., "Macromolecular Dif fractometer using a Position-sensitive

Detector", Pittsburgh Diffraction Conference, Pittsburgh, Pennsylvania,

November 9 , 1 984

.

Wlodawer, A., "Neutron Diffraction Studies of BPTI, RNase and Insulin",

Argonne National Laboratory, Argonne, Illinois, November 28, 1984.

Wlodawer, A., "Neutron Diffraction Studies of BPTI", University of Chicago,

Chicago, Illinois, November 29, 1984.

Wlodawer, A., "Neutron and X-ray Diffraction Studies of Proteins", George

Mason University, Fairfax, V A, February 22, 1985.

Wlodawer, A., "Protein Structure by Neutron and X-ray Diffraction", Staff

Research Seminar, National Bureau of Standards, Gaithersburg, Maryland,

March 21 , 1 985

.

234
V'.odawer, A., "Neutron Diffraction Studies of Proteins", Northern Virginia

Community College, Annandale, VA, May 24, 1985.

Wlodawer, A., "Determination of Protein Structure by Neutron Diffraction",

University of Regensburg, West Germany, June 25, 1985.

Wlodawer, A., "Determination of Protein Structure by Neutron Diffraction",

University of Uppsala, Sweden, July 5, 1985.

Wlodawer, A., "Joint Neutron and X-ray Structural Refinement of Porcine

Insulin", ACA Summer Meeting, Stanford University, California, August

20, 1985.

Wlodawer, A., "Neutron Diffraction Studies of Proteins", University of

California, San Francisco, California, August 23, 1985.
7. CHEMICAL THERMODYNAMICS DIVISION SEMINARS

Breganza, L.F., Institut Laue-Langevin , Grenoble, France, "High Pressure

Neutron Diffraction Studies of Biological Membranes", May 16, 1985.

Calton, Gary J., Purification Engineering, Inc., Columbia, Maryland,

"Industrial Use of Enzymes in the Production of Specialty Chemicals",

March 14, 1 985.

Chase, Malcolm W., Dow Chemical Company, Midland, Michigan,

"Thermochemistry of the Alkaline Earth Metals and their Compounds - Data

Evaluation, Theory and Experiment", July 15, 1985.

Gajewski, Ewa, National Bureau of Standards, "Thermodynamics of Fumarase

and L-aspartase Reactions", September 19, 1985.

Gershon, Nahum, National Institute of Health, Bethesda, Maryland, "Three

Dimensional Image Processing and Computer Graphics of Cytoplasmic

Structures", May 17, 1985.

Gilliland, Garry, Genex Corporation, Gaithersburg, Maryland, "The

Crystallization of Biological Macromolecules", September 20, 1985.

Lehmann, M.S., Institut Laue-Langevin, Grenoble, France , "Small-angle and

Single-crystal Neutron Scattering Studies of Ethanol-lysozyme

Interactions", November 2, 1984.

Lenz, Terry G., Chemical Engineering Department, Colorado State University,

Fort Collins, Colorado, "Chemical Equilibria in Diels-Aldler Processes",

August 5, 1985.

Orser , Donald, National Bureau of Standards, "An Algorithm for Producing

Alloy Phase Diagrams", March 1985.

Tewari, Yadu B. , National 3ureau of Standards, "Thermodynamic

Investigations of the Reactions Catalyzed by Glucose (xylose)

Isomerase" , February 26, 1985.

Thompson, Peter T., Swarthmore College, "Weak Forces in Chemistry

and Their Role in Biological Systems", March 12, 1985.

Tolbert, William R., The Monsanto Company, Saint Louis, Missouri,

"Perfusion Culture Systems for Production of Mammalian Cell

Biomolecules", January 23, 1985.

Biotechnology Seminars
3. TECHNICAL AND PROFESSIONAL COMMITTEE

PARTICIPATION AND LEADERSHIP

Abramowitz, S.

ASTM Committee E -38 on Resource Recovery, Subcommittee E38.01 Energy

Churney, K.L.

ASTM Committee E-37 on Thermal Measurements

ASTM Committee on Hazard Potential of Chemicals, Subcommittee E-27.02 on

Thermal Stability

ASTM Committee E -38 on Resource Recovery

Colbert, J.C.

ASTM Committee E -38 on Resource Recovery, Subcommittee E3 8 . 0 1 Energy

(Member

)

Ditmars, D.A.

ASTM Committee E37.05 (Thermal Measurements/Thermophysical Properties)

Section I (Thermodynamics) Task Group 1.5 (Drop Calorimetry ) , 1.6

(Adiabatic Calorimetry)

Division Safety Officer

Standards Committee, U.S. Calorimetry Conference (Member)

Domalski, E.S.

ASTM Committee E-27 on Hazard Potential of Chemicals, Subcommittee

E-27.07 Computational Methods (Member)

ASME Research Committee for Industrial and Municipal Wastes (Member)

ASTM Committee E -38 on Resource Recovery, Subcommittee E-38. 01 Energy

(Member

)

Garvin, D.

CODATA Task Group on Chemical Thermodynamic Tables (Secretary)

ASTM Committee E -38 on Resource Recovery (Member)

ASTM Committee E-27 Hazard Potential of Chemicals (Member)

Goldberg, R.N.

Councilor, U.S. Calorimetry Conference

Kirchhoff, W.H.

ASTM Committee E-47 on Biological Effects and Environmental Fate

(Chairman

)

ASTM Committee D— 1 9 on Water (Member)

ASTM Coordinating Committee on Environmental Activities (Member)

237
ASTM Committee E-^S on Biotechnology (Member)

IUPAC Commission 1.1. on Physicochemical Symbols, Terminology and Units

(Titular Member)

Kirklin, D.R.

ASTM Committee E -38 on Resource Recovery, Subcommittee E-38 . 01 on Energy

(Member) Subcommittee E- 38 . 02 on Research (Member)

Director, U.S. Calorimetry Conference

Division Property Officer

Neumann, D.B.

Hewlett-Packard HP1000 International Users Group (Member)

Parker, V.B.

IAEA Committee on Chemical Thermodynamics of Actinide Elements and

Compounds (Consultant), Subcommittee IAEA. WG. 01 Actinide Halide

Thermodynamics

CODATA Task Group on Chemical Thermodynamic Tables (Corresponding

Member

)

Wlodawer , A. Neutron Special Interest Group of the American Crystallographic

Association (Treasurer)

NIH Macromolecular Studies Program, Yale University (Member)

Conference on Protein Crystal Growth, Stanford University (Member)

238
9. PROFESSIONAL INTERACTIONS, CONSULTING

AND ADVISORY SERVICES

Abraraowitz, S.

Collaboration with I.W. Levin, National Institute of Arthritis and

Metabolic Disease, NIH, on vibrational analysis of small molecules and

some biological species.

Formulation of cooperative research program on high temperature

thermodynamics with AFOSR.

Interactions with the following agencies and organizations regarding the

NBS program in Biotechnology: President's Office of Science and

Technology Policy (OSTP), National Aeronautic and Space Administration

(NASA), National Academy of Science (NAS), National Foundation (NSF),

House and Senate Committees.

Ditmars, D.

Cooperation with R.A. Robie of the U.S. Geological Survey, Reston, Va.,

in preparing a sample of pure calcium and measuring the heat capacity

of the solid phases from 4 K to the melting point, 1112 K.

Commission on Standardization of Thermophysical Property 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

.

Physics Department, Brock University, Ontario, Canada; investigation of

high-temperature heat capacity of pure aluminum, pure copper.

Interaction with the following concerning research priorities of common

interest for environmentally resistant materials at high temperatures

Larry Kaufmamn, MANLABS, Cambridge, Massachusetts.

Domalski, E.S.

Cooperative planning 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

.

Participation in the U.S./U.K. collaboration for Waste Combustion.

Tentative plans were made for collaborative research to be conducted on comparison of (1) chlorine content analysis of municipal solid waste,

(2) calorific value data derived from U.S. and U.X. kilogram-capacity

calorimeters, and (3) combustion studies on threshold conditions for

the formation/destruction of chlorinated species.

239
Development of a research agreement 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 phosphorous compounds (CRDC) was begun.

Garvin, D.

CODATA; Preparation of Thermodynamic Data Bases and Tables, jointly with

groups at Harwell and University of Sussex (U.K.), University of

Grenoble (Fr) and Institute for High Temperatures (U.S.S.R.).

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.

CODATA analysis of data on aqueous solutions for the Task Group on Key

Values for Thermodynamics, and detailed review of their tables of

recommended values.

Report on progress of research program for the DoE Pittsburgh Energy

Technology Center on critical evaluation of data necessary for flue gas

clean-up procedures.

Goldberg, R.N.

Interactions with the following persons have taken place:

Robert H. Wood, University of Delaware, Newark, Delaware, Aqueous

Solutions and Thermodynamics.

Joseph Rard, Lawrence Livermore Laboratory, Livermore, California,

Aqueous Solutions and Thermodynamics.

Loren Hepler , University of Alberta, Edmonton, Alberta, Canada, Aqueous

Solutions and Thermodynamics.

Cecil E. Vanderzee, University of Nebraska, Lincoln, Nebraska, Aqueous

Solutions and Thermodynamics.

Peter Tremaine, Alberta Research Council, Edmonton, Alberta, Canada,

Aqueous Solutions and Thermodynamics.

Peter Huang, NBS Humidity Standards Division.

Kirchhoff, W.H.

Collaboration 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.

J.D. Fine, Surface Science Division, on the statistical analysis of

depth profile sputtering data.

240
Neumann, D.B.

Collaboration with the following persons have taken place:

J. B. Pedley, University of Sussex, Brighton, England; development of

data bases for the thermodynamic properties of inorganic and organic

compounds

.

Robert H. Wood, University of Delaware, Newark, Delaware; methods for

the computer readable transfer of solution data.

B.B. Molino, MBS Office of Standard Reference Data; development of

standard storage and retrieval methods for bibliographic information.

K. Marsh, Thermodynamics Research Center, Texas A&M University; chemical

thermodynamic data bases for organic species.

Robert Freeman, University of Oklahoma, Publication of the Bulletin of

Chemical Thermodynamics.

Parker, V.B.

Collaboration with F. Oetting, Rockwell International and J. Fuger

,

University of Liege, on the chemical thermodynamics properties of the

uranium halides and other actinide halides for IAEA.

Collaboration with members of CODATA Task Group on the preparation of

Chemical Thermodynamic Tables.

Collaboration with Malcolm Rand, AERE, Harwell on the chemical

thermodynamic properties of actinide halides and thermal functions for

calcium and its compounds.

Collaboration with Donald D. Wagman , former N3S staff scientist on CODATA Task Group on Chemical Thermodynamic Key Values and

Thermodynamic Tables.

Consultation with E.H.P. Cordfunke, Netherlands Energy Research

Foundation, Petten, Netherlands on the chemical thermodynamic

properties of the actinide elements and their compounds.

Anthony Mueller, OECD, Paris and Sidney Phillips, Lawrence Berkeley

Labs., chemical thermodynamic data base for nuclear waste disposal and

re-evaluation of thermodynamic data.

Schwarz, F. Collaboration with I.W. Levin, National Institute of Arthritis and

Metabolic Diseases, NIH on the thermal stability of clathrin.

Interaction with I.W. Levin on the thermal properties of the lipids.

Collaboration with A. Shrake, Office of Biologies, FDA on the thermal

stability of serum albumin.

241
Collaboration with C.J. Steer, Laboratory of Biochemistry and

Metabolism, NIH on the thermal stability of clathrin.

Interaction with P.D. Ross, National Institute of Arthritis, Diabetes,

and Digestive and Kidney Diseases, NIH, on the calibration and

performance of the Hart Differential Scanning Calorimeter.

Interaction with J. Matthews, Genex Corp. on the performance of the Hart

DSC and on the use of ribonuclease and lysozyme as potential standard

reference materials for calibrating DSC’s.

Smith-Magowan , D.

Collaboration with the following persons have taken place:

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.

S. L. Miller, University of California at San Diego, on the evaluation of

Gibbs energies of formation for metabolytes of the Krebs cycle.

B.R. Staples, U.S. Bureau of Mines, Albany, Oregon, on the correlation

of the thermodynamic properties of calcium chloride and evaluation of

Debye-Huckel limiting law parameters for water as functions of pressure

and temperature.

D. Ericsson, Energy Concepts, Annapolis, Md., on the thermodynamic

properties of aqueous solutions for use as adsorption ref rigerants

.

Tewari, Y.B.

Henry Zobel, Moffett Technical Center, CPC International, Summit-Argo,

IL., procurement and characteri zation of glucose isomerase for

microcalorimetric and equilibrium measurements

.

Weber, T.I.

Interactions with the following persons have taken place:

Dr. Sancar Adhya, NIH, on the crystallization and structural studies of

E. coli gal repressor.

Professor Herman Ammon, Department of Chemistry, University of Maryland,

on structural studies of glutaminase-asparaginases from several

bacterial sources.

Dr. Gary Gilliland, Genex Corporation, Gaithersburg , Md., on data

collection from crystals of catabolite gene activator protein.

Dr. Alan Peter kofsky, NIH, on the crystal structures of several mutants

of catabolite gene activator protein.

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 scructure of catabolite gene

activator protein.

242
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-dependent protein kinase.

Wlodawer, A. Collaboration with the following persons have taken place:

Professor Robert Huber, Max Planck Institute, Martinsried, West Germany,

on the neutron diffraction studies of the structure of bovine pancreatic

trypsin inhibitor and of photosynthetic reaction center.

Dr. Lennart Sjolin, Chalmers Polytechnic, Gothenburg, Sweden, on the

structural investigations of ribonuclease and bovine pancreatic trypsin

inhibitor

.

Dr. Franz Schmid, University of Regensburg, West Germany, on crystallographic studies of porcine ribonuclease.

Dr. David Moss, University of London, England, on comparisons of

independently refined structures of bovine ribonuclease

.

Professor Herman Ammon, University of Maryland, on cr ystallographic

studies of glutaminase-asparaginases from several bacterial sources.

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 complexes.

Dr. Ettore Appella, NIH, Bethesda, Md . , on crystallization of DNA

fragments

.

Dr. Joyce Jentoft, Case Western University, OH., on crystallographic

studies of the RNA-binding protein from the phage pp12.

Dr. Gary Gilliland, Genex Corporation, Gaithersburg , Md., on crystallographic studies of a sweet protein, monellin.

243
10. VISITING SCIENTISTS

The Thermodynamics Division has been host to the following scientists who

have worked with NBS scientists on problems of mutual interest.

Chandrasekharaiah , M.S., Bhabha Atomic Research Center, Bombay, India

discussed thermodynamic properties of uranium, iridium and platinum at

high temperatures and high temperature effusion measurements.

Chase, M.W., Dow Chemical Company, Midland, MI, worked on the development of

JANAF thermochemical tables and the evaluation and tabulation of thermal

functions for calcium and calcium compounds for CODATA Task Group on Chemical Thermodynamic Tables.

DeVoe, H. , University of Maryland, College Park, MD , performed measurements

of solubilities of non-electrolytes as a function of concentration and

temperatures in aqueous solution using high performance liquid

chromatography and designed an apparatus for the determination of

thermodynamic properties by HPLC methods.

Evans. W.H. - Former NBS employee, is an expert on the evaluation of chemical

thermodynamic data of relevance to resource recovery, the design of

computer codes for chemical thermodynamics, the preparation of catalogs

of evaluated chemical thermodynamic measurements. He is a consultant to

the CODATA key values task group.

Harrison, R.W., Yale University, New Haven, CT, Dr. Harrison is working on theoretical methods for the determination of biomolecular structure.

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 thermodynamic properties of organic compounds

and on strain energies in organic compounds.

Miller, M., University of Warsaw, Warsaw, Poland, Dr. Miller is working on crystallographic structure of proteins and DNA fragments.

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.

Pedley, A., Imperial College, London, England, spent time at NBS on the

development of interactive software for accessing thermodynamic data

bases of organic species and for predicting enthalpies of formation.

Pedley, J.B., School of Molecular Sciences, University of Sussex, Brighton,

England, spent time at NBS on the development and interactive

communication with a data-base on enthalpies of formation of organic

compounds, the development of estimation methods for calculating

enthalpies of formation of organic compounds and the thermodynamic

properties of transition metal chlorides.
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.

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 is performing both experimental and theoretical

research during his sabbatical at NBS.

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

.

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 biomolecules 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

.

245

MOLECULAR SPECTROSCOPY DIVISION

A. Weber, Chief

SUMMARY OF ACTIVITIES

Fiscal Year 1985

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 f ramework 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 energy transfer thrust has been 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.

2M7
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

workers. During the past year we have had thirteen guest workers and seven postdoctoral 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 workers, their permanent affiliations, and

their activities is given in Section 10 of this report.

C. Division Programs

With the technological advances of micro- and main frame computers

and the development of tunable dye and diode lasers that have taken place

during the last eight years, the fields of experimental molecular

spectroscopy and theoretical quantum chemistry have grown rapidly.

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 must be 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. The soundness of 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 isotope separation and

fusion, laser chemistry, and combustion diagnostics are a few of the many

important high-technology areas that depend on modern spectroscopic

techni ques

.

In order to meet the calibration and standards requirements for the

design and application of tunable infrared lasers and Fourier transform

instrumentation over the next decade, several frequency standards

activities are pursued in collaboration with several groups from within

and outside NBS. A project on spectral frequency standards is undertaken

jointly by scientists from the Time and Frequency Division of NBS/Boulder

and members of the HRS group. Details about our Calibration Standards

work are given in Section 2.B.

There has always been a need for accurate intensity parameters for

molecular transitions. Recently these needs have been emphasized and the

requirements for accuracy enhanced in connection with the determination

and monitoring of trace atmospheric species. Accordingly we are now engaged in the determination of accurate transition moments, line

•248
strenghts, and line broadening parameters of several molecular species

which are believed to play an important role in the chemistry of the

earth's atmosphere (see Section 2.C)

We continue to be involved in the spectroscopy of the environmental

and space sciences. Our work is directed toward the broadening of the

data base upon which spectroscopic measurements of trace atmospheric

constituents by means of ground based, balloon and satellite borne

instruments are performed and evaluated. This, as well as similar efforts

of interest to various branches of NASA and other user groups, is part of our continuing involvement in problems of national concern. Details about

these and other activities may be found in Section 2.C.

Our Division has significant other agency contracts with Air Force

Office of Scientific Research (AFOSR), Department of Energy (DOE),

National Aeronautics and Space Administration (NASA) , Chemical

Manufacturers Association (CMA) , and the National Foundation for Cancer

Research that help these agencies fulfill their missions. Details are discussed in the group reports. These efforts along with the lists of

consultations, talks, publications, and collaborative activities show our strong coupling with industry, other government agencies, and the research

community

.

The above constitutes only a sample of our involvement and response

to the needs of the user community. Our Division is host to several guest

workers from universities, other government agencies, and from overseas

countries (see Section 10). The numerous and varied interactions and

collaborations of the Division's staff with non-NBS scientists and user

groups are detailed in Section 9 - Professional Interactions, Consulting

and Advisory Services.

During the past year efforts of the LPC group have been redirected

and have acquired a stronger focus in the quantum-state specific studies

of molecular dynamics, especially in the role played by energy transfer in

the spectroscopy and kinetics of molecules in the condensed phase.

Investigations of energy transfer from vibrationally excited bonds in

liquids and solids, as well as in molecules bound to solid surfaces are described in Section 3-B. As an outgrowth of the work done in previous

years on infrared multiphoton dissociation experiments, new work has been

started on the dynamics of van der Waals complexes, especially on vibrational predissociation (see Section 3.D). These experiments,

performed in the time domain, measure directly the vibrational lifetimes

and supplement the work done in the frequency domain in which lifetimes

are inferred from spectral line widths (see Section 2.D as well as earlier

descriptions in the FY'83 and '84 Annual Reports).

Work was also carried forward in Matrix isolation spectroscopy

(Section 3.E) and the desorption of molecules from surfaces (Section 3.C).

Thermal desorption of molecules chemisorbed on well characteri zed surfaces

were studied with a dedicated facility incorporating several techniques

for surface sensitive analysis, a computer controlled data acquisition

249
system and a laser probe system with sub-Doppler resolution capability.

Since thermal desorption takes place slow enough to be modelled as an equilibrium process, new work has been started on fast desorption brought

about by rapid heating of the surface by non-resonant laser radiation.

The field of Quantum Chemistry has in recent years experienced

significant new developments which extend the range of reliable and useful

calculations to complex polyatomic systems. A new program to attack the

problems of the stabilities, conformations, spectroscopy and reactivity of

complex molecules, clusters, ions, radicals, and transition states, among

others, was successfully conducted for the third year 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

has been significantly enhanced through the acquisition of an I3M-4381

superminicomputer which forms the core of the newly formed Molecular

Structure and Modeling Facility of the Molecular Spectroscopy Division.

Details of the activities of the QC Group are given in the group report.

In the Annual Report for 1982 we described the results of our initial

work on the spectroscopy of molecular complexes in the gas phase. This

initial work, on the rotation-vibration spectrum of the hydrogen-bonded

HF-dimer has been expanded since that time to include the study of a variety of hydrogen- bonded and van der Waals complexes by all three groups

of the Division. Thus, detailed investigations are underway with new instrumentation of microwave and infrared high resolution spectra (see the

reports by the High Resolution Group in Section 2.D). The measurements

for these investigations are made in the frequency domain and knowledge

about the lifetimes of excited states is had only by inference from the

widths of the spectral lines. Direct information about lifetimes and,

especially, pre-dissociation rates is obtained from measurements made in

the time domain; these are performed in the Laser Photochemistry Group and

are reported in Section 3-D. These experimental efforts are often done in

conjunction with work done in the Quantum Chemistry Group (see report

4.B.2). The study of weak chemical interaction as exemplified by the

hydrogen bonding and van der Waals forces is of considerable interest for

the present and the forseeable future (see the Pimentel Report

"Opportunities in Chemistry", National Academy Press, Washington D. C.,

1985) and our Division is expected to fully participate in this field

during the coming years.

The research described in the following report was performed in a cooperative manner between the permanent staff of the Division, NBS/NRC

postdoctoral research associates, and guest-scientists from the U.S. and

abroad. Close collaboration also exists with members of the Surface

Science Division of the Center for Chemical Physics in areas of picosecond

spectroscopy, spectroscopic studies of surface desorption processes, and

energy transfer.

250
2 . HIGH RESOLUTION SPECTROSCOPY GROUP

J. W. Bevan, J. T. Hougen, B. J. Howard, D. E. Jennings,

W. J. Lafferty, R. W. Lovejoy, F. J. Lovas , A. G. Maki , I. M. Mills,

N. Ohashi , W. B. Olson, A. S. Pine, G. Rotter,

R. D. Suenram, G. A. Thompson, A. Weber, B. A. Wofford

A. Introduction

The work of this group involves experimental and theoretical applications of molecular spectroscopy for characterizing 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 novel molecular species, particularly floppy molecules.

The major activity of the Molecular Spectra Data Center, supported by

the Office of Scientific Reference Data (OSRD) is to provide evaluated

data on molecular rotational spectra in the microwave region and to

develop 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 N2O 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.

Molecular radioastronomy continues to demand accurate laboratory

microwave data and spectroscopic expertise and the measurement, critical

evaluation, and dissemination of microwave data of astrophysical interest

is being continued. Our collaboration with radio-astronomers provides the

contacts and experience necessary to insure that these evaluations and

compilations are both practical and useful.

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

251
conducted with the support of NASA and the Chemical Manufacturers

Association. These efforts will continue to play an important role in our work during the coming years.

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 group

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.

The work conducted during the past year has been aided through the

efforts of a number of guest-scientists from the U.S. and abroad.

Moreover, sustained collaboration with non-NBS groups serves to

disseminate the results of our work in the quickest and most far reaching

way to the user community. Such collaboration also benefits our work

through access to data and facilities not presently available at NBS.

Particularly noteworthy among the non-NBS institutions with which

beneficial collaborations have occurred during the past year are: The

University of Oulu, Oulu, Finland, The University of Illinois, The

University of Alberta, Texas A&M University, Lehigh University, Oxford

University, Oxford, England, The University of Reading, Reading, England,

The National Research Council of Canada, The Institute of Molecular

Science, Okazaki, Japan, Kanazawa University, Kanazawa, Japan, The Harry

Diamond Laboratories of the U.S. Army, The NASA-Greenbel t , NASA-Langley

NASA-Goddard , and NASA-Ames Laboratories , and The National Solar

Observatory at Kitt Peak, AZ.

In the following the group's activities are described according to

the three broad topics of calibration and Data Center activities,

environmental problems, and spectroscopy of weakly bound molecular

complexes. In addition to these programmatic activities there were others

of a more general and varied nature, including several studies in the

field of mathematical physics by one of our guest workers. These are described in the fourth section under General Spectroscopy and Theory.

B. 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, of compilations of critically

evaluated molecular constants for use in other disciplines, or occasionally of spectral fitting programs, for use in reducing data in

other laboratories. 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 in both the

infrared and microwave spectral regions.

252
1. Tying the Lower Vibrational Levels of N

2 0 to the Cesium Frequency

Standard

(A. G. Maki and J. W. Wells)

Our continuing collaborative effort with Dr. J. W. Wells (NBS

Boulder) this past year has seen some new frequency measurements that were

the key to tying all the lower vibrational energy levels of N

2 0 to the

cesium frequency standard. These levels previously had been measured using

wavelength measurement techniques, but now we have independent frequency

measurements of these levels. One of the most satisfying aspects of this

work was the incorporation of the very accurately measured N

2 0 laser

frequencies

.

The new measurements that were made in Boulder involved the 00°1-00°0

and 01*1 —0 1*0 transitions of N

2 0 which were measured against a CO laser

local oscillator in the 1257 to 13^0 cm

-1

region. The CO frequencies were

in turn measured with respect to combinations of C0 2 laser frequencies.

Since the well measured N

2 0 laser frequencies involved the 10°0-00°1

transition, combining these measurements gave accurate frequency values

for the 10°0-00°0 transitions between 2135 and 2268 cm

- "' (see Fig 2.1).

Energy Levels for N2O

0221. 0002 - (a) (b)

04°cr 1000-

cmi.

0330 - 0310'

0001. 0220 - 02°0

oro0000 '

observed

Wavenumbers

(cm -i)

1880

1767

1749

1284

1178 1168

589

-LLL

Frequency

Measurements

Calibration

Tables

1 not yet observed

l Figure 2.1. Energy level diagram that illustrates on the left (a) the

frequency measurements that have been made on the lower

levels of N

2 0 (solid arrows), or that we hope to make (dashed

arrows). On the right (b) are the resulting calibration

tables that can be prepared based on the frequency

measurements

.

253
Also, combining the new 01*1-0110 measurements with earlier ones on the

01 ' 1 -00 °0 transitions gave us good frequency values for the 01

1 0-00°0

transitions near 590 cm

-1

. These new frequency measurements

have been combined with older frequency measurements and with other

microwave and infrared data that determined some of the rotational

constants for the various states to obtain the best term values for the

lower vibrational states of ^0, all related to the cesium frequency

standard. These term values are being used to prepare the infrared

calibration atlas for ^0 described in the next section.

In the coming year we expect to be able to measure some of the weaker

hot band lines in the 1285 cm

-1

band of ^0 to obtain term values that

will provide frequency calibration in the 2000-3000 cm

-1 region. Our long

range goals also include the measurement of hot bands accompanying the

laser transitions near 940 cm

-1

and the frequency measurement of some lines due to the 10°0-02°0 transitions near 1060 cm

-1

. Finally, with a little bit of luck it may be possible to obtain a diode with enough power

in a single mode to make a few saturated absorption measurements on the

1285 cm

-T band of ^0. That would give an order of magnitude improvement

in the accuracy of the frequency measurements.

2. Infrared Calibration Atlas

(A. G. Maki)

During the past four or five years we have been developing infrared

spectral frequency tables for calibrating tunable IR laser spectrometers.

We have worked with several groups in obtaining highly accurate heterodyne

and Fourier transform spectra on many bands of the 0CS and ^0 molecules

which will form the basis of two reviews. Much of the manuscript and

tables for the 0CS review were completed previously. The new results on the \>2 band will be added to the existing tables to complete this review.

During the past year further heterodyne measurements on ^0 bands up to

2200 cm

1 have been obtained (see preceeding section) and allow

calibration tables to be produced in the regions of 520 cm \ 930 cm \

1300 cm

-1

, 1880 cm

-1

, and 2200 cm

-1 with each covering a range of 90-150

cm

-1

. Some additional measurements needed for calibration near 2700 cm

are being sought to complete the analysis and produce a set of tables

which will replace the previous publication on N

2 O in the Journal of

Chemical and Physical Reference Data. This work is supported by the 0SRD

.

3. Revised Recommended Rest Frequency List

(F. J. Lovas)

In May 1985 the manuscript entitled "Recommended Rest Frequencies for

Observed Interstellar Molecular Microwave Transitions - 1984 Revision" was submitted to J. Phys . Chem. Ref. Data by F. J. Lovas. This is a complete

revision and update of a 1979 publication in Astrophys. J. Supplement by

F. J. Lovas, L. E. Snyder, and D. R. Johnson. The reported astronomical

observations of new species and new rotational transitions of previously

identified molecules has more than tripled the number of lines reported in

the first publication.

254
Preprint copies of this manuscript have been distributed to the

nearly 300 astronomers and spectroscopi sts on our mailing list with the

request that they examine it for oversights or errors. A number of useful

responses have already been received. In fact among the responses was a preprint of a survey of Orion A between 247 GHz and 263 GHz which contains

more than 200 new transitions which were added to the table. We have also

filled a request for a magnetic tape copy of the data file to be used on

the new British - Dutch 15-metre submillimeter wave telescope being

constructed on Mauna Kea, Hawaii. The most pleasing aspect of the

responses has been the interest of the astronomy community in the accuracy

of the reported information as well as providing new observations to keep

it as up-to-date as possible. The manuscript has been submitted to J.

Phys. Chem. Ref. Data and the major tables of data have been converted

via a magnetic tape to the Bedford system used by OSRD. This work is

supported by the OSRD.

4. Microwave Spectral Tables

(R. D. Suenram and F. J. Lovas)

We continue to carry out the general literature search for all

published (and unpublished) microwave spectra for this project.

Evaluation and coding new data continues on the diatomic and triatomic

species to keep the computer files from the earlier publications current.

Work on the third publication of the Microwave Spectral Table series

"Hydrocarbons" is progressing. The spectral fittings of all the normal

symmetric top and asymmetric top species are complete. The corresponding

data files of the measured and predicted spectra have been produced and

all isotopic and vibrational species have been coded. The analysis of the

species with internal rotation remains to be accomplished since the

programs for these analyses were not fully implemented on the Univac.

Since we have moved all programs and data files to NBS’s new Cyber

computer, implementation of these programs on the Cyber is in progress.

This work is supported by the OSRD.

5. Supplement to Structural Data Tables for Polyatomic Molecules

(W. J. Lafferty)

Ten years ago members of the Molecular Spectroscopy Division

collaborated with spectroscopists from Japan, Germany and England to

produce a set of structural tables of polyatomic molecules. All

structures obtained for gas phase molecules by electron diffraction and

infrared, Raman, electronic, and microwave spectroscopy were included.

The tables were published by Landolt-Bornstein in their New Series (Group

II, Volume 8).

This year we have updated these tables. The literature has been

searched from 1974 to the beginning of 1985. All new structures as well

as structures whose parameters have been significantly improved have been

included in the tables. The entry for each molecule includes the

255
structural parameter as well as a schematic drawing of its structure.

This supplement will once again be published by Landol t-Bornstein. This

work is supported by the OSRD

.

6. Review of SOp

(F. J. Lovasj

After several years in the process, the publication of a review on the spectrum of SOp is forthcoming in J. Phys . Chem. Ref. Data Vol. 14

(1985). This is part 22 of the series "Microwave Spectra of Molecules of

Astrophysical Interest." This work is supported by the OSRD.

C. 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 Manufacturers' Association). The

interest of the latter 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 not

on band analyses per se, but rather 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 . High Resolution Spectrum of the v

2 and Bands of H0C2,

(W. J. Lafferty and W. B. Olson)

Our interest in the spectrum of H0C2, has been motivated by very

practical reasons. C2, atoms produced from the photolysis of freons in the

upper atmosphere react with stratospheric 0^ via the routes:

C2, + 0^ = C 2,0 + Op

and

C2,0 + 0 = C2, + 0p

There are a great number of competing reactions in the stratosphere, and

the extent of the damage done by the freons is at this point still

controversial . H0C2, can be produced from 02,0 by the reaction

C&0 + HOp = HOC 2, + 0

2

which, if the H0C2, formed is sufficiently stable, serves to withdraw 0 2, atoms from the chain reaction.

The stability of H0C2, in the upper atmosphere is still somewhat

uncertain. A number of laboratory studies have been carried out on these

and other reactions, but it appears that the most practical way in which

256
to get a handle on the role played by H0C2, in stopping or slowing the

ozone destroying chain reactions is to directly observe this species in

the stratosphere and directly monitor its concentration.

A number of unsuccessful attempts to detect HOC£ with both ground

based and balloon spectrometers have been made. One of the problems of

detection of this molecule arises from that fact that even in the

atmospheric windows, the H0C2, absorption bands are overlapped by the lines

of very minor stratospheric constituents which have about the same

intensities expected from the lines of H0C2,.

In order to positively identify the lines arising from the H0C2,

spectrum, it is necessary to have very precisely known line frequencies

since only a few lines of a band may fall in a clear spot in the spectrum.

We, therefore, with the partial support of the Chemical Manufacturers

Association, have recorded and assigned the two lowest frequency bands of

H0C2, with the NBS BOMEM FTS spectrometer with a resolution of 0.004 cm

1

. Careful attention has been given to frequency calibration; fortunately,

both bands fall in regions where there are very well measured calibration

lines. The v

2 band centered at about 1220 cm

-1

, was calibrated against

N

2 0 while the band was calibrated against C02 absorption lines. The

absolute frequency calibration of the BOMEM spectrometer was found to be

surprisingly good. Corrections of only a few ten thousands of a cm

-1

were

found to be necessary. We conservatively estimate that the absolute

precision is better than +/- 0.0005 cm

-1

; the relative precision is

somewhat better, and is on the order of 0.00002 cm

-1

.

Both v

2

, the bending vibration, and v^, the C£-0 stretching mode, are a- type bands. Figure 2.2 shows a much compressed scan over the v

2

band

.

The assignment is complicated by the presence of two chlorine

isotopes, but line assignment presented no difficulties; a very complete

assignment has been accomplished for both bands of both isotopic species.

The observed lines have been fit using a Watson Hamiltonian, and the

standard deviation of the fittings for all the bands was 0.0002 cm

-1

.

Currently relative line intensities are being measured for both bands

in order to determine the magnitude of the Herman-Wall is effect on the

intensities. When this is completed, line intensities will be computed,

and a band atlas including line frequencies and line strengths at several

temperatures will be produced. This work is supported by CMA.

2. Measurements on the Vo and Bands of Nitric Acid (HN0-O

(A. G. Maki)

The and bands of nitric acid were investigated in collaboration

with Prof. A. Fayt of the University of Louvain - la Neuve, Belgium. We

have used the NBS BOMEM interferometric spectrometer to measure the

257
HOCI Z4 BAND

K = 01 2 3 4 5 H03SCI

Figure 2.2 The V

2 band of H0C2, recorded under full instrumental

resolution of 0.00M cm

-1

. The sub-band centers of the major

isotopic species are labelled at the top.

spectrum of nitric acid (HNO^) in the 1250 to 1360 cm

-1 region which

includes the band at 1303 cm

-1

and the band at 1 326 cm

-

''. In

collaboration with Dr. Andre Fayt transitions for both of these bands

have been assigned and fit to appropriate asymmetric rotor constants.

These bands are used by certain laboratories for atmospheric

measurements since they fall in a spectral region where the atmosphere is

relatively transparent. It is important that the rotational line

structure of these bands be understood so that modeling calculations can

be used to simulate atmospheric spectra both to interpret the atmospheric

distribution of nitric acid, and also to cancel out the nitric acid

features when searching for underlying transitions due to other

atmospheric species, such as chlorine nitrate.

To supplement the BOMEM spectrum we have also measured diode laser

spectra for several small spectral regions in order to resolve some of

the more tightly clustered features such as the Q-branch. Figure 2.3

shows an example of the diode laser spectrum of v^. Although only the

K

c =0 , 1 transitions are labelled many other features seen in the figure have

been identified and assigned.

Thus far the spectra have been fit with a standard deviation of about

0.002cm” 1. It is not clear if the fit could be improved by including some interactions with nearby bands. In the coming year we hope to obtain some laser diode spectra of the band of HNO^ in order to see if some of the

258
10

Figure 2.3* Diode laser spectrum of the Q-branch for nitric acid

(HNO^). The lower trace is the fringe pattern from a solid

germanium etalon; FSR = 0.016cm

- "'.

more obvious deviations are artifacts due to incompletely resolved

clusters of lines. It appears, however, that there should be a weak Ak=2

interaction between and similar to what we have found between and

2vg. This work is supported by NASA.

3. New Intensity and Frequency Measurements on CIO

(A. G. Maki , and G. A. Thompson)

Chlorine monoxide (CIO) is one of the reactive intermediates involved

in the chlorine cycle in the atmospheric chemistry that governs the

concentration of ozone in the upper atmosphere. Much interest centers on measurements of the concentration of CIO in the atmosphere and a number of

techniques have been used to try to measure the concentration of CIO in

the atmosphere.

At the present time microwave techniques seem to have been most

successful in determining the concentration of CIO in the upper

atmosphere but there is an apparent disagreement between the ground based

microwave measurements^’^ and the ground-based infrared measurements.^

In particular, the ground-based measurements of Mumma et al.^ failed to

detect any CIO although the expected column density was expected to give a detectable signal. Since it has been suggested that errors in either the

259
frequencies or the intensities of the CIO lines might contribute to the

non-observation of CIO in the Mumma _et al. experiments, we have undertaken

an independent remeasurement of the intensities and frequencies of the CIO

spectrum in the infrared.

Accurate intensity measurements are not easy to make on stable

molecules and are even more difficult for unstable molecules since it is

normally necessary to know how many molecules are present in the

absorption path. The microwave measurements do not have this problem

since the microwave absorption intensity is proportional to the square of

the dipole moment and the dipole moment can be measured quite accurately

from the Stark effect. The several measurements that have been made of

the infrared intensity indicate that it is relatively weak and for that

reason Dr. Chackerian (NASA/Ames) has suggested the possibility that the

Herman-Wallis effect, which relates the infrared band intensity to the

ratio of the intensity of R-branch transitions to the intensity of the

P-branch transitions, can be used to determine the transition moment

(infrared intensity) without measuring the CIO concentration. Since the

measurement of the CIO concentration is quite difficult, we believe that

such a technique that by-passes that one difficult and controversial step

merits further investigation and we have began such a study.

What we plan to do is measure the intensity ratio of P- and R-branch

transitions that arise from the same energy levels (in order to eliminate

any temperature dependence). For maximum accuracy these measurements must

be made under identical operating conditions for both the R-line and the

P-line. We plan to switch back and forth between measurements of the

R-line intensity and the P-line intensity several times in order to verify

that the operating conditions are indeed identical. This work is

supported by NASA.

Table 2.1 gives an example of the intensity ratio expected for the

different band intensities suggested by various other papers.

Table 2.1. R- and P- Branch Intensity Ratio Calculated for CIO for

Different band Intensities.

Band Intensity (cm 2 atm 1 ) 32.0 1 1 .8 5.0

Intensity Ratio R ( 1 6 - 5 )/P( 16.5) 1 .243 1.334 1 .469

Finally, this project also includes a re-measurement and re-analysis

of the infrared frequencies of the CIO absorption lines in order to

improve the reliability of the calculated infrared spectrum of CIO.

(1) A. Parish, R. L. DeZafra, P. M. Solomon, J. W. Barrett, and E. R. Carlson, Science 211, 1158 (1981).

(2) P. M. Solomon, R. deZafra, A. Parish, and J. W. Barrett, Science 224 , 1210 (1984).

260
(3) M. J. Mumma, J. D. Rogers, T. Kostiak, D. Deming, J. J. Hillman, and

D. Zipoy, Science 221 , 268 (1983).

4. Self-Broadening in the Fundamental Bands of HF and HC1

(A. S. Pine and A. Fried (CAC))

In collaboration with Dr. A. Fried of the Center for Analytic

Chemistry, the self-broadened lineshapes have been measured for the

fundamental bands of HF and HC1 with the high-resolution tunable

dif f erence-frequency laser spectrometer in the Molecular Spectroscopy

Division. This is a continuation of a project to improve the data base on

the spectral band parameters (intensities, self- and N

2

~ and air-broadened

lineshapes and shifts) in support of the NASA Upper Atmospheric Research

Program (Project HALOE) to monitor ozone depletion caused by reaction with

halogen-containing molecules. Using the narrow-linewidth (-1 MHZ)

linear-scan-controlled tunable laser system, we observed spectral

lineshapes free of instrumental distortion that exhibited deviations from

the usual Voigt profile due to collisions! (Dicke) narrowing. In Figure 2.4

l oo

.80

QJO

S

60 n

c_o

in .40 jO

<

.20

0.00

Fig. 2.4. Self-broadened lineshape of the P(7) line of HF compared to

various collisional models.

3644.3 3644.0

Wavenumber

we show an example of the P(7) line of HF at 50.5 Torr least-squares fit

by a Voigt function and by the "soft" and "hard" collisional narrowing

models which yield much reduced obs.-calc. residuals. The self-broadening

coefficients and shifts for the v=1 <-0 transitions of HF and HC1 are displayed in Figure 2.5. No significant differences were found for the two

chlorine isotopes in the natural abundance sample. Particular care was taken in sample handling for these reactive, readily polymerizable, gases

to ensure accuracy, linearity and reproducibility in the pressure and

broadening measurements. This work is supported by NASA.

261
HF v= 1-0 H 35 C1 v= 1-0

m m

Fig. 2.5. Self-broadening coefficients and shifts for HF and HC1 at

T-295K.

5. Analysis of the Spectrum of H

2 02

(W. B. Olson)

The pooling of our data for hydrogen peroxide with those of Prof.

Robert Hunt of Florida State University has led to some reassignments of

the absorption lines in the OH stretching region of the spectra, and to a direct determination of energy differences between ground state rotational

levels and the levels perturbing them, up to J =* 25 on the most perturbed

levels (ground state K - 8) . The previous limit was J = 15. These

reassignments were made possible by a clarification of the group theory,

and enumeration of the types of perturbations possible in hydrogen

peroxide, provided by the permutation-inversion group theory treatment of

hydrogen peroxide by J. T. Hougen. 1

In addition to extending assignments, it has been possible, using

Hougen* s symmetry treatment, to introduce some reforms in terminology and

notation for hydrogen peroxide energy levels and transitions which we feel

will greatly simplify the understanding of hydrogen peroxide, and greatly

facilitate verbal and written communication. The basis of the new terminology is a two valued overall symmetry level (U for ungerade and G

for gerade), for the two torsional substates for a given principal

torsional quantum number, rather than the old four valued numerical t label.

262
Selection rules for transitions had been worked out in terms of the x labels, but these had no direct connection with overall symmetries, and

this led to considerable confusion as to the source of perturbations when

these were evident. A preliminary account of this work has been given in a report to NASA.

A coupled asymetric rotor program for simultaneous fitting of

combination differences in the ground state (OG) and perturbing first

excited torsional state (1G) was expected to be available in Sept. 1984,

but was delayed, and is now expected to available in Sept. 1985. Fitting

of our data with this program should lead finally to a definitive set of

ground state rotational constants for H

2 0

2

. This work is supported by

NASA.

(1) J. T. Hougen, Can. J. Phys . 62. 1 392-1402 (1984).

D. 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 about 25$ of the group's total

effort. In addition to studies using a difference frequency laser

spectrometer in the 3 micron region, this year brings forth studies using

the BOMEM Fourier transform spectrometer in both the mid- and farinfrared, studies using the new pulsed Fourier transform microwave

spectrometer (Flygare type), as well as theoretical studies. 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.

1. Hydrogen Bond Energies of the HF and HC1 Dimers

(A. S. Pine and B. J. Howard)

The dissociation energies of the hydrogen-bonded complexes, (HF) 2 and

(HC1) 2

, have been obtained from high-resolution measurements of absolute

infrared line strengths at a single temperature and pressure under the

assumption of minimally-perturbed local-mode behavior of the outer

hydrogen stretch. The measurements were made with a dif f erence-f requency

laser system on low pressure (P-1-2 Torr) gas samples cooled to near the

condensation point (T-219 K for HF, T-127 K for HC1 ) in a long path

(L-64-80 m) White cell. The observed absolute intensity pattern of the

r Q0 subbranch of the outer or "free H" stretching band, , of (HF) 2 is

shown in Figure 2.6 along with a simulated trace based on the usual

Hdnl-London and Boltzmann factors for the J assignments and tunneling

splittings obtained in our previous work. The transition lineshapes in

the simulated trace are Voigt profiles obtained by convolving the calculated Doppler distribution with a pressure-broadened Lorentzian of

half-width = 34 MHz. The agreement between the observed and calculated

spectra is excellent as can be seen in the subtracted residuals trace of

the bottom of Figure 2.6 which exhibits only the r R

Q lines and some hot band

structure not included in the model.

263
.40 rq

Q Otis. -Calc.

g oo .4. , ^..

'4 t ' » ^

3864 50 3864 » 3863 50 3863 00 3863 SO Wavenumber/cm - 1

Fig. 2.6. Observed, calculated and residual spectra of the r Q 0 subbranch

of the v.| band of the HF dimer.

The spectral intensities can be related to the dimer concentration

n

D

, and partition function, QD

, and the transition moment, <Ui>p > for

the band component measured using standard formulae. In turn, n^ and QD can be expressed in terms of the monomer concentration, nM , and partition

function, Q^, and the zero-point dissociation energy, D Q , under thermal

equilibrium by

K

eq

" n

D /(nM

)2 = (QD /QM2) e Do/kT

.

Since nM

is measured from the pressure assuming negligible polymerization

and Qm can be calculated trivially for a diatomic molecule, the only

unknowns in the problem are D Q and the transition moment for the dimer.

Recent ab Initio calculations have shown that the bond transition moment

for the outer hydrogen is only -10? enhanced over that of the monomer,

which is known quite accurately from our recent measurements of the

264
absolute Intensities of the monomers. Thus we need only to project the

value of this moment onto the b-axis of the dimer to relate it to the

< u«i observed.

We obtain zero-point dissociation energies for the HF and HC1 dimers

of D

Q

- 1038 (+43,-34) cm

-

' and 431 (±22) cm

- respectively. Estimates of

the zero-point energies of the low frequency intermolecular vibrations

enable us to obtain the well depths and the equilibrium dissociation

energies, D

0

- 1595 (+103,~94)cm 1 for (HF^ and 794 (± 86) cm for

(HC1 )

2

for comparison to ab initio and model calculations for these

complexes

.

2. Rotational Predissociation and Libration in the Infrared Spectrum

of Ar-HCl

(B. J. Howard and A. S. Pine)

Fully-resolved rotational structure in the high-frequency vibrational

region of the Ar-HCl van der Waals complex has been recorded under thermal

equilibrium conditions at T=127 K with a tunable difference-frequency

laser. Both the fundamental H-Cl stretch and its combination with the

low-frequency large- amplitude bend (libration) have been observed with

comparable intensities. The fundamental H-Cl stretch gives rise to a parallel-type band in the null gap of HC1 as shown in Figure 2.7. The

assigned Ar-HCl spectrum is indicated in the calculated trace below the

Ar-HCl Observed

P (HCl) =2 . 1 Torr

Ar-H37 Cl

J-60 Hju . m ill

J -60

2887 2886 2885 2884 2883 2882 2881 2880 2879 2878 2877 2876 2875 2874 Wavenumber/cm 1

Fig. 2.7. Observed and calculated spectra of the v-j fundamental H-Cl

stretching band of Ar-HCl.

265
observed spectrum which is unavoidably contaminated by HC1 dimer structure

(known from previous work) and hot bands. Both Cl isotopes contribute in

their natural abundance. The abrupt cutoff of the spectrum at J = 60

arises from rotational predissociation as the rotational energy exceeds

the binding energy and may tunnel through the top of the centrifugal

barrier. The rotational eigenvalues and predissociation have been modeled

with a one-dimensional radial potential of the Maitland-Smith form to give

a zero-point dissociation energy of D

Q=114„7 (±1.0) cm

-1

and a van der

Waals stretching frequency of = 31-3 (±1 .0)cm

_1

. These values are in

good agreement with empirical models based on precise microwave

measurements near the minimum in the potential well, but disagree

seriously with prior estimates based on the temperature dependence of the

low resolution infrared spectrum. The rotational constants in the ground

and excited H-Cl stretch vibrations yield a measure of the extension of

the center-of-mass separation due to the motion of the proton. The red

shift of the Ar-HCl spectrum from the isolated HC1 monomer implies a stronger van der Waals attraction upon excitation of the H-Cl stretch.

The combination band of the H-Cl stretch, v-| , with the van der Waals

band, is shown in Figure 2.8. It is a perpendicular- type band (n-E) of

anomalously high intensity transferred from the fundamental stretch by the

strong modulation due to the wide librational motion. The blue shift from

the fundamental band is about 34 cm’^ corresponding to the frequency of

the bending mode. The rotational constants yield the extreme shortening

of the van der Waals bond length upon bending the molecule, and they give

the 2,-doubling constant q-^ = Bq-B r

= + 34.2 (± 0.2) MHz arising from

Coriolis perturbations from nearby states with E-symmetry. These measurements should lead to improved estimates of the anisotropy of the potential

and its dynamical behavior.

We have also obtained preliminary assignments of hot bands arising

from v,, the van der Waals stretching mode, in the fundamental band region

of Ar-HCl. This gives us further information about the intermolecular

potential and about interactions between the low frequency modes. Spectra

have also been recorded for other rare gas (Ne, Kr , Xe)-HCl complexes to

obtain the trends of the van der Waals potential with regard to atomic

mass and polarizability.

3. Study of Hydrogen-bonded complexes in the Gas Phase Using Fourier

Transform Spectroscopy

(B. A. Wofford, J. W. Bevan, W. B. Olson, and W. J. Lafferty)

During the past year, we have had a very fruitful collaboration with

Professor John Bevan and B. A. Woffard from the Chemistry Department of

Texas A&M University. From designs developed by W. B. Olson (see Section

3.1), Prof. Bevan and his co-workers have built a long-path absorption

cell which can be cooled to ca. -100° C. At low temperatures, the

hydrogen-bonded complexes are present at higher concentrations. The long

absorption path (up to 64 meters) serves to enhance the instrumental

266
Wavenumber/cm 1

Fig. 2.8. Observed and calculated spectra of the v^v2 stretch-bend

combination band of Ar-HCl.

sensitivity. This cell has been coupled into the NBS BOMEM spectrometer

and used to study a number of rotation-vibration bands of several

hydrogen-bonded complexes including HCN»**HF, HCN»*HCN, and HCN**»HC1. At

this point the work on the HCN-HF complex is most complete. Five of the

absorption bands of this complex have been observed, and many of the

individual line transitions assigned. These bands arise from the C-H

stretching fundamental and its overtone, the CN stretching vibration, the

internal HCN bending vibration, as well as the bending vibration in which

one end of the complex twists with respect to the other end. The latter

vibration is unique to the hydrogen-bonded complex, and is not overlapped

by lines from either HCN or HF. The Q-branch of this band is shown in

Figure 2.9.

The dissociation energy for these weakly bound complexes is, of

course, rather low; e.g., for HCN«**HF, DQ

is about 1600 cm. Thus many

of the molecular vibrations lie above the dissociation limit, and high

resolution spectroscopy, in addition to providing information on the

energy levels of hydrogen-bonded molecules, allows one to approximate the

life time of molecules in energy levels above this limit. The width of a

267
7/ 1 HCN ••• HF 1/

6

40 30 20 10 Q(J)

WAVENUMBERS (cm- 1 )

Fig. 2.9 A Q-branch of the high-frequency bending vibration, , of the

hydrogen bonded complex HCN***HF recorded at a temperature of

-50°C. Despite the unusually high stability of this complex, a path length of 64 meters was required to obtain the spectrum

with a reasonable signal-to-noise level. This vibration is

unique to the hydrogen-bonded complex and there is no overlapping from lines of the parent species.

ro-vibrational line is inversely proportional to the lifetime of the

molecule in the upper state of the transition. The lines of several bands

of the HCN*»*HF molecule were found to be considerably broader than the

instrumental resolution, and, therefore, lifetimes of several vibrational

states could be estimated. For example, the lines of the C-H stretching

vibration at 3310 cm

-1 were not broadened and one can estimate that the

molecular lifetime of this state is at least 10

_

° sec. The overtone of

268
this vibration at 6517 cm

-1

is slightly broadened, and the lifetime of

this level is on the order of 2.4 ns. The CN group is directly involved

in the hydrogen bond, and the lines of the CN stretching vibration at 2121

cm” are very broad. The lifetime of molecules in this state is about

2.56 ns. Not surprisingly the lower frequency bands, which have

vibrational frequencies below D

Q

, have sharp lines, and only an upper

limit estimate of the lifetimes can be made for the upper states of these

vibrations

.

These studies will shortly be extended to the far infrared region to

study the rest of the vibrational transitions unique to the complex.

4. Pulsed Beam Fabry-Perot Cavity Fourier Transform Microwave

Spectrometer

(R. D. Suenram and F. J. Lovas)

The construction of a pulsed beam Fabry-Perot cavity Fourier

transform microwave spectrometer was briefly described in last year's

annual report.

The major emphasis of our efforts in the past year have involved

testing the new spectrometer with a number of previously observed hydrogen

bonded species and van der Waals complexes to obtain experience in the

operation of the instrument and optimization of the detected signals.

Two areas in which the instrument excels are high sensitivity and

high resolution. In order to assess the sensitivity a 2 % mixture of OCS

in argon was prepared and the 1-0 transition of the various isotopes of

OCS studied in natural abundance. Figure 2.10 shows the 1-0 transition of

. 38 •OCS J=1-0

• 88 • 98 I. J L. J L 2.70 3.98 4.58 S •o- O- 1 . E-2

R 1 28

-lJ^ H

’•OCS J=l-0

0.20%

3.19 3 23 338 9«8 • S3 F3-I14M SI3f*t« 3—1 WIWI

Fig. 2.10. Rotational spectrum of the J=1-0 transition of ^OCS. Left:

time domain spectrum obtained with 500 nozzle pulses. Right:

frequency domain spectrum; Fourier transform of spectrum shown

on the left. The signals were observed with a 2J mixture of

OCS in argon.

269
1 8

OCS which occurs in 0.21$ natural abundance. The trace is a summation

of signals for 500 nozzle pulses but this signal is easily observable on a single pulse. The weakest signal observable was that of ' a 0C^ 4 S which

occurs in 0.0086$ natural abundance. This signal was observed with a summation of 2500 pulses. The 1S 0CS signal, which is observable on a single pulse, corresponds to approximately lO 1 ^ molecules per pulse.

Several improvements of the instrument are planned for the next year which

should easily increase the sensitivity by an order of magnitude.

The high resolution aspect is shown in Figure 2.11 where the 1-0

transition of (H2 0) 2 is shown. The four individual peaks arise from the

spin-spin hyperfine interaction associated with the H nuclei. The

splittings are

Fig. 2.11. Time domain (left) and frequency domain (right) spectrum of the

J*1-0, E-state transition of the water dimer at v - 12321.0

MHz. The frequency splittings (right side) are approximately

16-20 kHz.

on the order of 16-20KHZ. We have found that with certain nozzle/ pressure

configurations we can obtain line widths on the order of 8-1 2kHz (FWHM).

The following two reports (D.5 and D.6) describe new results obtained

for Ar» • ^acrylonitrile and Kr***0CS.

5. Microwave Study of the Ar. . .Acrylonitrile van der Waals Complex

(F. J. Lovas and R. D. Suenram)

The van der Waals complex of argon with acrylonitrile (Ar . . ,CH2 CHCN)

has been observed with the pulsed beam instrument. This particular

complex was chosen as the first new molecular species for the new instrument for a variety of reasons. First the dipole moment is large so

270
1 4

the spectra should be quite intense. Second, the N nucleus provides

characteristic quadrupole splittings which should be predictable and thus

useful for the assignments of the transitions. Third, the species is

large enough so that the transition density is fairly high (a strong

transition every 100 MHz or so) which should enable several transitions to

be found without a great deal of searching. Last, there are a variety of

sites where the A r could bind to acrylonitrile. It will be extremely

interesting to see which conformation is the dominant one.

Two discrete sets of rotational transitions have been observed. For

one set, the energy levels lie approximately 0.5 - 1.0 cm

-1 higher in

energy than the other set. More than thirty transitions have been

observed and fitted for the low energy (ground state) and over twenty

transitions have been measured and fitted for the higher energy

(vibrational) state. Each of these transitions is split by the nuclear

quadrupole interaction associated with the nucleus.

From a rotational analysis of the transitions, and analysis of the

nuclear quadrupole hyperfine structure, the molecule appears to favor one

of the two possible structures shown in Figure 2.12. Further work with

deuterium isotope labeling will have to be done in order to discriminate

which is the true structure. Our intuitive feeling is that the "inside"

structure is probably the correct one, since the "outside" structure

requires an Ar...H distance that is shorter than for the normal van der

Waals radii of the atoms. In either case, the Ar atom lies at an angle of

approximately 40° with respect to the plane of the acrylonitrile subunit.

Ar "inside" Ar "outside"

Fig. 2.12. Favored structures for the argon-acrylonitrile van der Waals

complex.

6. Mirowave Study of the Kr...0CS van der Waals Complex

(F. J. Lovas and R. D. Suenram)

During Dr. B. J. Howard's visit at NBS the possibility was discussed

of looking for the microwave spectrum of neon and krypton bonded to

carbonyl sulfide. Work in the infrared region in his laboratory at Oxford

271
University had provided approximate values for the rotational constants of

both Ne...OCS and Kr...OCS in the ground state and v=1 of the CO

stretching vibration. Accurate values for the rotational constants of

these species in the ground state, obtained by microwave spectroscopy,

could be used in the analysis of the infrared spectra to obtain very

precise values for the upper state constants.

Some time was spent searching for Ne...OCS but no transitions were

found. Transitions of Kr...0CS on the other hand were readily observed.

Subsequent microwave- Infrared double resonance work on Ne...OCS in Oxford

indicated that the preliminary rotational constants were much more

uncertain than originally thought; as a result, we never searched the proper

region to detect a transition of Ne...0CS.

For Kr...OCS transitions for four isotopes (®**Kr, 57$; ®^Kr, 17$;

02 Kr, 11$; and °^Kr, 11$) have been observed and analyzed. The structure

of the complex is planar and T-shaped, similar to Ar...0CS (see Fig 2.13).

One note of interest is that nuclear hyperfine structure has been observed

o

t

Fig. 2.13. Structure of the Kr...OCS van der Waals complex

on ®^Kr...OCS transitions (see Figure 2.14). The ®^Kr atom has a nuclear

spin of 9/2 and thus, a nuclear electric quadrupole moment. Although the

electron orbitals of the atom are spherically symmetric, these are distorted in the van der Waals complex and cause hyperfine interactions.

Analysis of this hyperfine structure should enable us to study the

distortion of the spherical symmetry upon complexation

.

Quite recently we have incorporated a set of Stark plates into the

spectrometer for dipole moment measurments. These were placed -25 cm apart, so that the cavity Q would not be changed appreciably, and provide

AMj = ± 1 selection rules. Analysis is in progress on the Stark effect of

Kr***OCS. Figure 2.15 shows three Stark components of the 3

-j 2~ 2 02

transition.

272
Fig. 2.14. Time domain (left) and frequency domain (right) spectrum of

the J-1-0 rotational transition in °^Kr...OCS at 7505.11 MHz.

The AF-0 transition is not shown in the figure; it was found

at 7504.6 MHz.

Fig. 2.15. Time domain (left) and frequency domain (right) Stark spectrum

of the J=3~2 line of Kr..0CS obtained with a field of

155V/cm.

7. A Generalized Internal Axis Method for High Barrier Tunneling

Problems, as Applied to the Water Dimer

(J. T. Hougen)

When more than one large amplitude vibrational motion is present in a molecule, it is often not possible to define a global internal-axis-method

(IAM) coordinate system and set of basis functions. In the present work,

a method is presented for extending the IAM treatment to tunneling

problems in such cases, using as an illustration a model for the water

dimer with three large amplitude vibrational coordinates. The method

273
involves the construction of two different sets of local IAM-like

coordinate systems. The first of these contains n coordinate systems, one

for the small neighborhood surrounding each of the n equilibrium

frameworks. The second contains on the order of n^/2 coordinate systems,

one for each feasible tunneling path between each pair of frameworks.

Basis functions written in the second set of local IAM-like coordinates

are used to determine the complex phase factors associated in this method

with tunneling matrix elements of the phenomenological rotational

Hamiltonian in the high barrier limit.

These phase factors govern the way in which the various real

tunneling frequencies in the molecule constructively and/or destructively

interfere in the Hamiltonian matrix elements and final energy expressions.

Various mathematical approximations are involved in using the local

IAM-like basis sets to obtain matrix elements; the full extent of the

adverse effects of these approximations will not be known until an attempt

to fit experimental data is carried out.

E. General Spectroscopy and Theory

1 . Efficient Sampling Systems for the Fourier Transform Spectrometer

(Wra. Bruce Olson)

A transfer optics system has been designed, and constructed for the

coolable White cell made from our design by Prof. J. Bevan at Texas A&M

Univ. Prof. Bevan also had made an evacuable chamber for the transfer

optics. The utility of this system for use in the far infrared has been

demonstrated

.

A preliminary optical design using a single concave mirror has also

been worked out for the transfer optics to couple the BOMEM FTIR

spectrometer to an existing heat pipe for use in the far infrared. An

important feature of this and the previous system is that a single concave

mirror is used to accomplish two objectives. An image of the input

aperture of the FTIR is placed at the entrance of the cell, and an image

of the beamsplitter is placed on, and exactly fills, a back mirror of the

White cell, or exactly fills the exit aperture of the heat pipe. Under

these conditions a simple thin window, but no field lens is required at

the input of the sample cell, in order to pass the maximum possible signal

radiation, and the problem of a suitable optical material for a field lens

is eliminated.

2. Diode Laser Measurements on Unstable Diatomic Molecular Species

(A. G. Maki , G. A. Thompson, and A. Weber)

In an effort to study molecular species that are unstable in the gas

phase under ordinary conditions, we have used a high temperature technique

to measure the infrared spectrum of GeO, Lil, and LiD in the gas phase.

These are the first resolved gas phase infrared measurements to be made of

these species although the electronic and microwave spectra have been

studied in the gas phase. The extent of the measurements is indicated in

27 ^
Figure 2.16. which gives the range of vibrational and rotational levels

covered by these measurements for ^ Ge^ 0 and 'Li I. All five isotopic

germanium species of GeO have been measured in natural abundance as can be seen in Figure 2.17 which shows a portion of the measured spectrum. So far

only the most abundant isotopic species of Lil and LiD have been observed.

To analyze measurements of this sort we have developed a non-linear

least-squares fitting program to determine a set of Dunham potential

coefficients that define the lower part of the potential well for the

molecules under study. Most other workers use such measurements to

Fig. 2.16. Extent of data base for rotation-vibrational bands of GeO

(left) and Lil (right) determined from infrared diode laser

spectra. In these displays the vibrational states are depicted in strips one unit wide, and centered about the

integral value of the vibrational quantum number v.

determine directly a set of ro-vibrational constants that ignores the

underlying concept of a potential well and therefore may be in conflict

with any reasonable potential function.

We believe that a more useful analysis uses the data to determine the

potential function and then uses the potential function to determine a consistent set of ro-vibrational constants.

The problem with using ro-vibrational constants for calculations that

represent an extrapolation outside the range of observations is that the

constants are usually determined without restraining them to a physically

meaningful model. Our way of determining the ro-vibrational constants

gives them greater reliability for calculating levels and transitions

outside the range of measurements because the underlying concept of a potential function restrains many of the higher order ro-vibrational

constants to physically realistic values.

In the case of GeO all five measured isotopic species have been fit

to a single potential function which can be used to calculate the observed

transitions with an rms deviation of 17 MHz which we believe represents

the accuracy of the measurements.

275
GeO

76

•

I 74

74

U72

73

76

74

76

P o ( 5 7 )

P 2 ( 4 5 )

70

74 70

72

70

l 73

Vw>,

P 4 ( 3 1 )

P i ( 5 5 ) P*(30)

•i i P s ( 2 2

)

P , ( 5 2

)

9 1 0.80

Po(6o:

P 4 ( 3 2 )

9 1 1.00

_L

P a

( 4 1 ) *

i

j P 2

( 4 8 )

1

4 P 2 { 4 3

)

P 0 (59)

* P , ( 5 0

)

9 1 1.20 9 1 1.40

WAVENUMBER (cm- 1 ) Fig. 2.17 Portion of the infrared diode laser absorption spectrum of GeO.

Numbers in the top part identify the Ge- isotope. The

assignments of the individual rotation-vibrations are given in

the lower half; the subscripts label the vibrational state. The

line marked with an open circle is due to an impurity.

The work on LiD is not yet finished. In the coming year we expect to

also observe the spectrum of b LiD.

We have also been measuring transition frequencies and relative

intensities for CIO. Since those measurements are of interest for

atmospheric studies, they are described in section C on studies related to

atmospheric chemistry.

3. Fourier Transform Raman Spectroscopy of H

2 and D

2 in Flames

(A. Weber and D. A. Jennings)

The successful demonstration of the use of a Fourier transform

spectrometer to record Raman spectra of gases under high resolution was reported in last year’s Annual Report. Together with Dr. J. W. Brault of

276
the National Solar Observatory located at Kitt Peak, AZ, work on the high

temperature spectra of H

2 and D

2 has been done with the 1 -meter FTS

instrument of the McMath Solar telescope at Kitt Peak.

Laboratory spectra of high rotational transitions in H

2 are important

in astrophysics because they may be observable in hot stellar and

Interstellar sources, and have already been seen in quadrupole emission

from the Orion molecular cloud J The Orion emission lines are characteristic of an -2000K rotational temperature. Infrared spectra of H

2

and D

2 at high temperatures are difficult to obtain in the laboratory

because path lenghts of hundreds of meters are necessary to observe the

quadrupole absorption. Vibration-rotation coefficients obtained from room

temperature spectra cannot be extrapolated to the high-J lines observed in

Orion to within the accuracies of the astronomical measurements.

Prompted by these considerations, we have recorded Raman spectra of

high temperature molecular hydrogen and deuterium using a Fourier transform spectrometer. A diffusion flame source burning H

2 or D2 in air was placed at the focal point of a multi-pass mirror system. Figure 2.18

shows the pure rotation spectrum of D

2 obtained in this manner; the room

temperature spectrum is shown for comparison.

FTS— RAMAN SPECTRA OF 02 v 0-0

»6)

RAMAN SHIFT (cm**)

Fig. 2.18. Pure Rotational Raman Spectra of D

2 for a diffusion flame in

air (top) and a stagnant gas at room temperature (bottom).

As expected the higher temperature spectrum (flame) shifts the

intensity distribution toward higher J-values, with S(1 2) being the

highest transition observed. The noisy and varying background in the high

temperture spectrum is caused by the flame itself. Similar observations

were made on H

2 for which both the v=0-0 and v*1-0 spectra were recorded

277
to S(7) (v=0-0) and Q(5) (v=1-0) in the flame spectra. The data bases

for the v=0-0 and v=1 -0 transition of H

2 and D2 have been extended through

the inclusion of the Raman flame data. Improved ground state constants

for D

2 are listed in Table 2.2.

Table 2.2 Ground State Parameters of Dj (cm

1

).

Constant Flame + Room Temp. Room Temp. Only

B

DH

L

o

o

oo M

o AE m

29.91 371 (44)

0 . 01 1 527 ( 22 ) 6 . 84 ( 40 )x1 0

b -1.11 (29)x10_

3* 09 ( 69 )x1 0

1 ae 6 (j)

29.91 439(40)

0.01 1599(19).

9. 10(24)x10"b

AE 4 (J)

(1) R. F. Knacke and E. T. Young, Ap. J. (Letters) 249, L65 (1981).

(2) R. W. Hill, A. J. Mulac , and C. E. Hackett, Appl. Opt. J_6, 2004

(1977).

4. Infrared Spectrum of Cyanogen

(A. Weber, W. J. Lafferty, and W. B. Olson'

Previous work on the high resolution infrared spectrum on C

2 H2 was described in last year's Annual Report. In that work the and

fundamental bands were recorded with the B0MED DA3.002 Fourier transform

spectrometer using only a 20cm absorption path. The band was recorded

at a pressure of 5 torr which caused noticable pressure broadening of the

lines. In the present work a White cell (maximum path length 20 m) was employed to re-record the band system, as well as to obtain spectra of

the v-i+v^

1

, , \>i - ^, and v

2

- v^

1 combination and difference bands at an apodized resolution of 0.004 cm ^ . Because of the low lying fundamentals v

4 and these bands are accompanied by numerous hot bands which

complicate the assignment process, but which yield precise values for the

energy levels of the lower states. Figure 2.19 shows the region of the

band U3ing a path length of 2.25m and a gas pressure of 1.51 torr. The

OCS is present as an impurity in the gas sample. The v-|-vq^ band plus its

hot bands is now present with a good signal to noise ratio. In the

previous spectra only its Q-branch was visible, with very poor signal to

noise. Similarity the and bands of the isotopic species

^c^CNg, present in natural abundance, are observed in the present

spectra. Extensive structure was observed in the v-j+vc;

1 and

combination bands. The vi+v^

1 band contains an heretofore unreported

perturbation . The band system near 610cm 1 was recorded for the

first time under high resolution. This band is weak and, owing to the use

278
max . me it

Fig. 2.19 Region of the v^-band of C

2 N

2 recorded with the BOMEM DA3.002

Fourier transofrm spectrometer at a (opodized) resolution of

0 . 004 cm

-1

. The spectrum is the result of 64 scans taken one a time of 5 h. 20 m.

of the less sensitive HgCdTe detector, a rather high pressure of 39.9 torr

was necessary for its observation. The analyses of the various bands are well under way though the perturbation in the + vc identified. The upper state of the v*

1 -

I + and a Z a

- component, both of which have- been identified,

tft

band remainds to be

band is split into a This is only

e second known case (the other being C

2H2

) in which a Z g

- 1^ transition has been observed and identified. Besides improved values for the

constants of the v^, and v^+v^ band systems new results have been

obtained for the v

2 ~vc

1 system as well as for the ground state of

1 3q 1 _ Tno nvt-ano 1 -tro Hat-a Haao r\ f' Hia nomH tnaH nr anH H i f f or>o 2

* The extensive data base of the combination and difference bands

has also enabled us to obtain more accurate values for the frequencies of

the

\>i and v

2 fundamentals. These fundamentals are of species Z g

+ and are

thus only observable in the Raman spectrum. The present results are:

v-|=2330. 4847(5) and v

2 *845 .5965( 1 5)cm

-1

. They are more accurate than the

Raman results and will serve in the determination of a more accurate

force field of cyanogen.

5. Fourier Transform IR Spectra of Monodeuterosilane

(Wm. B. Olson and R. W. Lovejoy)

Assignments in the vibrational bands v^, v^, v^, v

2 and 2vg have been

greatly extended since last years report. Identification of perturbation

279
allowed transitions with high values of the K quantum number in and

has enabled for the first time a direct experimental determination of

D

q

k and a smaller error (by a factor of 150) than that of our previous

determiantion 1 of A

Q

.

We were unaware at the time of last year’s report that another group

of workers in Europe had taken the same spectra and had nearly completed

the assignments. This group is headed by Prof. H. Burger,

Universitat-Gesamthochschule, Wuppertal, West Germany. Since that group

had access to computer software for fitting the three bending

fundamentals, we (by agreement with Prof. Burger) abandoned work on these

and have concentrated on the analysis of the \>2 and 2vg parallel and

perpendicular bands.

The extreme weakness of the perpendicular component of 2v^ leads to no observable transitions in this band except those whose intensities are obtained by perturbations with V

2 and the parallel component of 2vg.

Several perturbations are observed, and about twenty transitions of 2vg

have ben assigned, but we do not yet have enough data for a reasonably

good analysis, and the slow assignment and checking process is still in

progress

.

(1) Olson, W. B. , and Lovejoy, R. W., J. Mol. Spectrosc. 66_, 31 330

(1977).

6. Far Infrared Spectrum of the Torsional 3and of Hydrazine

(N. Ohashi , W. J. Lafferty, and W. B. Olson)

Hydrazine has two large amplitude motions, an NH2 wagging vibration

(similar to the umbrella motion in NH^), and the torsional vibration.

Only recently have theoretical methods become available to treat the

observed spectra 1

, and they have been successfully used to fit the pure

rotational microwave spectrum. While the ground state has large

splittings arising from the inversion motion, torsional splittings in the

ground state are quite small.

We have studied the torsional vibration of ^H^ where the torsional

splitting contributions will be much larger than in the ground state

spectrum in order to further test the theory, as well as to attempt to

determine the barrier to internal rotation. The center of this band is at

376 cm1

. It is a b-type band, and since the A rotational constant of the

molecule is large, it covers a large portion of the spectrum from about

300 cm

1 to 450 cm

1 . The spectrum was recorded with the NBS BOMEM FTS

spectrometer at a resolution of about 0.01 cm

-1

.

Although the spectrum is somewhat complex due to the fact that each

rovibrational transition is split into either four or six components

(depending upon whether the lower state K of the transition is even or

280
odd), and also because of overlapping by "hot band" transitions, we have

been able to make a very satisfactory line assignment with the aid of

combination differences calculated from ground state constants obtained in

a recent microwave study.

The assigned transitions were combined with the observed microwave

data and fit using Hougen* s Hamiltonian. 1 The inversion and torsional

splittings of both the ground and torsional states were obtained. As

expected, the torsional splitting in the vibrational state (1824 Mhz) was

found to be many-fold larger than the torsional splitting in the ground

state (5.8 MHz). However, a surprisingly large vibrational change in the

inversion splitting was found. This splitting was determined to be 7976

MHz in the torsional state as compared to a splitting in the ground state

of 16040 MHz. The height of the barrier to internal rotation was estimated

to be 21 00 ± 50 cm

-1

.

(1) J. T. Hougen, J. Mol. Spectrosc. 89, 296 (1981).

(2) S. Tsunekawa, T. Kojima and J. T. Hougen, J. Mol. Spectrosc. 95, 133

( 1982 )

.

7. The Torsional-Wagging Tunneling Problem and the

Torsional-Wagging-Rotational Problem in Hydrazine

(N. Ohashi and J. T. Hougen)

Results derived previously for the rotational levels of the

eight-framework and three-large-amplitude vibrational problem in ^H^,

using a tunneling formalism based on a treatment of the vibration-rotation

problem as a whole, were rederived in a much simpler fashion, using a tunneling formalism based on separate treatment of the vibrational and

rotational problems. The present formalism is thus much more akin to the

usual vibration-rotation formalism, and the origins of the various

contributions to the vibration-rotation energy levels can be understood

relatively easily. It is convenient here, as earlier, to make extensive

use of permutation- inversion and extended-group (double-group) ideas, but

it is necessary in the present treatment to consider tunneling between 16

minima in molecular coordinate space, i.e. between a number of minima

which is twice the number of nonsuperimposible molecular frameworks that can actually be constructed for N

2 H^.

8. The Use of Extended Permutation-Inversion Groups for Constructing

Hyperfine Hamiltonians for Symmetric-Top High-Barrier Internal

Rotor Molecules like HgC-SiHg

(J. T. Hougen)

The m-fold extended group G-jg^, corresponding to the

permutation- inversion group G

1 g

for molecules like HgC-SiHg, has been

obtained. In this extended group, m is the smallest integer for which mp

is also an "integer," where p is the usual ratio of the moment of inertia

of the top about the rotational A axis to the moment of inertia of the

molecule about the A axis. The extended group has 1 8m elements, divided

281
into (9m+3)/2 or (9m+o)/2 classes, for odd and even values of m,

respectively. Using this extended group, it is possible to assign

definite symmetry species in an internal-axis-method (IAM) treatment to

laboratory-fixed, molecule-fixed, top-fixed and frame-fixed projections of

vector operators like the rotational angular momentum and the nuclear spin

angular momenta. Thus, it is possible to express the spin-rotation and

spin-spin contributions to the hyperfine interaction operator in terms of

rotational angular momentum components, nuclear spin angular momentum

components, and functions of the torsional angle, all of which have known

symmetry species and selection rules in the IAM basis set. Using a hyperfine Hamiltonian constructed from these considerations, it is

possible to understand the large variations in magnitude of some observed

hyperfine couplings in recent molecular beam studies of symmetric top

internal rotor molecules.

9. Improved Least Squares Determination of Potential Energy Surfaces

from Spectroscopic Data

(C . Leubner and J. T. Hougen)

The value of a knowledge of potential energy surfaces for the

understanding of the overall properties and behavior of a molecule can hardly be overestimated. With the exception of the simplest molecules, it can safely be stated that currently it is the observed spectrum that

contains the most complete - albeit indirect - information on the

molecular force field. As a consequence, much effort has been expended on

the retrieval of potential energy surfaces from spectroscopic data.

Vidal and coworkers have shown in a number of applications that such

a program - termed "Inverted Perturbation Approach (IPA)" and reviewed in

(1) - can indeed be carried quite far in the diatomic case, where a number

of problems are absent that become crucial in the polyatomic case. These

qualitative differences preclude a straightforward, similarly successful,

generalization of the IPA to the determination of potential energy

surfaces. However, the main ingredients of the IPA have been used by the

workers in the field of polyatomic molecules with more moderate results.

Chen et al . (2) recently showed that none of the surfaces determined by

these methods for the water molecule agrees with the observations to

within spectroscopic accuracy.

However, it is possible to identify three promising areas for the

improvement of the conventional approach. First of all, the variational

character of the IPA can be combined with the necessarily variational

calculation of the eigenvalues of the Schroedinger equation for a polyatomic molecule to give a very compactly formulated optimization

problem, the solution of which would, in principle, immediately give the

optimum potential energy surface corresponding to the measured energy

eigenvalues in a least squares sense.

282
Secondly, this optimization problem involves as a crucial step a sufficiently accurate determination of the ro-vibrational eigenvalues of

the Hamiltonian of the molecule under study. Chen and coworkers (2) have

reported encouraging results with the conventional expansion of the

eigenstates in products of "rotationless vibrational" wavefunctions and

symmetric top functions. Alternatively, one could invoke so-called

"distributed Gaussian bases", as recently introduced into the nuclear

molecular problem by Hamilton and Light (3), which, after all, have proved

superior to all other basis sets in the electronic molecular problem,

where they are now exclusively used.

Thirdly, one requires a sufficiently flexible representation of the

potential energy surface. As an improvement over the conventional Taylor

series expansion in suitably chosen coordinates around the equilibrium

point of the surface, we propose to supplement this by a Spline

approximation (4) that adequately incorporates the full symmetry of the

problem. The parameters of this Spline approximation are then to be

optimized in a least squares sense with respect to the observed spectrum.

An investigation that focuses on these three areas of improvement is

currently under way in collaboration with M. Wolfsberg of the Department

of Chemistry, University of California, Irvine, CA.

(1) C. R. Vidal: Accurate determination of potential energy curves

(preprint) 1985.

(2) C.-L. Chen, B. Maessen, and M. Wolfsberg: Variational

calculations of rotational- vibrational energy levels of water

(preprint) 1985.

(3) I. P. Hamilton and J. C. Light: On distributed Gaussian bases

for multi-dimensional vibrational problems (preprint) 1985.

(4) J. H. Ahlberg, E. N. Nilson, and J. L. Walsh: The Theory of

Splines and their applications (Academic: New York 1967).

10. The Proper Choice of the Lagrangian f or a Relativistic Particle

in External Fields

(C . Leubner)

It is an unsatisfactory feature of the educational literature that

renowned authors propose apparently conflicting prescriptions for the

construction of an appropriate Lagrangian to describe the interaction of a relativistic point particle with external fields. The point where

opinions sharply differ is whether, in the case where the independent

parameter is to be the proper time of the particle, the equations of

motion should be derived from Hamilton's principle by constrained or unconstrained variation. Therefore, it is shown that there exists a unifying point of view, which allows a consistent derivation of all these

seemingly unrelated or even incompatible Lagrangians, which completely

283
clarifies their status and interrelations, and, moreover, provides a sound

basis for discussing coherently a multitude of related issues that have

emerged in the literature in an often obscure and even misconstrued

manner. The results are to appear in the European Journal of Physics.

11.

A Note on the Uniform Asymptotic Expansion of Integrals with

Coalescing End Point and Saddle points

(C. Leubner)

Together with H. Ritsch of the University of Innsbruck we have

introduced a new method for the uniform asymptotic expansion of certain

types of contour integrals, one of whose critical points is an end-point

of the interval of integration. The method, which is alternative to

Bleistein's, has been tested numerically by way of a non-trivial physical

example. The results will be published in Journal of Physics A: Mathematical and General.

12.

Generalized Stirling Approximations to N!

(C. Leubner)

Generalized asymptotic approximations to r(x + 1 ) , which contain an arbitrary parameter, are derived both from the integral representation of

the Gamma function without assuming a knowledge of the Stirling series,

and through elementary rearrangements of the Stirling series. By

optimizing the arbitrary parameter according to appropriate criteria,

several known Stirling-like approximations are recovered in a unifying

way. These are as compact as but numerically superior to the standard

Stirling approximations, and are meaningful on intervals that even include

parts of the negative x-axis. It is pointed out that these results - arrived at by elementary but generally applicable asymptotic techniques - can be exploited in physics teaching to demonstrate the power and utility

of asymptotic methods in the analysis of a variety of physics problems.

The results are to appear in the European Journal of Physics.

13.

Accurate Emission Spectra from Planar Strong Field Wigglers with

Arbitrary Field Variation

(C. Leubner)

In collaborative work with H. Ritsch of the University of Innsbruck

we showed that the spectral and angular distribution of the single

particle wiggler signal can be conveniently evaluated by asymptotic

complex contour integration, if the wiggler magnetic field is an arbitrary

function of only the coordinate along the wiggler axis. The method is

efficient and accurate, especially in the most interesting range of

frequencies around the character i Stic frequency of the wiggler, where for

strong field wigglers the conventional procedure encounters serious

284
computational difficulties. The method exhibits promise for extensions in

various directions of experimental interest. The results will appear in

Nuclear Instruments and Methods in Physics Research.

14. Dynamical symmetries and equivalent Lagrangians for

one-dimensional systems

(C. Leubner)

In collaboration with M. A. M. Marte of the University of Innsbruck

we have shown that for one-dimensional Newtonian equations of motion a surjective mapping from the set of dynamical symmetries onto the set of

equivalent first-order Lagrangians can be established, where - up to an integration - the Lagrangian associated with a particular dynamical

symmetry is explicitly given.

15. On the Relationship of Normal Modes to Local Modes

(I. M. Mills)

A simple model for the effective vibrational Hamiltonian of the XH

stretching vibrations in H

2 0, NH^ and CH^ is considered, based on a Morse

potential function for the bond stretches plus potential and kinetic

energy coupling between pairs of bond oscillators. It is shown that this

model can be set up as a matrix in local mode basis functions, or as a matrix in normal mode basis functions, leading to identical results. The

energy levels obtained exhibit normal mode patterns at low vibrational

excitation, and local mode patterns at high excitation. When the

Hamiltonian is set up in the normal mode basis it is shown that

Dari ing-Denni son resonances must be included, and simple relations are found to exist between the xps , g tt , and Krrss anharmonic constants (where

the Darling-Dennison coefficients are denoted K) due to their

contributions from Morse anharmonicity in the bond stretches. The

importance of the Darling-Dennison resonances is stressed. The

relationship of the two alternative representations of this local

mode/ normal mode model are investigated, and the potential uses and

limitations of the model are discussed.

F. Future Plans

1 . Calibration and Data Center Activities

During the coming year we will devote a major effort to the

completion of ’’Microwave Spectral Tables III. Hydrocarbons". In

conjunction with this manuscript we will produce a magnetic tape of the

combined measured and calculated spectra which is too extensive to publish

in printed form. Eventually we will combine this data with the existing

files on diatomic and the triatomic species to form the initial spectral

line atlas. We will also begin extracting and evaluating data on a new

285
group of organic species. Hydrocarbons containing the heteroatoms, oxygen

or nitrogen will be selected for the next review in this series after we examine our files of literature references on these compounds.

In addition to the general search of the microwave literature we will

continue searching the astronomy literature for interstellar molecular

observations. Due to the rapid increase in new data during the 5 years

between revision of the Recommended Rest Frequency publication, we plan to

up-date the computer data files on a continuing basis in order to publish

subsequent revisions in a shorter time frame. Publication of revisions

every two years is the current plan.

Further work is planned in collaboration with NBS/Boulder on developing infrared calibration frequency standards. New heterodyne

measurements on hot bands of N

2 0 will be performed to extend the present

calibration tables into the 2800 cm

1 region. Preliminary results from

this work have already been provided to workers at NBS in support of their

work on N02

. Similar work will also be done on the v-d + 2v2 band of OCS near 1900 cm

- '

1 as well as on the fundamental band of NO.

2. Spectroscopy for Environmental Studies

Work on the spectroscopy of molecules of importance in the

chemistry of the earth’s atmosphere will continue in support of NASA and

CMA programs during the coming year. Intensity and frequency measurements

will be made on CIO. New infrared diode laser measurements on the

spectrum of nitric acid will be made and combined with existing microwave

and infrared data to develop an atlas of transition frequencies and

intensities for the range 1680-1740 cm

-1

. Work will also be done on the

Vc and 2vg bands of nitric acid. The analysis of these bands, which span

tne region from 850 to 930 cm

-1

, requires the inclusion of a perturbation

due to a AK=±2 interaction. Similarly, although the and vjj bands of

nitric acid have been assigned, they are found to be perturbed and are still to be satisfactorily analyzed.

The work on the collisional line-shapes of HF and HC1 undertaken in

support of the NASA project HAL0E will be concluded during the coming

year. We will examine the effects of collisions on the electronic fine

structure of NO as well as for overlapping Q-branch transitions, and make

precise frequency measurements on the fundamental band in collaboration

with the NBS/Boulder group.

3. Spectroscopy of Hydrogen-Bonded and van der Waals Complexes

As first reported in the report for FY82 the High Resolution

Group has embarked on a program of investigating the spectra of weakly

bond molecular complexes and the present report indicates the expansion of

these efforts. During the coming year we plan to continue to do tunable

infrared laser spectroscopy of hydrogen bonded and van der Waals

molecules. Using a coolable White cell with the gas under thermal

equilibrium conditions investigations of hydrogen-halide complexes will be

286
continued with the difference frequency laser spectrometer while the diode

laser spectrometer will be used in the study of heavier complexes (e.g.

NO-dimer) as well as for the study of the far-infrared van der Waals modes

of HX complexes.

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.

The good performance of the initial version of our pulsed-beam

spherical Fabry-Perot cavity microwave spectrometer has prompted us to

improve the sensitivity and efficiency of this instrument. Modifications

of the hardware in the signal detection and digitization systems coupled

with streamlined software will allow more rapid pulsing. Modifications

are also planned to improve the search efficiency of the instrument by

computer control of a number of current manually performed operations.

With these modifications we expect a five-fold improvement in the spectral

search over the present value of 100 MHz/day.

Several techniques are under investigation for producing pulsed beams

of non-volatile materials e.g. thermo-spray and laser ablation methods, to

broaden the range of studies possible with this spectrometer.

In addition to these instrumental improvements planned during the

coming year we will engage in spectral studies of hydrogen-bonded species

as well as van der Waals complexes. Several of these planned microwave

investigations will be carried out in conjunction with the infrared

studies done in the group.

The experimental studies planned for next year will be complemented

by theoretical investigations. In particular work will continue on the

problem of the water dimer.

4. General Spectroscopy

Several projects are planned in the realm of large amplitude

motions such as the study of the torsional band of methyl alcohol and the

spectrum of methyl amine. These projects will serve to further test the

Hamiltonian models for rotation-vibration spectra for the case of large

amplitude internal motions.

287
3. LASER PHOTOCHEMISTRY GROUP

D. F. R. Burgess, Jr., M. P. Casassa, R. R. Cavanagh, L. B. Elwell,

E. J. Heilweil, M. E. Jacox, D. S. King, D. A. Mantell , J. C. Mialocq,

J. Perry, J. C. Stephenson, and A. M. Woodward

A. Introduction

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.

The following staff changes have occurred in the year since July

1984. The 1984 annual report mentioned five post doctoral fellows working

in this group. One of them (Woodward) remains at NBS as an NRC post-doc.

Two (Perry, Mantell) left NBS to take permanent jobs in the private

sector. Two ( Heilweil and Casassa) agreed to join the Molecular

Spectroscopy Division staff. Don Burgess (post-doc, Div. 541) came to

NBS in January 1985 to study thermal and laser- induced desorption of

molecules from surfaces. A visiting senior scientist, Dr. Jean-Claude

Mialocq from CNRS (Saclay, France), spent eleven months on sabbatical at

NBS where he did picosecond photochemistry and pulse radiolysis

experiments

.

B. Condensed Phase Energy Transfer

(M. P. Casassa, R. R. Cavanagh, L. B. Elwell, E. J. Heilweil,

J. Perry, J. C. Stephenson, A. M. Woodward)

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.

For simplicity, the experimental results on VET have been organized

in four sections: T

1 times for surface vibrations; T1 for vibrations in

liquids; T

1 for vibrations in solids; and T ? times for vibrations in

liquids. This distinction among studies of’VET done in various phases of

matter is not fundamental. At least for the non-metallic systems we have

studied so far, VET is caused by short range forces, and the similarity of

results for the same vibration in different phases is striking. This work

is supported by AFOSR.

288
1 . t 1 (Vibrational Energy Relaxation) times for vibrations on surfaces

We used an infrared pump/probe method to do time-resolved measurements of the vibrational energy relaxation rate (T^

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.

Our initial measurements were on the surface hydroxyls (OH) bound to

dispersions of colloidal fumed silica (Degussa Aerosil 200, 120 A diameter

particles, 200 m

2 /gm surface area). We have since measured for several

different surface vibrations at the solid-vacuum interface and at the

solid-liquid interface. We explain the method for the OH-stretch (v=3750

cm

-1

) vibration; the same technique was used for all the vibrations we have studied. The surface hydroxyl v=0-H transition at the Si02 _ vacuum

interface was excited with a strong picosecond IR pulse which transferred

up to 10 percent of the hydroxyls from the v=0 to v=1 level. Due to

anharmonicity , OH (v = 1 ) does not absorb at the pump frequency, so excitation causes a transient increase in sample transmission, T. As

population relaxes, the sample transmission returns to its equilibrium

value, Tq; 2,n(T/Tg) is proportional to OH (v=1 ) population. Recovery of

sample transmission was monitored by a weak, time-delayed probe pulse

derived from the saturating pulse and a variable optical delay. At each

time delay (t D

), the probe pulse transmission was measured to 0.3 percent

accuracy with pump excitation and with the pump blocked using a dual

pyroelectric detector energy ratiometer. A typical data run is shown in

Figure 3*1. The population in OH (v=1 ) decreases exponentially with a characteristic decay time of T

1 = 216 ps.

The picosecond apparatus used in this investigation was based on a modelocked Nd

+ ^:YAG laser. Single 1.06 ym pulses of ~35 mJ and 10 Hz

repetition rate pumped a chain of three LiNbO^ crystals (0PA) to

parametrically generate tunable infrared picosecond radiation, which had a spectral bandwidth of 15 cm

-1

FWHM, duration of 20 ps FWHM, and delivered

about 400 yJ of pump energy to the sample.

The room temperature results for several surface vibrations, at the

solid-vacuum and solid-liquid interface are given in Table 3.1. For all

these systems, the bulk substrate Si02 was the same (fundamental substrate

modes are less than 1200 cm

-1

). The T

1 lifetime for 0H(v=1 ) on Si02 in

vacuum corresponds to roughly 2 x 10 4 vibrational periods. In various

solvents the 0H(v=1 ) T

1 lifetime decreases as the highest solvent

fundamental vibrational mode frequencies approach the 3700 cm

-1

OH

frequency. This is particularly evident for CH-stretch (-3000 cm

-1

) containing molecules such as CH2 C1 2 and CgHg where T

1 = 1 02 ± 20 ps and 87

± 30 ps, respectively.

289
Fig. 3.1. T 1 decay for isolated surface 0D(v-1 ) and 0H(v-1 ) on a dried

evacuated Si02 disk at T-293K. The exponential recovery of

transmission as a function of probe delay (tD

) yields a lifetime of T

1 - 1 35 ± 10 ps for 0D(v-1 ) and T

1 - 216 ± 20 ps

(1o) for 0H(v«1 ) from a least squares fit.

In the presence of adsorbed H

2 0, which possesses a broad, partially

overlapping OH absorption with SiOH, T

1 reduces even further to -56 ps.

In this case, direct V-V transfer from the surface OH to adsorbed water

may participate in the deactivation process.

Insight into vibrational energy transfer at surfaces may be gained by

studying other species bound to the silica substrate. In this way the

potential accepting modes of the bulk material remain unchanged while the

adsorbate local modes and adsorbate-substrate coupling are modified. The

simplest substitution for the OH group is isotopic exchange to 0D. In this case T.j is reduced from 220 ps for SiOH to 150 ps for SiOD (as pressed

disks in vacuum). Decay of the lower energy 0D quantum into the substrate

was expected to require fewer lattice quantum transitions than for OH

(i.e., Av 2 3 vs. Av Z 4) and result in faster decay rate. However, the

observed isotope effect was smaller than anticipated.

The hydroxyl T

1 lifetime for BOH modified silica (vQH - 3700 cm

-1

) in

vacuum or CCl^ is found to be -70 ps. Since the boron mass and

coordination to the surface oxygens is different from silicon, changes in

the local site bending and stretching frequencies must occur. This

surface modification is found to substantially alter the relaxation

lifetime of the surface OH species. Both NH-stretching modes of -NH2 were

found to saturate to the same extent (AT/T - 5$) although time-resolved

measurements produced an instrumental pulsewidth-limited response. While

precise T-j values could not be deduced from these results, the two modes

290
apparently exchange population rapidly and have comparable lifetimes (£20

ps). Attempts to saturate the CH-stretching transitions of -OCH^ were

unsuccessful, however. This may imply very fast vibrational relaxation

(T

1 < 5 ps) for the CH-stretches of chemisorbed methoxy. The above results

for adsorbates on Si02 suggest that increasing the complexity of adsorbate

vibrational level structure leads to more rapid vibrational energy

relaxation at the silica surface.

We have not yet directly measured where the energy goes when it

leaves the initially excited high frequency vibrations. To obtain

indirect evidence concerning the effective lattice accepting modes, we studied the isotope and temperature dependence of 0H(v=1 ) relaxation at

the S102 -vacuum interface. The results are shown in Figure 3.2. The solid

lines show fits to the data using the theory of multiphonon relaxation in

solids. For OH, the observed T dependence is well fit by a n=4 quantum

process, i.e. vQH (3750) 2*vlattice . For 0D the data are best fit by

n-3. i.e. \>q D (2760) 3vlattlce .

©

*3e

>*

CDU

©Q

©

©

cr

Fig. 3.2 Decay rates, T-j” 1

, for 0H(v-1) and 0D(v«1 ) on a dried evacuated

Si02 disk as a function of temperature T. Rates have been

normalized by dividing the 0D rates by 1/1 49 ps = 6.7 x 10^ s”

1

, and the OH rates by 1/220 ps = 4.5 x 10^ s . Error bars give

the 1o uncertainty in rate. The solid curves give the relative

multiphonon relaxation rates vs. T for an n-phonon process (see

text)

.

291
Table 3 • 1 • vibrational decay times at room temperature for the various

adsorbate/silica systems studied.

System v(cm 1 ) T

1 (ps) k(10 9 s

1 ) k'(109 s

_1

) a Notes

S iOH/ vacuum voh= 3 750 220±20 4.9 - Pressed Si02

disk

SiOH/CCl 4 voh=3 69 ° 1 59 ±1

6

6.3 1 .4 Dry Si02

dispersion

SiOH/CF2 Br 2 v0H

= 3690 1 40+30 7.1 2.2 Tt

SiOH/CH9 Cl 2 v

0h=3 66 ° 1 02±20 9.8 4.9 Tt

SiOH/C

6 H6 voh

= 3 625 87 ±30 1 1 .0 6.1 TT

SiOH/C 6 D

6 voh =3 6 25 80±30 12.0 7.1 IT

Si0H/H2 0/CCl l4 vOH =369 ° 56±10 18.0 13.0 SiOH T i

,

-5H 2 0/100A2 physisorbed

SiOD/vacuum vOD =276 ° 1 55 ±1

6

6.5 OD T-| with

672 OH re- placed by OD

BOH/vacuum

boh/cci 4

voh

= 3 700 -70 -14.3 Early decay

time; long

time com- ponent present

SiNH

2 /vacuum

SiNH

2 /CCl 4

vnh=3460

3520

<20 >50 Pulsewidth

limited

signal, AT/T

-52 for both

stretches

SiOCH^/vacuum v=2860

3000

<5 (?

)

>280 ( ?

)

No pulse

saturation

observed for

any CHstretching

mode

k

* =k - k vacuum

292
Acceptor mode frequencies compatible with this simple theory are also

consistent with the known frequencies of modes spatially near and hence

likely to be coupled to the surface 0H(v=1). For example, the Si-OH

stretch occurs at 970 cm

-1

, the Si-O-H bend at 795 cm

1

, and Si-0

stretching vibrations produce broad maxima at 800 and 1100 cm in the

vitreous silica phonon spectrum. The temperature dependence of the

multiphonon theory is inconsistent with energy going to the surface Si-OH

torsion vibration at 380 cm ^ (or to SiOD at - 270 cm ) . The n=4

process for 0H(v = 1 ) and the n=3 process for 0D(v=1 ) are in fact the lowest

order processes possible, in keeping with the propensity rule that the

most probable relaxation path will require the fewest simultaneous changes

of vibrational quantum numbers.

The observation that 0D on the surface relaxes faster than OH is

qualitatively consistent with the expected increase of T-| with increasing

energy gap between the excited level and the frequency of the accepting

modes. Multiphonon theories give the low T rate, Y(0), as Y(0) = aexp(-boj) or Y(0) = a(e) n where to is the OH or 0D frequency, n the order

of the process, and the constants a, b, and e (e < 1) depend on molecular

structure. However, it is surprising that the increase is only a factor

of 1.5 (220 ps OH vs. 150 ps 0D; e = .68) when the energy difference is

1000 cm

-1

. For comparison, measurements of the spin-orbit relaxation of

ions in crystals give values of e in the range 0.037 to 0.2 (i.e., the

rate for an n phonon decay is 5 to 27 times faster than an n + 1 phonon

decay in the same solid). We used a simple multiphonon relaxation theory

to estimate the relative rates for a 3 phonon (0D) and 4 phonon (OH)

relaxation of SiCU. If the accepting modes (t0

j_ = 930 cm ') are the same,

theory predicts YiO) for OD should be 13 times^YtO) for OH (e = .077).

Although theoretical estimates of the anharmonic coupling strength, and

hence of e, are uncertain, it seems difficult to reconcile the multiphonon

theory to both the isotope and temperature dependence.

In addition to the multiphonon theory, we have considered other

mechanisms of VET for these surface vibrations. The damping of

vibrational energy is not due to coupling to an image dipole formed in the

substrate, nor is damping by electron hole pair formation possible for

vibrations on a dielectric like SiOp. Forster energy transfer (site

hopping) is not important because of the small transition dipole moments

( Uqh

= *°35 D) and sparse adsorbate density ($ four OH/IOOA2 surface).

For molecules like CCl]j and CFpBrp, which have only low frequency

vibrations, VET to the solvents is unimportant, although the internal high

frequency modes of solvents like C^Hg may accept some of the energy.

Any theoretical approach to VET for vibrators on these dielectric

surfaces must also take account of the data available for VET in solids and

in liquids. Perhaps molecular dynamics simulations and classical

trajectory studies will provide a consistent method of understanding the

observed T-| values. Certainly a direct measurement of the pathways (i.e.

accepting modes) of VET will be of crucial importance to further the

understanding of this subject (c.f. Future Plans).

293
Spectral linewidths observed in surface vibrational spectroscopy have

sometimes been interpreted as uncertainty broadening. However, the

width of the absorption features on silica surfaces must arise from site

inhomogeneities or other dephasing processes, since the linewidths

corresponding to are 200 to 2000 smaller than observed. Note that

similar remarks pertain to T-j vs spectral linewidths for the solids and

liquids described in the next two sections.

2. T-] times for vibrations in liquids

Although there have been thousands of measurements of VET rate

constants for gas phase molecules where relaxation is caused by

bimolecular collisions, there is very little information available (< 20

measurements) about T-j times in room temperature liquids.

Over the past nine years, picosecond laser techniques have been used

by several research groups (most notably Laubereau, Kaiser, et al . , and

Chesnoy and Ricard) to measure vibrational energy relaxation times for

particular vibrational modes in room temperature liquids. Chesnoy and

Ricard measured T

1 for neat liquids of the simple diatomics HC1 , DC1, HBr,

and DBr. They found that the liquid phase relaxation rate constants were comparable to gas phase rate constants when corrections for dimer

formation in the liquids were taken into account.

Kaiser and Laubereau (KL) measured T-| for the stretching vibrations

(vch ~ 3000 cm

-1

) of eleven different hydrocarbons in solution (mostly

dilute in CCl^). They found T^ varying from < 2 ps (C 2 H

2

, CCl^H) to 100 ps

(CH^CClo). The dependence of T^ on molecular complexity was surprising

(i.e. why should a simple molecule with only one high frequency mode like

CCl^H relax rapidly while complicated molecules like acetone or trichloroethane relax 50 times slower?).

We have recently measured T-| for the OH and 0D stretching vibrations

of several alcohol and silanol molecules in dilute room temperature CCl^

solution using the same experimental technique as for the surface studies.

In part these experiments were done for comparison to the

results of KL. Of particular significance to our program is the

comparison between T

1 for vibrations such as OH, 0D, and NH2 bound to the

surface of a dielectric such as Si0 2

, and T^ for these same functional

groups attached to a small molecule (dissolved in a liquid like CCl^ which

has vibrational frequencies comparable to those of Si0 2

). If coupling to

nearest neighbor vibrational motions determines the VET rates, then those

small molecules may exhibit similar lifetimes to the surface systems.

The results we have obtained to date are shown in Table 3.2. T

1 times

for the OH (-3690 cm

-1

) and 0D (-2720 cm

-1

) stretching vibrations bound to

the Si atoms of silanols (in CCljj) are long. The T-| values are similar to

those for OH and OD bound to the Si atoms on a silica surface either at

294
Table 3.2. Vibrational relaxation times for 0H(v=1 ) and 0D(v=1 ) bonds of

alcohols and silanols dilute in 001^ at T = 295K.

Alcohols T

1 (ps) Silanols T

1 (ps)

Me^COH <15 <

—

Me

3

SiOH 205

Me^COD <15 <

—

Me

3 Si0D 245

Et^COH <15 <

—

Et

3

SiOH 1 85

Et^COD <20 <

—

Et

3 Si0D 224

<J)0D <15 4> 3

SiOH 206

c

6 F

5

°D <15 <i> 3

S10D 292

CH

3

0H <30 4>2^> i ( OH

) 2 85

CD

3 0H 73

CH

3

0D 52 <j> 2 S i ( 0D

) 2 134

cd

3 od 79

c

2 h

5

oh 70

Accuracy ±20?

the vacuum interface or interacting with liquid CC 1^ . For the surface

species in vacuum, 0D relaxes 50? faster than OH; for the liquid silanols

the OH relaxation rate is systematically slightly faster than the 0D rate

The relaxation rates for OH (-3620 cm

- ”

1 ) and 0D (-2680 cm

-1

) stretches in alcohols are much faster than for the corresponding silanols

For most alcohols T-, was too fast for us to measure accurately (T-|

ps); only for deuterated methanols and ethanol (OH) was T

1 long enough to

be determined. For the four instances where we studied both silanols and

the corresponding carbinols (i.e. Si substituted for central C), T^ is at

least twelve times shorter for the OH or 0D groups when bound to C than

when bound to Si. We are presently trying to interpret these results in

terms of coupling to specific adjacent vibrational modes and determine if

these rates relate to the chemical properties of these molecules.

All the T

1 results to date have been obtained with the one color IR

pump/probe method. With the aid of a new low f-number Raman spectrometer

(acquired in August, 1985), we hope to do further experiments on VET in

liquids, using the technique of IR vibrational excitation followed by

295
spontaneous anti-Stokes Raman scattering (SPARS) probing (with harmonics

of the Nd-YAG) of population in particular vibrational levels of these and

other systems. For example, if we probe the OH, NH, or OD vibrations

initially populated by the IR pulse, then we should obtain the same values deduced from the IR probe experiments. This will be an independent

verification of these results. Of more importance, the SPARS experiments

should permit us to identify the pathways of energy transfer (i.e., what

are the lower frequency accepting modes) during the relaxation. For

instance, using the IR pump/SPARS probe method, KL found that T-| for the

CH-stretch in ethanol is 40 ps, and we found for the OH stretch is 70

ps. If the CH stretching modes are transiently populated following

excitation and relaxation of the higher frequency OH-stretch, we should be

able to identify the rise and fall times of population in those modes. Of

course, by tuning our OPA to pump CH stretches, we could also

independently do the KL experiments.

3. T

1 for vibrations in solids

The IR pump/probe technique described above was also used to

determine T^ times for hydroxyl stretching vibrations in both amorphous

and crystalline solids. T-] times for hydroxyl groups coordinated to atoms

(ions) in a variety of crystals have been studied in order to assess the

importance of different local environments, including the mass of the

metal atoms (heavy atom effect) on VET. It may be easier to model, e.g.

via molecular dynamics simulations, the relaxation of bonds in these

crystalline materials than for liquids or amorphous solids like fused

silica.

The temperature dependence (T < 1450K) of the relaxation rate (T

1 ^)

of OH (v=1 ) impurity oscillators inside fused silica is given in Figure 3*3.

Note that the intrinsic vibrational relaxation rate for the bulk OH at room temperature is twice as fast as that for the surface OH on Si0 2

. The

T-dependence is perfectly fit by the multiphonon relaxation theory for an

n = 4 process, i.e. vQH (3690) * 4 v

i a ttice * The 0H impurity concen- tration in fused silica is so small (£ 460 ppm) that no dependence of T^ on OH concentration was observed.

The room temperature relaxation times for 0H(v=1 ) ions inside samples

of crystalline mica have very recently been measured. In these crystals,

OH is part of the unit cell, and the interatomic distances, the vibrational frequencies and the orientation of the OH bonds with respect to the

crystallographic axes are known. In the mineral muscovite, formula [ 0

-j q A l^ Si^ (OH )

2

K] 2

, the OH groups have a frequency of 3630 cm \ There are

four equivalent hydroxyls per unit cell, located in a plane such that each

is hexagonally surrounded by 0 atoms, and each OH is coordinated to two A1

ions. For these OH groups, T^ =100 ±20ps. In the mineral biotite, Mg

ions are substituted for some of the A1 ions in muscovite, and two

296
(A oTo

>*©

CO CCc

o

«-> ©

>< JO©

DC

Fig. 3 . 3 . Temperature dependence of the vibrational relaxation rate,

1 /T., , of OH (v-1) impurity oscillators in bulk fused silica.

The solid curves give the relative multiphonon relaxation rates

vs. T for an n- phonon process (see text).

different OH species (v-3660, 3590 cm

-1

) occur. For the 3660 cm

-1

vibration, T

1 - 210 ± 20 ps. These results are too recent to permit a detailed interpretation at this time. It should be emphasized that the

high frequency lattice vibrations in these crystals are similar to those

of fused Si02

, and the measured T

1 values are similar to the values found

for the surface OH on Si02

, for the bulk OH in Si02, and for OH bound to

Si atoms of silanol molecules in liquid CCl^.

4. T

2 (Vibrational dephasing) times for vibrations in liquids

Picosecond coherent anti-Stokes Raman scattering (CARS) determined the

dephasing times (T2

) for vibrations in simple liquids. Dephasing rates

(2/Tj) were determined at T-295K for the symmetric stretch of CS 2 (v^-656

cm

-1

) as a function of mole fraction in several solvents, and as a function

of temperature in neat CS 2

. Also, the dephasing rate of the ring

breathing mode of benzene (v * 991 cm

-1

) was studied as a function of its

dilution in CS 2

.

Since neither the apparatus nor the results have previously been

described in an Annual Report, details of both will be given below. We do

not anticipate any further studies of dephasing rates. However, the

apparatus used for the T

2 measurements, with some modification, will be

297
used in several future experiments, e.g. measurements of for C0(v-1) on

Pt ( 1 1 1 ) and measurements of vibrational predissociation times for van

der Waals molecules.

The apparatus is shown in Figure 3*4. Two dye lasers of independently

tunable wavelength (via 3 plate intracavity birefringent filters)

Fig. 3-4. Schematic diagram of apparatus used to measure T

2 for

vibrations in simple liquids by picosecond CARS.

are synchronously pumped by a modelocked Ar

+ laser operating at 82 MHz.

Tunable dye laser pulses at that repetition rate had about 0.6 nJ energy,

an autocorrelation width (FWHM) of 8 ps , and a spectral bandwidth (FWHM)

of 2.5 cm

-1

. If the pulses were Gaussian, this would correspond to a AvAt

product of 0.42, very close to the transform limit. The width of the cross correlation was about the same as the autocorrelation. A cw modelocked Nd-Yag laser (scheduled for delivery in November 1985) will

replace the Ar

+ laser in future experiments. Uncompressed dye laser

pulses of 0.5 ps duration have been reported with (doubled) Nd-Yag

pumping.

In our CARS experiment, the frequency difference between the dye

lasers ( 10 * 0) 1 -

012 ) was chosen to be resonant with the vibrational mode to be

studied. Pulses at and oj 2

, vertically polarized and overlapped in time were incident on the sample at the phase-matching angle. The pair of pump

pulses creates a coherent vibrational excitation in the liquid at

frequency o^-o^. At a delayed time t D a probe pulse at frequency a>i , horizontally polarized, is sent through the sample in the correct

propagation direction for phase matching the anti-Stokes frequency

a>o“2o)i -o> 2

. A CARS signal (different in both frequency and propagation

direction from the other beams) is generated by this pump pulse. The

intensity (i.e. pulse energy) of the CARS signal decays in time after the

298
pump pulses as S(tD

) - exp(-2tD /T2

) . The CARS signal, spatially and

spectrally filtered to eliminate scattered dye laser light, is detected by

a cooled photomultiplier operated in the pulse counting mode, and the

count rate is constantly stored in a computer. When necessary, neutral

density filters are inserted in the CARS beam to keep the count rate much

less than 82 mHz.

A typical experimental run to determine T

2 for the symmetric stretch

of liquid CS 2 is shown in Figure 3.5. Counts were summed for 10 sec at each

delay stage position t D

.

0.00

• Dephasing rate cs

2 656 cm'1

Response Function

52 -5.00

co

10.00 J I J L 60.0 0.0 60.0

TIME DELAY (PS)

100.0

Fig. 3.5. Typical experimental run for the determination of the

vibrational dephasing time T

2 for the totally symmetric

stretching vibration v-|*656 cm”' of CS 2 in the liquid state.

The CARS signal decays exponentially over at least 10 e-folding

times, with a characteristic decay time T

2 /2 = 10.2 ± 0.2 ps. This result

for neat CS2 agrees with previous work. Also shown in Figure 3-5 is the

measured apparatus response function for this experiment. For tD

> 10 ps,

the third order response function has a characteristic exponential decay

time (1/e point) of 1.8 ps. Therefore, if the CARS signal is sufficiently

strong, one may determine values of T

2 /2 almost as short as this response

time, despite the fact that the cross correlation FWHM is 8-9 ps. The

shortest T

2 we report below is 5.2 ps.

299
A summary of the room temperature dephasing rates of CS 2 (100) in

various liquid mixtures is shown in Figure 3.6. When CS2 is diluted in

CS

2

(•/• by volume)

Fig. 3.6. Room temperature dephasing rates (2/T2

) of CS 2 in the totally

symmetric vibrational state v

1 - 656 cm" in various liquid

mixtures. The points designated by filled triangles (A) are for

the ring breathing mode of benzene (v - 991 cm"') in CS 2

.

CCljj, the dephasing rate decreases compared to the pure CS2 rate. On

dilution in benzene, T

2 for CS 2 (100) is constant. Nitrobenzene, which

has a large permanent dipole moment, and ethanol, which can form hydrogen

bonds to other liquids, significantly decrease the dephasing rate of CS2

(100). This is probably due to the stronger long range forces that these

molecules can exert on CS 2

.

Also shown in Figure 3«6 is the dephasing rate of the ring breathing

mode of benzene (v-991 cm"') in CS2

. Our result for pure benzene (T2

- 5.2 ps) agrees with previous measurements. As benzene becomes more dilute

in CS2

, 2/T2 decreases. At low concentrations, so that each benzene

molecule is surrounded by CS 2

, T2 increases by a factor of 2.5 (T2 - 12

ps). This is completely different behavior from the relaxation of

CS2 (100) for which T

2 was independent of CS2 /benzene ratio.

We are presently working on the interpretation of these data.

Although the data in Figure 3*6 do not give straight lines, it nevertheless

appears that all the rates are consistent with an isolated binary

collision ( IBC ) expression of the form

2/T2

- p x k li g 11 (o) + p (1-x) k

i j g 1 j(o)

300
where x is the mole fraction of the molecule for which T

2 was determined,

p the liquid density, g^Co) the radial distribution function at

separation o, and k the bimolecular dephasing rate constants

(cm^/molecules/sec )

.

We have also measured the dephasing rate of neat CS 2 as a function of

temperature from its freezing point at T=165K to T=298K. Over the range

21 OK < T < 300K the rate decreases; then as T decreases further, 2/T 2

increases from 8.2 x 10 10

s _1

at 210K to 11.2 x 10 10 s" 1 at T = 170K. These

time-domain data may be compared to earlier frequency domain results for

the isotropic Raman linewidth Av of CS 2 (100). In principle, 2/T 2

= Av

(FWHM). The agreement is only fair. In this case the picosecond measurements are probably more accurate, since the linewidths are narrow (hence

difficult to resolve), and since the slope of the line in Figure 3.5 can probably be determined with more accuracy than a Lorentzian can be fit to

the Raman spectral line. We are presently interpreting these temperaturedependent results.

These T

2 experiments have supported the T

1 measurements which have

been done or are planned. Both T-j and T

2 experiments in liquids (or at

the solid/liquid interface) can make use of similar theoretical treatments

(which we are now attempting). The T

2 experiments have played a crucial

role in developing and testing our ability to use the synch-pumped lasers

which (when amplified) will form the basis for many future T^

measurements

.

C. Desorption of Molecules from Surfaces

(D. F. R. Burgess, Jr., R. R. Cavanagh, L. B. Elwell, D. S. King and

D. A. Mantell)

A dedicated experimental facility including surface sensitive analysis

(e.g., mass spectrometer, argon ion sputtering, LEED and Auger electron

spectrometer ) , computer controlled data acquisition and sub-Doppler (250

MHz) laser resolution is being applied to the study of the thermal

desorption of molecules chemisorbed on well characterized surfaces.

Results in past years have emphasized the N0/Ru(001 ) system.

In FY’85 measurements of the internal state distributions for NO

desorbing from a saturation coverage of NO on P t ( 1 1 1 ) were published as a communication in J. Chem. Phys . Results for an extensive study of the NO

coverage dependence, over a ten-fold range in coverage, and the influence

of co-adsorbates has been submitted to J. Chem. Phys. The results of the

work on the NO/P t (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.

301
The results of a series of thermal desorption experiments following

saturation coverage of NO on P t ( 1 1 1 ) are shown in Figure 3.7. The solid

Fig. 3*7. Dependence of rotational temperature of NO desorbed from a saturation covered P t ( 1 1 1 ) surface at various substrate

temperatures

.

curve is a thermal desorption spectrum obtained using a mass spectrometer

to measure the tptal NO desorption as a function of increasing surface

temperature. The data points (with 2 sigma error limits) give the

measured rotational temperatures describing the NO species desorbed during

intervals of 20 K (during a period of 2 sec) during the desorption heating

ramp. There are two distinct desorption features for the NO/P t (111)

system and from this figure it becomes obvious that the rotational

temperature of the desorbing species follows the instantaneous surface

temperature for both features. All this data fits in the narrow range of

having the rotational temperature being equal to 95±5? of the surface

temperature

.

Despite the fact that these results are consistent with the

expectations from transition state theory, such a theory would lead to the

additional expectation of a desorbing angular flux described by the cosine

law and a Maxwellian kinetic energy distribution at the surface

temperature. Preliminary results on Doppler profile measurements for NO

desorbing from saturation coverages from P t ( 1 1 1 ) indicate that these

expectations are not upheld. These measurements show equivalent Doppler

profiles for NO species desorbing in all final rotational states in the

range of 2.5<J<15.5, with energies from 13<E

r<426 cm

-1

, indicating no dependence of final kinetic energy on rotational state. Both the

302
rotational state distributions and the dependence of kinetic energy on

final rotational state are markedly different for the reactive N0/Ru(001 ) versus the non-reactive NO/P t ( 1 1 1 ) systems.

Thermal desorption samples processes occurring under "equilibrium"

conditions; this is to say that a heating rate of lOK/sec is much slower

than molecular energy transfer processes in condensed phases. We have

initiated a study of direct desorption processes following rapid heating

of the surface using non-resonant laser irradiation. Here it is hoped that

the short time scales for heating, i.e., 1-10 nsec, might allow desorption

to compete favorably with other energy exchange or relaxation processes.

Progress to date includes the assembly of an ultra-high vacuum chamber

designed for laser-heating/final-state resolved measurements. Initial

measurements have focussed on obtaining reproducible laser desorption

signals and achieving an understanding of the dependence of desorption

probability versus laser pulse energy. This work is supported by DOE.

D. Dynamics of van der Waals Molecules

(M. P. Casassa, L. B. Elwell , D. S. King, J. C. Stephenson and A. M.

Woodward)

These experiments represent a new direction of research, in part an outgrowth of infrared multiphoton photodissociation experiments. The

experiments consist of the characterization of the time scales and final

state distributions in the dissociation of van der Waals complexes excited

to well-defined vibrational or electronic states. The systems studied

during FY '85 included the electronic predissociation of NO-Ar, and the

vibrational predissociation of both NO-ethylene and NO-NO. The van der

Waals species were formed in a pulsed free jet expansion. Mass

spectrometric techniques have been used to characterize the cluster

distributions formed in our beam as a function of backing gas composition

and pressure. The dynamics studies consisted of a one-photon laser

excitation to a predissociating state, followed by measurements of the

rotational (J), spin-orbit (ft), and lambda doublet (A

+ /A~) distributions

of the NO photoproducts via laser excited fluorescence of the A —

X

transition at 226 nm. The spatial distribution of J-vectors (alignment)

and the velocity distribution (both speed and angular flux) were

determined by polarization and Doppler techniques.

NO-Ar undergoes an electronic excitation to the NO-like 3sa A state

at excitation frequencies near 44,200 cm

-1

. Although excited n states of

the NO-Ar species are stable and exhibit discrete electronic absorption

spectra, the A^E state is distinctly different. This is a Rydberg state,

with an electronic orbital radius that extends well beyond the NO-Ar

separation in the electronic ground state. Thus, in the Franck-Condon

excitation process, the excited state created through the absorption

process is more analogous to N0

+ -Ar, which should be more tightly bound

and have a shorter van der Waals radius. The result of this is that there

is a predissociative curve crossing involving the ground state potential

energy surface. The NO fragments formed in this predissociation are predominantly in the electronic ground state (>99$) and exhibit Doppler

303
profiles that indicate that the lifetime of the electronically excited

parent is substantially less than a rotational period — i.e., on the

order of or less than a few periods of the van der Waals vibration. Very

little of the total available energy appears as rotational excitation of

the fragments — only about 0.5%. Presumably this reflects a constraint

imposed in the conservation of angular momentum.

There has been substantial recent theoretical interest in the

vibrational predissociation of van der Waals molecules, but very few

experiments that have looked at either the final state distributions or obtained real time measurement of the dissociation lifetimes. Earlier

measurements (by Hoffbauer, Liu, Giese and Gentry and by Bomse, Cross and

Valentini) of the kinetic energy released in the dissociation of the

ethylene dimer excited at 950 cm

-1

to the ethylene vy mode indicated, in

consonance with theoretical expectations, that most of the available

excess energy went into rotational excitation of the two ethylene

fragments. In our experiments on NO-ethylene excited to the same ethylene-like vy mode by our short pulse CO2 laser we found very little

rotational excitation in the NO fragment and very little kinetic energy

released. Equal populations were found in the two NO lambda doublets.

This contrasts with the disequilibrium of lambda states found in the

products of the prompt electronic photodissociations of HOH and H0N0 and

in many direct collisional H-atom abstraction reactions. Presumably, most

of the available excess energy (i.e., roughly 50%) went into excitation of

a-axis rotation in the ethylene fragment. Doppler profiles were measured

for various orientations of the electric vector of the pump laser and the

directions of propagation of both the pump and probe lasers. Equivalent

Doppler profiles, of 0 . 060cm

-

1

FWHM , were obtained for NO products under

all conditions. This observation requires the distribution of NO

velocities to be spatially isotropic, i.e, not aligned with respect to the

pump laser electric vector. Similar spatial flux isotropy was reported

for the vy predissociation of the ethylene dimer; spatially anisotropic

flux distributions have however been reported for prompt photodissociation

processes. Real time measurements of the appearance of the NO fragment,

in a dual laser pump/delayed laser probe experiment, proved that the

lifetime of the vibrationally excited van der Waals complex was less than

10 ns. The isotropic flux suggests that the vibrationally excited

complexes survive more than one rotational period. At the temperature of our beam, the average rotational period is -35 psec., implying a lower

limit of = 50 psec on the predissociation lifetime of the excited

complexes

.

In the vibrational predissociation of the nitric oxide dimer,

following excitation by a frequency doubled short pulse C0 2 laser at 1870 cm

-1

, the total distribution of available energy was determined. The

rotational and spin-orbit states of both NO photofragments (for values of

internal energy <426 cm

-1

), are described by a rotational temperature of

110 K. This corresponds to only 20% of the available excess energy going

into rotational excitation of the two fragments in dramatic contrast to

the results obtained on the ethylene dimer. The two lambda doublet states

were observed to be statistically populated and the relative populations

304
of the two spin-orbit states were consistent with a spin-orbit temperature

equal to the rotational temperature, indicating equilibration of the

electronic spin- and nuclear rotation angular momenta in this reaction.

This is an unusual instance, where a singlet parent dissociates to form

two doublet state fragments since in previous examples (e.g., including

CH^ONO, HONO, and dimethyl methoxy phosphate) apparent selection rules

favored one spin-orbit component. Real time measurements of the fragment

appearance times indicated that the vibrationally excited complexes

dissociate within 10 nsec. We determined the NO fragment flux to be

spatially isotropic by measuring Doppler profiles at various experimental

configurations. This is similar to our results on ethylene-NO and

previous results on ethylene dimer and implies a lower limit on the

predissociation lifetime of - 50 psec

.

It is possible for us to probe the photodissociation dynamics of the

NO-ethylene van der Waals complex following excitation to several

different vibrational states. Of particular interest are the results

following excitations at 1870 and 1900 cm

-1

to either the NO stretch or the ethylene (vy+vg) combination band, respectively. Here there are several lower frequency vibrational modes that might act as receptors for

the available excess energy — on the order of 1500 cm

** . These mode

specific experiments are in progress. In addition, experiments are in the

planning stages (see section F) to determine the lifetimes of these

vibrationally excited species using psec lasers for excitation and

probing

.

E. Matrix Isolation Spectroscopy

(M. E. Jacox)

The assembly and testing of the vacuum systems and the cryogenic

cell for use with the high resolution Bomem interferometer have been

completed. Experimental studies using this apparatus are scheduled to

begin in September.

With the help of Dr. Thomas Buckley, Chemical Thermodynamics

Division, and Mr. Ricardo Metz, a summer worker in the Chemical Kinetics

Division, substantial progress has been made in the software development

for use with the Ebert visible-ultraviolet scanning monochromator. As

this is written, it is planned to resume the long-suspended studies of the

ultraviolet absorption spectra of transient molecules in the near future.

The work is supported by ARO.

1 . Fluorine-Atom Rections

A major effort was the preparation of a review paper, entitled

"Spectroscopy and Photochemistry of Free Radicals Formed by the Reaction

of F Atoms with Small Molecules," which has recently been published in

Reviews of Chemical Intermediates. This paper provides a comprehensive

review of both gas-phase and matrix isolation studies of the various types

of F-atom reactions (e.g., addition, H-atom abstraction) which have yielded

spectroscopic or photochemical data for the primary free radical products.

305
Because hydrogen-atom abstraction from a generalized molecule, RH, in an argon matrix leads to the formation of hydrogen-bonded R***HF, this review

has included an assessment of the extent of perturbation of the

HF-stretching vibration of R***HF species which results from trapping of

the complex in an argon matrix. Also included is a summary of shifts in

the molecular vibrations, observed in solid argon, upon hydrogen-bonding

of various types of molecules with HF.

Studies of the reaction of F atoms with methyl chloride, bromide, and

iodide were completed. Evidence was obtained for a steric effect on the

mechanism of F-atom reaction with these molecules, with two major reaction

channels for each system. Attack of the F atom at the halogen position

results in the formation of the CH^XF addition product, which has a moderately strong X-F bond and is photochemically stable at wavelengths as short as 250 nm. F-atom reaction with a hydrogen atom of the methyl halide

results in the stabilization of a weakly bound F***HCH

2 X complex,

intermediate to the formation of H

2 CX* • *HF in the solid. For all of the

species studied except CH^Cl, the barrier to the decomposition of this

complex is sufficiently great to require exposure of the solid deposit to

visible light for the production of H

2 CX*«*HF. A paper presenting these

results in detail is scheduled to appear in an October issue of Journal of

Chemical Physics.

Studies of the reaction of F atoms with formic acid were initiated,

with the objectives of determining whether the H-C0

2 structure has a ground-state potential minimum and of obtaining the spectra of the

important combustion intermediates cis- and trans-HOCO in solid argon.

(Previous studies in this laboratory had yielded the infrared spectra of

these two species in solid CO, with which H0C0 would be expected to

hydrogen-bond.) Although some of the isotopic substitution studies,

useful for a final normal coordinate analysis, remain to be completed, the

following conclusions are evident:

(1) If the H-C0

2 structure has a ground-state potential minimum, it

is formed with too much energy for stabilization in this

system

.

(2) Evidence for the formation of an HC00H***F intermediate when the

F atom attacks the OH bond of HC00H is provided by the

appearance of a high yield of C02 »*»HF, with little evidence for

isolated C0 2

, in the initial deposit.

(3) F atoms abstract H directly from the C-H bond of HC00H, leading

to the stabilization of isolated HOCO, as well as of H0C0***HF.

(4) Trans-HOCO is more stable than the cis-rotamer.

Preliminary studies of the important F + SiH^ reaction system

indicated that extensive reaction occurs.

306
2.

Excited Rare-Gas Atom Reaction

The interaction of excited argon atoms with formic acid was found to

lead to the stabilization of trans-HOCO in solid argon. Studies of this

reaction system were extremely valuable in the detailed assignment of

absorptions in the corresponding F-atom reaction study to isolated HOCO and

to HOCO---HF.

The interaction of excited argon atoms with silane was found to

provide a relatively "clean" yield of SiH2

, with only weak contributions

of other products to the observed infrared spectrum.

3. Vibrational and Electronic Energy Levels of Transient Molecules

A paper entitled "Ground-State Vibrational Energy Levels of

Polyatomic Transient Molecules," summarizing both gas-phase and inert

matrix data for almost 500 species containing from 3 to 1 6 atoms, was published in the October 1984 issue of the Journal of Physical and

Chemical Reference Data. In keeping with the rapid pace of new developments in this field, on May 1 a supplement containing data for 76

molecules which had appeared in the literature since August 15, 1984, was prepared for distribution with the reprints. An up-to-date digital record

of developments in this fast-moving field is being maintained, and in one

or two years it is planned to publish a supplement.

A proposal entitled "Spectroscopic Properties of Excited Electronic

States of Small Polyatomic Transient Molecules" was submitted to the

Office of Standard Reference Data, and beginning on September 1 will be

supported for a period of two years. The output of this project will be a critically evaluated compilation of the experimentally determined

spectroscopic properties of the bound and dissociative excited electronic

states of covalently bonded transient molecules containing from three to

six atoms. Spectroscopic data observed for transient molecules in the gas

phase and in dilute solid solution in the rare gases or in non-polar

small-molecule solvents will be included. The extent of deviation of the

transition origins, vibrational fundamental frequencies, and radiative

lifetimes of transient molecules observed in these media from the values

reported for the gas-phase species will be assessed, in order to provide

an estimate of the expected deviations for molecules for which gas-phase

data are not available.

4. Reaction Intermediates in the Decomposition of Energetic Materials

With support from the Army Research Office, studies of the infrared

and ultraviolet spectra of reaction intermediates derived from the

decomposition of benzene and nitrobenzene are being pursued.

Spectroscopic identifications are also being sought for a number of othe^

small free radicals which play important roles in the decomposition of

explosive or propellant molecules.

307
Preliminary infrared studies have been made of the photodecomposition

of benzene isolated in solid argon by 254-, 122-, and 105-107-nm

radiation. There is evidence for the stabilization of at least four

products: phenyl radical, benzyne (CgH^), and two or more other species,

one of which photodecomposes when the sample is exposed to the full light

of the medium-pressure mercury arc.

Preliminary studies were also conducted of the photodecomposition of

nitrobenzene isolated in solid argon, using the highly dilute

Ar: nitrobenzene = 2000 samples which could be prepared in a conventional

sampling system. Photolysis sources were 254-nm mercury-arc radiation and

a beam of excited argon atoms, which provides a source of energy in the

11.5-11.8 eV range. Infrared absorptions of new products did not appear

in either system. Previous studies had indicated that in the 254-nm

spectral region the most important photodecomposition process is 0-atom

detachment, but that some N02 is also produced. No photodecomposition

products were detected in the preliminary experiments. Since 0 atoms can diffuse from the site of their photoproduction in solid argon, failure to

detect nitrosobenzene or 0-atom reaction products suggests that previous

studies may have overestimated the extent of 0-atom photodetachment in the

primary decomposition of nitrobenzene. Phenyl radical and N02

, products

of the other primary photodecomposition process, would be expected to

undergo cage recombination to re-form nitrobenzene or, possibly, to form

the previously unobserved species phenyl nitrite. The negative results

obtained in these preliminary studies are most consistent with the

formation and recombination of phenyl radical and N02

. Experiments with more concentrated nitrobenzene samples will be necessary in order

definitively to exclude the formation of ni trosobenzene and/or phenyl

nitrite under these conditions. Construction of an auxiliary vacuum manifold to permit higher concentration studies of low vapor pressure

materials is in progress.

In a search for infrared absorptions of the H

2 CN free radical, which

may play an important role in the decomposition of RDX and HMX , studies of

the infrared spectra of the products of the H + HCN reaction were

initiated, using a microwave discharge through an Ar:H

2 mixture as the

H-atom source. Rather weak infrared absorptions of CN and of three other

products were detected. Positive identification of these three products,

which differ in their photodecomposition thresholds on exposure of the

sample to filtered mercury-arc radiation, must await the completion of

planned isotopic substitution studies.

F. Future Plans

1 . 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

1

, 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?

Experiments are planned to answer these questions.

308
We have measured vibrational relaxation rates for high frequency

vibrations on dielectric surfaces at the solid/vacuum and solid/liquid

interface, in liquids, in amorphous and crystalline dielectric solids. We

do not have one simple theory to interpret all the results in a consistent

fashion. It appears qualitatively that one may interpret all the results

in simple terms of masses connected by springs. However 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 linewidths observed for high frequency vibrations on metals

really are 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.

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 is to use the same technique for ordered

monolayers on large metal single crystals under UHV conditions. A third

approach involves IR excitation of a molecule 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 laser pulses of suitable energy, bandwidth, frequency, and

duration. The present Nd-Yag pumped OPA setup has several important

limitations. Only frequencies > 2600 cm

- can be generated, which

restricts us to high frequency vibrations. However, because of its large

transition dipole moment, and because of the wealth of surface information

available, we want to study CO on metals. This requires = 2000 cm

-1

, not possible with the present setup. Also, the pulse duration of 15-20 ps

with the present system is too long for many experiments (e.g. NH2 on Si0

2

, and probably 00 on metals). The broad spectral bandwidth from the

OPA is also undesirable for many reasons (e.g., for the experiment to work

an extremely large anharmonicity is required).

Therefore, in future T^ experiments we will produce tunable IR

radiation by generating the difference frequency , ojj R

= between

two visible laser pulses in non-linear crystals. For frequencies co-r^ ^ 1800 cm

1 we will use LilO^ and for lower frequencies 900 < < 1800 we have tried AgGaS 2

. We are trying two approaches to generate the necessary

visible pulses to be used for mixing. At a 20 Hz repetition rate we will

amplify the outputs of both synch-pumped tunable dye lasers so that each

has an energy of 0.5 mJ/pulse (as of 7/85 one of the two necessary

amplifiers was operational). An alternative is to double the Nd

+ ^:YAG

light to synchronously pump a dye laser cavity. The dye laser output

should be of significantly shorter duration than the 532 nm pumping

pulses. The tunable IR, generated by difference frequency mixing (w.^ = w532 " wdye^ should have the duration of the input dye pulse. Both

309
difference frequency schemes should be capable of generating 1-10 pJ

pulses in the 5 um region. This should be sufficient to perform

experiments described below.

It is conceptually straightforward to do the one color IR pump/probe

transmission IR experiment to measure T

1 for CO (v=1 , 2000 cm

- "

1 ) on dispersed Pt particles supported on a Si0 2 disk. The transmission IR

spectra of such samples have been extensively studied over the last 30

years. During the past year we have attempted this type of experiment for

higher frequency vibrations (3000-4000 cm

-1

) of molecules chemisorbed on dispersed metals (M-OH, M-NH, M-C 2 H

2

) without success. Two major problems

- sample damage by the pump pulse and excessive scattering of pump light

into the probe detector - have been solved by improved sample preparation.

However, it is difficult to chemisorb these species in sufficient

concentrations for study. Previous work shows that this should not be a problem for CO on metal surfaces. Also, molecules which absorb in the

high frequency range tend to have relatively low vibrational transition

dipole moments compared to CO chemisorbed on metals. Thus CO/metal

systems offer important advantages. We expect in 1986 to perform the

simple pump/probe experiments to measure T

1 for C0(v=1) bound to a variety

of dispersed supported metals.

In principle the IR transient saturation experiment is applicable to

any sample for which ordinary IR absorption spectroscopy is possible,

including monolayers on metal single crystals. For most vibrations on single crystals, infrared reflection-absorption spectroscopy (IRAS)

requires the detection of very small absorptions, typically 2 x 10

With our present detectors and poorly behaved OPA pulses, we can only

detect transmission changes greater than 0.3%; to determine the slope of

the In (T/Tq) plot (i.e. T-| ) presently requires a change in T (caused by

the pump) of at least 1.5?. The present apparatus thus has two orders of

magnitudes less sensitivity than that necessary to measure T^ for typical

surface vibrations. We expect that our sensitivity can be significantly

improved since other laboratories have claimed 1 part in 10^ using pulsed

lasers. In fact, for CO on metals, sensitivity limitations are not as severe since absorptions of 1-2? are usually reported in IRAS experiments.

We are working toward attempting to measure T 1 for CO on P t ( 1 1 1

)

or related metal single crystal surfaces using the IR pump/probe method.

Better laser pulses, better pulsed IR detection and signal averaging, and

significant additional surface preparation and characterization (e.g. high

resolution IRAS capability) equipment will be needed.

A direct measurement of the pathways (accepting modes) involved in

the VET experiments requires a determination of population in different

sample vibrational modes. Time-dependent Raman or IR spectroscopy may be

used. For samples of good optical quality, such as colloidal silica

particles suspended in CCl^, or for the liquid samples of R^Si-OH

molecules (which may be models for the surface vibrations) , we will

perform IR pump/SPARS probe experiments (using either OPA/532 nm or IR

difference frequency systems) in 1986. To decrease background signals

from the thermal population in very low energy modes the samples may be
cooled (as done for the CS 2 T

2 experiments). It is likely that other

samples (pressed disks, dispersed supported metals) will scatter too much

visible light to permit detection of the expected weak SPARS signals. For

these samples 2 color IR transmission spectrosocpy (pump one mode, probe

another) may be used. This approach is likely to be successful only for

a few surface species where energy flows from one high frequency vibration

to a neighboring high frequency mode before dissipating to the low

frequency (v < 1200 cm

-1

) lattice modes. As an alternative to SPARS

probing of vibrational population (e.g. OH v = 1 ) , we may try CARS probing.

The CARS method has the advantage of generating more detected signal

photons per pulse, but the disadvantage of requiring large excited state

densities and three coincident laser pulses.

To date our surface T-| measurements have been for molecules on collidal Si0

2

, a surface which has little catalytic activity. One way we hope to explore the relation between VET and surface chemistry is to study

T i for systems with important catalytic activity. For instance, the

hydroxyl groups inside zeolite catalysts are associated with active

Bronsted acid sites, and there have been many transmission IR studies of

these OH sites in the 3700 cm

-1 region. In collaboration with Dr. R. Wormsbecher at W. R. Grace (Columbia, MD) we hope to measure T.| times for

OH stretching vibrations in a number of zeolites of different catalytic

activi ty

.

2. Dynamics of van der Waals Molecules

The same synch-pumped picosecond laser apparatus which will generate

IR pulses suitable for studying VET rates for bonds on metal surfaces,

will also generate pulses suitable for doing VET studies involving the

photodissociation of van der Waals molecules. An example of a van der

Waals experiment which we should do in 1986 is the photodissociation of

N0*C

2 H^ by Vj R

= 1900 cm

1

1900cm

-

”

1 t

CrHjij • NO C

2 H

4

( Vy + vg )

• NO > C

2 H

4

+ NO ( J , 0 , A

)

1870cm

-1

x > C

2 H 4 -N0(v=1) > c

2 h

4

+ NO ( J , G , A)

There is a significant controversy about the value of x, the predissociation lifetime. The photodissociation spectrum in the C

2 H

4 vy region

is a Lorentzian (FWHM = 6cm ”*), which has been interpreted as implying x = 0.9 ps. Our time-resolved measurements of product appearance using

nanosecond lasers proved that x < 10 ns. However our measurement of

isotropic flux distribution suggested that x ^ x r

, where the rotational

time of N0*C2 H 4 in our beam is x p

= 35 ps.

We will generate tunable IR at 1900 or 1870 cm

-1 by generating the

difference frequency in LilO^ of the two amplified synch-pumped lasers.

One of them (at \ = 575 nm) is frequency doubled; the \ = 288 nm is summed

with Nd-Yag (1.06 pm) in a KD*P crystal to generate light at 226 nm (P,

head = 44176 cm

1 ) suitable for LEF detection of the NO photoproduct on

311
the product yield has an exponential build-up as N0(t) = [1 -exp(-t/x) ] , as predicted by statistical theories, and to see if there is any relationship

between t and photodissociation line widths. Excitation of the out-ofplane Vrj motion which corresponds to the reaction coordinate, may give a short t, while there may be a significantly longer time for NO stretching

energy to flow into the van der Waals bond leading to dissociation.

Similar experiments are planned in which C-H stretching modes of van der

Waals clusters will be excited with picosecond IR pulses. The necessary 3 pm light will be produced by the same dye lasers by difference frequency

generation.

3- Desorption of Molecules from Surfaces

Several years ago we undertook a joint research project involving

staff and expertise of the Molecular Spectroscopy and Surface Science

Divisions of the Center for Chemical Physics to examine in greater detail

molecular dynamics at the gas-surface interface. The thrust of this

program was to use laser based, state and velocity selective diagnostics

to study molecules being thermally desorbed from well-characterized single

crystal metal surfaces in an ultra high vacuum environemnt. The results

of our work on N0/Ru(001 ) and NO/P t ( 1 1 1 ) have been published and are reviewed herein. What is important about these experiments is that they

are extremely, perhaps uniquely, sensitive to the interactions between gas

molecules and different metallic surfaces.

The future directions of this research effort can be broken up into

two branches. First, in view of the marked differences for NO/Pt, where

there is only simple molecular desorption, versus Ru, where decomposition

competes with desorption, during FY’86 we plan to explore the desorption

of NO from 1) co-adsorbed layers of NO and ammonia on Pt(111) where there

appears to be a co-operative interaction during the desorption process; and

2) Ir ( 1 1 1 ) where a major source of the desorbing NO is from atom-atom

recombination. Although all our present work has emphasized interactions

with the NO adsorbate, we hope to acquire a second dye laser to enable us

to extend our laser probe capabilities into the vacuum ultra-violet and

study the molecule-surface dynamics of other, chemically interesting

species such as hydrogen and CO.

Thermal desorption studies are sensitive to the molecular dynamics

and energy flow in the region of the top of the chemisorption potential

energy well - a region important in the making and breaking of chemical

bonds. In the thermal desorption experiment the heating rates

traditionally used are much slower (e.g. 10 K/sec.) than other molecular

relaxation processes, which is good if one's goal is to study the dynamics

of a highly energetic system under "equilibrium" conditions. A deeper

level of understanding can be obtained regarding molecule-surface energy

transfer by attempting to study non-equibl ibrium conditions, such as might

be achieved following laser irradiation of the adsorbate covered surface.
We hope during FY'86 to successfully characterize the internal state

distributions, kinetic energy and angular flux distributions of the NO

driven off a P t

(

1 1

1

) surface by non-resonant laser excitation at, 532 nm. Estimates of the anticipated signal levels for desorption of 10

4 of a monolayer per laser shot indicate that we should be able to determine the

vibrational as well as rotational partition functions. These experimental

results will provide a stringent test of the theoretical treatments

currently being applied to model laser-surface heating and energy

transfer processes.

4 . Matrix Isolation Studies

The high sensitivity and extended spectral range afforded by the

Bomem interferometer will be crucial to the study of a number of important

systems during the coming year. Among the first systems to be studied

will be the photodecomposition of acetylene to produce HC2 and C2*

Electronic transitions for both have recently been reported near 4000

cm

-1

. Observation of the absorptions resulting from these electronic

transitions in a rare-gas matrix will aid in the definitive identification

of the C2 transition and in the assignment of the bands arising from

vibrationally unexcited HC2, which has an unusually low ground-state

bending vibrational frequency.

Priority will also be given to the studies of the H + HCN reaction,

in which the greater sensitivity of the Bomem interf erometer will be

valuable for the definitive assignment of the infrared spectra of ^CN and

of cis- and trans-HCNH. A search will also be made for near infrared

transitions of these species, each of which, like the isoelectronic

species HCO , may have a low-lying electronic transition.

As reported one year ago, the feasibility of detecting the infrared

and electronic spectra of molcular ions produced by codepositing a beam of

excited neon atoms with a suitable precursor molecule isolated in solid

neon has been demonstrated. The energy range accessible using excited

neon atoms (16.6-16.8 eV ) will substantially broaden the range of

molecules whose ions are accessible over that covered in earlier

experiments in this laboratory using excited argon atoms, permitting a search for such important ions as HC0

+

, H20+, NH^, and CH^. These

long-planned studies have been deferred until they could be conducted on the

Bomem interferometer, since the enhanced sensitivity of this instrument is

especially important when liquid helium must be used as the coolant. It

is hoped that studies of these experiental systems can proceed during

FY'86. Such studies may provide much previously inaccessible information

on the vibrational and electronic spectra of molecular ions, important in

a variety of high energy systems ranging from combustion to high-speed

fl ight

.

The higher sensitivity of the Bomem interf erometer will permit

studies of such other important classes of molecule as carbon-13

substituted species present in natural abundance and products of 0-atom

reactions in discharge sampling experiments. Observations of the

313
carbon-13 species will aid in product identification and will provide

valuable data for infrared spectral analysis. Since water and oxygen

impurities generally lead to the formation of 0 atoms in discharge

sampling experiments, the greater sensitivity of the Bomen intef erometer

will both facilitate and mandate a series of studies of the reactions of 0

atoms with small molecules. Such studies of the reactions of 0 atoms with

benzene and with nitrobenzene form an important part of the current

program of research being supported by the Army Research Office.

Preliminary studies have indicated that species of formula HCN 2 are stabilized by the reaction of photochemically generted CH with a nitrogen

matrix. Further studies will be conducted in order to obtain a definitive

identification of this product, which may play important roles in

processes as diverse as the decomposition of explosive or propellant

molecules and the generation of "prompt" NO on atmospheric combustion of

hydrocarbons

.

In order to obtain as complete as possible a characterization of the

spectra of the products of elementary reactions of silane, studies will be

continued not only on the reaction of excited argon atoms and of F atoms

with silane, but also on the corresponding H- , Cl- and O-atom reactions.

Because F-atom reaction studies have provided an extremely valuable

tool for obtaining free radical spectra, they will continue. Emphasis will

be placed on studies of the ultraviolet absorption spectra of the products

of F-atom reaction with such species as CH^NC^, CH^CHO, CH^CN, and HCOOH,

for which infrared studies have provided definitive identifications of

free radicals.

As it becomes possible to stabilize a wide variety of molecular ions

and O-atom reaction products in rare-gas matrices, it will be increasingly

important to determine their laser-excited fluorescence spectra, in order

to provide a more complete characterization of their energy levels and to

establish a basis for their detection in atmospheric and combustion

systems. This need will mandate construction of a laser-excited

fluorescence system dedicated to matrix isolation studies. This system

will also permit unique experiments to determine previously inaccessible

low-lying molecular electronic states; cage recombination of molecular

fragments formed on laser photodissociation of the matrix-isolated

molecule may populate such low-lying states, which may then be deactivated

by fluorescence or phosphorescence.
4. QUANTUM CHEMISTRY GROUP

H. Basch, P. Jasien, P. S. Julienne, M. Krauss,

F. H. Mies and W. J. Stevens

A. Introduction

Atomic and molecular electronic structure and scattering methods are developed and applied to chemical and spectroscopic problems where

experiments are difficult to perform or so complicated that the theory is

needed to model the results.

The electronic structure method and code development and applications

now include chemical problems with large molecular systems including models

of biomolecules. The applications to the biotechnology area utilize the

recently acquired IBM-4381 in the Molecular Structure and Modeling Facility

(MSMF ) and are described in part in the competence summary.

B. Electronic Structure

1 . Theoretical Proton Affinities

(W. J. Stevens, P. Jasien)

A combination of several state-of-the-art ab initio quantum chemistry

methods has been applied to the quantitative determination of the proton

affinities of small molecules containing the Group VI elements, 0, S, Se, and

Te. Several series of molecules have been studied including CX, CX2

, OCX,

and H

2 CX (where X is the Group VI atom). Comparisons with available

experimental data are very good, and the estimated accuracy of the

theoretical results is ± 2.5 kcal/mole. These are the first such accurate

calculations ever carried out for compounds containing selenium and

tellurium. In addition to the proton affinities, trends down the Periodic

Table are now available for favored protonation sites, vibrational frequency

shifts upon protonation, and structural distortions due to protonation.

Compact effective potentials (CEP), which were developed at NBS , allow

the chemically unimportant core electrons to be eliminated from the molecular

wavefunctions with little loss of accuracy. Thus, all of the Group VI

elements were treated as six electron atoms. Relativistic effects are incorporatd through the use of Dirac-Fock atomic wavefunctions in the

determination of the core potentials.

Full analytic energy gradient geometry optimizations of all neutral and

protonated species were carried out at the single configuration

self-consistent-field (SCF) level using accurate "double-zeta plus

polarization" basis sets. At the optimized geometries, harmonic force

constants were determined from numerical first derivatives of the analytic

energy gradients, and zero-point vibrational energy contributions to the

proton affinities were calculated. Electron correlation energy contributions

were evaluated by configuration interaction calculations including all single

and double excitations from the single configuration SCF wavefunctions.

315
This work is described in: P. G. Jasien and W. J. Stevens, J. Chem.

Phys. 83, 2984 (1985).

2. Hydrogen Bonding of Water and Methanol with Formamide

(W. J. Stevens and P. Jasien)

The characterization of the hydrogen bonding between water and formamide

has been of considerable interest to experimentalists and theoreticians

alike. This interest stems from the fact that formamide may be viewed as the

simplest molecule containing a peptide linkage. As such, the formamide-water

complex provides the simplest model for the hydration of proteins.

We have carried out detailed calculations on several conformers of the

formamide-water complex at a level of accuracy significantly beyond all

previous theoretical studies. Full gradient energy optimizations using

double-zeta plus polarization basis sets were carried out for each conformer.

The effects of electron correlation were determined by configuration

interaction including all single and double excitations from the SCF

configuration.

These accurate calculations show hydrogen bonding of water to the

carbonyl group to be favored by about 0.5 kcal/mol over bonding to the amide

group. However, a cyclic structure in which the water is hydrogen bonded to

the carbonyl and amide groups simultaneously is found to be most stable (9.5

kcal/mol) and is a likely candidate for molecular beam microwave spectrocopic

studies

.

Fig. 4.1. Most stable hydrogen-bonded complexes of (a) water-formamide and

(b) methanol-formamide illustrating near coincidence of the two

structures

.

Calculations were also carried out on methanol-formamide complexes to

determine if any fundamental differences exist in the hydrogen bonding of the

alcohol versus the water. The results show virtually identical structural

316
and energetic behavior of the methanol-formamide complexes when compared to

the water-formamide complexes. Again, the cyclic, doubly hydrogen-bonded

conformer is the most stable. Figure 4.1 shows the striking similarity of the

two cyclic structures.

The systematic study of basis sets, geometry optimizations, and

correlation energy for these hydrogen bonded complexes have allowed us to set

up general guidelines for future calculations of this type.

3. Localized Electron Pair Polarizabilities

(W. J. Stevens, P. Jasien)

The coupled, perturbed Hartree-Fock method (CPHF) has been used to

calculate the dipole polarizabilities of several prototypical non-aromatic

molecules containing H, C, 0, and N. The list of molecules studied and the

principal components of their calculated polarizability tensors are shown in

Table 4.1. All calculations were carried out with triple-zeta basis sets

augmented by two polarization functions on each atomic center. The resulting

polarizabilities are very close to the Hartree-Fock limit of accuracy, which

is generally within 15 % of experimental values for the isotropic part.

It is possible to transform the Hartree-Fock molecular orbitals, via a unitary transformation, into localized orbitals that can be identified as bonds and lone pairs. The same unitary transformation may be applied to the

orbital components of the CPHF molecular polarizability. In this way,

electron-pair polarizability tensors may be derived that are transferable

from molecule to molecule. Preliminary transferability studies have been

made using average bond and lone pair polarizabilities extracted from the

saturated molecules listed in Table 4.1. Table 4.2 compares spherically

averaged CPHF polarizabilities to polarizabilities obtained as a sum of

transferable bond and lone pair components. The agreement is within a few

percent. Anisotropic behavior and unsaturated bonds are still under

investigation but show similar promise. A functional group analysis (e.g.

methyl group, hydroxyl group, amide group) may be required in order to take

full advantage of anisotropic tensor contributions.

Transferable polarizabilities are a key ingredient in the ab initio

reaction field method being developed by the Quantum Chemistry Group. A reaction field computer code will allow the study of very large molecular

systems by treating a small portion fully quantum mechanically while

representing the surrounding environment by a distribution of polarizable

point multipoles. The distribution of the point multipoles and their

polarizabilities will be determined from ab initio calculations on prototypical molecules and fragments whose properties are assumed to be

transferable.

317
Table 4.1. Ab initio CPHF polarizabilities and selected experimental

values for comparison (in A^).

Molecule °1 a2 a

3 a

h

2

o CPHF

EXP

1 .21 1 .34 1.10 1 .22

1 .49

nh

3 CPHF 1 .89 1 .85 1 .85 1 .87

ch 4 CPHF

EXP

2.37

2.62

2.37

2.62

2.37

2.62

2.37

2.62

HCN CPHF 3-30 2.00 2.00 2.43

h

2 co CPHF

EXP

3.13

2.76

2.39

2.76

1 .77

1 .83

2.43

2.45

HCCH CPHF 4.62 2.78 2.78 3.39

c

2 h 4 CPHF 5.25 3.68 3.27 4.07

C

2 H6 CPHF

EXP

4.31

4.99

3.83

4.22

3.83

4.22

3.99

4.48

ch2 nh CPHF 4.29 3.01 2.42 3.24

CH

3 0H CPHF

EXP

3-13

4.09

2.85

3-23

2.64

2.65

2.87

3.32

ch

3 nh2 CPHF 3.90 3-36 3-35 3.54

c

2 h

5 oh CPHF

EXP

4.97

5.76

4.64

4.98

4.13

4.50

4.58

5.08

CH

3 OCH3 CPHF

EXP

5.16

6.38

4.41

4.94

4.18

4.39

4.58

5.24

c

3 H 4 CPHF 7.31 4.27 4.27 5.29

c

3 H

6 CPHF 7.39 5.30 4.62 5.77

CH

3 CN CPHF

EXP

5.61

5.74

3-50

3.85

3.50

3.85

4.20

4.48

CH

3 CHO CPHF 4.92 4.07 3.31 4.10

c

3 h

8 CPHF

EXP

6.17

7.66

5.57

5.74

5.32

5.74

5.68

6.38

nh

2 cho CPHF

EXP

4.63

5.24

3-57

a

2

+ a

3

2.66

= 7.01

3.62

4.08

318
Table 4.2. A comparison of CPHF molecular polarizabilities and

polarizabilities constructed from transf errable average

bond and lone-pair contributions.

Molecule aCPHF (A3) aTRANS (A3)

ch4 2.28 2.27

ch

3

oh 2.87 2.98

c

2 h

5

oh 4.58 4.63

C

2 H6 3.99 3.95

c

3

h

8 5.68 5.62

c

2 h6° 4.58 4.73

4. Binding of Pt Complexes to DNA

(H. Basch, M. Krauss , W. J. Stevens)

The binding of the Pt diamine moiety to DNA was found to occur predominantly in a cis intrastrand chelate between neighboring guanine bases.

The stereospecificity of the binding was recently called into question by the

observation of anti-tumor properties for both cis and trans Pt diammine

ascorbate molecules. Calculations of the relative trans effects and binding

energies for the carbon and oxygen ligand binding sites have shown that the

carbon site is less labile than the ammonia ligand. As a result cis chelates

can be formed with the DNA in reaction with either the cis or trans Pt

ascorbate molecules.

Substituted amines have also been considered in the binding of

PtCR-N^)^ to one or two imidazole ligands. The imidazole is used to model

the N7 binding site in guanine. The binding energies for R=CH^ or cyclopropyl are found to each reduce in turn by 6 % from the unsubstituted

values for R=H. These relatively slight variations in binding energy are not

expected to play a role in the binding behavior of the substituted Pt amines

to DNA. Steric effects are now being modeled to analyze the effect of the

aliphatic substitution. Preliminary results indicate that steric effects are

not significant for R = CH^ or cyclopropyl. This work is supported by the

National Foundation for Cancer Research.

319
5. Reaction Field Methods

(W. J. Stevens, H. Basch, M. Krauss)

All-valence-electron quantum mechanical self-consistent-field (SCF)

calculations are limited to relatively small prototypes of biomolecular

systems. Using the compact effective potentials (CEP), calculations are possible at the double zeta level of basis set for molecules with 30 to 40

atoms. Systematic generation of the CEP for the elements between Na and Rn

has been continued so that calculations including metal atoms can now be done

with a consistent, accurate set of CEP. Nontheless, calculations on systems

of the order of 1000 atoms are desirable and the reaction field method will

approximate the SCF for such a system. The system is divided into two

regions. In the quantum mechanical (QM) region all valence electrons are treated explicitly, while in the classical (CM) region, the charge

distribution contributes to the SCF hamiltonian through the interaction of

localized molecular orbital charges, moments, and polarizabilities centered

at the orbital centroids of the QM charge distribution. At the boundary

between the QM and CM regions, effective fragment potentials (EFP) emulate

the exchange and orbital exclusion of the orbital paris that are treated

classically. Approximate EFP have been generated for the interaction of

non-bonded systems and are now being tested for multimers of formamide and

imidazole

.

6. Relative Energetics of Dipeptide Conformers

(M. Krauss, W. J. Stevens)

Double zeta level SCF calculations have been completed for a number of

conformers of the dipeptides,

0 H H 0

II I I II HoC — C — N — CII— C — N — CHo ,

R H

with R = H (glycine-GLY) , CH^ (alanine-ALA ) , CH2 0H ( serine-SER) , CH2 SH

&upQwameaC ! f*@$ !; 2 C0»0H (aspartic acid-ASP). The conformer geometries are

at equilibrium positions obtained with the molecular mechanics ECEPP code

(ECEPP data supplied by Dr. S. Chin, IBM Kingston) or at published quantum

optimized structures. In addition to providing data for the reaction field

code development, these calculations offer a comparison of energetics with

the available quantum and the classical mechanics values as seen in Table

4.3.

The agreement with the quantum results of SchSfer et. al . is

reasonably good. Since the presently used basis is more flexible, this

implies that the larger molecules allow for considerable basis superposition

and improved conformational energetics. For GLY 3d polarization functions

320
were added to all heavy atoms except the two methyl carbons. The second

GLY conformer was then found to be lowest in energy. This result can be

rationalized in terms of the importance of H-bonding in the conformers. The

GLY-1 conformer contains a seven member ring with the amide hydrogen of one amide group bonded to the carbonyl oxygen in the other amide group. Double

zeta calculations have been found to overestimate H-binding, and adding

polarization functions provides lower and more accurate SCF values.

The comparison with the ECEPP energy orderings is not as good.

However, comparison with an empirical method requires the evaluation of the

dispersion interaction. Simple London type dispersion calculations for all

non-bonded interactions shows very little variation with conformation. For

example, the dispersion energy difference between the Cl, C2, and C6

conformers of GLY is less than 0.2 kcal/mole. More accurate analyses of the

correlation energy are sufficiently difficult that this estimate suggests

much effort would not be rewarded. The discrepancy with classical energetics

at specific conformers is likely to remain. Whether the topography of a iJj, q map will be qualitatively different, needs to be explored for specific

dipeptides

.

Table 4.3. Comparison of Dipeptide Conformer Energetics Energy (kcal/mole)

Peptide Conformer DZ DZP Ref. 1 Ref. 2 Ref. 3

GLY QM1 0.0 0.5 0.0 0.0

QM2 0.02 0.0 0.8 0.8

QM3 4.5 3.8 4.7 1 .0

QM4 4.0 3.2 4.3 1 .2

Cl 0.3 0.0

C2 0.0 0.7

C6 8.7 1.7

C8 7.7 5.1

ALA QM1 0.0 0.0 0.0

QM2 0.5 1 .4 0.4

QM3 2.6 2.6 8.8

SER Cl 0.0 0.0

C2 3.8 1 .2

CYS Cl 0.0 0.0

C3 4.2 0.2

ASP Cl 2.8 0.0

C3 0.0 0.3

1. Calculations with ECEPP; communicated by S. Chin, Kingston, IBM.

2. J. N. Scarsdale, C. V. Alsenoy, V. J. Klimkowski, L. SchSfer, and F. A. Momany, J. Chem. Phys . 1_05 » 3438 (1 983).

3. S. S. Zimmerman, M. S. Pottle, G. Nemethy, and H. A. Scheraga

,

Macromolecules 10, 1 (1977).

321
C. Scattering in the Presence of Radiation

1. Radiative Redistribution

(P. Julienne)

We have continued close coupled scattering calculations to calculate

the fine structure branching ratios to 2

P j = 1/2 and j=3/2 when a Na atom is

excited to a dissociative ^

1

or state during a collision with a rare gas

perturber atom, He, Ne, or Ar . We have also predicted the alignment

(orientation) of the 2P j=3/2 atom if a linearly (circularly) polarized

photon is absorbed. These calculations have been carried out in conjunction

with Drs. Linda Vahala and Mark Havey of Old Dominion University, Norfolk,

Va., and have successfully explained Dr. Havey* s radiative redistribution

experiments. These calculations and experiments study the molecular dynamics

which occur between the time a photon is absorbed into a particular molecular

state and the time it is re-emitted later as fluorescence. The nonadiabatic

dynamics describe the way in which the coupling of orbital, spin , and

nuclear rotation angular momenta changes as the excited atoms separate.

This work is supported by AFOSR.

Fig. 4.2. Branching fraction f into Na ^P(j=1/2) when Na 2

P j=3/2 or 1/2

is produced following excitation of Na(^P) by photon absorption

in the wings of the Na ^P «- 2 S transition broadened by

collisions with Ar (solid line and filled circles) or He

(dashed line and open circles). The detuning A is measured

relative to the mean energy of the fine structure doublet. The

lines give the results of close coupled scattering calculations

using ab initio potentials. The points represent the measured

values

.

322
2.

Application of Generalized Multichannel Quantum Defect Theory

(MCQDT)

(P. S. Julienne, F. H. Mies)

The generalized MCQDT applied to molecular potentials gives a way of

relating the transition amplitudes for the closely related processes of

photodissociation and radiative redistribution. The theory also permits, for

suitable systems, the factorization of the transition amplitude matrix for

both phenomena into separate factors representing short range Franck-Condon

excitation and nonadiabatic final state interactions which occur at longer

range and control the distribution of product states. We have tested this

factorization for the Na( 2 P) + rare gas system studied above by applying the

recoil limit for fine structure branching and polarization. The recoil limit

for fine structure branching applies at sufficiently high fragment relative

separation velocity, and was found to apply at much lower relative fragment

kinetic energies for the light collision partner He than for A r. Significant

departures from the recoil limit apply at thermal energies, reflecting the

influence of the molecular potentials on the nonadiabatic dynamics. An

invited paper on the MCQDT analysis of molecular dissociation was presented

at the International Conference on the Physics of Electronic and Atomic

Collisions

.

3.

Product Distributions in Molecular Photodissociation

(P. S. Julienne and F. H. Mies)

For some time we have been using close coupled scattering calculations

to calculate the nonadiabatic free-free redistribution phenomena. We are now generalizing our close coupling scattering codes to incorporate weak coupling

to a bound state so we can calculate bound-free matrix elements for a final

close coupled scattering state. This will enable us to calculate

product distributions in molecular photodissociation. We have obtained the

photodissociation code of Singer, Freed, and Band, and it is running on the

University of Maryland VAX + FPS array processor computer system. We are currently implementing the renormalized Numerov algorithm of this code in our close coupling scattering code on the NBS CYBER 205 supercomputer

.

This work is supported by AFOSR.

4.

Atomic Lineshapes and Resonance Fluorescence Spectra

(F. H. Mies and P. S. Julienne)

We are progressively expanding the capabilities of our close-coupled

scattering codes to include many aspects of radiative coupling and

laser- induced phenomena in molecular continuum spectroscopy. The programs

incorporate the effects of non-adiabatic couplings and the resultant

breakdown of the Born-Oppenheimer approximation. We directly extract the

photon scattering cross-sections and redistribution spectra from the

close-coupling codes, without any commitment to perturbation theory. Also we can systematically increase the intensity of the pumping laser field and

achieve saturation. Our calculations yield the resultant non-linear response

323
of the absorption cross-sections in the presence of inelastic collisions.

Further we have begun to incorporate two separate laser fields into our calculations. At present the second field is treated as weak and allows us

to extract the resonance fluorscence spectrum in the presence of saturation

by the pumping laser field. We are now calculating the pressure-broadened

half-widths of the three peaked Mollow lineshape for the resonant transition

in Sr. The following are four separate accomplishments associated with this

program for FY85. This work is supported by AFOSR.

a. Continuum- continuum Matrix Elements in Atomic Lineshape Theory

(F. H. Mies and P. S. Julienne)

The calculation of^the pressure-broadened lineshape for the atomic

transition A^ + hoo^ A*. requires the evaluation of the following

continuum-continuum matrix element

STM = -iTpfi <i|;-(E ) |nL Ut(E+ )>. ( 1 )

where the field-free multichannel wavefunctions iJj* incorporate non-adiabatic

effects and the breakdown of the usual Born-Oppenheimer Approximation. This

expression applies in the weak-field limit, when the Rabi frequency

associated with thg photon is very small and when the radiative scattering

matrix element can be evaluated in perturbation theory. The precise

details of the lineshape analysis depends on the extent to which thg incident

photon is detuned from the exact atomic resonance energy = (E^ -E.^),

A fi - WL

( 2 )

In the wings of the line, where is very large compared to the

homogeneous width of the atomic transition, the absorption coefficient is

directly proportional to the radiative scattering cross section determined

by the transition matrix elements in Eq. (1). The impact approximation to

the pressure-broadened half-width in^tjhe vicinity of the line center can can also be expressed in terms of .

For dipole allowed atomic transitions the radiative matrix element

which defines the pressure-broadened atomic lineshape is only

conditionally convergent. Using a commutator technique to redefine the

integral we can isolate, and ultimately reject, the contribution of an indeterminant asymptotic surfce integral which is associated with the

energy normalization of the continuum wavefunctions which describe the

binary collision of the atom and its perturber. The remaining

contributions to the atomic lineshape are absolutely convergent. Since

the transformed integrals apply as well to the multichannel wavefunction
ir.ey encompass the effects of non-adiabatic and inelastic scattering.

Fortner we show the relationship of the commutator integral to the exact

requirements of close-coupled scattering theory for radi at ively- induced

collisions. This scattering analysis suggests that we should interpret

one convergent lineshape as an expression of multichannel inelastic

collisions between field-dressed atomic states. The same interpretation

applies both in the impact and the static limit. We would advocate that,

since stable close-coupling codes are required to generate the

multichannel wavefunctions in Eq. (1), it is a simple matter to merely

expand the set of coupled equations to directly include the radiative

coupling between channel states as required by the dressed atom boundary

conditions and completely avoid explicit numerical quadrature of the

multichannel matrix elements in Eq. (1).

Impact Limit in Weak Laser Fields

(F. lies and P. 3. Julienne)

Care must be taken when one attempts to apply the perturbation

expression near the impact limit for allowed transitions. As the detunings

i,, ,• , approach zero, the major contributions to the matrix element (1 occur in the asymptotic regions R=® and 377 becomes proportional to

(

A

f , , -K) ) - \ v , i | ’jjj i > 7 2 Af> i

,• i

. ur ^ | f ^ -i f i J (3)

This divergent limiting form is oredicted by the imoact theories of Shafer

and Cordon and 3en-Reuven, T " P act = we car. numerica_iv extract this matrix

element from the full close-coupling codes for small Ar*,..-, and then emoloy

these same impact theories to obtain accurate estimates of the ccllisional

half-widths of pressure broadened lines. Note that the near resonance photon

simultaneously causes a collective coupling among all the asymptotic channel

states bf.it and b-- * and we can never factor Eq. (3) into distinct products of

.erms

.

- We have- *oerforned multichannel close-coucled calculations of the

3r( S' •* Sr( P) transition broadened by Ar. A comparison of the exact

close-coupled raditive scattering matrix elements to eq. (3) confirms the

validity and utility of our numerical procedures for obtaining pressure

broadened half-widths in the weak field limit. This procedure should enjoy

substantial application throughout lineshape theory.
c. Impact Limit and Pressure Broadening of Mollow Sidebands in Intense

Fields

(F. H. Mies)

Our close-coupled procedures for evaluating avoid any commitment to

raC[ weak fields or perturbative estimates of . Of course, in the weak field

limit, we should choose a representative Rabi frequency sufficiently small to

insure that Eq. (1) remains linearly proportional to and yet sufficiently

large to insure numerical accuracy of the close-cgupled radiative scattering

matrix elements. As long as the magnitude of remains below about 10*"^

there seems to be a one-to-one correspondence to Eqs. (1) and (3).

Of course true deviations from linearity must ultimately prevail as the

actual field strength increases. Such effects become particularly important

in the impact limit, and ultimately become manifest as pronounced sidebands

in the fluorescence spectrum of the pressure-broadened atomic lineshape

symmetrically located at frequencies ±0^ from the scattered Raleigh line.

Experimental observations of the three-peaked Mollow lineshape have

been made for Sr+Ar. We have made some preliminary calculations for Sr+Ar in

the strong-field limit and confirm that our close-coupling procedures

reproduce the dressing of the asymptotic Sr states and yields a three-level

version of Eq. (3). We are now in the process of calculating the complete

impact limit half-width for each of the separated peaks as well as the

expected polarization properties of the intense field fluorescence.

In addition to the spectrum there have been experimental estimates (and

semiclassical calculations) of the inelastic collisional energy transfer

between the dressed Sr atomic states which causes collisional redistribution

of the resonance fluorescence. These cross-sections are also being extracted

from our calculations.

D. Multiphoton Effects in Resonance Fluorescence Spectra

(F. H. Mies)

Until now we have only allowed for a single photon transition in our close-coupled equations. In order to calculate the redistribution spectrum

in intense fields we have introduced a second laser field with Rabi frequency

ftp and frequency co p

. So far we have only permitted a weak probe intensity Q

p and have obtained a beautiful mapping of the Mollow lineshape for Sr+ Ar as a function of the probe detuning.

In view of our encouraging results with a weak probe field our ultimate

goal is to also saturate this field and examine the close-coupled

calculations for effects associated with four wave mixing. Again, such

effects have been observed in Sr + Ar and we are confident that our techniques can derive reliable estimates of the appropriate cross-sections.

326
E. Future Plans

In the area of electronic structure calculations the Quantum Chemistry

Group intends to move ahead in 1) the development of the reaction field

methods and code, 2) the calculation of accurate prototype energy and

properties for amides and nucleic acid components, and 3) model problems on H-bonding in enzymes, metal binding to both proteins and nucleic acids, and

the analog behavior of phosphates and vandates in nucleus-substrate binding.

The reaction field development is the major thrust. As we improve the

methods and the code we intend to apply the model calculations in category

three to enzyme binding and spectroscopy problems. In the interim

calculations in category two will provide insight into polarizabilities and

dispersion interactions in large aromatic systems, the electronic structure

of phosphorus and vanadium five-coordinate molecules, accurate

hydrogen-bonding energies comparing H, 0, and S sites, and metal binding to

small amides and isolated nucleic acid bases.

Future plans in the scattering analysis call for further development

and implementation on the CY3ER 205 of efficient numerical algorithms for

calculating accurate photodissociation transition amplitudes to a manifold of

strongly coupled final states. Such codes enable us to calculate product

state distributions following photodissociation. Initial calculations will

be on diatomic systems with later generalization to small polyatomic systems.

Specific calculations are planned for the NaK molecule in conjunction with

experimental studies to be done at the University of Maryland. In addition

to our numerical studies, we also will continue to develop an analytic

half-collision theory of photodissociation and photo-assisted collisions

based on generalized multichannel quantum defect theory. This approach leads

to much insight into photodissociation dynamics and suggest various limiting

approximations which need further testing, such as recoil or frame

transformation approximations for product alignment or fine structure

branching. We will also continue to develop the nonadiabatic theory of atomic

line broadening in two areas. First, we will study the Lorentzian asymmetry

of the core profile. Second, we will incorporate the effect of strong laser

fields, including the effect of collisions in broadening the Mollow line

shapes and the effect of AC Stark shifts in modifying inelastic collision

cross sections.

327
5. PUBLICATIONS

(a) Publications of Past Year

Casassa, M. P., Heilweil, E. J., Stephenson, J. C. , and Cavanagh, R. R.,

"Time-Resolved Measurements of Vibrational Relaxation of Molecules on Surfaces: Hydroxyl Groups on Silica Surfaces," J. Vac. Soc. Tech. A3_,

1655 (1985).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R., and Stephenson, J. C.,

"Temperature Dependence of the Vibrational Population Lifetime of

OH(v=l) in Fused Silica," Chem. Phys. Letters, 117, 185 (1985).

Heilweil, E. J., Casassa, M. P., Cavanagh, R. R., and Stephenson, J. C .

,

"Vibrational Deactivation of Surface OH Chemisorbed on Si0 2

: Solvent

Effects," J. Chem. Phys. 82, 5216 (1985).

Heilweil, E. J. , Casassa, M. P., Cavanagh, R. R., and Stephenson, J. C.,

"Vibrational Energy Relaxation of Adsorbates on Surfaces," SPIE

Proceedings 533, 15 (1985).

Heilweil, E. J., Casassa, M. P. , Cavanagh, R. R., and Stephenson, J. C.

,

"Picosecond Vibrational Energy Relaxation of Surface Hydroxyl Groups on Colloidal Silica," J. Chem. Phys. 8j_, 2856 (1989).

Hougen, J. T. and Ohashi , N., "Group Theoretical Treatment of the Planar

Internal Rotation Problem in (HF)p," J. Mol. Spectrosc. 109, 139-165

(1985).

Hougen, J. T., "Summary of Group Theoretical Results for Microwave and

Infrared Studies of H

2

0

2 ," Can. J. Phys. 62, 1392-1902 (1989).

Jacox, M. E., "Ground-State Vibrational Energy Levels of Polyatomic Transient

Molecules," J. Phys. Chem. Ref. Data 1

3

, 995-1068 (1989).

Jacox, M. E., "Spectroscopy and Photochemistry of Free Radicals Formed by the

Reaction of F Atoms with Small Molecules," Rev. Chem. Intermed. _6, 77-120 (1985).

Julienne, P. S., "Collision Induced Radiative Transitions at Optical

Frequencies," in Phenomena Induced by Intermolecular Interactions , ed.,

by G. Birnbaum (Plenum Press, 1985).

King, D. S. and Stephenson, J. C. , "Kinetic Energy Disposal in the

Unimolecular IRMPD of Methyl Nitrite," Chem. Phys. Letts. 119, 961

(1985).

328
King, D. S. and Stephenson, J. C., "Infrared Multiphoton Dissociation of

Methyl Nitrite in a Molecular Beam; Internal States of the Nitric Oxide

Fragment," J. Chem. Phys. _82_, 2236 ( 1985).

King, D. S., Mantell, D. A., and Cavanagh, R. R., "NO Thermally Desorbed from

a Saturation Coverage on Pt (111): Internal State Distributions," J.

Chem. Phys. _82_, 1046 (1985).

King, D. S., "Product State and Kinetic Energy Distributions in the

Ultraviolet Photodissociation of the NO-Ar van der Waals Molecule," J.

Chem. Phys. _82, 3629 ( 1985).

King, D. S. and Stephenson, J. C. , "Energy Distribution in the Nitric Oxide

Fragments from the Vibrational Predissociation of NO-C2 H 1J," J. Chem.

Phys. 82, 5286 (1985) .

Krauss, M. and Stevens, W. J., "Electronic Structure of FeO and RuO , " J.

Chem. Phys. _82, 5584 ( 1985).

Lovas, F. J., "Microwave Spectra of Molecules of Astrophysical Interest XXII.

Sulfur Dioxide (S0 2 )," J. Phys. Chem. Ref. Data J_4 , 395-488 (1985).

Lovas, F. J., "Microwave Spectra of Atmospheric Species," Proc. of CMA/NBS

Workshop on Atmospheric Spectra, (ed., by A. Weber, June 1985)

p. IIIA14.

Lovas, F. J., "Critically Evaluated Microwave Spectral Data," Proc. of

CMA/NBS Workshop on Atmospheric Spectra, (ed., by A. Weber, June 1985)

p. I V21

.

Maki, A. G. , "Infrared Spectra and Atmospheric Chemistry," Proc. of CMA/NBS

Workshop on Atmospheric Spectra, (ed., by A. Weber, June 1985) p. I I IB 1

.

Maki, A. G. , Pine, A. S., and Dang-Nhu, M. , "A Doppler-Limited Study of the

Infrared Spectrum of Allene from 2965 to 3114 cm

1 ," J. Mol. Spectrosc.

112, 459-481 (1985).

Maki, A. G. and Wells, J. S., "High Resolution Spectrum of the Band of

Nitric Acid (HNOo) Near 880 cm

1

, " J. Mol. Spectrosc. 103, 1 7— 30

(1984).

Mies, F. H., "Adiabatic Analysis of Distant Perturbations: Application to

Herzberg-Teller Vibronic Coupling Theory," Molec. Phys. 5_4, 1423~1 1j 36

(1985).

Mies, F. H. and Julienne, P. S., "A Molecular Half Collision Analysis of

Atomic Lineshapes in Spectral Lineshapes ," Vol. 3, (ed., F. Rostas) W. de Gruyter and Co., Berlin, pp. 393-420 (1985).

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.

Biomol. Struct. Dynam. 2, 1157 (1985).

329
Ohashi , N. and Hougen, J. T. , "The Torsional-Wagging Tunneling Problem and

the Torsional-Wagging-Rotational Problem in Hydrazine," J. Mol.

Spectrosc. 112, 384-400 (1985).

Petersen, F. R., Wells, J. S., Jennings, D. A., and Maki, A. G. , "Improved

Deuterium Bromide 1-0 Band Molecular Constants from Heterodyne Frequency

Measurements," J. Mol. Spectrosc. 1 07, 43-61 (1984).

Pine, A. S., Fried, A., and Elkins, J. W. , "Spectral Intensities in the

Fundamental Bands of HF and HC1," J. Mol. Spectrosc. 109, 30-45 (1985).

Pine, A. S., Lafferty, W. J., and Howard, B. J., "Vibrational Predissociation,

Tunneling and Rotational Saturation in the HF and DF Dimers," J. Chem.

Phys. 8J_, 2939-2950 ( 1984).

Pine, A. S., "Tunable Laser Spectroscopy of Upper Atmospheric Molecules,"

Proc. of CMA/NBS Workshop on Atmospheric Spectra, (ed., by A. Weber,

June 1985) p. Ill B8.

Pollock, C. P., Petersen, F. R., Jennings, D. E., Wells, J. S., and Maki, A.

G. , "Absolute Frequency Measurements of the 00°2-00°0, 20°1-00°0 Bands

of NpO by Heterodyne Spectroscopy , " J. Mol. Spectrosc. 107, 62-71

(1984).

Raab, M. and Weber, A., "Amplitude Modulated Heterodyne Polarization

Spectroscopy," J. Opt. Soc. Am. B_2, 1 476 ( 1985).

Ratcliff, L. , Konowalow, D. D. , and Stevens, W. J., "Transition Moments for

Low-Lying Excited States in NaK," J. Mol. Spectrosc. 110, 242 (1985).

Rumble, J. R., Jr., Stevens, W. J. , and Truhlar, D. G. , "Effective

Electron Correlation in the Target Wavefunction on Electron-Molecule

Scattering," J. Phys. Q]7_, 31 5 ( 1984).

Snyder, L. E. , Henkel, C. , Hollis, J. M. , and Lovas, F. J., "Observations of

the Si0 2 Radical Toward IRC + 10216 at 1.27 Centimeters," Astrophys. J.

(Letters) 290, L29-L33 (1985).

Stevens, W. J., Basch, H., and Krauss, M. , "Compact Effective Core Potentials

and Efficient Shared-Exponent Basis Sets for the First- and Second-Row

Atoms, Li-Ar," J. Chem. Phys. _8l_, 6026 ( 1984).

Suenram, R. D., Lovas, F. J., and Stevens, W. J., "Reaction Products from a Microwave Discharge of N 0 and H

2 S, The Microwave Spectrum Two Conformers

of Sulfur Diimide (H-N=s4n-H) ,J. Mol. Spectrosc. (1985).

Weber, A., "Proceedings of the CMA/MBS Workshop on Atmospheric Spectra,"

November 3 -

4, 1983, (June 1985).

Wells, J. S., Jennings, D. A., Hinz, A., Murray, J. S., and Maki, A. G.

,

"Heterodyne Frequency Measurements on N

2

0 at 5.3 and 9.0pm," J. Opt.

Soc. Am. B2 , 857-861 (1985).

330
)b) Publications in Progress

3asch , H., Krauss, M. , Stevens, W. J., and Cohen, D., ’’Electronic and

Geometric Structures of Pt(NH

2 )§

+

, PttNH^^Cl-?, PttNH^gX and

Pt(NHg) 2 XY ( X , Y = H

2 0,0H),’’ J. Inorg. Chem. (in press).

3asch, H., Krauss, M. , and Stevens, W. J., ’’Cation Binding Effect on H-3onding," J. Am. Chem. Soc. (submitted).

3asch, H., Krauss, M. , Stevens, W. J., and Cohen, D., ”3inding of

Pt ( NH^ ) to Nucleic Acid Bases," J. Inorg. Chem. (submitted).

3asch, H., Krauss, M. , Stevens, Vi. J.. and Cohen, D., "Electronic and

Eleometric Structures of Pt(NHo)| +

, Pt(NHg)

2

Cl 2

, PtOlH^gX,

Pt ( NHg

)

2 XY ( X, Y = OH”, H

2 0)," inorg. Chem. (submitted).

3asch, H. Krauss, M. , and Stevens, W. J., "Cation Binding Effect on H-Bonding," J. Am. Soc. (submitted).

3odaness, R. S., Heller, D. F., Krasinski, J., and King, D. S. , ."Direct

Two-Photon Excitation of the Tumor Localizing Photo-Sensitizer

Hematoporphyrin Derivative at 750 nm via the Soret Band System," J.

3iological and Biochemical Sciences (WERB review).

Casassa, M. P., Heilweil, S. J., Stephenson, J. C. , and Cavanagh, R. R.,

"Time-Resolved Measurements of 0H(v=1) Vibrational Relaxation on Si0

2

Surfaces: Isotope and Temperature Dependence," Phys. Rev. Lett,

(submitted)

.

Casassa, M. P., Heilweil, E. J., Stephenson, J. C. , and Cavanagh, R. R.,

"Time-Resolved Measurements of Vibrational Relaxation at Surfaces," J.

Electronic Spectry. (accepted).

Dang-Nhu, M. and Pine, A. S., "Intensities des Raies d’Absorption dans la

Bande Chaude vg + - v-j

i de l'Allene," Can. J. Phys. (in press).

Heilweil, E. J. , Casassa, M. P., Cavanagh, R. R. , and Stephenson, J. C.

,

"Vibrational Energy Decay of Surface Adsorbates," Proceedings of the

1985 Conference on Time-Resolved Vibrational Spectroscopy,

Spr inger-Verlag (in press).

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_, (in press).

Hougen, J. T., "A Generalized Internal Axis Method for High Barrier Tunneling

Problems, as Applied to the Water Dimer," J. Mol. Spectrosc. (accepted'.

Howard, 3. J. and Pine, A. S, "Rotational Predissociation and Libration ;n the Infrared Spectrum of Ar-HCl," Chem. Phys. Letters (submitted).

331
Jacox, M. E., "Comparison of the Ground-State Vibrational Fundamentals of

Diatomic Molecules in the Gas Phase and in Inert Solid Matrices," J. Mol. Spectrosc. 1 1 3 > (in press).

Jacox, M. E., "Reaction of F Atoms with Methyl Halides. Vibrational Spectra

of CH^XF and of H

2 CX***HF Trapped in Solid Argon," J. Chem. Phys. 33 ,

( in press )

.

Jasien, P. G. and Stevens, W. J., "Calculated Proton Affinities for Some

Molecules Containing Group VI Atoms," J. Chem. Phys. (in press).

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.

(submitted).

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. (in press).

King, D. S. and Cavanagh, R. R., "Laser Studies of Molecule-Surface

Interactions," Review prepared for Springer Series in Chemical Physics

( submitted)

.

Krauss, M. , Stevens, W. J., and Basch, H., "Relativistic Effective Potential

SCF Calculations of AgH and AuH," J. Comp. Chem. (in press).

Lovas, F. J., "Recommended Rest Frequencies for Observed Interstellar

Molecular Microwave Transitions," J. Phys. Chem. Ref. Data (submitted).

Mantell, D. A., Cavanagh, R. R., and King, D. S., "Internal States

Distributions of NO Thermally Desorbed from Pt(111): Dependence on Coverage and Co-adsorbed CO," J. Chem. Phys. (submitted).

Mialocq, J.-C. and Stephenson, J. C. , "Picosecond Laser Study of the

Collisionless Photodissociation of Dimethylnitramine at 266 nm," Chem.

Phys. Lett, (submitted).

Mialocq, J.-C. and Stephenson, J. C. , "Picosecond Laser Induced Fluorescence

Study of the Collisionless Photodissociation of Nitrocompounds at 266

nm" Chem. Phys. (in WERB review).

Mies, F. H., Julienne, P. S. , 3and, Y. B. , and Singer, S., "A Convergent

Analysis of Radiative Matrix Elements in Atomic Lineshape Theory," J. Phys. B (submitted).

Miller, K. J., Taylor, E. R., Basch, H., Krauss, M. , and Stevens, W. J., "A

Theoretical Model for the Binding of Cis-Pt (NH^)

2

+ to DNA," J.

Biomol. Str. Dyns. (in press).

Ohashi, N., Lafferty, W. J., and Olson, W. B., "Fourier Transform Far

Infrared Spectrum of Hydrazine," J. Mol. Spectrosc. (submitted).

Pine, A. S., Maki, A. G. , and Chou, N.-Y., "Pressure Broadening, Lineshapes,

and Intensity Measurements in the 2«-0 Band of NO," J. Mol. Spectrosc.

( in press )

.

332
Pine, A. S. and Fried, A., "Self Broadening in the Fundamental Bands of HF

and HC1," J. Mol. Spectrosc. (in press).

Pine, A. S. and Howard, B. J., "Hydrogen-Bond Energies of the HF and HC1

Dimers from Absolute Infrared Intensities," J. Chem. Phys. (submitted).

Rosenkrantz, M. E. and Krauss, M. , "Damped Dispersion Interaction Energies

for He-H

2

, Ne-H 2, and Ar-H 2 ," Phys. Rev. (submitted).

Suenram, R. D., Lovas, F. J. , and Pickett, H. M. , "Millimeter Wave Spectrum

of Peroxynitric Acid," J. Mol. Spectrosc. (submitted).

Thompson, G. A., Maki, A. G. , and Weber, A., "The Infrared Spectrum of GeO,"

J. Mol. Spectrosc. (submitted).

Vahala, L. , Julienne, P. S., and Havey, M. D., "Nonadiabatic Theory of

Fine-Structure Branching Cross Sections for NaHe, NaNe, and NaAr , " Phys.

Rev. A (submitted).

Wells, J., Hinz, A., and Maki, A. G. , "Heterodyne Frequency Measurements on

N q 0 Between 1257 cm

1 and 1 3-40 cm

1

, " J. Mol. Spectrosc. (in press).

333
6. TALKS

Casassa, M. P., "Time-Resolved Measurements of Vibrational Relaxation on Molecules on Surfaces," 31st National Meeting of the American Vacuum

Society, Reno, NV, December 1984.

Casassa, M. P., "Time-Resolved Measurements of Vibrational Relaxation on Surfaces," Gordon Conference on Dynamics of Gas-Surface Interactions,

New London, NH, July 1985.

Casassa , M. P .

,

Surfaces ,

"Time-Resolved Measurements of Vibrational Relaxation on Exxon Research and Engineering Co., Annandale, NJ, May 1985.

Casassa, M. P.

,

Surfaces ,

"Time-Resolved Measurements of Vibrational Relaxation on IBM Watson Research Center, Yorktown Heights, NY, June 1985.

Casassa , M. P .

,

Surfaces ,

"Time-Resolved Measurements of Vibrational Relaxation on General Motors Research Labs, Warren, MI, May 1985.

Casassa, M. P.,

Surfaces,

"Time-Resolved Measurements of Vibrational Relaxation on Sandia National Laboratory, Livermore, CA, May 1985.

Casassa , M. P .

,

Surfaces,

"Time-Resolved Measurements of Vibrational Relaxation on Aerospace Corporation, Los Angeles, CA, May 1985.

Casassa , M. P .

,

"Dynamics of Vibrational Energy in Molecules: Vibrational

Relaxation of Molecules Chemisorbed on Surfaces," Sandia National

Laboratory

,

, Albuquerque, NM, March 1985.

Casassa, M. P.,

Surfaces ,

"Picosecond Measurements of Vibrational Relaxation on Surface Science Division, National Bureau of Standards,

Gaithersburg, MD, February 1985.

Casassa, M. P., Heilweil, E. J., Cavanagh, R. R., and Stephenson, J. C.,

"Vibrational Energy Relaxation of Adsorbates on Surfaces," Symposium on Surface Bonds, ACS National Meeting, Chicago, IL, September 1985.

Heilweil, E. J., "Time-Resolved Vibrational Energy Decay of Surface

Adsorbates," Microphysics of Adsorbates Conference, Santa Fe, NM,

February 1985-

Heilweil, E. J., "Time-Resolved Vibrational Energy Decay of Surface

Adsorbates," Sandia National Labs, February 1985.

Heilweil, E. J., "Time-Resolved Vibrational Energy Decay of Surface

Adsorbates," Howard University, April 1985.

Heilweil, E. J., "Vibrational Energy Decay of Surface Adsorbates," Virginia

Commonwealth University, April 1985.

334
Heilweil, E. J., "Vibrational Energy Decay of Surface Adsorbates,"

Time-Resolved Vibrational Spectroscopy Conference, Bayreuth, West

Germany, June 1985.

Heilweil, E. J., "Picosecond Vibrational Relaxation of Adsorbates at

Colloidal Interfaces," Gordon Research Conference, Chemistry at

Interfaces, July 1985.

Hougen, J. T., "Point-Groups, Permutation-Inversion Groups and Extended

Groups," IMS Colloquium, Okazaki, Japan, November 1984.

Hougen, J. T., "The Philosophy and Mathematics of Constructing Effective

Hamiltonians for Molecules with Large Amplitude Vibrational Motions,"

Seminar for the Theoretical Group at IMS, Okazaki, Japan, November 1984.

Hougen, J. T. , "Selected Topics from Atomic and Molecular Spectroscopy," IMS,

Okazaki, Japan, November 1984.

Hougen, J. T., "The Avoided Crossing Technique of Meerts and Ozier: Its

Application to A values and Barrier Heights, and One Selection Rule

Puzzle," Seminar for the High Resolution Group at IMS, Okazaki, Japan,

December 1984.

Hougen, J. T., "A Generalized Internal Axis Method for High Barrier Tunneling

Problems," Seminar for High Resolution Group at IMS, Okazaki, Japan,

December 1934.

Hougen, J. T., "Application of Vibration-Rotation Tunneling Theory to the Gas

Phase Water Dimer Spectrum," Molecular Spectroscopy Division Seminar,

NBS, January 1985.

Hougen, J. T., "Tunneling Motion in the Water Dimer," Lawrence Berkeley

Laboratory and Department of Chemistry, University of California,

Berkeley, CA, April 1985.

Hougen, J. T., Four lectures on "Group Theory in Molecular Spectroscopy," at

the Chemistry Department, University of California, Berkeley, CA, April

1985.

Hougen, J. T., "A Generalized Internal Axis Method for High Barrier Tunneling

Problems, as Applied to the Water Dimer," Washington Meeting of the

American Physical Society, Washington, D.C., April 1985.

Hougen, J. T. , "A Generalized Internal Axis Method for High Barrier Tunneling

Problems, as Applied to the Water Dimer," 40th Symposium on Molecular

Spectroscopy , Columbus, OH, June 1985.

Hougen, J. T. and Ohas’ni, N., "The Torsional-Wagging Tunneling Problem and

Torsional-Wagging-Rotatinal Problem in Hydrazine," 40th Symposium on Molecular Spectroscopy, Columbus, OH, June 1985.

Hougen, J. T. , "The Use of Extended Permutation-Inversion Groups for

Constructing Hyperfine Hamiltonians for Symmetric Top Internal Rotor

Molecules Like H^C-SiHo," 40th Symposium on Molecular Spectroscopy,

Columbus, OH, June 1985.

335
Hougen, J. T., "Symmetry Beyond Point Groups in Molecular Spectroscopy,"

Department of Chemistry, University of Chicago, Chicago, IL, July 1985.

Hougen, J. T., "Symmetry Beyond Point Groups in Molecular Spectroscopy,"

Seventeenth International Symposium on Free Radicals, Granby, CO, August

1985.

Hougen, J. T., "A Generalized Internal Axis Method for High Barrier Tunneling

Problems, As Applied to the Water Dimer," American Chemical Society,

Chicago, IL, September 1985.

Hougen, J. T., "The Use of Extended Permutation-Inversion Groups for

Constructing Hyperfine Hamiltonians for Symmetric-Top High-Barrier

Internal Rotor Molecules," Ninth Colloquium on High Resolution Molecular

Spectroscopy, Riccione, Italy, September 1985.

Howard, 3. J. and Pine, A. S., "Near-Infrared Spectra of Rare-Gas-HCl

Complexes," 40th Symposium on Molecular Spectroscopy, Columbus, OH, June

1985.

Jacox, M. E., "Spectroscopic Studies of the Early Stages in the Decomposition

of Energetic Materials," Workshop on the Initiation of the Chemical

Decomposition of Energetic Materials, Office of Naval Research,

Annapolis, MD, October 1984.

Jacox, M. E., "Spectroscopy of Intermediates in the Decomposition of

Energetic Materials. Experimental Studies at the National Bureau of

Standards," Workshop on Diagnositics for Ignition Mechanisms, Army

Research Office, Aberdeen, MD, November 1984.

Jacox, M. E., "Spectra of Free Radicals Formed in the Primary Reaction of F Atoms with the Substituted Methanes," 7th Winter Fluorine Conference,

Division of Fluorine Chemistry, American Chemical Society, Orlando, FL,

February 1985.

Jacox, M. E., "Dolphus E. Milligan - A Scientific Retrospective," Dedication

Symposium, Dolphus E. Milligan Science Research Institute, Atlanta

University Center, Atlanta, GA, March 1985.

Jacox, M. E. , "Matrix Isolation Studies of the Decomposition and Ionization

of Small Molecules at Energies Between 11.5 and 1 6 . 3 eV," Symposium on Ultraviolet Photochemistry, 68th Canadian Chemical Conference, Kingston,

Ontario, Canada, June 1985.

Jacox, M. E., "Spectra of Free Radicals Formed in the Primary Reaction of F Atoms with the Methyl Halides," 40th Symposium on Molecular

Spectroscopy, Columbus, OH, June 1985.

Jacox, M. E., "Spectra of Free Radicals Formed in the Primary Reaction of F Atoms with the Substituted Methanes," 5th International Colloquium on

the Spectroscopy of Matrix Isolated Species, Fontevraud, France, July

1985.

336
Jacox, M. E., "The Vibrational Spectrum of the COOH Free Radical Trapped in

Solid Argon," 17th International Symposium on Free Radicals, Granby, CO,

August 1585.

Jacox, M. E., "Vibrational and Electronic Spectra of Transient Species

Trapped in Solid Argon and Neon," Symposium on Theoretical and

Experimental Studies of Transient Species, 190th National Meeting of the

American Chemical Society, Chicago, IL, September 1985.

Jasien, P. G. and Stevens, W. J., "Proton Affinities of Some Molecules

Containing Group VI Atoms," 40th Symposium on Molecular Spectroscopy,

Columbus, OH, June 1985.

Jennings, D. E., Weber, A., and Brault, J. W. , "Fourier Transform Raman

Spectroscopy of H

2 and D 2 in Flames," 40th Symposium on Molecular

Spectroscopy , Columbus, OH, June 1985.

Julienne, P. S., "Theory of Atomic Collisions in Laser Fields," Physics

Department Seminar, University of Missouri, Rolla, MO, October 1984.

Julienne, P. S., "Nonadiabatic Half-Collision Theory of Line Broadening,

Laser-induced Collisions, and Photodissociation," Atomic and Molecular

Theory Group Seminar, Lawrence Livermore Laboratory, Livermore, CA,

December 1984.

Julienne, P. S., "Analytic Multichannel Theory of Molecular Dissociation,"

International Conference on the Physics of Electronic and Atomic

Collisions," Stanford University, Palo Alto, CA, August 1985.

King, D. S. , "State Selective Studies of Molecular-Surface Dynamics," Optical

Society of America National Meeting, San Diego, CA, October 1984.

King, D. S. , "State Selective Studies of Molecule-Surface Interactions,"

University of California, Irvine, CA, November 1984.

King, D. S. , "Dynamics in Chemical Bond Breaking Processes," Molecular

Spectroscopy Division Seminar, NBS, February 1985.

King, D. S., "Energy Distributions in Thermally Desorbed Molecules,"

Conference on the Dynamics of Molecular Collisions, Utah, July 1985.

Krauss, M. , "Electronic Structure of Metal Oxides," IBM, Kingston, NY,

February 1985.

Krauss, M. , "Effective Potentials in Quantum Chemistry," Rensselaer

Polytechnical Institute, NY, April 1985.

Lafferty, W. J. and Olson, W. B., "High Resolution Spectrum of the v

2 and ,0

Bands of HO Cl," 40th Symposium on Molecular Spectroscopy, Columbus, OH

June 1985.

Lovas, F. J. and Suenram, R. D., "Pulsed Beam Microwave Study of the van ier

Waals Complex Ar • • ‘Q^CHCN, " Spring Meeting of the American Physical

Society, Crystal City, MD, April 1985.

337
Lovas, F. J., "Rotational Studies of Weakly—Bound Molecules by Conventional

and Fourier Transform Microwave Spectroscopy," Institut fur

Physikalische Chemie der Universitat Kiel, Kiel, Germany, September

1985.

Lovas, F. J. and Suenram, R. D., "Pulsed Beam Microwave Study of the van der

Waals Complexes Ar---CH2 CHCN and Kr--*0CS," Ninth Colloquium on High

Resolution Molecular Spectroscopy, Riccione, Italy, September 1985.

Lovejoy, R. W. , Schaeffer, R. D., and Olson, W. B. , "High Resolution Infrared

Spectrum on SiHoD," 40th Symposium on Molecular Spectroscopy, Columbus,

OH, June 1985.

Maki, A. G. , "Laboratory Studies of Atmospheric Molecules at NBS," Workshop

on the Spectroscopic Studies of Atmospheric Species, NASA-Langley

Research Center, Hampton, VA, October 1984.

Maki, A. G. , Pine, A. S. , Wells, J. S., Jennings, D. A., Fayt, A., and

Goldman, A., "Laboratory Studies of the Infrared Spectra of Atmospheric

Species," Topical Meeting on Optical Remote Sensing of the Atmospheric,

Incline Village, Nevada, January 1985.

Maki, A. G. and Pine, A. S., "Pressure Broadening and Intensity Measurements

lor the 2-0 Band of NO," 40th Symposium on Molecular Spectroscopy,

Columbus, OH, June 1985.

Mies, F. H., "Collisional Redistribution of Resonant Radiation in Intense

Laser Fields," Conference on Dynamics of Molecular Collisions, Snowbird,

Utah, July 1985.

Ohashi, N., Lafferty, W. J., and Olson, W. 3., "Far-Infrared Spectrum of the

Torsional Band of Hydrazine," 40th Symposium on Molecular Spectroscopy,

Columbus, OH, June 1985.

Pine, A. S., "Difference-Frequency Laser Spectroscopy of Hydrogen-Bonded and van der Waals Complexes," Joint MIT-Harvard Physical Chemistry

Colloquium, Harvard University, Cambridge, MA, December 1984.

Pine, A. S. , "High-Resolution Studies of Predissociation in Hydrogen-Bonded

and van der Waals Complexes," Chemistry Department, University of

California, Berkeley, CA, January 1985.

Pine, A. S. , "Infrared Spectroscopy of Hydrogen-Bonded and van der Waals

Complexes Using a Dif ference-Frequency Laser," Western Spectroscopy

Association Meeting, Asilomar, CA, February 1985.

Pine, A. S. , "Difference-Frequency Laser Spectroscopy of Hydrogen-Bonded and van der Waals Complexes," American Physical Society Spring Meeting,

Washington, D.C., April 1985.

Pine, A. S. and Fried, A., "Intensities and Self-Broadenings in HF and HC1,"

40th Symposium on Molecular Spectroscopy, Columbus, OH, June 1985.

Stevens, W. J., "Compact Effective Potentials and Basis Sets," IBM

Laboratories, Kingston, NY, October 1984.

338
Stevens, W. J. f "Cation Binding Effect on Inidizole Tautomerism, " 5th

International Congress on Quantum Chemistry, Montreal, Canada, August

1985.

Suenram, R. D. and Lovas, F. J., "Microwave Spectrum of the

Ar •• -Acrylonitrile van der Waals Complex" 40th Symposium on Molecular

Spectroscopy , Columbus, OH, June 1985.

Stephenson, J. C., "Vibrational Energy Transfer," Chemistry Department,

Howard University, April 1985.

Stephenson, J. C., "Vibrational Energy Transfer in Adsorbates on Surfaces,"

Chemistry Department, MIT, May 1985.

Stephenson, J. C., "Vibrational Energy Transfer in Adsorbates on Surfaces,"

Gordon Conference on Molecular Energy Transfer, July 1985.

Stephenson, J. C., "Vibrational Relaxation of Chemical Bonds in Liquids and

on Surfaces," International Conference on Photochemistry, June 1985.

Thompson, G. A., Maki, A. G. , and Weber, A., "More Diode Laser Spectra of

Diatomic Molecules," 40th Symposium on Molecular Spectroscopy, Columbus,

OH, June 1985.

Thompson, G. A., Maki, A. G. , and Weber, A., "Infrared Measurements of High

Temperature Diatomic Species," XVII European Congress on Molecular

Spectroscopy, Madrid, Spain, September 1985.

Weber, A., Lafferty, W. J. , and Olson, W. B., "High Resolution Infrared

Spectrum of Cyanogen," 40th Symposium on Molecular Spectroscopy,

Columbus, OH, June 1985.

Weber, A., Jennings, D. E., and Brault, J. W. , "Fourier Transform Raman

Spectroscopy of Gases," XVII European Congress on Molecular

Spectroscopy, Madrid, Spain, September 1985.

Weber, A., Jennings, D. E. , and Brault, J. W. , "Fourier Transform Raman

Spectroscopy of Gases," Ninth Colloquium on High Resolution Molecular

Spectroscopy, Riccione, Italy, September 1985.

Weber, A., "Recent Work in High Resolution Molecular Spectroscopy at NB3,"

Physics Department, University of Bayreuth, Bayreuth, Germany, September

1985.

339
7. MOLECULAR SPECTROSCOPY DIVISION SEMINARS

Allen, L. C., Department of Chemistry, Princenton University, Princenton, NJ,

"Electronic Mechanism of Carbonic Anhydrase," March 1985.

Andrews, L., Department of Chemistry, University of Virginia,

Charlottesville, VA, "High and Low Energy Species: Spectroscopy of

Molecular Ions and HF Complexes in Solid Argon," November 1984.

Band, Y. B. , Ben-Gurion University, Israel, "Optical Properties of

Molecules with Large Excited State Absorption," July 1985.

Band, Y. B., Ben-Gurion University, Israel, "Photodissociation of Diatomic

Molecules to Atoms with Non-vanishing Angular Momentum," July 1985.

Bowen, K. H., Department of Chemistry, Johns Hopkins University, Baltimore,

MD, "Negative Ion Photoelectron Spectroscopy of Negative Cluster Ions,"

May 1985.

Evenson, K. , Time and Frequency Division, NBS, Boulder, CO, "Tunable Far

Infrared Spectroscopy," November 1984.

Fraser, G. T., Chemistry Department, Harvard University, MA, "Nonrigidity and

Vibrational Predissooiation in Ammonia van der Waals Complexes," March

1985.

Herman, R., Physics Department, Penn State University, "Collisional

Interference in the Vibration-Rotation Spectra of H 0 and HD," October

1984.

Hirota, E., Institute for Molecular Science, Myodaiji, Okazaki, Japan,

"Infrared Laser Kinetic Spectroscopy," April 1985.

Hochstrasser , R. M. , Department of Chemistry, University of Pennsylvania, PA,

"Ultrafast Relaxation Processes in Condensed-Phase Molecular Systems,"

May 1985.

Howard, B. J., Physical Chemistry Laboratory, Oxford University, England, "IR

Studies on Intermolecular Interactions in Weakly Bound Species," April

1985.

Jackson, W. M. , Chemistry Department, Howard University, "Laser Studies of

Reaction Dynamics in Gases and on Surfaces," September 1985.

Kunz, T., Department of Chemistry, Rice University, Houston, TX,

"Photochemistry of Formyl Fluoride," February 1985.
Ladik, J., University Er langen-Nurnberg , Germany, "Quantum Theory of

Polymers: Solid State Aspects," September 1985.

Mills, I. M. , University of Reading, England, "Molecular Vibrations Seen as Local Modes," April 1985.

Moore, R., Department of Chemistry Virginia Commonwealth University, VA,

"Picosecond Intermolecular Vibrational Relaxation in the Gas Phase,"

January 1985.

Pickett, H. M. , Jet Propulsion Laboratory, Pasadena, CA, "Spectroscopy in the

World Above One Terahertz," March 1985.

Schweitzer, E., Chemistry Department, MIT, Cambridge, MA, "Spectroscopic

Probes of Infrared Multiphoton Dissociation," February 1985.

Shostak, S., University of Rochester, Rochester, NY, "Studies of Infrared

Laser Excited Molecules by MBER and Maser Spectroscopy," February 1985.

van Duijnen, P., Theoretical Chemistry Group, Laboratory of Chemical Physics,

Cromingen, The Netherlands, "Reaction Field Hamiltonians and

Applications to Biomolecules," June 1985.

>1
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, Reviews 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 14: Fundamental Spectroscopic Data.

Mak i , A . G

.

Member, Editorial Advisory Board, Journal of Molecular

Spectroscopy.

Weber, A.

Editoral Advisory Board, Journal of Raman Spectroscopy.

Member, Program Committee, 10th International Conference

on Raman Spectroscopy, 1986.

Chairman, Williams-Wr ight Awards Committee, Coblentz Society.

Director and Chairman, Organizing Committee, NATO Advanced Research

Workshop on "Structure and Dynamics of Weakly Bound Molecular

Complexes .
9. PROFESSIONAL INTERACTIONS, CONSULTING

AND ADVISORY SERVICES

Casas sa, M. P.

Dr. R. R. Cavanagh, Surface Science Division, on picosecond infrared

laser studies of vibrational relaxation of adsorbed molecules.

Dr. K. C. Janda, California Institute of Technology, on studies of the

infrared photodissociation of van der Waals molecules.

Heilweil, E. J.

Professor R. M. Hochstrasser , University of Pennsylvania, on transient

grating phenomena in molecular solutions.

Professor G. Ritchie, Department of Physics, Rider College, on dielectric perturbations of surface plasmon dynamics.

Dr. C. Sandhoff, AT & T Bell Communications, on pressure dependent

lifetimes of colloidal semiconductor excited states.

Hougen, J. T.

Distinguished Visiting Foreign Professor, IMS, Okazaki, -July-December

1984.

Professor R. Saykally and students, University of California,

Berkeley, on spectra of floppy molecular ions.

Professor T. Oka and students, University of Chicago, on spectra of

floppy molecular ions.

Jacox, M. E.

Professor R. F. Curl, Department of Chemistry, Rice University,

on the infrared spectrum of HC 2

.

Professor L. Andrews, Department of Chemistry, University of Virginia,

on the infrared spectra of partially deuterated ethylenes.

Dr. Victor Maroni, Argonne National Laboratory, on the infrared spectrum of

FON.

Professor E. K. C. Lee, Department of Chemistry, University of

California, Irvine, on the spectrum of matrix-isolated H

2 S.

Professor P. Thaddeus, Goddard Institute for Space Studies and Physics

Department, Columbia University, on the spectrum of C^H-,.

343
Professor Douglas D. Davis, Department of Chemistry, Georgia Institute

of Technology, on the spectra of matrix-isolated nitrogen oxides.

Julienne, P. S.

Dr. M. Havey, Old Dominion University, on interpretation of

radiative redistribution experiments.

Dr. J. Weiner, University of Maryland, on interpretation of Naj

photodissociation experiments.

Dr. S. Singer, University of Pennsylvania, on development of a close

coupled photodissociation code.

Dr. Y. B. Band, Ben-Gurion University, on calculating atomic line

broadening matrix elements.

King, D. S.

Dr. R. Bodanness, NIH, on the role of biphotonic processes in the

photo-activated generation of singlet oxygen.

Dr. R. R. Cavanagh and Dr. W. Gadzuk, on experimental and theoretical

aspects of molecular dynamics of the gas-surface interface.

Krauss, M.

Dr. E. C. Clementi and Dr. M. Dupuis, IBM, Kingston, NY, on biochemical

molecules

.

Dr. K. J. Miller, Department of Chemistry, Rensselaer Polytechnic

Institute, Troy, NY, on Pt amine drug interactions with DNA.

Lafferty, W. J.

Dr. J. P. Sattler, Harry Diamond Laboratory, consulting on optically pumped far infrared laser line assignments.

Lovas , F . J

.

National Science Foundation, member of the Physics and Astronomy

Panel for the 1984 Graduate Fellowship Program.

Professor L. E. Snyder, University of Illinois and Dr. J. M. Hollis,

NASA/Goddard Space Flight Center, collaborations and consultations

on interstellar molecular searches.

Dr. R. Wattenbach and Dr. T. Wilson, Max-Planck Institute for

Rad ioastronomie , Bonn, provided spectroscopic information on 0^

and H

2 CS for atmospheric and interstellar measurements.
Maki, A. G.

Dr. A. Goldman, University of Denver, collaboration on studies

of Nitric Acid spectra.

Dr. A. Fayt, Universite Catholique de Louvain, Belgium,

collaboration on the analysis of the x>2 and bands of HNO^ and on Lamb-dip measurements of laser-Stark spectra.

Dr. J. Kauppinen, University of Oulu, Oulu, Finland, collaboration on the measurement and analysis of spectra of OCS, CO2, and N2O for use

in the calibration of spectrometers and tunable laser devices.

Dr. J. Wells, Time and Frequency Division, NBS-Boulder, collaboration

on the frequency measurement an analysis of N2O and NO absorption

lines using heterodyne techniques.

Dr. C. Chackerian, NASA Ames Research Center, Moffett, CA,

collaboration on the use of the Herman-Wallis effect to measure the

intensity of the CIO fundamental band.

Pine, A. S.

Dr. A. Fried, Gas and Particulate Science Division, NBS, collaboration

on spectral line intensities and broadenings in HF and HC 1 .

Dr. R. M. Herman and J. P. Looney, Department of Physics, Penn State

University, University Park, PA, collaboration on line broadening

mechanisms in HF and HC 1 .

Stephenson, J. C.

Dr. J. W. Perry, Jet Propulsion Laboratory, Pasadena, CA, on picosecond studies of energy transfer in liquids.

Stevens, W. J.

Dr. M. Dupuis, Lawrence Berkeley Laboratory, on quantum chemistry

calculations for large molecules.

Suenram, R. D.

Professor L. E. Snyder, University of Illinois, collaborations on radio astronomy searches for interstellar molecules.

Dr. H. M. Pickett, Jet Propulsion Laboratory, collaborations on analysis of (HOONC^) and CH2FOH rotational spectra.

Professor C. W. Gilles, Rensselaer Polytechnic Institute, advice on construction of pulsed Fourier transform microwave spectrometer

.

345
Dr. G. T. Fraser, Harvard University, consultation and data on Ar-'^NH^, and NH^’^NH^ van der Waals complexes.

Professor R. L. Kuczkowsky, and Dr. K. W. Hillig, II, University of

Michigan, advice on construction of pulsed Fourier transform microwave

spectrometer.

Professor S. G. Kukolich, University of Arizona, advice on construction of pulsed Fourier transform microwave spectrometer

.

Professor S. Ross, University of Alberta, data fitting for H2C0***HF

hydrogen bonded species.

Weber, A.

Professor L. Henry, University de Paris, collaborative research

on the Fourier transform spectroscopy of metal clusters.

Dr. J. W. Brault, National Solar Observatory, Tucson, AZ,

collaboration on Raman Spectroscopy of gases with Fourier transform

techiques

.

Dr. K. Narahari Rao, Ohio State University, Columbus, OH, discussions

on the organization of the 1985 Columbus Symposium.

Drs. A. Harvey, Naval Research Laboratory, I. W. Levin, National

Institute of Health, Dr. G. Rosasco, Temperature and Pressure

Division, NBS, and Dr. J. Nibler, Chemistry Department, Oregon State

University, discussions on the planning for the 10th

International Conference on Raman Spectroscopy, 1986.
10. VISITING SCIENTISTS

The Molecular Spectroscopy Division has been host in the past year to

the following scientists who have worked with NBS 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.

Bevan, John W. , Chemistry Department, Texas A & M University, worked with

W. J. Lafferty and W. B. Olson on the Fourier transform infrared

spectra of hydrogen bonded molecules.

Bodaness, Robert S. , National Institutes of Health, worked with D. S. King

on laser photosensitization processes in biological samples.

Chou, N.-Y., Chemistry Department, Howard University, worked with A. S.

Pine on collisional line broadening problems.

Ho, P.-T., Electrical Engineering Department, University of Maryland,

worked with J. C. Stephenson on research with picosecond lasers.

Hollis, Jan Michael, NASA/Goddard Space Flight Center, works with

F. Lovas and R. Suenram on software development for automated microwave

spectrometer and collaborates on astronomical studies.

Howard, 3rian, Oxford University, Oxford, England, worked with A.

S. Pine on high resolution infrared spectroscopy of the rare gas-HCl

van der Waals molecules.

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.

Leubner, Christoph, J., Institut fur Theoretische Physik, Universit&t

Innsbruck, Austria, worked with J. T. Hougen on improved least squares

determination of potential energy surfaces from spectroscopic data.

>7
Lovejoy, Roland VJ. , Chemistry Department, Lehigh University, works

with B. Olson on the infrared spectrum of deuterated silanes.

Mialocq, John-Claude, Department de Physico-Chemie , Centre d'Etudes

Nucleaires de Saclay, France, worked with J. C. Stephenson on problems

of vibrational relaxation, photo-dissociation, and fluorescence and

absorption spectroscopy on a picosecond time scale.

Mills, Ian M. , Department of Chemistry, Reading University, Reading,

England, worked with W. J. Lafferty on the spectroscopy of hydrogen

bonded molecules and the theoretical relationships between normal and

local mode models of molecular vibrations.

Ohashi, Nobukimi, Kanazawa University, Physics Department, Japan,

works with A. S. Pine, J. T. Hougen, W. J. Lafferty and B. Olson on high

resolution infrared spectroscopy of hydrazine and of hydrogen bonded

molecules

.

Sattler, Joseph P., Harry Diamond Laboratories, U. S. Army,

collaborates with W. Lafferty and A. Maki on precise line frequency

measurements in the infrared.

Vahala, Linda L., Physics Department, Old Dominion University, Norfolk,

VA, worked 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.

Wofford, Billy A., Chemistry Department, Texas A & M University, worked

with W. J. Lafferty and W. B. Olson on the Fourier transform infrared

spectra of hydrogen bonded molecules.
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NBS-114A REv. 2 -40

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET ( See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 85-3257

2. Performing Organ. Report No 3. Publication Date

4. DECEMBER 1985

TITLE AND SUBTITLE

Technical Activities 1985

Center for Chemical Physics 5.

AUTHOR(S)

Pierre Ausloos

6.

PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON. D.C. 20234

7. Contract/Grant No.

S. Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

10.

supplementary notes

_ Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a significant

bibliography or literature survey, mention it here)

This report summarizes research projects, measurement method development,

testing and data evaluation activities carried out during Fiscal Year 1985

in the h2P Center for Chemical Physics. These activities fail in the areas

of surface science, chemical kinetics, chemical thermodynamics arc

molecular snectroscop”

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by ser~.cc " . Chemical kinetics; chemical physics; molecular spectroscopy ; surface scier. ' r-: thermodynamics

13. availability

I X Unlimited For Official Distribution. Do Not Release to NTIS

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