NBSIR 75-344

NATL INST. OF STAND & TECH

miiir

REFEREHGI

PUSUCATiONS

A11107 DSflin

NATIONAL MEASUREMENT SYSTEM FOR

THE PHYSiCAL PROPERTIES OF ATOMS AND MOLECULES

J.W. Cooper

A.V. Phelps

SJ. Smith

Laboratory Astrophysics Division (JILA)

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

September 1976

160

/?76

NBSIR 75-944

NATIONAL MEASUREMENT SYSTEM FOR

THE PHYSICAL PROPERTIES OF ATOMS AND MOLECULES

J.W. Cooper

A.V. Phelps

S.J. Smith

Laboratory Astrophysics Division (J I LA)

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

September 1976

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward 0. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director
Abstract

National activity in measurement, compilation, evaluation,

and dissemination of atomic and molecular data, estimated at 20-25

million dollars annually, impacts directly upon applied research

and development projects costing over one-third billion dollars

annually. NBS atomic and molecular programs, costing about 3 million dollars annually, provide the basis for the accepted

standards for length, time and frequency; provide advanced

measurement techniques; set rigorous performance standards for

generation of atomic and molecular data, and provide for the

construction of a sound data base for the user community. The

largest users are programs aimed at energy generation and con- version. Basic sciences of aerodynamics, astrophysics, atmospheric physics and plasma physics are important users. Benefits

for a broad range of industrial research activities are potentially

large. It is recommended that NBS undertake to ensure the

reliability and adequacy of the data base needed for important

national programs, expand its contacts with private industry,

develop increased awareness of the methodology for applying

atomic and molecular data to technological devel opment, and

encourage effective utilization of this sector of the measurement system for the benefit of the economy.

Keywords: Atom; energy generation; industrial technology;

molecule; primary standards; properties.

ii
CONTENTS

PAGE

EXECUTIVE SUMMARY 1

1 . INTRODUCTION 2 2. STRUCTURE OF MEASUREMENT SYSTEM 3 2.1 Conceptual System 3 2.2 Basic Technical Infrastructure 4 2.2.1 Documentary System 4 2.2.2 Instrumentation System

.

5 2.2.2.1 Measurement Tools and Techniques 5 2.2.2.2 The Instrumentation Industry 6 2.2.3 Reference Data 6 2.2.4 Reference Materials ." 7 2.2.5 Science and People 7 2.3 Realized Measurement Capabilities 7 2.4 Dissemination and Enforcement Network 9 2.5 Direct Measurements Transactions Matrix 9 2.5.1 Analysis of Supplier and User Interactions . 9 2.5.2 Identification of Major Users and User Needs 9

3. IMPACT, STATUS AND TRENDS OF MEASUREMENT SYSTEM 11 3.1 Impact of Measurements 11 3.1.1 Functional, Technological and Scientific Applications 11 3.1.2 Economic Impacts—Costs and Benefits 11 3.1.3 Social, Human, Person-on-the-Street Impact 11 3.2 Status and Trends of the System 11 4. SURVEY OF NBS SERVICES 12 4.1 Historical Background 12 4.2 The Present—Scope of NBS Services 14

4.2.1 Description of NBS Services 14

4.2.2 Users of NBS Services 16

4.2.3 Alternative Sources 17 4.2.4 Funding Sources for NBS Services 18 4.2.5 Mechanism for Supplying Services 19 4.3 Impact of NBS Services 19

4.3.1 Economic Impact of NBS Services 19

4.3.2 Technological Impact of NBS Services 19

4.3.3 Pay-off from Changes in NBS Services 21 4.4 Evaluation of NBS Program 23

4.5 The Future 24

5. SUMMARY AND CONCLUSIONS 24

Appendix A. Methodology of the Study 25

Appendix B. Exarmoles of Interactions with Atomic and Molecular Data Users. 26 Appendix C. Atomic and Molecular Physics and Energy Research 29

Appendix D. Atomic and Molecular Physics ard Energy Research Matrix 32

REFERENCES 33

i i i
LIST OF TABLES

PAGE

Table 1 Accuracy of measurements of representative physical properties

of atoms and molecules 8

Table 2 Direct measurements transactions matrix for physical properties

of atoms and molecules 10

Table 3 NBS projects in measurement system for physical properties of

atoms and molecules 15

Table 4 Budgets for research and development areas utilizing measurement

system for atomic and molecular properties 20

i v
THE NATIONAL MEASUREMENT SYSTEM

FOR THE PHYSICAL PROPERTIES OF ATOMS AND MOLECULES

J.W. Cooper, A. V. Phelps and S. J. Smith

Institute for Basic Standards

September 1976

EXECUTIVE SUMMARY

The national activity in the measurement,

compilation, evaluation, and dissemination

of atomic and molecular data is represented

here as a component of the national measurement system. The significance and validity

of this representation rests largely on the

role of the National Bureau of Standards in

the development of measurement techniques,

the encouragement of standards of measurement performance and in efforts to generate

an adequate and well -documented data base

effectively constructed to meet the needs of

the user community.

The level of national activity in this

field is estimated to be in the range of

20-25 million dollars annually, and the

NBS programs in atomic and molecular mea- surements and in data evaluation and dissemination are approximately 3 million dollars

of the total. The output of this activity

has a direct impact upon applied research

and development projects currently funded

at a level well in excess of a third of a billion dollars annually. The largest of

these are ERDA-supported programs aimed at energy generation and conversion (conventional controlled thermonuclear research,

laser fusion, laser isotope separation,

coal -burning magnetohydrodynamic generators,

etc). There are large potential benefits

for a broad range of industrial research

and development activities. Atomic and

molecular measurements are also extremely

important to basic research in astrophysics,

atmospheric physics, plasma physics and

aerodynamics.

Examples of recent and current contributions with large impact range from data on specific single processes which play a determining role in some development problems, such as the control of ion propulsion

engines for NASA, to entire data sets with

which the behavior of a laser plasma or an MHD generator may be programmed and studied

with electronic computers. The maturing

of this kind of computational capability

is of the greatest significance for the

advancement of the technology of plasma

devices. This significance is well recognized by the atomic and molecular research

community which sees it as the vehicle for

meaningful contributions toward solution of

urgent economic and social problems. It is increasingly recognized within ERDA energy

source development programs as an essential

tool for orderly progress in their projects.

It is generally less widely recognized in

the industrial development community.

Certain atomic and molecular properties

are used at the limits of achievable accu- racy as the basis of the accepted standards,

for length, time and frequency. An atomic

standard for mass is foreseen. Precision

measurement techniques developed by workers

in the field of atomic and molecular physics

have been incorporated in the development of

standards for measurements of other quantities, for example, gas pressure and radiant

flux.

It is recommended that the National

Bureau of Standards undertake activities

which involve direct participation and

interaction with the major ERDA projects,

that it use this experience to guide

development of new measurement methodology

in atomic and molecular physics, and that

it undertake to ensure the reliability and

adequacy of the data base needed for these

projects. Furthermore, it is recommended

that the NBS expand its contacts with

private industry, develop increased awareness of the methodology for applying atomic

and molecular data to technological development, and provide such advice and guidance

as will assure the effective utilization of

this sector of the measurement system for

the benefit of the economy.
1. INTRODUCTION

Atoms and molecules are the basic building blocks of matter. Everything that we humans do is conditioned by their properties.

Knowledge of the physical properties of

atoms and molecules is important for such

diverse purposes as understanding the beginnings of the universe and mastering new sources of light and energy.

Generation of data about the physical

properties of atoms and molecules comprises

a modest but extremely important portion of

the National Measurement System. The

resulting data are a significant subset in

the National Standard Reference Data System

for which NBS has prime responsibility.

During the last decade needs have arisen in

a number of applied areas for more precise

and complete atomic and molecular data. For example, precise data on the detailed reactions involving constituents of the earth's

atmosphere are needed to allow adequately

detailed modeling studies of phenomena

occurring at various altitudes. Such

studies in turn are of extreme importance to problems of national interest such as missile detection and the possible destruction

of the shielding ozone layer in the atmosphere. However, the major need for new atomic and molecular data arises from the

sophisticated new devices that are fast

becoming a part of our current technology

and will become even more important in the

future. Gas lasers, plasma devices of all

kinds, and many instruments for chemical

analysis all depend for some of their principal characteristics directly on specific

properties of atoms and molecules; and

therefore on a wel 1 -def i ned body of atomic

and molecular data both for their design and

development and for the detailed interpretation of their use. Industrial devices, such

as industrial lighting systems and magnetohydrodynamic coal-fired electrical generators also require atomic and molecular data

input for efficient design and operation.

Nationally and internationally the mea- surement of the physical properties of atoms

and molecules has been carried out in colleges and universities, in NBS, in federally

funded research and development centers

administered by universities or by other

non-profit corporations, and to a lesser

extent in large industrial research laboratories. An estimated 20-25 million dollars

is expended annually in the United States [13

on the measurement of basic properties of

atoms and molecules, about half of this

amount in colleges and universities. The

NBS program in development of methods of

measurement, data generation, data compilation and evaluation involving atomic and

molecular properties costs about three

million dollars annually (see table 3). The

largest concentration of work at NBS is in

two Divisions of the Institute for Basic

Standards, the Optical Physics Division

(232.00) in Gaithersburg, Maryland and the

Laboratory Astrophysics Division (274.00) of

the Joint Institute for Laboratory Astrophysics in Boulder. Other substantial NBS

programs are supported in the Time and Frequency Division (277.00) in Boulder and the

Physical Chemistry Division (316.00) of the

Institute for Materials Research.

These basic programs have a direct impact

on applied research and development programs

in which federal funds estimated at a third

of a billion dollars are committed annually

(see table 4). These include most notably

several major long-range energy conversion

projects, but also important components of

the space program, environmental projects,

and certain areas of application of physical

sciences such as aeronomy and astronomy.

Earlier attempts to characterize the

national effort in atomic and molecular

physics [1,2, 3D were based primarily on statistical surveys of the academic community covering only the academic effort in

this field, and on data collected from federal agencies regarding their funding of

academic research. The present study of the

national measurement system for the physical

properties of atoms and molecules provides a different perspective from those earlier

surveys. The interface with the user commu- nity is explored more extensively here, and

questions are raised concerning the roles of

the measurement of atomic and molecular

properties as an element of the national

measurement system. In this study important more recent changes in the technological and

economic environment which effect all of

atomic and molecular physics are recognized.

The opportunities for major contributions to society have become more apparent in the

light of current national needs; hence the user community is now more clearly perceived

and appreciated by the atomic and molecular

physics communi ty--and vice versa. The

focus is again on the interface. Finally

this study concentrates on delineating the

functions of NBS atomic and molecular physics programs, especially as they relate to this interfacing role and the uniqueness of

the NBS fulfillment of that role. This

question is appropriately considered within

the framework of the National Measurement

System study.

-2-
2. STRUCTURE OF MEASUREMENT SYSTEM

Since this impact study is concerned

with the measurements needed to characterize a wide variety of properties and

interactions of many different atoms and

molecules and since attempts to critically

evaluate and systematically improve

measurement techniques and the resultant

data for this field are rather recent,

many of the structural elements found in

other portions of the National Measurement

System have not been formally established

here. Formally recognized elements are

the portions of National Standard Reference

Data System (NSRDS) and the associated data

centers which are concerned with the compilation, evaluation and dissemination of

atomic and molecular data. The prime

responsibility for the National Standard

Reference Data System is assigned to NBS.

Other elements of this sector of the mea- surement system, i.e., research laboratories,

mission-oriented government agencies,

developmental laboratories, etc., are less

formally recognized as part of the system

but are key elements because they carry out

measurements, decide priorities, and apply

the data.

2.1 Conceptual System

The term "measurement system" as applied

to atomic and molecular data refers to the

data themsel ves ; to the processes by which the

data are acquired, evaluated, reformulated,

compiled, disseminated and applied; and to the factors that determine the priorities

for the acquisition and use of the data.

It is convenient to divide atomic and molecular data into those data that characterize

the structure of isolated atoms and of

molecules, and those data that describe the

probabilities or rates of interactions of

atoms and molecules with radiation, charged

particles and other atoms or molecules.

The atomic and molecular data characteristic of isolated atoms and molecules

include their energy levels, the data

describing the perturbation of these levels

by uniform electric and magnetic fields and

the data characterizing the behavior of the

atoms and molecules in non-uniform or slowly

varying electric and magnetic fields. The

energy level data are obtained by measurements of the characteristic frequencies at which electromagnetic energy is absorbed or emitted by the atoms or molecules using a wide variety of experimental arrangements or

by theoretical calculations utilizing analytical and computational solutions to the

appropriate quantum mechanical equations.

The atomic and molecular data that

describe the probabilities or rates of

interactions of atoms and molecules with

electromagnetic radiation, with charged

particles or with other atoms include:

a) radiative transition probabilities and

the associated cross sections for the

absorption of photons resulting in excitation or ionization of an atom or molecule,

or photodetachment of an electron from

negative ion; b) cross sections for stimulated emission of radiation (as in a laser);

c) cross sections for the elastic or inelastic scattering of a charged or neutral atom

or molecule by a target atom or molecule;

d) cross sections for the excitation, deexcitation, or ionization of an atom or molecule by electrons; and e) coefficients

describing the simultaneous emission or absorption of a photon and the collision of

two atoms or molecules or of a charged particle and an atom or molecule. In addition

to these data, which describe the interactions under precisely specified conditions,

it is often useful to express the atomic

and molecular data in terms of rate coefficients representing averages of the cross sections over a range of particle collision

energies and directions. These rate coefficients are particularly useful for characterization of the interactions of charged

and neutral particles with atoms and molecules at the high gas densities used in

energy generation and conversion devices,

e.g., high power lasers and magnetohydrodynamic generators.

The atomic and molecular physics commu- nity is concerned with accurate quantitative

characterization of the properties falling

within the above classifications. These

efforts include few strictly routine

experimental and theoretical procedures.

Even in relatively routine spectroscopic

surveys considerable sophistication is

required to avoid invalidation of results by

subtle extraneous effects, and analysis of

results is exceedingly complex. In theoretical work it has long been known that the

simplest, least expensive procedures fail

completely for just those processes which

would be vital in most useful plasma devices.

Highly trained, experienced and resourceful

investigators are required. Since the

field of investigators is not uniform

in this respect, a range of quality and

utility exists in the data found in the

open unevaluated literature.

-3-
The user community is sometimes concerned

with those principal characteristics of specific atoms or molecules which determine

corresponding principal characteristics of some plasma device, such as the atomic transition probabilities that determine laser

gain, or the specific momentum transfer

cross sections that may determine conductivity in a magnetohydrodynami c (MHD) generator. More often the user finds that he

must confront an array of competing processes, so that his model may consist of a system of equations with data input for each

of the several processes. In either case

the specification of accuracy requirements

for data input to such a model must be met

by reliable statements of the accuracy and

applicability of the data available.

The user of atomic data is always faced

with the problem of evaluation. For some processes, only a single measurement or theoretical calculation is available, so that

the main task of evaluation is in determining the probable accuracy of the given

measurement or calculation. However, there

are often several independent and inconsistent determinations of the same set of data

by alternative theoretical and experimental

techniques; and the user is faced with the

problem of selecting the best data in addition to estimating its probable accuracy.

The accuracy with which measurements of cross sections and rate coefficients for

atomic and molecular processes can be made

has improved slowly but steadily during the

past thirty years. For example, as the

result of the improvement in techniques for

absolute radiant energy and gas pressure

measurements and the development of improved

electron guns, optical filters, etc. it is now possible to measure selected cross sec- tions to an accuracy of better than 3%.

Somewhat higher accuracies (<1%) are claimed

for selected rate coefficients. However,

according to studies sponsored by the

National Standard Reference Data System most

of the available cross section and rate

coefficient data are much less accurate than

these values. Furthermore, the effort cur- rently devoted to the systematic measurement

of cross sections and rate coefficients for

a wide range of atoms and molecules is short

of that required to meet the needs of, for

example, the high power laser development

programs for the generation of energy by

laser induced fusion and for laser induced

isotope separation (according to officials

in charge of these programs).

The development of procedures for

insuring accurate measurements of the physical properties of atoms and molecules has

often the form of extremely careful mea- surements (called benchmark measurements) of

a small sample of the properties of a few

atoms and molecules. In a few cases the

results of these measurements have become

the basis for the international standards,

e.g., frequency and wavelength. In some cases professionally evaluated data compilations and critical reviews provide a basis for the individual researcher to select data for use as a standard with which

to compare measurements of a given property

for other species. However, in many cases carefully evaluated (or standard reference)

data are not available. The researcher

thus cannot make comparisons with reference

data and so merely uses the latest published

val ues

The measurements system in atomic and

molecular physics has a unique relationship

to measurement systems described in other

reports of this series. On the one hand,

extremely precise measurements of radiant

fluxes and energies, frequencies and gas

pressures often at the limit of the stateof-the-art, are needed to perform benchmark

measurements. The system thus relies upon

the measurement systems for radiometry and

photometry, vacuum-ultraviolet radiation,

time and frequency and pressure. On the

other hand, precise atomic and molecular

data is often needed, either for

instrumental calibrations or to provide a basic understanding of complicated measurements procedures which form a part of

other measurement systems, in particular

those concerned with laser parameters,

spectrophotometry and surface physical

measurements

2.2 Basic Technical Infrastructure

2.2.1 Documentary System

The documentary aspects of the national

measurement system for atomic and molecular

data include the publication of bibliographies, data compilations, data evaluations,

review papers, etc. by data centers associated with the (U.S.) National Standard Ref- erence Data System (NSRDS); the Oak Ridge

Atomic and Molecular Processes Information

Center; journals devoted to data publication,

data compilations by contractors to the

Department of Defense, bibliographical data

-4-
retrieval systems set up by universities and

private companies (e.g., Lockheed); original

research and review articles published in U.S. and foreign professional journals; and

books printed by private publishers. Only

the NSRDS and associated Data Center publications have an official role in the mea- surement system.

National Standard Reference Data System

publications in the area of atomic and

molecular data make ud over half of the

forty-seven NSRDS publications. See NSRDS

publications list 7.4". Journals publishing

atomic and molecular data are the Journal of

Physical and Chemical Reference Data (NSRDS)

and Atomic and Nuclear Data Tables . Recent

data compilations issued by DoD contractors

include the Defense Nuclear Agency's Reaction Rate Handbook 151 and the Air Force

sponsored Spectroscopic Constants for

Selected Keteronucl ear Diatomic Molecules

16 _. One of the most readily available

computer-based retrieval system for bibliographical data is the Lockheed Aircraft

Corporation System.

Because of the limited fraction of the

atomic and molecular species covered by

compilations and reviews sponsored by NSRDS

and associated data centers, the normal

scientific literature forms a very important

source of information on measurement techniques and data. The development engineer

or scientist from another field is often

unable to evaluate the relative merits of

the published experimental techniques or

data. Choices are often made on the basis

of the scientific reputations of the institute at which the work was carried out. Among such institutions NBS is particularly

noted for its precision measurements and for

its collaboration with user groups.

Formal documentary standards, such as treaties and voluntary engineering standards,

play only a minor direct role in this field,

and vice versa. However, many of the documents described above, especially those o*

the National Standard Reference Data System,

often function informally as such standards.

2.2.2 Instrumentation System

2.2.2.1 Measurement Tools and Techniques

The scientific and technological base for

modern measurements in atomic and molecular

physics includes a very broad range of

sophisticated new techniques:

1) High vacuum technology and molecular

beam techniques are basic to performing

measurements on individual atoms and

molecules including reactive species,

effectively free of interactions with

near neighbors and under controlled

conditions of ambient fields, and/or

incident flux of photons or other particles.

Systems of advanced design can be built to reduce background populations to as low as

"-10 6 atoms and molecules per cubic centimeter and to extend mean free-flight

times to hours.

2) Particle mass and particle energy

selectors based on a variety of physical

principles are available to define the

species content of beams as well as to define beam kinetic energy.

3) Monochromatic sources of electromagnetic radiation, notably those of the laser

family, are revolutionizing modern spectroscopy. Tunable lasers in particular have

greatly facilitated measurements of structure of molecules and are opening the way to investigation of interaction properties of

short-lived excited states.

4) New detectors, based on photoelectric

and photoconducti ve properties of solids

recently discovered by solid state physicists, allow extremely sensitive measurements of photons, electrons and other

particles. In many circumstances these are individually detected, counted and processed

using

5) sophisticated digital electronic

systems and compact laboratory minicomputers, which make it practical to handle

large quantities of data automatically.

The accuracies required in measurements

of atomic and molecular properties typically

strain the measurement system in two areas:

1) Gas densities are exceedingly difficult to measure to accuracies of a few percent as sometimes required, especially for

gases that are reactive to any degree, as in

the low pressure regimes typical of atomic

and molecular properties measurements. The

most reliable measurements are accomplished

at high pressures; and pressure divider

techniques can be used to generate known

density low pressure samples of non-reactive

gases such as helium.

2) Radiant flux is difficult to measure

in a laboratory situation, even using standard lamps supplied by NBS. In addition,

interaction geometry is often a limiting

factor.

-5-
Other quantities are measurable with

quite sufficient accuracy using commercially

calibrated instruments ultimately referred

to the national standards. Wherever

possible in the case of particle fluxes and

photon fluxes, intensity measurements are reduced to counting procedures using single

particle detectors and digital electronics,

techniques borrowed from nuclear physics.

The concept of benoh.ma.rk measurements has

been applied by NBS as a technique for providing a convenient method of calibration

and/or measurement assurance for several

types of measurements. A well -defined

property, such as the probability for electrons exciting principal radiations of the

helium atom, may be measured with extraordinary care at NBS, utilizing the shortest

possible chain to the primary standards.

This carefully measured property may then be

used to calibrate, in a relatively simple

procedure, measurements of the corresponding

properties of other atoms and molecules.

2.2.2.2 The Instrumentation Industry

Commercial optical spectroscopic and mass spectrographic instrumentation grew up in close

association with atomic and molecular physics

and has become amultimillion dollar industry.

Atomic clocks are widely used in satellite

tracking and timing, in connection with elaborate navigation systems, and in the television industry. Magnetometers based on properties of alkali vapors have been standard

instrumentation in satellite and rocket mea- surements of magnetic fields in space. The

continuous-wave gas laser is currently the

basis for development of a multimillion dollar commercial laser metrology industry involving length measurement and control as well as holographic instrumentation. Some of

these developments are treated in more detailin other measurement study reports.

The field of atomic and mol ecular physics

is relatively small , specialized and varied,

so that no distinctly identifiable measurement instrumentation industry exists to support it: A wide variety of commercial instrumentation and technology common to larger

fields such as nuclear and sol id state physics

and space science, provide a base for this

field. However, advanced work typically re- quires unique instrumentation, designed and

built in-house.

2.2.3 Reference Data

Only a small subset of the available data

on atomic and molecular properties has been

critically evaluated either by NBS or by

other leading authorities in particular

subfields. This subset constitutes the

reference data of this sector of the

national measurement system. The atomic

energy levels tables (NBS Circular 467) are

an example of these types of data. It should be noted that the NSRDS-sponsored

critical reviews and data evaluation publications exert an influence far beyond their

immediate area of concern through the

setting of criteria for reporting experimental conditions, of estimating errors, of

critical evaluation and of making impartial

choices among available data and experimental techniques.

Specific examples of measurements at NBS

of data suitable for reference data are the

wavelenqths of selected atomic transitions

used as standards in applied spectroscopy;

the proposed international standards of

wavelength utilizing lasers stabilized to spectral lines in the infrared and visible;

the frequencies of various infrared molecular transitions being used in connection

with the development of optical frequency

standards; and cross sections for the

electron excitation of selected spectral

lines of helium. Examples of such measurements elsewhere are the very precise mea- surements of electron drift velocity and

diffusion coefficients for selected qases

made at the Australian National University

and measurements of atomic hyperfine structure at various universities. One should

note that there is a major requirement for

additional reference data regarding rates

of interactions with atoms or molecules.

Chemical rate data are not included in

this study.

The users of the reference data developed

by the measurement system include scientists

and engineers in industry- and governmentsupported R and D concerned with lasers

[7-91, high efficiency illumination [103,

electrical power generation and distribution

[11,12], missile reentry [13], radio

propagation [5], and chemistry [15].

The current methods of data acquisition

for the properties of atoms and molecules

generally involve design, construction and

testing of specialized apparatus by individual scientists followed by computer

controlled recording and computer analysis

of data. The development of measurement

techniques capable of yielding referencedata-quality results is particularly time

consuming and is seldom undertaken outside

laboratories such as NBS where there is an inherent appreciation of the desirability

of extension of precision measurements.

-6-
One pattern of data use is for scientists

and engineers engaged in invention and

development to make computer models of their

devices and systems using the most recently

published data where available and educated

guesses elsewhere. These models are used to understand the current devices and to predict the behavior of larger devices. Reference data on a particular species are also

used to test similar measurements on other

atoms and molecules

2.2.4 Reference Materials

There are no examples of formally defineStandard Reference Materials in this field.

See, however, discussions of benchmark

measurements elsewhere in this document.

Such benchmark data in combination with

commonly available high-purity materials

and well-defined experimental conditions

fulfill a role comparable to the role of

Standard Reference Materials. They are

useful for the calibration of measurement

systems in this and other fields. Examples

are the intensity of radiation emitted from

hydrogen atoms in a prescribed hydrogen arc,

the frequency reference achieved by stabilizing lasers to certain infrared absorption

lines of methane under prescribed conditions, and the radiation flux excited per

incident electron in certain spectral lines

of pure hel i urn.

2.2.5 Science and People

Fields of science and technology supporting the national measurement system for

the properties of atoms and molecules

include computer science, laser technology,

physical chemistry, surface science, high

temperature technology, vacuum technology,

electronic component and equipment technology. These fields support the measurement

system by helping to make possible improved

measurements over a wider range of experimental variables; improved analyses, storage

and retrieval of data; more accurate calculations of individual atomic and molecular

properties; and more realistic modeling of

applications of the data.

Contributions of the national measurement

system to science include new techniques for

making and analyzing measurements, better

understanding of correlation between experiment and theory, better cal culational techniques for theory, and better ways of

integrating individual measurements into

model s

Professional societies relevant to this

measurement system are the usual ones for

physicists and physical chemists, i.e.,

American Physical Society, American Chemical

Society, Optical Society of America, plus

groups such as the Division of Electron and

Atomic Physics of the American Physical

Society, the International Conference on the Physics of Electronic and Atomic Collisions, and the Gaseous Electronics Conference.Knowledge is disseminated by standard

publications, e.g., Physical Review , Reviews

of Modern Physics , Journal of Chemical

Physi cs , and Reviews of Scientific Instruments . Data are also disseminated through

preparation of articles for data journals,

e.g., Atomic and Nuclear Data Tables and

Journal of Physical and Chemical Reference

Data , and for handbooks, such as the Defense

Nuclear Agency's Reaction Rate Handbook . The educational institutions and procedures for the scientists participating in

this measurement system are those typical

of physicists and chemical physicists.

Relatively few people who are trained in

other fields participate in this system.

Important exceptions are the engineers who

utilize much of the data generated by the

system.

2.3 Realized Measurement Capabilities

Measurement range, accuracy and precision

vary widely with effort devoted to and

difficulty of measurement. Thus, for lifetime measurements of visible lines to determine oscillator strengths (a benchmark mea- surement) the highest attainable accuracy

is ^±1%, while the current accuracy of

measurement of the wavelength of the methane

stabilized laser is about one part in 10 lu when averaged over thirty seconds. Table 1 contains approximate values for the highest

accuracy yet attained, representative

applications for a few of the physical

properties of atoms and molecules. This

list of properties is only a small fraction

of the list of importance to technology and

science, e.g., ten categories compared to the over fifty categories in a recent report

[16] to NSF on energy-related atomic and

molecular physics. Similarly, only a fraction of the available experimental techniques and of the present and potential

applications are cited. Note that in every

case cited the accuracy required for applications equals or exceeds the accuracy generally available. Also, it should be noted

that in cases in which very high accuracy has

been achieved, technological advances have

rapidly made use of the accuracy.

-7-
QJ O "

r c

QJ TO U

u a. o

3 OJ i— a.-- cOJ TO fV. 4J E

c u

oj c :

cl E 4-> o to at

4-> -a -o

TO VI TO VI 3

qj C C VI XI — — —

in ft) m w VI <— -C "O V)

•i- 0) o o c

> T5 E E C O OI

i- E TO TO TO

CD E E —

5 i. l/l t/l "D

QJ CT> QJ OJ VI 3

E TO EC TO — *J Cv— C QJ •— •— C

O -O O -i- QJE

Qj -~- '— 1- O- I- QJ TO > - -COO QJ 4-> 1. 2 TO QJ V) QJ QJ 3 — S C QJ OU "O TO "C X l/l O QJ Q.

s- o- i- vi

*— o-> *— TO 3 Bl

QJ •!- C X — to rc

i— r— t— t— r— CVJ

<— VI i— CT> O O S- QJ o o o in o oo »— m cm m

cr —

r- i— ir>

»-S *S S-5 SSO W O LO O r— r- LT5

CSJ I—

— O) c >— u

01 OI c OI V. c QJ T3 o U QJ c TO 1. QJ o CL V Vi O

E s- o TO TO TO 3

D. O S- XI (_> cn cn —

S- QJ cn C VI 3 t*- o 4-> VI C (- >> OJ o o <_> VI U TO •i- QJ u c f- J- £ vt V) *0 X) QJ i— S- 4-> 4J c >, 4-1 4-> TO E QJ OJ QJ TO O. OJ TO QJ o> a. 3 U TO (-) TO O u

VI "C3 4-J i- E 3 o r— QJ QJ 01 QJ QJ 3 c c

QJ QJ QJ Cn O cr i_> 01 O C X XI X X "O o QJ 4-> > -D M E i- OJ Vi > Vi VI TO 3 C 01 u

TO QJ O — 4J s- O TO QJ "C a f_) C«T Vi 4J

1- f— S- TO U M— s i_ c QJ 01 QJ >> o. 01 o TO 4-J 4-J QJ O 4-> o TO Vi m Li VI 4-1 U im s- i_ VI

&_ 1. X> u v c. •i- u 1- X E VI t/i 0J VI U— 0J QJ O o O c

U V- TO OJ VI o OJ u cn oj o O O -t- VI 01 VI 3 TO C 4-1 Q. S- TO £X QJ i_ u 3 i» i- TO X XI L. '1 •*- VI vi u i- Vi E x: i-j u u e l_> "0 — TO 4-J

c — —

p— 1- .o O — =

C C O 4-> *-»

4-J t/l ITS (/)

<T1 C 5w C

4-) f0 -O U

E Tl CJ <U o a. i— =

r— CM n

U E ns QJ rc QJ

a. c >— — <— t. p- 4-> -C 13

4-> (JO

-8-
2.4 Dissemination and Enforcement Network

Since the national measurement system for

the physical properties of atoms and molecules involves rapidly changing measurement

techniques, a very large number of properties and species, and a user community with

changing interests and accuracy requirements, it is very important that evaluated

data be rapidly and widely disseminated.

However, there is no mechanism for the

enforcement of the use of recommended

measurement techniques for obtaining atomic

and molecular properties or for the use of

recommended data. Peer evaluation and the

need for more accurate data for specific

applications are the main forces that promote the use of better available techniques

and data.

Regulatory agencies, e.g., the Environmental Protection Agency, are ultimate users

of the output of the atomic and molecular

properties measurement system through their

recommendation and enforcement of the use of

techniques developed to measure the concentrations of, for example, pollutants. These

agencies also participate in the measurement

system through their encouragement and

occasional support of the development of

new measurement techniques.

The dissemination of the measurement

techniques and properties of atoms and

molecules has been discussed in Section

2.2.1

2.5 Direct Measurements Transactions

Matrix

2.5.1 Analysis of Supplier and User

Interactions

The following "Direct Measurements

Transactions" matrix, Table 2, is intended

to show the principal interactions among and

within the organizations associated with the

national measurement system for the physical

properties of atoms and molecules. The flow

of data, measurement techniques, etc. is from the organization given in the left hand

entry to the organization with the number

given at the top of the column. Entries on the diagonal describe the flow within an organization. The code used within an entry is given at the bottom of the matrix

table.

2.5.2 Identification of Major Users and

User Needs

A very important aspect of the measure- ment system for the physical properties of

atoms and molecules is the identification

of the classes of users and the needs of

these users for data and measurement techniques so as to enable an allocation of resources and to provide justifications

for the measurement system. An example

of an initial attempt to identify the user

needs for those concerned with electrical

power generation, transmission and

utilization is given in Appendix C. A more detailed discussion of the needs of research

on the magnetic confinement approach to controlled thermonuclear reactions is given

in a report entitled "Atomic, Molecular and

Nuclear Data Needs for CTR" [17] preoared

for the Atomic Energy Commission. Of particular value at the present time would be

an assessment of the current and future

needs for measurements of the physical

properties of atoms and molecules by the

laser development programs of the Enerqy

Research and Development Administration

(ERDA) and of the Department of Defense.

While currently foreseen needs of technology should play an important role in the

allocation of resources for measurements of

atomic and molecular properties, it is

essential that a significant fraction of the resources be devoted to the measurement of new properties and to the development of new measurement techniques. There are numerous recent examples in which the development of

improved techniques for the measurement of

properties of atoms and molecules has led

to the proposal of a potentially important

new laser mechanism. One example is the

improved measurement of metal vapor-rare

gas interactions in connection with excitation transfer measurements at NBS/JILA which

led to the proposal of excimer lasers utilizing the radiation emitted by molecules

formed from metal atoms and rare gas atoms

[18,19]. A second example is the study of

"inner shell" ionization and X-ray production which led to the proposal for the use of these processes for X-ray lasers [20].

-9-
Table 2

Direct measurements transactions matrix for physical properties

of atoms and molecules

SUPPLIERS

U

s

ER

S

1 2 3 4 5 6 7 8 9

1 Knowledge

Community & Publ ications

4 2 4

4

4 2 4

4

2 0

3

2

4 0 4

2

4 3

3 2

2 3 4

4

3 3 4

0

2 3 4

2

2 3

3 0

2 Data Processing

Organizations: NSRD,

Data Centers, etc.

3 0

3

2

X 0

2 0

3 2

3 0

4

2

3 0

4

2

3 0

3

2

3 0

4

2

3 0

3

2

3 0

3

2

3 Instrumentation

Industry

2 0

4

2

2 0

1 0?

2 0

3 2

2 2

3

2

3 2

3 2

3 2

3 0

3 0 3

2

2 3

2

2 4 NBS 3 0

4

2

3 0

4

3

2 1 2 2

3 0 0

4

2 0

4 2

3 0

4

3

3 0

4

2

3 0

4

2

3 0

3

2

5 Energy Res. and Dev. Admin.

Maq. C.T.R.

3 3 2

2

4 2 3

3

7 4 2

3

2

X X X

2 1 2 2

2 3 2

2

6 ERDA: Laser Fusion & Laser Isotope2 0

3

2

2 0

3

2

2 1 3 22 1 4

2

X X

2 2

3

3

4 2 3 4

2 2

3

2 7 Dept. of

Defense

2 3 2 0

2 3 2

0

2 3 3 0

2 3

3 0

X

2 2 3

2

2 2 0

2

2 2

3 0

1 2 2

0 8 Industry:

Lasers

2 3

2 0

2 3

2 0

2 1 3 0

2 1 3

2

2 0

2 4

3 2 4

2

3 2 4

0

2 0

0 0

1 0

1 0

9 Industry

Electrical Power

Gen. , Trans. & Use

2 3

2 0

2 3 2 0

2 1 3

0 J

2 0

2

2

3 0

4

2

2 1 2

2

2 0

2 0

2 2

3 2

2 0

0

2

KEY TO MATRIX ENTRIES

C - IMPORTANCE OF TRANSACTIONS

1 = Purely convenience

2 = Strongly desirable

3 = No real alternatives

4 = Essential

B - RATE OF CHANGE

N = Declining

0 = Stable

2 = Growing

4 = Growing explosively

R = Flow of requi rements infr/" dominates

? = Unknown,

D - ( INADEQUACY OF SERVICES

0 = No improvements needed

1 = Could be improved

2 = Marginal

3 = Serious deficiencies

4 = Out of control

- MAGNITUDE OF TRANSACTIONS

0 = Trivial

1 = Minor

2 = Moderate

3 = Important

4 = Major

Not studied, Blank = 0

-10-
3. IMPACT, STATUS AND TRENDS

OF MEASUREMENT SYSTEM

3.1 Impact of Measurements

3.1.1 Functional, Technological and

Scientific Applications

New methods of making and analyzing

measurements of atomic and molecular

properties and measurements of critical

data are used to obtain data and understanding needed in the initial design,

diagnostics, optimization and extrapolation

of plasma devices. Atomic and molecular

data are used in plasma models of varying

degrees of complexity. In many cases the

number of interactions which one can con- sider is limited by the size of available

computers

Technologies effected are lasers; electrical power generation and switching;

commercial, highway and home illumination;

isotope separation; information displays;

thin film production; radio frequency,

satellite and radar transmission; radiation

detection; chemical processing; arc welding

and metal processing; pollution monitoring;

air cleaning; pyrotechnic flares; etc. Scientific fields effected include

molecular kinetics and structure, non-linear

radiative processes, collision theory and

experiment, radiation and charged particle

transport, studies of spectral line shapes,

gaseous electronics, astrophysics, aeronomy,

and aerodynamics.

3.1.2 Economic Impacts—Costs and Benefits

The cost of all measurements in atomic

and molecular physics carried out in the

United States is estimated to be $20-25

million per year, based in 1968 data

(approximately S15 million per year) for

federal support of universities III adjusted

for inflation, and a rough estimate as to other federal and non-federal ly supported

programs

The economic benefits of measurements of

atomic and molecular properties cannot be

precisely estimated, but one example can be

given. Economic data available for one type

of gas discharge lamp—the high pressure arc

lamps for commercial and highway illumination—show annual sales of $60 million per

year and a growth rate of --20 :

; per year

[10~J. The primary effect of an increase in

efficiency or reduction of size of these

lamps through the use of atomic and molecular data would be a reduction of sales of

other types of lamps. Thus, the major

impact would be energy conservation . Estimates of the portion of electrical

energy used for all illumination purposes

range from 8% to 20% DO].

A recent estimate [_211 gives a 1975

budget of $55.5 million for laser research

and development. Most of the effort will

be directed toward laser fusion and isotope

separation for use in the generation of

energy.

3.1.3 Social, Human, Person-on-the-Street

Impact

Although this portion of the measurement

system has no immediate direct effect on everyday lives, its indirect effects are of great

potential importance. For example, it

provides the basis for future improvements

in energy generation, distribution and

utilization; improvements in reliability

and ease of communications; more effective

defense systems; more reliable fire detection, explosion prevention, and lightning

protection; and more effective monitoring

and alleviation of pollution. Social

benefits of applications measurements of

atomic and molecular properties ultimately

will be determined in economic terms.

Alternative benefits, such as energy con- servation will be decided on an economic

basi s

3.2 Status and Trends of the System

In selected areas of atomic and molecular

physics NBS has very successful projects

devoted to improving measurement and calculation techniques, collecting and evaluating

critical data and improving techniques for

data utilization. Areas that are well cov- ered include electron-ion (positive and

negative) collisions and excitation of

neutral species by electron impact, radiative transport, atomic and molecular

spectroscopy at all energies, and atomic

transition probabilities. Some other areas, e.g., ion-molecule reactions and atom-molecule energy transfer measurements, are covered reasonably well by other laboratories (NOAA, U. of Pittsburgh, Stanford

Research Institute). On the basis of

requests for data ^Appendix BI on the

physical properties of atoms and molecules

in systems of current technological interest, it appears that some very important

areas to current technology, e.g., electron

transport coefficients, are being ignored

by the U.S. research community.

-11-
A factor which limits the effort devoted

to the measurement of the physical properties of atoms and molecules by the major

development laboratories —Energy Research

and Development Administration, Department

of Defense and industry—is that in most

cases these laboratories [22] are being

forced by current techni cal goals and market

pressures to adopt very short-range time

scales for their research programs. Most

universities do not have the continuity of

support or the incentive required for the

development of new techniques needed to obtain the large amounts of accurate data

on physical properties of atoms and molecules. Barring major changes in research

management it will be up to laboratories

such as NBS to provide the environment and

support which will allow the long term,

e.g., three years, investment in new mea- surement and theoretical techniques for

data generation and, as well, the longterm investment in new data utilization

techniques

Examples of new and rapidly growing

technologies that demand a broad range of

data obtainable only by long-range research

efforts are those which depend on the development of new classes of high power lasers

for isotope separation and possibly for

laser fusion, and also those directed to the development of controlled thermoncul ear power using plasma confinement techniques.

Without improved data "sets as the basis for more effective modeling and for more effective analytical and diagnostic measurements,

development of these technologies will be

handicapped [21].

4. SURVEY OF NBS SERVICES

4.1 Historical Background

NBS has been active in the measurement

of the physical properties of atoms and

molecules since the early 1920's. NBS work

in this area has always consisted of three

complementary steps, generally performed

within the same laboratory as follows:

1. Development of new measurement techniques . 2. Data generation using these techniques

and development of analysis techniques to interpret data thus obtained.

3. Compilation and critical review of

all available data either within a particular category of atomic and molecular data

or applicable to a particular perceived

need

The way in which these three aspects of

atomic and molecular measurements have been

pursued at NBS is aptly illustrated by the

work in atomic spectroscopy, a field in

which NBS has played a leading role over

much of its history. Early work by Foote

and Mohler was concerned mainly with development of techniques for measuring spectral

wavelengths. Their work was continued and

extended during the period of the 1 930 1 s

40 's by Meggers and his associates and an attempt was made to provide as much information as possible on spectral line positions and the inferred energy levels. The

motivation for these measurements was the

need for these data in chemical analysis

and for the analysis of astrophysi cal data.

The compilation and systematic analysis of

data of this type have been ongoing projects

ever since, and NBS continues to maintain a current listing of all data in this welldefined area as a part of the National

Standard Reference Data System. In this

particular field a large part of the data

available have been measured or analyzed

by NBS staff workers either working in their

own laboratories or in close collaboration

with other workers in universities or other

government laboratories.

The early work in spectroscopy at NBS

showed a remarkable amount of foresight

concerning atomic data and measurement

calibration techniques that would be needed

in the rapid expansion of technology that

occurred in the period following the second

world war. One of the crowning achievements

of this work was the publication in 1949-52

of NBS Circular 467, a tabulation of most

of the known atomic energy levels grouped

by atom and charge state available at that

time. This three-volume set compiled by

Charlotte Moore-Si tterly using the extensive

files of bibliographic and numerical data

accumulated at NBS during the previous

decades continues to serve as the prime

reference source of atomic spectral data

and as a model for further tabulations of

this type.

The close relationship of work in atomic

physics and basic standards of measurement

is illustrated by the work on precise wavelength standards. In 1950 an electrodeless

mercury vapor using Hg 198 which had been

obtained in pure form via transmutation of

gold in a reactor was announced by Meggers

and Westfall. This development and subsequent work on precise wavelength sources at NBS played an important role in the eventual

adoption in 1960 of the krypton lamp which

is the current international standard of

length.

-12-
In addition to playing a leading role in

the measurement of well -establ ished physical

properties of atoms and molecules, NBS has

pioneered in the development and application

of measurement techniques for properties

previously unmeasured or poorly measured.

For example, measurements by F. L. Mohler

and associates of the absorption and emission of radiation by cesium vapor plasmas

in the early 1 930 ' s provided the basis for

testing newly developed theories of the

emission of light by gases and, when chemically resistive ceramics became available

after World War II, for the development of

highly efficient metal vapor lamps. The

work of Branscomb, et aj_. provided much of

the data and methods of analysis of the

interaction of photons and negatively

charged particles in the ionosphere. The

work of Broida, et_ a_l_. provided the field

of chemical physics with many of the mea- surement techniques now being used to study

the ionospheric ozone problem and laser

induced chemistry.

During the period from 1950 to 1962 the

overall efforts in atomic and molecular

physics were greatly expanded, chiefly in

response to needs for atomic and molecular

data from other government agencies (AEC,

DoD and, after 1959, NASA). The efforts in

atomic spectroscopy were extended to molecules by the formation of groups whose

prime concern was the infrared and microwave spectroscopy of molecular systems.

New programs in electron and far ultraviolet

physics were added. In addition, NBS moved

actively into the area of measuring rates

for atomic processes, i.e., transition probabilities between atomic states and cross sections for photon induced processes.

The formation in 1962 of the Joint In- stitute for Laboratory Astrophysics (JILA),a

cooperative effort between NBS and the University of Colorado, resulted in a further

strengthening of NBS research in the area of the measurement of the physical properties of atoms and molecules. Since its

formation JILA has become one of the leading

laboratories for the measurement and calculation of atomic and molecular properties.

Particularly significant activities of the

past five years are the measurements of the

properties of negative ions; development of

the methane stabilized laser and its application to the precision measurement of wavelength; the measurement of electron excitation and recombination cross sections for

neutral and ionized atoms and molecules;

the measurement and interpretation of radiation emitted by metal vapor-rare gas molecules; the measurement of the distribution

in energy of the products of electroninduced ionization of atoms and molecules;

and the reviews, evaluations and compilations of the collision properties of atoms

and molecules.

A theoretical program directed toward

calculating atomic and molecular properties

which cannot easily be measured or which

provide a basis for understanding and

evaluating measurements has developed. The

theoretical program also provides accurate

and efficient means for calculating the

energy transport, degree of. ionization, etc.

in ionized gas systems. Recently, close

ties have been established with scientists

and engineers engaged in the development of

devices utilizing the measurement techniques

and data of this measurement system. This

activity has resulted in a considerable

increase in the JILA/NBS effort directed

toward data utilization through the modeling

of ionized gas devices and systems.

At NBS/Gai thersburg more recent program

evolution includes the application of

highly refined design techniques to the

development of apparatus for measurement of

electron collision cross sections and to the composition analysis of gas samples;

the measurement of absolute spectral emissivity of plasmas and of spectral line

shapes under plasma conditions for use as a radiation standard and as a plasma diagnostic; measurements of atomic transition

probabilities; compilation and evaluation

of atomic transition probabilities and

compilation of references on spectral line

shapes; the critical calculations of atomic

transition probabilities; theoretical predictions and understanding of atomic structure, radiative absorption and collisions;

applications of laser techniques to the

measurement of frequencies of molecular

transitions and to the enhancement of

molecular interactions; the accurate mea- surement of the frequency of stabilized

visible lasers; and the experimental and

theoretical identification of interstellar

and laser emission lines.

Other NBS programs concerned with the

physical properties of atoms and molecules

include the identification of and measurement of frequencies of molecular transitions; the development of heat pipe technology for spectroscopic studies of high

temperature material such as metal vapors;

the measurement of molecular energy relaxation rates; the prediction of molecular

interactions and energy levels; and the

development of accurate theories of

spectral line shapes in plasmas.

-13-
The period since 1970 has resulted in a major shift in motivation for the measurement of the physical properties of atoms

and molecules at NBS. Whereas during the

1 960 1 s atmospheric and astrophysi cal problems provided a focal point for major

efforts, the major need for atomic and

molecular data at present is in the detailed

interpretation and prediction of the operation of devices or industrial processes

involving interactions among radiation,

electrons, atoms and molecules. Examples

are gas lasers of all types, gas discharge

lamps, magnetohydrodynamic generators and

controlled thermonuclear fusion devices.

Through its numerous contacts with user groups in qovernment and industry NBS has

responded rapidly and effectively to these

changing needs.

4.2 The Present—Scope of NBS Services

4.2.1 Description of NBS Services

The major NBS organizational units participating in the measurement system for

the physical properties of atoms and molecules are Divisions 232 (Gai thersburg) and

274 (part of J I LA in Boulder). Approximately three-eighths of the Division 232

program and half of the Division 274 program

fall in the sector of the measurement system

included in the present study. The detailed

division of this effort among projects is

given in Table 3. As indicated above, other

divisions of NBS contain projects which

could properly be classified as part of the

measurement system for atomic and molecular

properties but which have somewhat closer

ties to other parts of the national measure- ment system. A detailed description of the

rationale for the choice of projects

included is given in Section 4.2.4.

The scope of NBS services extends to all

phases of the national measurement system

for the physical properties of atoms and

molecules as defined in Section 2.1. Thus,

in addition to performing measurements and

disseminating resulting data , NBS services include development of measurement methods of instruments for precise atomic and molecular mea- surements and of techniques for the analysis

and orderly classification of atomic and

molecular data. Detailed computational methods are also developed for use in the ana- lysis and classification of data and for

theoretical prediction of data that are not

accessible to measurement. Other services

provided are: preparation of critical

reviews; consulting services as to sources

of data, recommended data and the utilization of data; interpretation of user needs;

participation on review committees of various

government agencies to assess data needs;

and recommendations to funding agencies as to data needed and the best people and places

for getting work done. The NBS position of

neutrality in these matters is crucial to the review and advisory services.

The technical base for these services

includes the following components:

The atomic spectroscopy laboratory in

Gaithersburg is well equipped with spectrographs covering the range 40-12,000 A and

data reduction procedures have been evolved

utilizing present NBS computational facilities. An important part of the data analysis capability consists of a large set of

theoretical computational programs which

are used either to predict energy levels

from theoretical parameters or alternatively

to systematize available data by obtaining

empirical parameters from measured spectra.

The technical base in molecular spectroscopy is similar to that in atomic spectroscopy. A number of high resolution instruments are used to obtain raw data in the

microwave, infrared, visible, and ultraviolet spectral regions. Computerized data

reduction is used here to systematize the

data via the calculation of molecular con- stants which may in turn be compared with

theoretical predictions.

Instrumentation for photoabsorption

measurements of metallic vapors and gases

is largely built about the NBS SURF-II

facility, the principal source of high

intensity ultraviolet radiation. This

facility is complemented by several lower

intensity laboratory sources. Several high

resolution spectrometers, designed and con- structed at NBS, are available. Absorption

cells are provided by a number of heat pipe

absorption furnaces which have been specifically designed and constructed at NBS for

far ultraviolet absorption measurements.

Design and testing of newer devices of

this type is an ongoing effort.

Electron scattering and excitation cross sections are measured with high resolution

electron spectrometers designed and con- structed at NBS. These devices, which are continuously being modified and improved

to meet the needs for new data, are operated

under the control of a small computer and

utilize computer techniques to identify and

separate the contributions of up to four

gas components.

-14-
Table 3. NBS projects in measurement system for physical properties

of atoms and molecules

Sponsor

Nati onal Nati ona

Other

Project # Bureau of Standard

Standards Reference Agency

Data System

274012 1/2 of Visiting Scientists Program 140

2740141 Energy Deposition in Gases 202

2740158 Radiation and Energy Balance in

Gas Discharge Lasers 93 20

2740180 Atomic Physics Cross Sections

Information Center 149

2740190 Transfer of Radiation Through

Gaseous Media bU

0 7 A no C A Low Temperature Plasma Collision

Parameters 1 U J 00

2740540 CTR and High Temperature Plasma

Collision Parameters 73 a n 4U

fa / 1 1 LO

'71 3/1 \\o7o) 1 1 1°/ \

{ 1 J/oJ 2320165 Electronic Spectra 62

2320125 Laser Applications to Air

Qual ity Analysi

50

2320170 Transition Probabilities 327

2320171 Transition Probabilities

Data Center 50

2320474 Data Center on Atomic Lines,

Shapes and Shifts 5 2320477 Transition Rates 175

2320102 Consultants on Theory 64

2320110 Rare Earth Atomic Spectra 151 2320111 p & d Shell Atomic Spectra 143

2320112 CTR Atomic Data 127 60

2320115 Atomic Energy Levels Data Center 70 40

2320120 Infrared Research 100

2320121 Microwave Spectroscopy 171 2320133 Infrared Reference Standards 53

2320124 Application of IR Measurements

to Air Pollution 65

2320126 Laser Chemical Physics 34

2320128 Molecular Electronic Spectroscopy 29

2320129 Microwave Spectral Tables 42

2320229 Diatomic Spectra Data 20

2320426 Metal Oxide Molecular Spectroscopy 7 2320134 Ref ractometry 23

2320139 Refractive Index Evaluation and

Compilation 5 2320151 Electron Scattering in Gases 95

2320155 Electron Spectroscopy for

Gas Analysis 24

1500 182 310" (75%) (9%) (16%)

GRAND TOTALS - 2937 2171 331 435

Exclude NSRDS (74%) 01%) (15%)

(83%) (17%)

-15-
Unique measurement methods and instruments have recently been developed at J I LA and applied to the determination of a number

of accurate cross sections: for electron

collisional excitation of radiating states

of atomic ions including highly excited

metal vapor atoms, degenerate states of

neutral atoms, and metastabl e -or slowly

radiating states of molecules; for

distributions in angle and energy of

positive and negative ions produced by

electron induced dissociative ionization

and attachment; and for photodetachment

thresholds and cross sections for a wide

range of atomic and molecular and molecular

negative ions. Other measurement techniques

have been developed for the determination of

molecular potential curves for ground and

lower excited states of alkali atom-rare

gas atom molecules.

Techniques have been developed for the

calculation of cross sections and rate

coefficients for the electron and photon

excitation and ionization of light atoms

and of ions; of the spectral distribution

and intensity of radiation emitted by

plasmas; of the electron scattering and

electron induced radiation ( bremstrahl ung)

emitted by a wide range of atoms; of the

electron transport coefficients in a wide

range of weakly ionized gas mixtures; and

of the growth of current, temperature, etc.

in a pulsed electrical discharge.

A primary function of the atomic and

molecular research groups in NBS is to exploit the technical base described above

to generate reference data in specific

areas. These data may be obtained by

experimental measurements or via theoretical

computations. The primary modes of dissemination are via the NSRDS Data Centers or

via publication in scientific journals,

e.g., the Journals of the American

Physical Society and American Chemical

Society, the NBS Journal of Research,

Atomic and Molecular Data and the Journal

of Physical and Chemical Reference Data. Data often are distributed rapidly as NBS

internal reports or are communicated via

private communication to users by NBS scientists. Because of the close interactions of

NSRDS Data Center personnel with those

engaged in the measurement of atomic and

molecular properties the data become available to the scientific and engineering

community by becoming part of the data

collections maintained by the various data

centers supported by NSRDS in the two divisions.

The inputs received by the NBS atomic

and molecular data groups are primarily

requests for data from industry and other

government agencies, but also include

judgments of the principal NBS scientists

as to what is needed to solve development

problems. The other factors in determining

the directions of programs are the state-ofthe-art, opportunities for increasing

physical understanding and for comparison

of theory and experiment; and the scientist's

perception of NBS goals as reflected in the

availability of NBS and other agency funds.

Outputs other than atomic and molecular data

(i.e., measurement techniques, methods of

data analysis, instrumentation, etc.) are generally disseminated as publications in

scientific journals, either as parts of

papers describing specific measurements or

as papers devoted solely to descriptions of

particular instruments or techniques. Critical reviews of given subfields, which

describe the state-of-the-art of measurement

in a particular area and assess the accuracy

of the available data base are often produced

by senior NBS staff workers or by visiting

scientists at J I LA , under NSRDS sponsorship.

Atomic and molecular data generation at NBS has always been closely connected with

basic research in atomic and molecular

physics. While most of the basic research

in this area is carried out in colleges and

universities either in the U.S. or abroad,

NBS plays a key role in this area by

providing new measurement techniques and

methods of data analysis and by performing

key measurements which may be used to compare with theoretical predictions.

4.2.2 Users of NBS Services

Users of NBS services in the area of

atomic and molecular properties generation

incl ude:

1) Industrial and governmental energy

generation groups concerned with the

development of coal-fired and non-equilibrium

magnetohydrodynamic generators.

2) Government, industrial and university

groups engaged in the development of laser

technology or in the use of lasers for

various applications, e.g., national defense,

energy generation, isotope separation, laserinduced chemical processes, etc.

3) National measurement systems at NBS

and elsewhere concerned with the development

of standards of length, frequency, etc.,

based on atomic and molecular properties.

-16-
4) Basic scientists engaged in aeronomy,

e.g., those studying the problems of energy

deposition, radio propagation through and

light emitted by the earth's atmosphere, and

the factors producing changes in the ozone

1 ayer.

5) Groups engaged in the study of energy

deposition in matter caused by energy losses

of incident electrons and photons, as in irradiation of biological materials.

6) Industrial and government groups designing and evaluating anti-ball istic missile

systems, very low frequency communication

systems and other defense systems operating

in the earth's atmosphere.

7) Industrial groups engaged in the development of more efficient and more easily

used gas discharge lamps for commercial,

highway, and home use.

8) Astrophysicists and astronomers studying stellar atmospheres and interstellar

media

9) Basic research groups in atomic and

molecular physics concerned with testina re- lationships between theory and experiment in

the areas of atomic and molecular collisions

and structure.

10) Spectrochemi sts concerned with the

quantitative analysis of chemical reactions

through spectroscopic observation.

11) Other NBS programs, parti cularly those

concerned with measurements in such fields as air pollution, laser chemistry and fundamental physical constants and with precise measurement techniques of basic quantities such

as length, frequency, pressure, and light

intensity (radiometry)

4.2.3 Alternative Sources

Alternate sources for the atomic and

molecular data generation services of NBS

are universities, research foundations, industrial and other federally funded laboratories, e.g., Stanford Research Institute,

General Electric Research Laboratories and

Los Alamos Laboratories. Al though university

laboratories have made and are making ex- tremely important contributions to the fundamentals o* atomic and molecular physics,

the measurement, calculation and interpretation of atomic and molecular data, such as cross sections and rate coefficients, are not favored areas in physics or engineering

departments because of rapid turnover of

workers (graduate students). Most of the

university work in data generation has been

by those interested in applications to astrophysics (Harvard) or to aeronomy (Pittsburgh)

The research program in atomic and molecular

data generation at one other institute, i.e.,

Stanford Research Institute (SRI), is much

like that at NBS but has been concentrated

on collisions among atoms and molecules

rather than interactions of electrons and

radiation with atoms and molecules. Also,

SRI has concentrated relatively more effort

cn data production and less on inventing new methods of measurement, and has been less

involved in the collection and evaluation of

data through critical reviews. Research in industry leading to new measurement techniques and to new methods of analysis and

calculation of atomic and molecular data has

declined drastically in the past six years

because of reduced government support and

because of greatly increased emphasis by industrial research management and federal

agency sponsors on short-term goals. The

increased emphasis on short-term goals has

seriously reduced the ability of governmental laboratories, e.g., the ERDA and DoD

laboratories, to invest the development time

and to make the careful measurements, ac- curate calculations and new interpretations

required for the assessment and integration

of the large number of individual collision

processes that occur in plasma devices and

systems

The question of the degree to which the

needs of users are now being met is best

answered on the basis of the ability of the

data centers concerned with the physical

properties of atoms and molecules to supply

reliable data requested by the users. Ex- amples of contacts involving such requests

in particular areas are given in Appendix B. A list of needs not now being met includes:

a) the needs of research programs in con- trolled thermonuclear fusion for information

on the energy levels, cross sections for ex- citation, and transition probabilities of

multiply ionized atoms 17 ; b) the needs of the laser development

groups for more extensive and more accurate

data regarding electron transport, excitation, dissociation, attachment, and ionization coefficients in the less common gases

and in mixtures of these gases with the more

common gases see Appendix B ; c) the needs of laser, isotope separation,

gas discharge lamp and anti-ballistic missile development groups and of astrophysics,

physical chemistry and aeronomy research

groups for experimental or theoretical data

for a large variety of molecular systems on the radiation emitted in collisions between

excited atoms and molecules and other atoms

and molecules see Appendix B ; and

d) the needs of laser development, isotope separation, and aeronomy research

groups for accurate experimental data or

-17-
theoretical prediction techniques for the

transfer of energy among the excited states

of atoms and molecules and for the col 1 i

sional quenching of excited atoms and molecules [see Appendix B3.

NBS has a number of unique advantages with

regard to its services in the area of atomic

and molecular physics properties measurement.

They are:

1) Its recognized objective of making

careful and controlled measurements leading

to documented precision and accuracy. This

emphasis on reliability and thorough investigation of sources often is incompatible

with the developmental objectives of industry and the mission-oriented governmental

agencies which generally take a short-range

approach to supporting research in atomic

and molecular physics. The projects selected

for university research are generally chosen

to allow completion in the two or three years

available from a given graduate student's

training, while NBS has the option of devoting longer periods to the development of

apparatus and computational techniques. For

example, the three years required for the

development of the multi-stage interferometer

for the study of the very weak, far-wing

radiation emitted in collisions between ex- cited alkali-atoms and rare gas atoms probably could not be quantitative explanation

for long-standing anomalies but has opened

the possibility of a new class of high power

lasers. In principle, the non-profit institutes, e.g., SRI, could exercise the option of taking the time and spending the

money required to improve the accuracy of

measurements as distinguished from making new

types of measurements. However, this has not

been, and is not likely to become their usual

approach, given the present attitude of most

funding agencies, on which they depend for

support.

2) An extremely capable and active atomic

and molecular group is very closely asso- ciated with a very capable and active university astrophysi cal group. The advantage

arises from the extensive needs of astrophysics for atomic and molecular data, from

the extensive experience of astrophysicists

in the modeling of the role of atomic and

molecular processes in astrophysical plasmas

and from the capable atomic and molecular

scientists both in this country and abroad.

3) NBS is uniquely neutral in questions of

industrial and governmental laboratory com- petition since most of its financial support

does not depend upon contracts with other

agencies. Thus, NBS personnel are asked to serve on advisory committees which judge proposals submitted by industry, universities,

and non-profit organizations, and which advise mission-oriented agencies accordingly.

The participation in such advanced planning

by mission-oriented agencies allows NBS to adjust its data generation activities so as to better meet current and future needs, to alert users as to available resources and,

in some cases, to lead the developmental programs into new areas.

4) Active collaboration with visiting

domestic and foreign workers through guest

worker and visiting scientists programs.

4.2.4 Funding Sources for NBS Services

In order to assess the funding sources of

atomic and molecular data generation at NBS some judgments have to be made as to what

specific projects are included in the program. These judgments are somewhat subjective for the following reasons. First, the

dividing line between NBS projects which are specifically designed to generate atomic and

molecular data or implement its use and those

which provide other services is by no means

clear. For example, studies of radiative

transport carried out at J I LA could alternatively be classified as a service intended

to provide effective use of atomic and molecular data, or as an internal user of such

data. Similarly, some of the projects con- cerned with laser chemistry in Division

232.00 are aimed at supplying needed atomic

and molecular data, others are devoted to applications, and some to both.

Second, there are projects whose primary

function is instrumentation that will even- tually be used in both atomic and molecular

data generation and in other activities.

The recent conversion of the NBS synchrotron

to a storage ring is an example of this type

of instrumentation. It will be used both for

atomic and molecular data generation and to provide precise vacuum-ultraviolet radiation

standards.

Finally, the data centers, maintained by

NSRDS, devoted to atomic and molecular data

collection, compilation and dissemination

play a special role. They can be classified

as part of the NSRDS effort of data collection and dissemination but are also important to the program of atomic and molecular

data generation since they provide a strong

coupling between outside users and NBS ser- vices in their respective areas. With the above points in mind we have

identified a number of NBS projects in

Divisions 274.00 and 232.00 which appear to

be primarily concerned with atomic and molecular data generation services as defined in

this report. Fiscal data for these projects

are shown in Table 3 classified by division,

project and source of funding. The special

role of the NSRDS data centers is indicated

by listing NSRDS support separately from

-18-
other NBS funding. While these data centers

should properly be considered as a part of

the NSRDS program, the NSRDS support is included in the totals of Table 3 to give an estimate of the amount of effort devoted to related data center activity. Table 3 indicates that approximately 15% of the atomic

and molecular data generation program (as

defined by the projects included) is supported by other agency funds (NASA, AF,

ARPA, ERDA). While the outside support is

generally of limited duration and can only

be used for the specific data needs of the

sponsoring agencies, it plays an important

role in defining the direction of atomic and

molecular generation programs. Currently

about 70% of the other agency funds are from

ERDA and are used for projects which will

supply data needed for controlled thermonuclear reactions.

4.2.5 Mechanism for Supplying Services

NBS supplies the services of its atomic

and molecular data measurements program

through a) direct consultation and correspondence with user groups, b) reports at user-producer workshops, c) speeches and

papers at scientific meetings, d) reports to sponsors, e) publication in scientific journals, and through f) compilations and critical reviews including NSRDS publications.

4.3 Impact of NBS Services

The economic and technological impacts of

atomic and molecular data generation are difficult to assess due to the rather complex way in which these services are propagated. The basic difficulties encountered

in such an assessment spring from the following factors:

1) The services supplied consist of a number of indirect services such as the development of techniques and procedures for

the analysis of atomic and molecular data or for their use in specific fields of application.

2) The users community as outlined in

Section 4.2.2 is diverse. It ranges on the one hand from workers engaged in atomic and

molecular data generation efforts very similar to those of NBS workers in the same

field, to workers in specific applied fields

(e.g., industrial lighting) with little interest or connection with NBS programs other

than as a source of specific data.

3) The users of NSB data are, for the

most part, engaged in what would normally be

called research or development activities.

Thus, the eventual economic or technological

impact of NBS work on any broad area of

activity (e.g., energy generation by con- trolled thermonuclear fusion, chemical separation or synthesis via lasers) can only be

assessed relative to the subsequent impact

of R & D effort in these areas.

4) The output of NBS services is difficult to trace to the eventual users. The

impact of formal publication in the open

scientific literature can only be gauged indirectly by analysis of reprint requests or citations by workers in allied fields.

4.3.1 Economic Impact of NBS Services

As stated above most of the users of NBS

atomic and molecular data generation ser- vices are workers engaged in research and

development in various technologies. One

approach to assessing economic leverage is to compare the NBS effort with the total re- search and development efforts in various

activities upon which this sector of the

measurement system impacts. This kind of

comparison is given in Table 4 which lists

a number of areas of research and development funded by industry and government users of atomic and molecular data generation services. As seen from Table 4, NBS activities,

at about three million dollars annually, are

a small (less than 1%) part of the overall

R&D activity in the areas listed. The

potential economic leverage to be realized

by essential current services in terms of

atomic and molecular data generation can be

as large as 100:1 in terms of current annual

expenditures for national programs. Overlooked in this assessment is the permanent

value of the data base being generated. A major NBS responsibility is to ensure that

the data base is of high permanent value,

i.e., is of adequate quality and scope to meet future needs and avoid high future

costs of repeating and extending measurements as national programs evolve and as new needs arise.

4.3.2 Technological Impact of NBS Services

Since most of the output of the atomic

and molecular data generation activity is via publication in the "open" literature,

tracing the use of this information would be

extremely difficult. In addition, the statistical information obtained from a survey

may be misleading or possibly incorrect due

to the difficulty of identifying the body of

users. There is no basis for conducting a survey among a representative sample.

-19-
Table 4. Budgets for research and development areas utilizing

measurement system for atomic and molecular properties

R&D Category Major Sponsor

Fundi ng M$

Problem Area

Controlled Thermonuclear

Reactions

High power lasers

Laser induced chemistry

(Isotope separation, etc.)

ERDA

ERDA, DoD and Industry

ERDA, DoD

Energy Generation by MHD Office of Coal Research

and Bureau of Mines

DoD, NASA

Commercial plasma devices Industry

Atmospheric Science and

Aeronomy

Astrophysics and astronomy NSF, NASA, DoD

Research in atomic and NSF, ERDA, DoD

molecular physics

Instrumentation

NBS (excluding other

agency funding)

Industry

100

100

15

15

40

5

18

20

10

2.5

325.5

Energy

Energy, defense and

materials processing

Energy

Energy

Defense, Air quality,

communications

Illumination, electrical

power dist. , air

cleaning, etc.

Space science

Basic research, measurement methods, etc.

Chemical analyses

-20-
The technological impact of NBS services

may be illustrated by the direct day-to-day

involvement (see Appendix B) that NBS staff

members have with other research and development laboratories to which they supply atomic

and molecular data and/or technical advice on the solution of specific problems. Several

results of this type of activity at NBS are briefly described below:

1 ) Most laser development laboratories con- cerned with the C0 2 laser use the sets of electron

excitation cross sections for C0 2 , N 2 and He derived and recommended by NBS personnel.

2) An intercompari son and analysis by NBS

personnel of differing predictions of electrical conductivities and electron densities

used by several federally funded and industrial MHD development projects showed that

the size of the MHD generator proposed by one industrial laboratory was 30% to small

to deliver the desired output. When electron

collision cross sections suggested by NBS were used, the design discrepancy was reduced

to within 10%.

3) The results of recent theoretical calculations of cross sections for rotational

excitation of CO and N 2 were used to show

that the predictions of gas heating being

used in calculations of power output and efficiency in lasers were extremely optimistic.

Gas heating effects are particularly important for CO lasers because of the requirement

that they be operated at low temperatures,

e.g., 77°K, in order to produce efficient

energy extraction.

4) Techniques developed at NBS for ex- Dlaining the continuum radiation emitted by

excited alkali metal atoms in the presence

of high densities of rare gases have been

applied by two different industrial laboratories to the prediction of the radiation

emitted by high intensity discharge (HID)

lamps used for industrial and highway

lighting. In one case NBS scientists were

told that these analyses were considered to have resulted in very significant improvements in the commercial lamp. For proprietary reasons, details are not available

from the company involved.

5) Measurements of the cross sections for

the production of certain Hg II spectra lines

made at NBS at NASA's request have shown that

a scheme which they have been developing for

monitoring the operation of mercury ion propulsion engines is likely to fail. Alternate

schemes have been proposed to them.

6) Initial attempts by an industrial

group to predict the usefulness of electron

impact excitation of HC1 for laser operation

resulted in the prediction that most of the

electron energy would be lost in rotational

excitation because of the very large electric dipole moment of HC1 . However, using

improved methods of data analyses and very

old data, NBS personnel showed that in spite

of the large losses to rotational excitation

there is a suitable range of mean electron

energies where there is efficient excitationof vibrational levels of HC1 . Very recent

results by others using electron beam scattering confirm this result. Furthermore, a successful laser has subsequently been re- ported using electron excitation of the very

similar molecule, HF.

7) Computer programs developed by NBS for

radiation transport, which are normally applied by astrophysicists to stars, have been

used to model pyrotechnic flares used for

illumination by the Department of Defense.

8) The simple analytical and partially

empirical approximations to the detailed

computer results developed by NBS personnel

have been applied by industrial development

groups to the approximate prediction of the

energy radiated and absorbed by elements

with many-line spectra. These simplified

treatments, when used with NBS tables of

line positions and oscillator strengths,

allow rapid screening of the periodic table

for the gas mixtures with highest luminous

efficiency and with satisfactory color.

9) The techniques described in 4) above

have been the subject of two reports (JILA

#110 and #114) which have been distributed

to the laser community and have resulted in

the initiation of several laser development

programs (see Appendix B) based on the

alkali-rare gas atom interaction and on alkali dimers as the active laser media.

4.3.3 Pay-off from Changes in NBS Services

One of the principal changes in NBS ser- vices in atomic and molecular data generation during the past few years has been the

increased emphasis on visits to the industrial and government laboratories utilizing

the technologies discussed above. This increased personal contact has made it possible

for NBS to adjust its NBS funded and, especially, other agency funded programs to provide data measurement and analysis techniques

that reflect the rapid changes in the active

areas of technology and to provide a portion

of the leadership in the choice of new areas of emphasis.

-21-
A second, and not unrelated change, is the

increased emphasis of theory and experiment

on obtaining data for more compl icated highly

ionized atoms, i.e., less emphasis on simple

systems and more work on atoms with one or more electrons outside closed shells and on multiply-ionized atoms. This change has

been in response to data needs of astrophysicists and of plasma physicists engaged in

controlled thermonuclear research. These

changes have been made possible by a significant increase in the sophistication of

theoretical methods and computer codes used

by and partially developed at NBS for calculating energy levels, electron scattering

cross sections and radiative transition probabilities. These advances have resulted in

the generation of much additional data re- quired by astrophysicists for their models of

stars and by plasma physicists interested in

the properties of highly ionized atoms.

These studies have also made possible a number of important tests of theory. The change

in emphasis has also resulted in some de- crease in activity in some more sophisticated

areas of theory and experiment and their intercompari son, e.g., the recent measurements

and theory of quantities such as alignment

and orientation of electron excitation of

atoms

Some specific areas in which NBS might

change its participation in the national

measurement system for the physical properties of atoms and molecules are:

a) the generation, tabulation and dissemination of "best available" sets of data

for atoms and molecules of high current technological interest. The objective of such a program would be to provide readily available

and frequently updated cross sections, transition probabilities, etc. for species of

interest in areas, such as laser, CTR, magnetohydrodynami c power generation research and

development. This program would complement

the more careful, long term critical reviews,

such as have been carried out by NBS in the

past, and so satisfy one of the more immediate needs, as well as the long term need of

science and technology. Such a program has

recently been initiated in connection with

the CTR proqram.

b) the building up of data center activity in areas such as radiative transition

probabilities and excitation transfer and

quenching rate coefficients for molecules.

These areas are of high current interest for

laser development, isotope separation, gas

phase chemistry, etc. Such a program should

be of sufficient interest to the Energy Re- search and Development Administration for

this agency to support the NBS effort. Their

support of such a program would add to the

official recognition of the NBS role already

obtained in connection with the Controlled

Thermonuclear Reactor program.

c) the deveopment and application of ex- perimental techniques for the generation of

large amounts of data in areas of special

need and neglect. One example is the need

for electron transport coefficients in

gases, such as ionization rate coefficients,

for designing high power electrical discharge lasers. Currently the U.S. has no effort in this area. An example of the suc- cessful development of such a program is the

work at the National Oceanic and Atmospheric

Administration on the measurement of ionmolecule reaction rate coefficients of at- mospheric interest.

d) the development of a comprehensive

program directed toward establishing standards, etc. for the measurement of the more important properties of ionized gas systems,

such as electron density and energy. Except

for the very successful work with the ra- diating properties of high current arcs, this topic has been one of considerable

controversy and little progress at NBS. The

fact remains that the measurement of these

properties is important to the technology of

ionized gas devices, including controlled

thermonuclear reactors, electric discharges,

lasers and electrical switchgear. As an example of the importance of such measurements, the recent near capture of the international market for small electrical circuit

breakers by the Swiss has been attributed to the use of improved measurement techniques.

-22-
4.4 Evaluation of NBS Program

Strong points of the NBS program in atomic

and molecular data generation

1) A strong research program in atomic

and molecular physics with emphasis on the development of new and accurate measurement techniques, on the accurate measurement

of data and on techniques of data appl ication

in the areas of the interactions of photons

and electrons with atoms, ions, and molecul es

2) An active and successful visiting scientist program which attracts the world's

leading atomic and molecular scientists to JILA/NBS for a year's association with the

NBS programs.

3) An active program of visits by NBS scientists to industrial and governmental development to laboratories to allow NBS atomic

and molecular data generation programs to re- spond to the changing needs of technology and

to facilitate the transfer of and utilization of data.

NBS support coupled with other agency support, and at JILA, University of Colorado

support of postdoctorates and graduate students, enables NBS to maintain an excellent

program of atomic and molecular data generation in areas such as the development of

measurement techniques and the measurement

of the interaction of electrons and radiation with atoms and molecules. This does

not mean that the NBS program is able to satisfy fully the rapidly growing and changing needs of technologies, such as high

power lasers and isotope separation. Also,

NBS has not attempted to support a comprehensive program in areas such as studies of

collisions among atoms and molecules. The

NBS program of evaluating existing data in

several areas of atomic and molecular physics

is at present not as user oriented as it

might be. More emphasis needs to be given to selection of useful data from among the

available experimental and theoretical data,

analysis of these data to obtain the best

available sets for a specific purpose and

making the results available to the users rapidly and easily. Also, NBS should concern itself much more with the way the data

it supplies are to be used in computer

models, etc. The needs for NBS services are determined

by the NBS scientists through requests for

data, the availability of funds, and the scientists' judgment as to the more productive

and opportune areas of work. The Divisions

274.00 and 232.00 evaluation panels have

played an important role in the general

health of the atomic and molecular program

through their recommendations.

Priorities among users are assigned on the basis of the individual judgment of the

NBS scientist, influenced strongly by the users, and their willingness to support the

work directly or indirectly. The programs

are monitored by NBS management and by con- tract monitors of various government agencies.

There are important aspects of the NBS

atomic and molecular measurement, data

generation, and data review programs which

are not fully duplicated in other types of

laboratory operations. The. question of

whether these programs could be subcontracted would require a careful examination of those contributions which are unique

to and characteristic of NBS and a judgment

as to whether these could be preserved in the transfer of functions to industry, to universities, or to federally funded university (or non-profit) managed laboratories.

In this field of atomic and molecular physics the NBS provdes leadership in the development and implementation of measurement

capability as well as in the organization

and utilization of data. In both areas the

NBS sets standards of performance for the

whole community. These functions rest on the existence of a highly competent careerprofessional staff oriented to public service; immediate access to a broad base of

technical and scientific capability, a high

degree of internal communication encompassing and interrelating the functions of

measurement and data evaluation; and a base

for access to both the academic-scientific

community and to agencies and industries involved in the technological applications of

atomic and molecular physics. No plan for

piecemeal contracting of NBS atomic and

molecular programs to a number of scientific

organizations of any type could preserve

these aspects.

Re-establishing a program of the same

level of technical competence as the current

NBS effort would require development of a single dedicated standards and measurements

laboratory with initial funding at a very

high level, and in any case would require

many years of development. Such a program

would have to duplicate in some way the

rather sophisticated apparatus and data

handling techniques currently available at NBS and would also have to attract a technical staff of roughly the same technical

competence as the present staff.

-23-
4.5 The Future

Basically, the service provided by

the NBS atomic and molecular portion of the

measurements system is to focus the output

of the atomic and molecular physics community into the generation of an adequate and

reliable data base for mathematical representation of the principal properties of

plasma devices and to permit mathematical

analysis of factors that determine efficiency. Corresponding applications of the

data base will occur in the sciences, notably

plasma physics, aeronomy, astrophysics, and

aerodynamics.

This will involve the invention of new methods of measurement to obtain properties

of various species of atoms and molecules

not measurable by traditional methods, and

will be concentrated on the data needs of

the following areas:

1) Control led-Thermonuclear Research—

Thermonuclear reactors are currently viewed

as a very long-range solution of man's need

for energy. Current research efforts in this

field have a need for new data, particularly

properties of multiply-ionized atoms, which

are not currently available. A major effort

to supply these types of data is now being

carried out at NBS and is expected to con- tinue in the near future.

2) Laser-Development and Applications —

Atomic and Molecular data, particularly on molecular and atomic excitation cross sec- tions by electron impact for various species, are currently needed. Future NBS work will

be devoted to supplying these but will probably also make contributions to the overall

understanding of how given devices or pro- cesses work, and will provide detailed

model s

3) Industrial Processes Requiring Atomic

Data—This is an area in which NBS has not

been much involved in the past but

to which it is currently making contributions (e.g., work on MHD coal-fired generators and commercial lighting). Applications

of this type require close personal contact

with industrial research and development

efforts and NBS staff specialization in this

type of problem. Work of this type probably

will be expanded at NBS.

4) Commercial measuring devices which re- quire atomic data for their design or interpretation—While there are a number of such

devices currently in use (electron spectrometers for chemical analysis (ESCA), microprobes, commercial spectrometers of all

types, etc.) very little has been said of

their need for atomic and molecular data

generation services simply because these

needs have not been assessed in this report.

Atomic and molecular data requirements for

the calibration of such instruments has

generally been left for the user to obtain

by using secondary standards for pressure,

radiant flux, electrical current, etc. It

is expected that NBS will become increasingly involved in direct generation and com- pilation of atomic and molecular data for

such purposes for the following reasons:

a) There is a need for a well-defined

body of reference data relating to each instrument of this type. Presumably this data

base will eventually become an integral part

of the National Standard Reference Data

System.

b) There are a number of such devices

currently being used at NBS on other projects. See, for example, "The National

Measurement System for the Measurement of

Surface Properties" Vol. IV of this series.

5) Aeronomy and Atmospheric ScienceActivity directed to these areas will probably decrease as a result of high priority

of other areas.

5. SUMMARY AND CONCLUSIONS

The national activity in atomic and molecular properties measurements includes work

carried out on a relatively small scale in

a large number of different university departments, industrial laboratories, government laboratories and federally funded re- search centers. The objectives are diverse

(pure basic research, product improvement,

weapons design, astrophysical and atmospheric modeling, instruments and standards

for measurement, and the development of new energy conversion systems) and the levels

of sophistication and competence are not

uniform. These activities are informally

coupled through the recognized scientific

literature, through the report literature

and through the activities of the professional societies, all strongly academically

oriented. Other types of coupling include

the agency sponsored workshop designed to focus attention of a limited sector of the

community on specific agency objectives, and

the discipline or mission-oriented compilation of data (most mature for atomic and

molecular data are those oriented toward

aeronomy and astronomy).

The National Bureau of Standards has historically been very active in this field and

today provides unique services which tend to tie this community more tightly into a measurement system for atomic and molecular data.

These services include the setting of standards

of performance in measurement; the development

of measurement capability; the compilation,

evaluation, and dissemination of data; and

the establishment of benchmark data.

-24-
Essential to this role as a focus for this

sector of the measurement system has been a high level of access to and communication

with the user communities. Through the era of concentration on atomic and molecular

structural information a principal interface

was with the astrophysical community. The

two decades just past have seen emergence of

reliable measurements and calculations of

the dynamic properties of atoms and molecules-; and, in addition, a new preoccupation

of the astrophysical community and the

closely related controlled thermonuclear

research community with the dynamics of

stellar atmospheres, of interstellar media,

and of plasma confinement efforts aimed at energy production. A major new user interface developed in the field of aeronomy,

substantially motivated toward Department of

Defense projects in ballistic missile detection, effects of severe man-made atmospheric

disturbances, and in communications.

The further evolvement of measurement ca- pability and of more complete and adequate

data sets are now converging with advances

in computer sciences and computational capability to provide an opportunity for a much

broader and more direct technological impact.

Urgent national requirements for advancements

in industrial technology, the development of

new energy sources, and the more efficient

transmission and use of energy require that

NBS should move rapidly to expand its interaction with the industrial community and

with national laboratories where development

projects depend on the ability to describe

and predict properties of gases for absorbing, converting, or transmitting intense

energy fluxes, as well as their aerodynamic

and electrodynamic properties.

Specifically recommended are:

1) Expansion of coordination of NBS atomic

and molecular programs with the search for

new laser media and with the scaling refinement of existing types of high power lasers

for the purpose of directing more effectively its own measurements of critical

atomic and molecular data.

2) Improvement of the NBS coordination

with groups developing and testing methods

of using atomic and molecular data for industrial design of new plasma devices and

for introducing improved efficiency factors

in existing devices.

3) Expansion of the NBS role in the

Controlled Thermonuclear Research (CTR) program, for the purpose of more effectively

directing its own measurements of critically

needed parameters, for supplying CTR fusion

laboratories with the essential atomic and

molecular data to Dermit more reliable diagnostics of high temperature pi asma and to form

the basis for better modeling calculations.

4) Re-examination and expansion of its

atomic and molecular data compilation,

evaluation, and dissemination activities to ensure that maximum effective utilization is made of the data output potential of the en- tire atomic and molecular community, the

needs of the most urgent development projects are met by development and issuance

of specialized data sets, and that the goal

of realizing a generally accessible, generally useful and thoroughly reliable base of

data and methodology directed to the needs

of the industrial and scientific communities

be kept in view.

5) Continuation of NBS support of meas- urement activities of the entire atomic and

molecular physics community through development and testing of measurement techniques

for properties needed by and not available

to the user communities; execution of se- lected benchmark measurement programs; re- examination of transfer standards for meas- urement of gas density and radiant flux;

and continuation and strengthening of NBS

sponsorship of critical reviews and evaluated compilations with the objective of promoting quality output in areas of critical

need.

Appendix A. Methodology of the Study

This study has been conducted 1) through

a survey of literature relating to the scope

of the field of atomic and molecular physics,

relatinq to the activities and needs of many

of the user groups, and where available re- lating to economic data and activity levels

in principal areas of application; and 2)

through extensive personal contacts with

persons involved in pertinent research and

development programs.

The literature has consisted of several

types including surveys of levels of basic

research activity conducted by the physics

community, and studies and statistical surveys by organizations such as the National

Science Board and the Electric Power

Institute. There is a substantial body of

literature directed at the research com- munity which includes magazine articles

and other reports intended to bring scientists up to date on areas of application of

atomic and molecular physics. Finally the

magazine Laser Focus is almost unique in its

reporting on levels of activity in the laser

industry.
Information and insight into the role of

atomic and molecular data in other ongoing

industrial programs are usually not spelled

out in the literature. With some exceptions

the atomic and molecular input is not represented by products identifiable with this

field so thatproduct information is not very

helpful. In this area heavy reliance has

been placed on personal contacts with industrial scientists to obtain insights into cur- rent activities and needs for atomic and

molecular data and measurement capability.

Appendix B. Examples of Interactions with

Atomic and Molecular Data Users

A. Development of high power and ultraviolet lasers in industry and government.

INPUT--primari ly requests for evaluated

data on the interaction of electrons, ions

and radiation with atoms and molecules of

present or potential laser interest and re- quests for advice on interpretation of ex- periments, sources of data and areas of re- search to be investigated.

OUTPuT--tabulation of evaluated cross sections and rate coefficients for electron collision processes; measurement and calculation

of radiative properties of potential laser

molecules; development of new experimental

techniques for the determination of atomic

and molecular properties; and the development

of new modeling techniques for the prediction

of the electrical and radiative properties of

lasers.

1) Industry

a) Airesearch Research Co. (Garret

Corp.

Principal contact: Dr. J. Kennedy

Interaction topics: supplied cross section sets for C0 2 and CO laser design; checked results of electron

transport calculations in C0 2 mixtures.

b) Avco Everett Research Laboratories

Principal contacts: Drs. R. E. Center, D. H. Douglas-Hamilton, R. L. Taylor (formerly), and G. E. Caledonia

(formerly)

Dates of interactions: vists to 1/72, 3/72 and 12/73 and from 2/72,

7/72 and 3/74; phone call s--numerous--

three since 7/74; technical letters--

6/73, 7/73 and 7/74.

Interaction topics: supplied electron collision cross section and transport coefficient data, negative ionmolecule reactions rates and rate

coefficients for C0 2 , CO and excimer

laser processes; assisted in interpretation of electron loss data in CO.

c) Bell Telephone Laboratories

Principal contact: Dr. P. W. Smith

Interaction topic: discussions of

possibilities for and data concerning

electron transport and excitation in

organic vapors, e.g., gas phase dye

1 asers.

d) Comarco Inc. Principal contact: D. F. T. Wu Interaction topic: supplied cross section set used in recently published

analyses of CO lasers.

e) CALSPAN (Cornell Aeronautical

Laboratories

Principal contact: DR. J. C. Rich

Interaction topics: supplied electron collision cross section sets for

C0 2 and CO laser design; supplied

theory and preliminary results on heating of CO in laser discharges.

f) Hughes Research Laboratories and

Hughes Aircraft Co. --Laser Division

Principal contacts: Drs. R. Lind

and J. Palmer

Dates of interactions: visit to 5/74; technical letters--6/74, 10/74;

phone calls--5/73, 6/73, 9/73 plus

several discussions at conferences.

Interaction topics: supplied cross section sets for C0 2 laser modeling

and references on alkali-rare gas

plasma processes; suggested technique

being used for alkali density measurement; pointed out error in analyses of

discharge instability growth; and supplied source of unpublished, foreign

data on vibration relaxation at low

temperatures. Note that their work

on alkali -rare gas systems was initiated as the result of J I LA Report

#110.

g) Intercom Radiation Technology Inc. Principal contact: Dr. J. T. Dowell

Interaction topics: supplied ref- erences on electron-positive ion re- combination to alkali metal -rare gas

pi asmas

h) International Business Machines

Research Laboratories

Principal contact: Dr. R. T. Hodgson

Interaction topics: suppl ied NBS data

on secondary electron energy distributions

produced by ionizing collisions.

-26-
i) Mathematical Sciences Northwest

Principal contact: Dr. S. Byron

Dates of interactions: technical

letters— 3/74, 7/74, 10/74; phone

calls— 10/74.

Interaction topics: supplied electron collision cross section data for

C02 and CO lasers; supplied references

on electron attachment to carbonyl impurities in CO; discussed their evidence for role of metastable N 2 in N 2 and C0 2 -N 2 -He discharges; discussed

operating conditions for electron beam

sustained HF laser; discussed their

evidence regarding rate of heating of

gas in CO laser; supplied our revised

cross sections for vibrational and

electronic excitation of 0 2

. j) Northrop Corp.

Principal contacts: Drs. M. L. Baumick and B. Lacina

Dates of interactions: visit from

7/72; technical letters 2/72; phone

calls-3/73, 5/73 and 8/73.

Interaction topics: supplied electron excitation rate coefficients for

HC1 as determined from electron transport data; data and principles of ex- cimer laser design; electron cross section data for C0 2 lasers; role of collisions of second kind in laser discharges.

k) Physical Sciences Inc. Principal contacts: Drs. R. L. Taylor and G. E. Caledonia

Dates of interactions: phone calls

8/74; technical letters— 7/74, 8/74,

9/74.

Interaction topics: supplied old

electron cross section set and new references for H 2 and D 2 in connection

with undisclosed laser scheme; supplied unpublished scheme for calculation of gas heating by rotational ex- citation near resonance; supplied re- vised electron excitation cross section set for 0 2

. 1) Science Applications Inc. Principal contacts: Drs. R. E. Meredith and T. S. Chang

Interaction topics: discussion of

the physics of excimer laser processes

and a critical review of a contract

report prepared by them on this subject.

m) United Aircraft Research

Laboratories

Principal contacts: Drs.R.Bullis,

W. L. Nighan and W. J. Wiegand

Dates of interactions: visit from

72; numerous phone calls and long discussions at technical committee

meetings

Interaction topics: supplied electron collision cross sections for C0 2 , CO and HC1 lasers and for impurities

such as H 2 and H 2 ); compared in detail our calculations with their calculations of stability of laser discharges; supplied data on electron

attachment and negative ion-molecule

reactions in laser discharges, provided critical evaluation of processes

in their MHD-laser scheme,

n) Westinghouse Research Laboratories

Principal contacts: Drs. J. J. Lowke, L. J. Denes, L. E. Kline and

R. L. Humstad

Dates of interactions: visits to 6/72, 1/73, 8/73 and 8/74, from 4/72,

11/72, and 3/74; numerous phone calls.

Joint paper with J. J. Lowke and

B. W. Irwin, J. Appl . Phys. 44, 4664

(1973).

Interaction topics: developed and

applied electron cross section set for

analysis of C0 2 lasers and joint

paper; discussed significance of NBS

interpretation of their data showing

extremely low electron-ion recombination coefficients in C0 2 laser discharges; found error in their calculation of gas heating in laser discharge; compared theories of growth

of current leading to constriction and

shorting of laser discharge.

2) Government

a) Los Alamos Scientific Laboratory

Drs. C. A. Fenstermacher , W. Leland,

G. York and S. Rockwood

b) Air Force Weapons Laboratory

Drs. L. A. Schlie, D. Drummond,

W. H. Proctor and Ma j . R. Weber

c) Lawrence Livermore Laboratories

Drs. C. K. Rhodes and P. Hoff

d) Naval Research Laboratories

Dr. A. Ali

e) Sandia Laboratories

Dr. J. W. Gerado

f) Office of Naval Research

Dr. W. J. Condell , Jr. and Dr.

J. G. Dardis (contract monitor)

g) Naval Ammunition Depot

Dr. B. E. Douda

h) Naval Ordinance Lab

Dr. M. Plummer

-27-
3) Other Governments

None

4) Journals

None recent

5) Other NBS

Division 271.00 (consulting and con- tract contacts)

Drs. E. W. Smith, M. M. Hesse! , K. B. Persson, E. R. Mossburg, Jr., and

D. L. Fransen

6) Educational Institutions

a) Wayne State University

Dr. E. Fisher

Exchange of results of modeling calculations; critical evaluation of

modeling calculations at Wayne State.

b) University of Colorado

Dr. E. A. Crawford

Collaborative experimental study of

the collapse of glow discharges in high

pressure laser configurations. Published in Appl . Phys. Letters.

c) Stanford University

Prof. S. Harris

Discussions of excimers and molecular absorption in alkali rare gas

systems.

B. Development of efficient, coal-burning

energy conversion devices.

INPUT--primarily requests for evaluated

data and new data for use in the design and

evaluation of coal -fired magnetohydrodynamic

generators.

0UTPUT--compilations and evaluation of

collision cross sections, electron mobilities, and electron affinities of species of

significance in MHD devices.

1 ) Industry

a) Avco-Everett Research Laboratories

Dr. R. L. Taylor

b) Westinghouse Research Laboratories

Dr. T. C. Tsu

2) Government

a) Bureau of Mines, Department of

Interior

Dr. F. E. Spencer, Jr.

C. Prediction of disturbed ionospheric

properties

INPUT--statement of data needs by DoD

agencies and contractors and by NASA supported labortories.

0UTPUT--measured values of critical cross sections; reviews of available data relevant

to ionospheric phenomena; calculations of cross sections not available from experiment.

1) Industry

a) General Electric Company

G. E. Tempo: Mr. A. Feryok

G. E. Valley Forge: Drs. T. Baurer

and M. H. Bortner

Writing of two chapters for DNA

handbook.

b) R & D Associates

Dr. F. R. Gil more

c) Mission Research Corp.

Drs. M. Schiebe and P. G. Fisher

2) Government

a) NASA supported laboratories:

i) LASP--Uni versity of Colorado

Dr. M. Rees (secondary electron energy data)

ii) University of Florida

Dr. A. E. Green (secondary

electron energy data)

b) Defense Atomic Support Agency

i) Dr. R. Huffman (ARCRL contract

moni tor)

(Measurement of rates of excitation of infrared emitting levels

of molecules and advice on ionospheric heating model)

ii) Dr. R. Mace (ARO(D) contract

moni tor)

(Measurement of photodetachment cross sections for complex

negative ions of ionospheric interest)

iii ) Dr. E. Bauer (IDA)

(Calculations of infrared

emissivity of ionospheric plasmas

at moderate temperatures)

iv) Served on DNA committee to evaluate their program.

D. Development of higher-efficiency,

good-color, more easily used lighting.

INPUT--statements of needs and discussions of problems by industrial development

groups for data required for the prediction

of the electrical and radiative properties

of electric discharge lamps.

OUTPUT--measurements of radiative properties of molecules obtained by the use of

experiment and theory developed at LAD; compilations and evaluations of published

experimental data.

1 ) Industry

a) Sylvania Electric Company

Dr. J. F. Waymouth

b) Westinghouse Research Laboratories

Drs. R. J. Zollweg and J. J. Lowke

E. Development of miscellaneous industrial devices such as ozonizers, information

displays.

INPUT —needs of industrial and university

groups as determined by discussion and by

study of publications.

OUTPUT--recommendations of data and calculation techniques; development of new techniques for modeling of electrical discharges in gases.

1) Industry

a) Avco-Everett Research Laboratories

Dr. D. H. Douglas-Hamilton

Collision processes of importance

in chemical production by electrical

discharge devices.
Appendix C. Atomic and Molecular Physics

and Energy Research

This appendix summarizes some of the areas

in which research in atomic and molecular

physics can be expected to contribute significantly to increasing our ability to generate, distribute and utilize electrical energy

in an efficient and environmentally acceptable manner. The various areas of research

are categorized by the area of application

rather than by the scientific specialty in

order to make the material more readi ly understood by those primarily concerned with energy

problems. It will be noted that since the

topics discussed are concerned with the

generation, distribution and use of electrical

energy, we omit most of the research concerned with other energy forms and the closely

related branch of chemical physics. Also, we

have attempted not to include areas normally

considered as plasma physics, i.e., the collective phenomena occurring in essentially

fully ionized gases.

I. Electrical Power Generation

A. Controlled thermonuclear reactions

1. Magnetically confined plasmas

Research in atomic and molecular physics

provides data required for measurement of

the properties (diagnostics) of CTR plasmas;

the development of neutral beams for fuel

injection and plasma heating; the prediction of plasma cooling due to impurities;

and the understanding and optimization of

the interaction of the plasma and radiation with surfaces. As indicated in the

Liess Report of March 1974 [17] these re- quirements show the need for extensive re- search in areas such as atomic radiative

transition probabilities; collisions of

ions with gases, surfaces and electrons;

and the collisions of charged particles

and radiation with bulk solids.

2. Laser induced, controlled thermonuclear reactions

Laser induced fusion is a much newer

area of energy research than that of magnetic confinement and is much more in need

of supporting research from fields such as atomic and molecular physics. This is

particularly true for the problems of high

power laser development and the propagation of laser energy. The needs for atomic

and molecular data in the area of the properties of the veryhigh temperature (~10 7 K)

fuel pellet are similar to those of the

magnetic confinement approach. In the

search for a laser medium capable of generating the extremely short pulses and

high powers needed for laser induced fusion much use has been made of atomic and

molecular collision cross section and

radiative property data which have been

generated with support from DoD programs

concerned with the modeling of high altitude nuclear explosions and with missile

reentry into the earth's atmosphere.

Unfortunately such data are not available

for the more exotic molecules now under

consideration as laser r,,edia and neither

the DoD nor the AEC has been supporting

the research required to develop the new techniques required to handle these gases

and to obtain the data.

B. Isotope separation for conventional

nuclear power fuel

Recent research appears to have shown that

the highly monochromatic, high intensity ra- diation from lasers can be used to prepare

atoms and molecules of different isotopes in

different states so as to allow significant

separation of the isotopes. Effective ex- ploitation of this technique will require

extensive research in the areas of variable

wavelength, highly stable, high power lasers

and of the effects of differing isotopes on atomic and molecular structure and collision

cross sections for ground and excited (or

ionic) states of these atoms or molecules.

C. Magneto-hydrodynamic power generation

Although the primary research needs in

the area of MHD are concerned with erosion,

conductivity and electron emission of impacted wall materials, seed recovery, and

pollution by combustion products, there is a serious lack of reliable data which would

allow prediction of the electrical conductivity of the thermal and non-equilibrium

plasmas. In particular, there are the needs

from A&M research for electron affinity

data, electron transport (collision) data,

and for the development of reliable diagnostic techniques for plasma composition,

temperature, etc. The understanding and

control of the products of high temperature

combustion will eventually require measurements of the individual collision processes

which determine the chemical species present,

the temperature at which energy relaxation

is incomplete, etc. Similarly, surface ero- sion depends upon rate of colli si onal energy

and momentum transfer, rates of evaporation

and nucleation, etc.

-29-
D. Thermionic converters for power generation

Thermionic converters make use of ionized

metal vapors to neutralize space charge and

so make possible the flow of usefully large

electron currents between mechanically realizable surfaces of widely different temperatures. In addition to solutions to the severe fabrication and materials compatability problems there is a need for better

understanding of the properties of electron

emitting surfaces, the collisions among the

electron and the charged and neutral atoms,

and of radiation transport.

E. Conventional power generation

Areas of conventional combustion driven

steam and gas turbine generators in which

atomic and molecular physics may make significant contributions are: the more efficient

and/or environmentally acceptable burning of

fuel through the sensing and control of flame

condition, electric discharge aiding of com- bustion, and the measurement, understanding

and prediction of the role of flame additives. As in the MHD systems there is a need for better understanding of the pro- cesses of turbine blade erosion by collisions

of molecules, droplets and unburned fuel, and

the factors determining the end products of

combustion. Finally, there is the control of

pollutants through devices, such as electrostatic air cleaners with their numerous gas

discharges, surface conductivity, and other

similar problems.

II. Electrical Power Transmission and

Switching

A. High voltage systems

The desire to reduce losses in the transmission of electrical energy has led to the

use of high voltages with a resultant in- crease in insulation problems and in corona

loss and interference. Although significant

progress has been made in obtaining engineering data, we are a long way from being able

to predict or understand the path of a long

electrical spark in air or along a surface

or to describe or predict quantitatively the

variations in corona discharges which occur

with changes in geometry, moisture concentration, etc. Although we believe that data

describing the most relevant collision pro- cesses are available, a few have not been

studied quantitatively and, most importantly,

only in the simplest geometries and gas mixtures can we synthesize these processes so as

to make predictions and provide understanding. As examples, we still do not know the

role of electron detachment from negative

ions in air at atmospheric pressure nor can we describe quantitatively the reasons for

the crooked path or the step-like propagation of the current in a long spark.

B. Lightning protection

The high probability that electrical

transmission systems will be struck by

lightning has led to significant investments

in protective switching, etc. As for the

long sparks discussed above our predictive

ability for lightning is almost entirely

empirical largely because of our limited

ability to synthesize the large number of

atomic and molecular processes with real istic

geometries, etc.

C. Electrical switchgear

The understanding of electrical switchgear requires that one bring together the

results of research in mechanics, fluid

dynamics, metallurgy, and atomic and molecular processes. An example is the crucial

role of molecular dissociation in causing a sharp peak in the temperature dependence of

the specific heat with the resultant large

temperature gradients in the arc temperature

profile and the rapid diffusion of heat when

an attempt is made to interrupt the arc current. A second example is the important

role of radiative energy dissipation in the

higher current, higher pressure arcs used at high power levels.

III. Electrical Energy Utilization

A. Illumination

The application of atomic and molecular

radiative processes is the basis for recent

improvements in the efficiency of sources of

illumination which range from fluorescent

lamps to high intensity sodium lamps.

Through improved understanding of the individual collision processes and improved

ability to describe the relations among

large numbers of important processes one expects to develop illumination sources of

higher efficiency, better color rendition

and longer life. As an example, techniques

are just beginning to be developed for predicting quantitatively the intensity of the

broad-band radiation which dominates the

output of many high pressure lamps.

-30-
B. Material processing

The use of electrical arc furnaces for the

melting and processing of steel has become a large consumer of electrical energy and often

taxes the ability of regional distribution

and generation systems to supply a constant

voltage. Although it is not clear at this

time what atomic and molecular physics stu- dies would be of help in optimizing the use

of electrical energy in these systems, the success of arc symposia held at conferences

sponsored by the professional societies shows

that arc physicists can make use of the re- sults of atomic and molecular data and techniques. Thus, the studies of the welding arc have included an accounting for energy flow

by conduction, convection and radiation, the

processes leading to electron production at the cathode and ion production near the

anode, and the effects of various gas or vapor additives or shields. Another type of arc which has been investigated in terms of

atomic and molecular processes is the plasma

jet used for crystal growth and metal shaping.

Low pressure electrical discharges are used

for growth of oxide surfaces on semiconductors, sputtering thin films onto

surfaces, etc.

C. Chemical processing

Although the use of electrical energy for

chemical processing is expensive compared to more conventional chemical processing, there

are a number of commercially important pro- cesses. One of these is the production of ozone in the ozonizer discharge, i.e., a series of short high voltage discharges.

It has been suggested that ozone should

replace chlorine for water purification.

Unfortunately, we understand very little

about the electrical discharge and chemical

processes occurring in these devices. A second example is the use of plasma jets,

with or without magnetically induced

rotation, to produce acetylene. As yet

unsuccessful attempts have been made to use electrical discharges to produce

hydrazine and other high energy content

fuel s

-31-
ro co co S- 4-> re c +-> JO S- o o ro <_> O o c S- Ol s_ CL

to o +J c_ CL 4-> CO o CO CO i. re

CO c CD o ro — s_ o Cl a. s_

O o CO ro ro CO 4-> o o 4-> JC c o 1 u 3 CO ro

(_> <_> CO S_ 4->

u i 4-1 ai re <U 4->u

q; c 3 o roC OJ o cu +-> o s_ P

UJ »—

CC s: I— _J LU c c o s

CL o 4-> 4-> o •a (O

S- s- o CL >) ro

O

CL CD 4-1 CD o

CO

u CD 5- CO

C IliU ro

u c -Q co

ro (f- OJ ro ro

S- s_ s_ o OJ <4- Cl— +J CD 3 ro <_> S_ 4— ro S_ J3 CO <4— ro 3 (O U <o +J S_ 4- CO

ro 3 S_ 1 S- 3

S_ 4-> CO 3 4-> (J

4-> 4->

u 1 CO 4-> C_> o CD

QJ c 1 3 CD

tu OJ

O > tuO Z Z Ul JZ Z UJ UJ

-32-
REFERENCES

[1] Atomic and Molecular Physics , Report of the Committee on Atomic and Molecular Physics

(National Research Council -National Academy of Sciences, 1971).

[2] Physics: Survey and Outlook , NAS-NRC Publ . 1295 and 1295A (National Academic of

Sciences-National Research Council, Washington, D.C., 1966).

[3] Physics in Perspective , Physics Survey Committee (National Research Counci 1 -National

Academy of Sciences, Washington, D.C., 1972).

[4] Publication List, National Standard Reference Data System.

L~5] Reaction Rate Handbook , ed. by M. H. Bortner and T. Baurer (DoD Nuclear Information and

Analysis Center, Santa Barbara, 1972), esp. Chap. 5. [6] Spectroscopic Constants for Selected Heteronucl ear Diatomic Molecules , S. N. Suchard

(Aerospace Corporation, Los Angeles, 1974).

[7] "Laser Program Briefing," a collection of slides used in August 1974 in briefing

discussions at Lawrence Livermore Laboratories.

[8] See, for example, "More Laser Power with Electron Beam Control," Physics Today, p. 17 (January 1972).

[9] J. L. Emmett, J. Nuckolls and L. Wood, "Fusion Power by Laser Implosion," Scientific

American (June 1974).

[101 H. A. Anderson, "Lighting Trends for '74," Lighting Design and Application (January

1974).

[11] See, for example, "From Fossil Fuel to Fusion: A Milestone Century of Technological

Progress," 100th Anniversary Issue, Electrical World, 1 June 1974.

[12] See Appendix C. [13] S. S. Penner and D. B. Olfe, Radiation and Reentry (Academic Press, New York, 1968).

[14] See, for example, "Recent Progress in Laboratory Astrophysics," Astron. J. 79_, 1260

(1974).

[15] W. C. Lineberger, "Laser spectroscopy of gas phase ions," in Chemical and Biochemical

Applications of Lasers , Vol. 1, pp. 71-101 (C. B. Moore, Ed., Academic Press, New York,

T974T

[16] Letter of 2/14/75 to R. M. Sinclair, NSF, from F. T. Smith transmitting preliminary re- port by B. Bederson entitled, "Energy-Related Atomic and Molecular Physics Research."

[17] "Atomic, Molecular, and Nuclear Data Needs for CTR," Report of the Research Panel on Atomic, Molecular, and Nuclear Physics in CTR, March 29, 1974, J. E. Leiss, Chairman.

[18] A. V. Phelps, "Tunable Gas Lasers Utilizing Ground State Dissociation," J.I.L.A.

Report #110 (September 15, 1972).

[19] G. York and A. Gallagher, "High Power Gas Lasers Based on Alkali-Dimer A-X Band

Radiation," J.I.L.A. Report ^114 (October 15, 1974).

[20] R. C. Elton, "Analyses of X-Ray Laser Approaches," NRL Memorandum Report 2906

(October 1974).

[21] "Review and Outlook 1974," Laser Focus, January 1975.

[22] Private conversations with research directors at Lawrence Livermore Laboratories,

Los Alamos Laboratory, Westinghouse Research, and Avco Everett Research Laboratory.

-33-
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

RIR1 lOftRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 75-944

2. Gov't Accession 3. Recipient's Accession No.

4. TITLE AND SUBTITLE

National Measurement System for the Physical

Properties of Atoms and Molecules

5. Publication Date September 1976

6. Performing Organization Code

274.00

7. AUTHOR(S)

J. W. Cooper, A. V. Phelps and S. J. Smith

8« Performing Or^£in» Report No«

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 2741900

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as Item 9.

13. Type of Report & Period

Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

National activity in measurement, compilation, evaluation, and dissemination of

atomic and molecular data, estimated at 20-25 million dollars annually, impacts direct^

upon applied research and development projects costing over one-third billion dollars

annually. NBS atomic and molecular programs, costing about 3 million dollars annually,

provide the basis for the accepted standards for length, time and frequency; provide

advanced measurement techniques; set rigorous performance standards for generation of

atomic and molecular data, and provide for the construction of a sound data base for the

user community. The largest users are programs aimed at energy generation and conversion. Basic sciences of aerodynamics, astrophysics, atmospheric physics and plasma

physics are important users. Benefits for a broad range of industrial research activities are potentially large. It is recommended that NBS undertake to ensure the

reliability and adequacy of the data base needed for important national programs, expand

its contacts with private industry, develop increased awareness of the methodology for

applying atomic and molecular data to technological development, and encourage effective

utilization of this sector of the measurement system for the benefit of the economy.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Atom; energy generation; industrial technology; molecule; primary standards;

properties

.

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

38

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

$4.00

18. AVAILABILITY [XX Unlimited

_ For Official Distribution. Do Not Release to NTIS

J Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. C13

Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

USCOMM-DC 29042-P74

USCOMM • ERL