Ionization potentials, appearance potentials, and heats of formation of gaseous positive ions

298 Pages·2016·19.32 MB·English

by  Franklin, J. L.

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UNITED STATES DEPARTMENT OF COMMERCE
Maurice H. Stans,Secretary
5 NATIONAL BUREAU OF STANDARDS A. V. Astin, Director
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Ionization Potentials, Appearance Potentials, and Heats of Formation of Gaseous
Positive Ions
J. L. Franklin and J. G. Dillard
Rice University, Houston, Texas 77001
H. M. Rosenstock, J. T. Herron, and K. Draxl
Institute for Materials Research
National Bureau ofStandards
Washington, D.C. 20234
and
F. H. Field
Esso Research and Engineering Company
Linden, New Jersey 07036
NSRDS
NSRDS-NBS
26
i Nat. Stand. Ref. Data Ser., Nat. Bur. Stand. (U.S.), 26, 289 pages (June 1969)
CODEN: NSRDA
Issued June 1969
Forsaleby theSuperintendent ofDocuments, U.S. Government PrintingOffice
Washington,D.C.20402-Price $4
NATIONAL BmUREAU OF STANDARDS
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Library of Congress Catalog Card Number: 68-62689
Foreword
The National Standard Reference Data System is a Government-wide effort to provide for
the technical community of the United States effective access to the quantitative data of physical
science, critically evaluated and compiled for convenience, and readily accessible through a
variety of distribution channels. The System was established in 1963 by action of the President’s
Office of Science and Technology and the Federal Council for Science and Technology.
The responsibility to administer the System was assigned to the National Bureau of Standards
and an Office of Standard Reference Data was set up at the Bureau for this purpose. Since 1963,
this Office has developed systematic plans for meeting high-priority needs for reliable reference
data. It has undertaken to coordinate and integrate existing data evaluation and compilation
activities (primarily those under sponsorship of Federal agencies) into a comprehensive program,
supplementing and expanding technical coverage when necessary, establishing and maintaining
standards for the output of the participating groups, and providing mechanisms for the dissemina-
tion of the output as required.
The System now comprises a complex of data centers and other activities, carried on in Gov-
ernment agencies, academic institutions, and nongovernmental laboratories. The independent
operational status of existing critical data projects is maintained and encouraged. Data centers
that are components of the NSRDS produce compilations of critically evaluated data, critical
reviews of the state of quantitative knowledge in specialized areas, and computations of useful
functions derived from standard reference data. In addition, the centers and projects establish
criteria for evaluation and compilation of data and make recommendations on needed modifications
or extensions of experimental techniques.
Data publications of the NSRDS take a variety of physical forms, including books, pamphlets,
loose-leaf sheets and computer tapes. While most of the compilations have been issued by the
Government Printing Office, several have appeared in scientific journals. Under some circum-
stances, private publishing houses are regarded as appropriate primary dissemination mechanisms.
The technical scope of the NSRDS is indicated by the principal categories of data compila-
tion projects now active or being planned: nuclear properties, atomic and molecular properties,
solid state properties, thermodynamic and transport properties, chemical kinetics, colloid and
surface properties, and mechanical properties.
An important aspect of the NSRDS is the advice and planning assistance which the National
Research Council ofthe National Academy ofSciences-National Academy ofEngineering provides.
These services are organized under an overall Review Committee which considers the program
as a whole and makes recommendations on policy, long-term planning, and international collabora-
tion. Advisory Panels, each concerned with a single technical area, meet regularly to examine
major portions of the program, assign relative priorities, and identify specific key problems in
need of further attention. For selected specific topics, the Advisory Panels sponsor subpanels
which make detailed studies of users’ needs, the present state of knowledge, and existing data
resources as a basis for recommending one or more data compilation activities. This assembly
of advisory services contributes greatly to the guidance of NSRDS activities.
The NSRDS—NBS series of publications is intended primarily to include evaluated reference
data and critical reviews of long-term interest to the scientific and technical community.
A. V. Astin, Director.
hi
Contents
Page
Foreword
iii
1. Introduction 1
1.1. General 1
1.2. Literature coverage 1
1.3. Order of presentation 2
1.4. Reliability of data and criteria for evaluation 2
1.5. Thermochemical considerations 3
1.6. Selection of “best” values 4
1.7. Units 4
1.8. Concluding remarks 4
1.9. References 4
2. Order of ion presentation 5
3. Table 1. Ionization potentials, appearance potentials and heats of formation of gaseous
positive ions 14
4. Table 2. Heats of formation of gaseous neutral species derived from the data of
table 1 238
5. Bibliography for tables 1 and 2 245
6. Author index for tables 1 and 2 256
7. Appendix 1. Heats of formation used in tables 1 and 2 260
8. Bibliography for appendix 1 282
9. Appendix 2. Table of group equivalent values 285
IV
Ionization Potentials, Appearance Potentials, and Heats of Formation of
Gaseous Positive Ions
J. L. Franklin and J. G. Dillard
Rice University, Houston, Texas 77001
H. M. Rosenstock, T. Herron, and K. Draxl
J.
Institute for Materials Research, National Bureau of Standards, Washington, D.C. 20234
and
F. H. Field
Esso Research and Engineering Company, Linden, New Jersey 07036
This is a compilation ofionization and appearance potentials of positive ions published from 1955
through June 1966. The compilation lists the ion formed, the parent species from which it was formed,
the other products of the process, the threshold energy for the formation of this ion, and the method
by which this data was obtained.
Where feasible, the heat of formation at 298 K of the positive ion has been computed for each
entry using auxiliary thermochemical data. From these computed values “best” values have been
chosen.
Key Words: Appearance potential; compilation; data; heat of formation; ionization potential;
ions; positive ions.
1. Introduction
1.1. General As there is considerable variation in the quality
of the data in this field it would have been simpler
Since the publication of “Electron Impact to include only the well-determined numbers.
Phenomena and the Properties of Gaseous Ions” However, in some cases the only values available
by F. H. Field and J. L. Franklin [l],1 which con- were obtained by imprecise methods, and in the
tained a compilation of ionization and appearance belief that an approximate value is better than none
potentials reported through 1955, the study of we decided to include all available data in the
gaseous ionization phenomena has undergone an compilation.
explosive growth in the number and variety of
pertinent research studies. This field now includes
aspects of vacuum ultraviolet spectroscopy, inelas- 1.2. Literature Coverage
tic electron scattering, photoionization, photoelec-
tron spectroscopy, mass spectrometry, charge Literature references were obtained initially
exchange, and theoretical chemistry. from unpublished annual bibliographies compiled
The present volume is intended to cover the by volunteers for ASTM Committee E—14 on Mass
literature published since 1955. It is our hope Spectrometry, the compilations of Kiser [2], bib-
that it will serve several purposes. First, it will liographies published in “Advances in Mass
present essentially all of the values of appearance Spectrometry” [3], references given in various
potentials of positive ions obtained since 1955; review articles, and since 1964, by scanning
second it will provide a set of “best” values of “Current Content, Physical Sciences” and “Physics
hseeartvse aosfafogrumiadteiotontohfe lgiatseeraotuusre.ions; third, it will AWbestrfaecetls.t”hatThceovecruatgoeffisdarteaaswoansablJyuntehor30o,ugh196f6o.r
experimental papers but rather spotty for theoretical
1Figuresin brackets indicate the literaturereferenceson page4. and semiempirical treatments.
1
1.3. Order of Presentation Table A. Experimental techniques
The heart of this work is table 1, which gives
ionization potentials, appearance potentials, prob- Estimated pre-
able mechanisms, the method by which the data Abbre- Method Reference cuisrieomneinntmoefa—s-
was obtained, and computed heats of formation of viation
the various positive ions. The order of presentation
of the ions is that of increasing atomic number IP(eV) AP(eV)
(except for the rare gases, which are given to-
gether) and molecular complexity. Section 2, S Optical spectroscopy 27 ±0.01
“Order of Presentation,” lists the ions and the PI Photoionization 19,20-24 ±0.01 ±0.05
EM
order and page of their appearance. RPD ERleetcatrrdoinngmopnotoecnhtiraolmator 92,5,1206 ±±00..0055 ±±00..105
For each ion, the various processes of ion for- difference.
mation are arranged in order of increasing com- PE Photoelectron spec- 16,17,18 ±0.1 —
plexity, and for each order of complexity, in order troscopy.
SI Surfaceionization 29 ±0.1
of decreasing reliability of method. Thus direct CS Criticalslope 4 ±0.2 ±0.3
ionization processes are given before fragmentation SL Semi-logplot 8,28 ±0.2 ±0.3
processes and spectroscopic measurements before EVD Extrapolatedvoltage 1,8, 11 ±0.2 ±0.3
electron impact measurements. The mechanisms difference.
FDP Firstdifferentialplot 12 ±0.2 ±0.3
listed are usually, but not necessarily, those given MSD Morrison2nddifferential 12 ±0.2 ±0.3
in the original paper. Where more than one neutral plot.
product is proposed, we have usually considered VC Vanishingcurrentor 1,8 ±0.2 ±0.3
the mechanism to be too speculative to warrant VDF Volintiatgiaeldbirfefaekr.ence at 7,28 ±0.3 ±0.4
using the resulting heat of formation in arriving at fixedpercentofion
a “best” value. Appearance potentials are given current at standard
along with the investigator’s estimate of the pre- intensity.
cision of their measurements. These are usually EC Energy compensation 7,8 ±0.3 ±0.5
LE Linearextrapolation 1,8 ±0.4 ±0.5
average deviations from the average appearance NRE N'throotextrapolation 13, 14, 15 ? 9
pmoetaesnutiraelmeanntd.in no sense limits of accuracy of the TCCTS TChheaorrgeetitcraalnscfaelrcuslpaetcitorna 85,6 ?9 —
NS Unspecifiedelectron - - —
The method of measurement is indicated in an impactmethod.
abbreviated form along with each appearance po- D Derived — — -
tential. Table A lists the abbreviations, their mean-
ing, and at least one reference in which the method
is discussed in some detail. Theoretical calcula-
tions are included for completeness. The table also
includes an estimate ofthe reliability ofthe methods, 1.4. Reliability of Data and Criteria
which is discussed later. for Evaluation
For most measurements for which a reason-
ably unambiguous mechanism could be devised by As noted above, the basic information is of
either the investigator or, in a few instances, our- quite variable quality. The responsibility for this
selves, a heat of formation of the product ion has rests partly with the molecules and partly with the
been computed and listed in table 1. This calcula- experiments and their interpretation. A detailed
tion will be discussed below. In some instances discussion of these factors will not be given here;
where the heat of formation of the ion is well estab- some pertinent review articles are cited in refer-
lished but that of the neutral species, either reac- ences [1, 30, 31], The following general remarks are
tant or product, is not, we have computed the heat offered. Above the ionization threshold there exists
of formation of the neutral. The heats of formation a wide variety of cross-section behavior both for
of the neutrals thus determined are collected for atoms and molecules. In the former case an impor-
convenience in table 2. tant factor is autoionization from Rydberg levels
Finally, for each appearance potential given leading to electronically excited states of the ions.
in table 1, a numerical reference to the bibliography For molecules, in addition, there may be differences
of appearance potentials is listed. This bibliography between the equilibrium configuration of the mole-
follows table 2. The numbers were assigned in the cule and the molecule ion. Because of the Franck-
order in which the papers were read and, to sim- Condon principle this produces additional vibra-
plify the problem of seeking results by a particular tional structure in the cross-section curve. Thus, in
author, an author index is included. some cases doubt arises as to whether the ionization
2