national Bureau ->f Standards

Library, n.w. Bidg Reference book not to be

JUL 8 1964 foljpp frnm tb"

'"

^ecknlcaL viete 243

SURVEY OF MULTIPLY CHARGED IONS

FRED L. MOHLER

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

Technical Note 243

ISSUED MAY 27, 1964

SURVEY OF MULTIPLY CHARGED IONS

Fred L. Mohler

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 - Price 10 cents

.
Survey of Multiply Charged Ions

Fred L. Mohler*

This is a survey of experimental results on multiply

charged rare gas ions, molecule ions and radical ions with

emphasis on simpler compounds that may be of astrophysical

interest. Tables of rare gas ions, simple molecules and a few hydrocarbon molecules include data on relative abundance

and appearance potentials of the ions.

lo Introduction

Interest has been expressed in the occurrence of multiply charged

molecule ions and rare gas ions that are observed or could be expected

in atmosopheres of planets and stars. Wilkinson [l] listed possible

molecules, atoms and radicals as; rare gases, N9

, 0~, NO, NH_, NH , oxides

of carbon, CH,, C^, C

2

H,, CH

2

, C

2 H, C

2

, C , CN, H

2 0, HCN and SiC

2

.

Mrs. Charlotte Moore Sitterly suggested that there is also interest in

BO, N

20, N2 0,, TiO, BH, A1H, MgH, SiH, CaH, SiF, and ZrO„ OH has

recently been reported in the radio spectrum of a nebula Many of these

compounds are radicals rather than molecules., This is true of NH_,

CH

2

, C_H, SiC~, BO, OH, the listed metal mono -hydrides; SiF and ZrO.

In the case of radicals one can look for the doubly charged radical ion

as a product of ionization of a molecule,

I have included doubly charged ions of a number of other simple

compounds in this report as the interest in this subject is not limited

to astrophysics.

*Retired Staff Member
Rare gas ions of multiple charge have been identified and classified

spectroscopically for all the rare gases [2j» Research on multiple

ionization of atoms and molecules by electron collision has been stimulated by theoretical studies by Wannier [3] and Geltman [4]. They

indicate that the probability of n-fold ionization will increase above

the threshold as the nth power of the excess voltage above the threshold. The excitation function begins to round off within 10 volts of

the threshold and approaches a flat maximum within 100 volts.

In the preparation of this report, the book by Field and Franklin

on electron impact phenomena [5] has been a valuable assistance. It

gives a quite complete survey of all experimental work on the subject

up to 1957. A paper by Dorman and Morrison on double and triple ionization of molecules [6] published in 1961 in J. Chem. Phys, was also very

helpful. In view of the fairly complete coverage of data to 1961, I

have not attempted to report all the research on this subject but list

for each molecule only the results of one or two researches which I

consider to be the most accurate and most complete.

In the case of molecular ionization it requires mass spectrometric

analysis to identify doubly charged molecular ions and in the case of

14 14 2+

simple symmetrical molecules this method may fail. Thus N N will

14+

not be distinguished from N . In recent years highly enriched heavy

isotopes of the common gases have been available and one can study unsymmetrical molecules such as N N , and deuteroacetylene

CH-CD to distinguish doubly charged molecules of apparent mass 14,5 16.5

and 13.5 from singly charged fragment ions.

Relative abundance is expressed in a variety of ways. API tables

2

m^iMa^BiMi
[7] give abundance at 70 volts relative to the maximum peak in the mass

spectrum. Others use the abundance at some other fixed voltage or at

the maximum of the excitation function. While abundance is commonly

expressed in terms of the ion current, Fox [8], [9] gives abundance in

terms of the relative number of ions at the maximum of the excitation

function. Thus the number of doubly charged ions is proportional to the

current ratio divided by 2.

2 Results

Table 1 lists data on the rare gas ions. Spectroscopic values of

the appearance potentials are available to Ne , Ar , Kr and Xe

In recent years there have been a number of mass spectrometric studies

of rare gas ions and the choice of data cited in table 1 is rather

arbitrary o Fox [8,9] as noted above compares the number of ions and

Melton [11] compares ion currents at 3<>5 KeVo

Tables 2 and 3 give data for simple molecules and some hydrocarbons.

Column one gives the chemical formula of the molecule, column 2 the

formula of the ion, column 3 the abundance, column 4 the appearance

potentials and column 5 references. Double entries in column 4 are

double series limits. Experimental errors given in these tables are

values given by the authors.

Only a few hydrocarbons are listed in table 3 as interest was

primarily in simple molecules. There are fairly complete data on

abundances of the molecule ions and fragment ions of C 9 hydrocarbons.

Table 2 lists data for simple inorganic molecules. Direct experiments on the appearance potentials of N„ and 0« are complicated by

the impossibility of distinguishing atom ions from doubly charged

3
molecules in symmetrical N„ and „ Quite recently there has been

14 15++ research on the appearance potentials of N N at m/e 14.5 Fl2,6]

and 16 17

at m/e 16.5 [12].

There are some significant omissions from this table. Of the

halogen acids all but HF give doubly charged ions and Dorman and

Morrison [6] find HF less than 10 of HF . Of the halogen molecules

F and I are monoisotopic and F_ and I

' cannot be distinguished

+ -j- from F and I by a mass spectrometer. Dorman and Morrison [6] also

find H„0 less than 10 and undoubtedly the same applies to OH for

a mass peak of 8 1/2 would not escape observation.

Some qualitative observation of carbon ions are included in the

table. These and heavier ions to C Q are obtained in a vacuum spark

discharge between graphite electrodes. Chupka and Inghram [28] ionized

carbon evaporated from incandescent carbon and found C , C„ and C„ in

the ratios 1 to .5 to 1.6 at 17 volts but did not look for doubly charged carbon molecules . Only a few hydrocarbons are listed in table 3

acetylene, ethylene and ethane, benzene, methyl benzene and maphthalene.

It is convenient to use monodeutero compounds for then the doubly

charged molecule ions have half integer values. Data on the appearance

potentials are incomplete

This report is primarily concerned with the simpler compounds but

a few remarks on other hydrocarbons are in order. Multiply charged

molecule ions become relatively abundant in the fused ring aromatic

compounds naphthalene, anthracene, phenanthrene, etc [6,7]» In an

early survey of doubly charged hydrocarbon compounds [25] it is pointed

out that in compounds with 5,6 or 7 carbon atoms the more abundant

4

mma^
doubly charged ions come from molecules with most of the H atoms removed,

A qualitative explanation of this is that when electrons are removed from two radicals in a polyatomic molecule single bonds tend to

be broken but double bonds do not. Mohler, Dibeler and Reese | 30] have

identified fragment ions from the disruption of doubly charged molecules

by the kinetic energy gained from the Coulomb repulsion,,

3. References

[1] P.G. Wilkinson, J» Mol„ Spectrosc 6_, 1 (1961).

[2] Charlotte E. Moore, Atomic Energy Levels Volo III, Table 34, NBS

Circo 467. (May 1, 1958).

[3] Go Wannier, Phys Rev. 90, 817 (1953)=

[4] So Geltman, Phys. Rev. 102, 171 (1956).

[5] FoH. Field and J»L. Franklin, Electron Impact Phenomena and the

Properties of Gaseous Ions, Academic Press, New York, 1957.

T6] JoH. Dorman and J.D. Morrison, J» Chem„ Phys. 35, 575 (1961)^o

[7] American Petroleum Insto Catalog of Mass Spectral Data«

[8] RoE. Fox, Advances in Mass Spectrometry, p 397, Pergamon Press,

London (1959).

[9] RoE. Fox, Jo Chem. Phys» 33, 200 (1960).

[10] W. Bleakney, Phys. Rev. 35, 1303 (1930).

[11] Charles E. Melton, J. Chem. Phys 37, 562 (1962).

[12] JoD. Dorman and J.D. Morrison, J Chem. Phys D 39_, 1906 (1963).

[13] JoT. Herron and V.Ho Dibeler, J. Chem Phys. 32, 1884 (1961)»

[14] Kusch, Hustralid and Tate, Phys Rev. 52, 843 (1937).

[15] JoWo Warren and J„D. Craggs, Mass Spectrometry, p. 36, Insto of

Petroleum, London (1952)

5
[16] VoH. Dibeler and F.L. Mohler, J. Res. NBS 40, 25 (1948) RP 1853 .

[171 R.Fo Baker and J.T. Tate, Phys Rev. 53, 683 (1938)

[18] RoH. Vought, Phys, Rev. 71, 93 (1947).

[19] Mohler, Dibeler, Williamson and Dean, J. Res. NBS 48, 188 (1952)

RP 2304 .

[20] Dibeler, Mohler and deHemptinne, J. Res. NBS 53_, 107 (1954) RP

2522 .

[21] Edith Quinn and F.L. Mohler, J. Res. NBS 65A (Phys. and Chem.

)

No. 2, 93 (1960).

[22] M.E. Wacks and V.H. Dibeler, J. Chem. Phys. 31, 1557 (1959).

[231 V.H. Dibeler and F.L. Mohler, J. Am. Chem. Soc. 70, 987 (1948).

[24] Dibeler, Mohler and Williamson, J. Res. NBS 44, 489 (1950) RP

2095 .

[25] F.L. Mohler, E.G. Bloom et al, J. Res. NBS 42, 369 (1949) RP

1975 .

[261 von E. Dornenburg and H. Hintenburger, Z. f. Naturforsch 14a,

765 (1959).

T27] Kusch, Hustralid and Tate, Phys. Rev. 52, 840 (1937).

[28] W.A. Chupka and M.G. Inghram, J. Chem. Phys. 21_, 371 and 1313

(1953).

[29] J. A. Hippie, Phys. Rev. 53, 530 (1938).

[30] F.L. Mohler, V.H. Dibeler and R.M. Reese, J. Chem. Phys. 2_2,

394 (1964).

[31] Amos S. Newton, J. Chem. Phys. 40, 607 (1964).
Table I. Multiply Charged Ions of Rare Gases

Ion Abundance Ref. Appearance Pot. Ref.

He+

1 24.58 Spect. [2]

He

2+

.0042 [81 78.98 Spect. [2]

Ne

+

lo [10] 21.56 Spect. [2]

M

2+

Ne .11 [10] 62.63 Spect. [2]

M

3+

Ne .003 no] 126.13 Spect. [2j

Ne 223.15 Spect. [2]

m 5+

Ne 349.45 Spect. [2]

Ne

6+

507.36 Spect. [2

Ar

+

1.0 [91 15.76 Spect. [2]

A 2+

Ar .17 [9] 43.38 Spect. [2

A 3+

Ar .007 [9] 84.28 Spect. [2]

A 4+

Ar .0008 [9] 144 . 07 Spect. [2]

A 5+

Ar .0004 [11] 219.07 Spect. [2]

A 6+

Ar . 00006 [111 310.37 Spect. [2]

A 7 +

Ar .00003 mi 434.37 Spect. r 2]

a 8+

Ar .000008 [in 577.83 Spect. [2]

Ar

9+

1000.4 Spect. [2]

Kr

+

1 [91 14.00 Spect. [2]

Kr .21 [91 38.56 Spect. [2]

V 3+

Kr .06 [9] 75.46 Spect. [21
(Continued) Table I

Ion Abundance Ref

.

Appearance Pot. Ref.

v

4+

Kr .008 [91 147±2 ^9]

Kr .001.008 r 9,10] 218±10 [9]

v 6+

Kr .002 [11] 350110 L9J

V

7 +

Kr .0005 [11]

Kr

8+

.00005 [11]

Xe

+

1.0 [8] 12.12 Spect. [21

Xe

2+ 0.40 [8] 33.33 Spect. [2]

Xe

3+

.17 [8] 65.5 Spect. [2]

Xe

4+

.064 [8] 111. Spect. [2]

Xe

5+ .019 [8] 187. Spect. [2]

Xe

6+

.0022 [8] 255. ±3 [8]

Xe

7+ .00017 [8] 390 ±10 18]
Table II. Multiple Ionization of Simple Molecules

Molecule Ion Abundance

Percent

Appearance

Pot. e.v

Ref.

N

2

N

14

N

15++

42.7,43.811 12

0o2 43,5 6

°2

NO

o^o17"" 36.31.5 12

NO""" 0.1 39o8 6

CO 00++ 3xl0" 241.8,45.9 6

co

2 CO^ 4xl0" 2

36.4,41.91.3 6

NH

3

NH

3

^

5xl0"333. 7, 36.8+.

6

HC1 HCl""" 7xl0"

3 35.51.5 6

DBr DBr""" 0.1 33.21.3 6

HI HI*"" Ool 30.01.5 6

C1

2

ci- 32.6 13

Br

2

Br

2

30.0 13

HCN hcn4

"

1" 0.88 40.311 14

CF

4

nT1 ++

CF

3

0.58 45.51.5 15

CF

4

CF~ lo7 43.81.3 16

CF

4

CF- lc35 44.11.5 15

CF

4

CF- 4.9 44.31.5 16

CF

4

CF++ 6xl0"

2

16

CF

3

C1 CF

2

Cl"

hH

.6 38.81.5 15

CF

3

C1 CFCl4

"

1" .7 41.01.3 15

CF

2 C1

2

CF

2

C1++ 36.31.5 15
Continued Table II

Molecule Ion Abundance

Percent

Appearance

Pot. e.v

Ref

.

CF

2

C1

2

CFCl^ 36.5±.5 15

CFCl CFC1

2

++

2o4 34.51.3 15

CFCI3 cci

2

+4" 3.0 15

CC1.

4 < 33.1 15

CC1,4 CClj4*

34.2 17

SiF.

4

SiF

3

++

1.12 16

SiF.

4

SiF./"" 3.75 16

SiF.

4

SiF*4

" .71 16

SF

6

SF4^ 9.7 40.6±.5 16

SF

6

SF~ 1.1 16

SF

6

SF- 6.0 46.5±.5 16

^6 SF++ .68 16

SiCl.

4

SiCl^ 4.9 33.81.5 18

SiCl.

4

SiCl^ .65 37.31.5 18

SiCl,4SiCl"^ 1.2 4211 18

B

2

H

6

B^B1 ^

.43 23

B

2

D

6

B

10

B

U

D

2

^

.40 24

SbCl SbCl

2

++

5.2 32.1 27

SbCl

3

SbCl"*"

4

" 4.5 34.8 27

AsCl

3

AsCl

2 ++

3.0 33.1 27

10
Continued Table II

Molecule Ion Abundance

Percent

Appearance

Pot. e.v

Ref.

PC1

3

pci

4-1" 2.4 27

cs

2

cs^ 27.4±.2 31

cs

2 cs^ .07 53.6±.5 31

COS cos""" 5.2 7

COS cos"""

4

" .0007 31

C

2

N

2

C N +++

.0005 31

-6

Graphite C~ } C, and heavier ions in vacuum spark [26]

Table II addendum-negative results

I

I I 1 I 1 1 1 HF , H^O } OH , CH, are not observed and are less than 10

of the singly charged ion [6].

F_ and I„ are unmeasurable as they are indistinguishable from

F and I and C

? N_ is not reported as it is masked by CN .

II
Table III. Multiply Charged Ions of Hydrocarbons

Molecule

Ion

Abundance

Percent

Appearance

Pot. e.v Ref.

G

2

HD

Ethylenes

C

2

H

3

D

C

2

H

4

Ethanes

C

2

H

5

D

C

2 HjD

C

2

H

5

D

C

2

H

6

C

2

H

6

C

2

H

6

C

2

H

2

D

4

C

2

H

2

D

4

C

2

H

2

D

4

Benzene

C,HC D

6 5 C,HC D

o J

Toluene

C

6

H

5

CH

3

C

2

HD

C

2

H

3

D

C

2

H

3

C

2

H

3^

C

2

H

5

D

C

2

H

3^

C

2

H

5

C

2

H

5

-

C

2

H

3

C

2 HD4

C

2

HD

3

-

C

2

HD

2

"

C

6

H

5

D

C

6

H

5

D

C

6

H

5

CH

3

and C

2

H

3

D

and C

2

HD

_H

2.70

.28

.38

.3

.01

»84

o 09

.54

.06

.20

.59

.03

2.0

-4

10 7.

0.1

36.0

32.2±1.5

26.0

44±5

24.5±2

19

20

20

14

21

21

21

21

29

21

21

21

21

6

6

12
Continued Table III

Abundance Appearance

Molecule Ion Percent Po t a e . v Refo

C

6

H

5

CH

3

1 | j Cs HC CH

O _> J 10" 7% 42±5 6

Naphthalene

-

C 10H

8

C

10

H

8

.2 22.8±„2 6

C

10

H

7 D °10H

7 D++ 12c 19

C

1()H

7 D C10

H

7

D++ 22,7 22

C 10H

8

1

C10H

8

3xl0" 5 40+5 6

13

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