The adiabatic I.P. of Si2H6 obtained by a photoionization mass spectrometric study at two temperatures is 9.74±0.02 eV. The first fragment, Si2H+4, initially appears with a shallow slope at ≤10.04±0.02 eV, and with a much steeper slope at ≤10.81±0.02 eV. It is argued that the initial onset corresponds to formation of H2SiSiH+2, while the steeper onset is attributed to formation of H3SiSiH+. The second fragment, Si2H5, has an appearance potential of ≤11.59±0.02 eV (11.41±0.03 is a probable value). Successive decomposition leads to Si2H+2 (from Si2H+4 ) and Si2H+3 (from Si2H+5 ). The photoion yield curve for Si2H+3 also displays shallow and steep onsets. Upper limits for the appearance potentials can be readily extracted, but the true thermochemical onsets are less well defined. Heats of formation (or upper limits) are presented for each of these species. For Si2H+6, Si2H+5, and Si2H+4, the experimental values are in good agreement with recent abinitio calculations. For the daughter species, the experimental values exceed the calculated ones, as expected.

1.
M. L.
Mandich
,
W. D.
Reents
, Jr.
, and
K. D.
Kolenbrander
,
J. Chem. Phys.
92
,
437
(
1990
);
M. L.
Mandich
,
W. D.
Reents
, Jr.
, and
M. F.
Jarrold
,
J. Chem. Phys.
88
,
1703
(
1988
).,
J. Chem. Phys.
2.
J.
Berkowitz
,
J. P.
Greene
,
H.
Cho
, and
B.
Ruscic
,
J. Chem. Phys.
86
,
1235
(
1987
).
3.
L. A.
Curtiss
and
J. A.
Pople
,
Chem. Phys. Lett.
144
,
38
(
1988
).
4.
H.-J.
Kohler
and
H.
Lischka
,
Chem. Phys. Lett.
112
,
33
(
1984
).
5.
H.-J.
Kohler
and
H.
Lischka
,
Chem. Phys. Lett.
98
,
454
(
1983
).
6.
H.
Lischka
and
H.-J.
Kohler
,
J. Am. Chem. Soc.
105
,
6646
(
1983
).
7.
H.
Lischka
and
H.-J.
Kohler
,
Chem. Phys. Lett.
85
,
467
(
1982
).
8.
H. J.
Kohler
and
H.
Lischka
,
J. Am. Chem. Soc.
104
,
5884
(
1982
).
9.
P.
Ho
and
C. F.
Melius
,
J. Phys. Chem.
94
,
5120
(
1990
).
10.
P.
Ho
,
M. E.
Coltrin
,
J. S.
Binkley
, and
C. F.
Melius
,
J. Phys. Chem.
90
,
3399
(
1986
).
11.
J. S.
Binkley
,
J. Am. Chem. Soc.
106
,
603
(
1984
).
12.
D. S.
Horowitz
and
W. A.
Goddard
III
,
J. Mol. Struct.
163
,
207
(
1988
).
13.
J. A.
Boatz
and
M. S.
Gordon
,
J. Phys. Chem.
94
,
7331
(
1990
).
14.
M. S.
Gordon
,
T. N.
Truong
, and
E. K.
Bonderson
,
J. Am. Chem. Soc.
108
,
421
(
1986
).
15.
B. T.
Colegrove
and
H. F.
Schaefer
III
,
J. Chem. Phys.
93
,
7230
(
1990
).
16.
B. T.
Colegrove
and
H. F.
Schaefer
III
,
J. Phys. Chem.
94
,
5593
(
1990
).
17.
A. F.
Sax
and
J.
Kalcher
,
J. Phys. Chem.
95
,
1768
(
1991
).
18.
J.
Kalcher
,
A.
Sax
, and
G.
Olbrich
,
Int. J. Quantum Chem.
25
,
543
(
1984
).
19.
G.
Olbrich
,
Chem. Phys. Lett.
130
,
115
(
1986
).
20.
K.
Raghavachari
,
J. Chem. Phys.
92
,
452
(
1990
).
21.
K.
Raghavachari
,
J. Chem. Phys.
88
,
1688
(
1988
).
22.
L. A. Curtiss, K. Raghavachari, P. W. Deutsch, and J. A. Pople, J. Chem. Phys. (submitted).
23.
R. S.
Grev
,
B. J.
Deleeuw
, and
H. F.
Schaefer
III
,
Chem. Phys. Lett.
165
,
257
(
1990
).
24.
B.
Ruscic
and
J.
Berkowitz
,
J. Chem. Phys.
95
,
2416
(
1991
).
25.
S. T.
Gibson
,
J. P.
Greene
, and
J.
Berkowitz
,
J. Chem. Phys.
83
,
4319
(
1985
).
26.
H.
Bock
,
Angew. Chem. Int. Ed.
28
,
1627
(
1989
);
see also
H.
Bock
,
W.
Ensslin
,
F.
Feher
, and
R.
Freund
,
J. Am. Chem. Soc.
98
,
668
(
1976
).
27.
P.
De Bievre
,
M.
Gallet
,
N. E.
Holden
, and
I. L.
Barnes
,
J. Phys. Chem. Ref. Data
13
,
809
(
1984
).
28.
P.
Potzinger
and
F. W.
Lampe
,
J. Phys. Chem.
73
,
3912
(
1969
).
29.
K.
Watanabe
,
J. Chem. Phys.
26
,
542
(
1957
);
K.
Watanabe
,
22
,
1564
(
1954
).,
J. Chem. Phys.
30.
H.
Chatham
,
D.
Hils
,
R.
Robertson
, and
A.
Gallagher
,
J. Chem. Phys.
81
,
1770
(
1984
).
31.
P.
Potzinger
,
A.
Ritter
, and
J.
Krause
,
Z. Naturforsch.
30a
,
347
(
1975
).
32.
S. G.
Lias
,
J. E.
Bartmess
,
J. F.
Liebman
,
J. L.
Holmes
,
R. D.
Levin
, and
G. W.
Mallard
,
J. Phys. Chem. Ref. Data
17
, Suppl. 1,
623
(
1988
).
33.
The rationale for making this correction is given by
P. M.
Guyon
and
J.
Berkowitz
,
J. Chem. Phys.
54
,
1814
(
1971
). The actual computation for Si2H6 is given in Ref. 25.
34.
See, for example, J. Berkowitz, “Photoabsorption, Photoionization and Photoelectron Spectroscopy (Academic, New York, 1979), p. 305.
35.
J. Berkowitz, Ref. 34, pp. 300–301.
36.
H. M.
Rosenstock
,
R.
Buff
,
M. A. A.
Ferreria
,
S. G.
Lias
,
A. C.
Parr
,
R. L.
Stockbauer
, and
J. L.
Holmes
,
J. Am. Chem. Soc.
104
,
2337
(
1982
).
37.
Landolt-Bornstein Tables, New Series, Vol. 7, Structure Data of Free Polyatomic Molecules (Springer-Verlag, Berlin, 1976), p. 95.
38.
G. W.
Bethke
and
M. K.
Wilson
,
J. Chem. Phys.
26
,
1107
(
1957
);
J.R.
Durig
and
J. S.
Church
,
J. Chem. Phys.
73
,
4784
(
1980
).
39.
K. Raghavachari (private communication).
40.
R. E.
Kutina
,
G. L.
Goodman
, and
J.
Berkowitz
,
J. Chem. Phys.
77
,
1664
(
1982
).
41.
Z.
Prasil
and
W.
Forst
,
J. Phys. Chem.
71
,
3166
(
1967
).
42.
S. R.
Gunn
and
L. G.
Green
,
J. Phys. Chem.
65
,
779
(
1961
).
43.
M. W.
Chase
, Jr.
,
C. A.
Davies
,
J. R.
Downey
, Jr.
,
D. J.
Frurip
,
R. A.
McDonald
, and
A. N.
Syverud
,
J. Phys. Chem. Ref. Data
14
, Suppl. 1,
1211
(
1985
).
44.
B. H.
Boo
and
P. B.
Armentrout
,
J. Am. Chem. Soc.
109
,
3549
(
1987
).
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