A R T I C L E S
Wang and Andrews
Table 1. Infrared Absorptions (cm-1) Observed for Reactions of
Laser-Ablated Group 14 Elements Co-deposited with Pure
Hydrogen or Deuterium at 3.5 K
Si
Ge
Sn
Pb
H
2
D
2
H
2
D
2
H
2
D
2
H
2
D
2
identification
1501.3 1076.2 MH, site
1497.8 1069.2 MH, site
1834.0 1316.1 1645.5 1183.1 1494.1 1066.8 MH
1825.3 1313.6 1643.9 1180.5 1488.3 1063.9 MH
1858.5 1338.4
1543.7 1108.6 MH2
1856.4 1335.7 1669.6 1200.7 1540.7 1105.1 MH2
1854.5 1332.7 1665.4 1197.6 1537.1 1103.0 MH2
902.8 646.5
925.3 668.7 2093.3 1500.9 1851.7 1330.7 1692.9 1217.4 MH3
722.9 545.7 853.5 632.3 457.2 MH3
2183.5 1593.2 2104.9 1516.8 1899.5 1664.4 1815.0 1302.0 MH4
703a
MH2
908.4 670.9 816.8 590.9 677.5 486.6
1114.2
MH4
978.2 737.5 M2H2
1096.4
970.3
911.7 665.3 789.4 575.9 M2H2
Figure 1. Infrared spectra in the 2220-1680 cm-1 region for laser-ablated
Si or Ge co-deposited at 3.5 K for 25 min with 2.5 mmol of normal
hydrogen: (a) Si + H2, (b) after annealing to 6.3 K, (c) after λ > 240 nm
irradiation, (d) Ge + H2, (e) after annealing to 6.3 K, and (f) after λ > 240
nm irradiation.
2035b 1481
1459.2c 1045.8c M2H4
2009b 1468
959.5c 702.6c M2H4
2170.0 1580.6 2078.7
2156.5 1546.0
900.8 679.0
837.7 619.6 750.3 542.0
1841.7
M2H6
M2H6
M2H6
M2H6
-
1709.6
1383
995
MH3
stretching region is illustrated in Figure 1. Not shown are the
broad 4781, 4548, and 4222 cm-1 and sharp 4736, 4502, and
4147 cm-1 absorptions characteristic of solid hydrogen.15 Very
strong 2183.5 and 908.4 cm-1 absorptions are due to SiH4: these
bands and the 2189.4 cm-1 satellite, which increases on
annealing, are in very good agreement with hydrogen matrix
spectra of authentic SiH4 co-deposited with hydrogen at 2 and
4 K.17 Weak 925.3 and 722.9 cm-1 absorptions are due to the
SiH3 radical, and again the ν3 fundamental of SiH3 is covered
by the strong SiH4 absorption, but absorptions of Si2H6 (Table
1) are shown in the figure.33 Additional sharp bands due to Si2H2
1255.7 924.7 PbxHy
a New weak bands in solid argon at 702 and 501 cm-1 track with PbH2
and PbD2 bands on annealing and photolysis. b Probably GeH2GeH2 isomer.
c HPb(µ-H)2PbH isomer, matrix splittings at 966.9 and 712.0 cm-1
.
tion, annealing, and filtered UV-vis irradiation. We annealed solid
hydrogen samples to 6.0-6.8 K using resistance heat on the refrigerator
cold stage: the samples were above 6 K for less than 30 s.
Density functional theory frequency calculations were helpful in
assigning lead and platinum hydride spectra,4,27 so similar B3LYP/6-
311++G**/SDD calculations were performed for dilead hydrides.28-31
Comparable results were obtained using the BPW91 functional.32
Although these calculations are only approximate, they provide a useful
guide for assigning vibrational spectra.
at 1096.4 cm-1 disappear on annealing, and those due to SiH3
-
at 1841.7 cm-1 disappear on photolysis (Figure 1b,c): neon
matrix counterparts at 1100 and 1837 cm-1 behave similarly.33
A weaker 1858.7 cm-1 band may also be due to SiH3-. The
yield of Si2H2 in these experiments is much smaller than that
produced from thermal evaporation of Si atoms in a recent
investigation.35 Note the complete absence of SiH2 and SiH
absorptions, which would appear in the 2000-1950 cm-1 region
between the neon and argon matrix counterparts observed
previously. The failure to trap SiH and SiH2 in solid hydrogen
attests to their great reactivity with H2.
Results and Discussion
Infrared spectra from Si, Ge, Sn, and Pb atom co-condensation
reactions with pure hydrogen will be reported. Table 1 compares
the product absorptions, which are assigned by comparison with
previous neon, deuterium, and argon matrix work.4,33,34
Silicon. Matrix isolation investigations were done with silicon
and pure hydrogen using two laser energies, and the Si-H
A recent investigation of Si atom reactions with SiH4 in
excess argon reported spectra of the SiH2SiH2 and SiH3SiH
isomers.36 This work shows that the 2150, 2145, 857 cm-1 bands
previously assigned to Si2H4 must be due to another transient
species, and SiH3SiH is a good possibility assuming that the
strong 1963 cm-1 band is masked by the strong SiH absorption
we observed in solid argon.33 Any SiH2SiH2 absorptions in pure
H2 are masked by strong SiH4 absorptions, and the strongest
SiH3SiH absorption at 1963 cm-1 is clearly not observed in the
present pure hydrogen experiments (Figure 1).
(27) Andrews, L.; Wang, X.; Manceron, L. J. Chem. Phys. 2001, 114, 1559
(Pt + H2).
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R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
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R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
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Germanium. Infrared spectra of germanium reaction products
are shown in Figure 1d. The most obvious difference with silicon
is the observation of strong GeH2 (1858.5, 1854.5 cm-1) and
GeH (1834.0, 1825.3 cm-1) absorptions and weak GeH4
(29) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Stevens, P. J.; Devlin,
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(33) Andrews, L.; Wang, X. J. Phys. Chem. A 2002, 106, 7697 (Si + H2).
(34) Wang, X.; Andrews, L.; Kushto, G. P. J. Phys. Chem. A 2002, 106, 5809
(Ge + H2).
(2112.2, 2104.9, 816.8 cm-1) and GeH3 (2093.3, 853.5 cm-1
)
absorptions. This demonstrates that GeH and GeH2 are much
(35) Maier, G.; Reisenauer, H. P.; Meudt, A.; Egenolf, H. Chem. Ber. 1997,
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(36) Maier, G.; Reisenauer, H. P.; Glatthaar, J. Chem.-Eur. J. 2002, 8, 4383.
9
6582 J. AM. CHEM. SOC. VOL. 125, NO. 21, 2003