Infrared spectra and density functional calculations of the SiCO4 molecule in solid argon

Article abstract of DOI:10.1016/S0009-2614(02)00145-8

The SiCO₄ molecule has been produced by reaction between silicon dioxide and carbon dioxide molecules in solid argon. Silicon dioxide molecules were prepared by reactions of laser-ablated silicon atoms with oxygen in excess argon. When carbon d

Full text of DOI:10.1016/S0009-2614(02)00145-8

2
5 March 2002
Chemical Physics Letters 355 (2002) 31–36
www.elsevier.com/locate/cplett
Infrared spectra and density functional calculations of
the SiCO molecule in solid argon
4
Jian Dong, Lei Miao, Mingfei Zhou *
Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry and Laser Chemistry Institute, Fudan University,
Shanghai 200433, PR China
Received 5 December 2001; in final form 17 January 2002
Abstract
4
The SiCO molecule has been produced by reaction between silicon dioxide and carbon dioxide molecules in solid
argon. Silicon dioxide molecules were prepared by reactions of laser-ablated silicon atoms with oxygen in excess argon.
When carbon dioxide molecules were added in the reagent gas, new product absorptions at 1934.9, 1326.1, 1070.2 and
ꢀ1
8
66:0 cm were produced spontaneously on annealing. Based on isotopic substitution and density functional theo-
retical calculations, these absorptions are assigned to the vibrational fundamentals of the SiCO molecule that has C2v
symmetry with two terminal O atoms and two bridging O atoms. Ó 2002 Elsevier Science B.V. All rights reserved.
4
1
. Introduction
should have the slipped parallel C2h structure [4].
The slipped parallel structure was supported by
later spectroscopic studies [5,6] as well as high level
theoretical calculations [7–10].
While the silicon dioxide and carbon dioxide
molecules are quite similar, their dimers are very
different. Although the carbon dioxide dimer is a
weakly bonded van der Waals complex, the silicon
dioxide dimer is a strongly covalent bonded mol-
ecule. The silicon dioxide dimer was first produced
The stabilities, structures and spectra of small
carbon and silicon oxides have gained considerable
attentions. The simplest of carbon dioxide clusters
ðCO Þ has been the subject of several experi-
2
2
mental [1–6] and theoretical studies [7–10]. It is
well known that carbon dioxide molecules can
only form weak van der Waals dimer complex via
electrostatic interaction. Earlier experimental in-
vestigations in the gas phase [1,2] and in rare gas
matrices [3] suggested that the carbon dioxide di-
mer has a T-shaped structure, but a later molec-
ular beam diffraction study showed that the
carbon dioxide dimer had no dipole moment and
2 2 2
by reactions between Si O and O in a solid matrix
and identified by its infrared absorption spectrum
[11]. The ground state structure is deduced to be a
symmetric D2h molecule with two terminal O at-
oms and two bridging O atoms. This D2h structure
is consistent with a later photoelectron spectro-
scopic study [12] and a theoretical prediction [13].
In this Letter, we report the first vibrational
*
Corresponding author. Fax: +86-21-65-64-35-32.
E-mail address: mfzhou@fudan.edu.cn (M. Zhou).
spectra of the SiCO
4
molecule produced by
0
009-2614/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved.
PII: S0009-2614(02)00145-8

32
J. Dong et al. / Chemical Physics Letters 355 (2002) 31–36
reaction between silicon dioxide and carbon di-
oxide molecules in solid argon. The structure de-
duced from the spectra is also confirmed by
density functional theoretical calculations. The
deposition at 11
ꢀ
K
revealed strong SiO
2
1
ꢀ1
ð1416:4 cm Þ and SiO ð1226:2 cm Þ absorptions
ꢀ
ꢀ1
þ
4
[20,21] and weak O ð953:7 cm Þ; O ð1118:4
4
ꢀ
1
ꢀ1
cm Þ and O
3
ð1039:5 cm Þ absorptions [22,23].
4
structure and bonding of SiCO molecule is similar
Sample annealing to 25 and 28 K decreased the
ꢀ
þ
4
to the silicon dioxide dimer. It has planar C2v
symmetry with two terminal O atoms and two
bridging O atoms.
O ; O absorptions and increased the SiO and
2
4
O3 absorptions. Another experiment was done
using 0.5% CO in argon as reagent gas. Weak SiO
2
and CO absorptions were present directly after
sample deposition and increased on broadband
photolysis.
2
. Experimental and computational methods
New product absorptions were produced when
The experimental setup for pulsed laser ablation
O
The spectra in the 1970–1850 and 1430–820 cm
regions are shown in Fig. 1, with the product ab-
sorptions listed in Table 1. Besides the silicon ox-
ide and oxygen cluster absorptions that are
2
=CO
2
=Ar mixtures were used as reagent gas.
ꢀ
1
and matrix infrared spectroscopic investigation
has been described previously [14]. The 1064 nm
Nd:YAG laser fundamental (Spectra Physics,
DCR 150, 20 Hz repetition rate and 8 ns pulse
width) was focused onto the rotating silicon target
using low laser energy (2–10 mJ/pulse). The ab-
lated silicon atoms were co-deposited with oxygen
ꢀ
common to silicon and oxygen reactions, the CO
ꢀ
4
1
absorptions (1891.6, 1257.0 and 691:2 cm Þ
[24,25], together with a new family of absorptions
1
ꢀ
(
0.5–1.0%) and carbon dioxide (0.2–0.5%) mix-
at 1934.9, 1326.1, 1070.2 and 866.0 cm were
ꢀ
tures in argon onto a 11 K CsI window, which was
mounted on a cold tip of a closed-cycle helium
refrigerator (Air Products, Model CSW202) for
one hour at a rate of 2–4 mmol/h. Infrared spectra
were recorded on a Bruker IFS113V spectrometer
observed on sample deposition. The CO absorp-
4
tions decreased slightly on annealing and almost
disappeared on broadband photolysis. The new
absorptions at 1934.9, 1326.1, 1070.2 and 866.0
ꢀ
1
cm were greatly enhanced on 25 K annealing.
13
ꢀ
1
at 0:5 cm resolution using a DTGS detector.
Matrix samples were annealed at different tem-
peratures, and selected samples were subjected to
broadband photolysis using a high pressure mer-
cury arc lamp with the globe removed.
2 2
The experiments were repeated with CO =O ,
1
2
6
13
18
16
CO
18
2
þ CO
2
=O
2
, CO
2
= O
2
and CO
2
= O
samples, and the results are sum-
2
þ
1
18
O O þ O
2
marized in Table 1. Representative spectra in se-
lected regions are shown in Fig. 2.
The absorptions at 1934.9, 1326.1, 1070.2 and
Density functional theoretical calculations were
performed using the GAUSSIAN 98 program [15].
The three parameter hybrid functional according
to Becke with additional correlation corrections
due to Lee, Yang and Parr was used (B3LYP)
ꢀ
1
4
866:0 cm are assigned to the SiCO molecule.
These absorptions maintained the same relative
intensities throughout all the experiments, sug-
gesting that they be due to different vibrational
ꢀ
1
[
16,17]. The 6-311 + G(d) basis sets were used for
modes of the same molecule. The 1934:9 cm
ꢀ
1
13
all three kinds of atoms [18,19]. The geometries of
the calculated species were fully optimized, and
harmonic vibrational frequencies were calculated
with analytic second derivatives, and zero point
vibrational energies (ZPVE) were derived.
band went to 1888:1 cm with CO and gave an
2
12
13
isotopic C= C ratio of 1.0248. In the mixed
13
1
2
CO þ CO experiment, no intermediate ab-
2
2
sorption was observed. The isotopic shift and
ꢀ
1
splitting showed that the 1934:9 cm band is due
to a terminal C–O stretching vibration and only
ꢀ
1
one CO subunit is involved. The 1326:1 cm band
showed no carbon-13 shift, but was shifted to
1288.2 cm with CO
at 1320.2 cm is due to the natural abundance Si
3
. Results and discussion
ꢀ
1
18
2
= O
2
sample. A weak band
ꢀ
1
29
Laser-ablated silicon atoms were first co-de-
posited with O in excess argon. One hour sample
16
18
isotopic counterpart. The isotopic O= O ratio of
2

J. Dong et al. / Chemical Physics Letters 355 (2002) 31–36
33
ꢀ1
Fig. 1. Infrared spectra in the 1970–1850 and 1430–820 cm regions from co-deposition of laser-ablated silicon atoms with
:5% CO in argon. (a) One hour sample deposition at 11 K, (b) after 25 K annealing, (c) after 20 min broadband
photolysis, and (d) after 28 K annealing.
0
2
þ 1:0% O
2
Table 1
ꢀ1
2 2
Infrared absorptions (cm ) from co-deposition of laser-ablated silicon atoms with O =CO in excess argon
16
12 16
16
13 16
18
12 16
O
2
þ
C O
2
O
2
þ
C O
2
O
2
þ
C O
2
Assignment
1
1
1
1
1
1
1
1
934.9
891.5
416.4
403.5
326.1
257.0
226.2
070.2
1888.1
1831.1
1416.4
1403.5
1325.2
1248.3
1226.2
1054.4
863.5
1931.8
1892.9
1379.8
1366.5
1288.2
1254.8
1182.3
1055.9
850.8
SiCO
ꢀ
4
CO
4
2
8
SiO
SiO
2
2
4
29
SiCO
ꢀ
CO
SiO
4
SiCO
4
8
6
66.0
91.2
SiCO
ꢀ
4
681.2
688.0
CO
4
2
8
29
1.0294 and Si= Si ratio of 1.0045 are indicative
of a terminal Si–O stretching vibration. When a
brations of the CO
ꢀ
3
subunit. A strong band at
ꢀ1
1
1084:9 cm tracked with the 1070:2 cm band in
the CO =O experiments, but the relative intensi-
ties of these bands vary widely in different isotopic
16
16 18
18
CO = O þ O O þ O sample was used as
2
2
2
2
2
reagent gas, a quartet at 1326.1, 1323.1, 1292.3 and
ꢀ
1
ꢀ1
1
288:2 cm was observed. These absorptions are
16
substituted experiments. The 1084:9 cm band is
most probably due to a combination or overtone
band that is in Fermi resonance with the
16
16
due to vibrations of the OSið O
2
ÞCO; OSi
16
18
18
16
18
16 18
ð O OÞ CO; OSið O ÞCO and OSið O OÞ
2
ꢀ
1
CO molecules.
1070:2 cm band. The spectra in this region be-
come rapidly congested and difficult to interpret
when more than one isotopic species is presented.
To provide insight into the structure and
ꢀ
1
The 1070.2 and 866:0 cm bands shifted to
ꢀ
054.4 and 863:5 cm with CO =O sample, and
2 2
to 1055.9 and 850:8 cm with CO = O sample.
2
1
13
1
ꢀ
1
18
2
These two bands are due to C–O stretching vi-
bonding of the above assigned SiCO molecule,
4

34
J. Dong et al. / Chemical Physics Letters 355 (2002) 31–36
ꢀ
1
2 2
Fig. 2. Infrared spectra in the 1960–1850 and 1360–820 cm regions from co-deposition of laser-ablated silicon atoms with CO =O in
1
3
12
13
18
excess argon. (a) 0:5% CO
2
þ 1:0% O
2
, (b) 0:5% CO
18
2
þ 1:0% O
2
, (c) 0:5% ð CO
2
þ
CO
2
Þ þ 1:0% O
2
, (d) 0:5% CO
2
þ 1:0%
2
O ,
16
16 18
and (e) 0:5% CO
2
þ 1:5% ð O O O þ
2
þ
O
2
Þ.
Fig. 3. Calculated geometric parameters (bond length in angstrom, bond angle in degree) for the SiCO
cules.
4
; ðCO
2
Þ2 and ðSiO Þ2 mole-
2
we turn to density functional theoretical calcula-
tions. Recent studies in this laboratory have
shown that B3LYP/6-311 + G(d) calculations is
relatively cheap and can provide quite reliable
predictions on the structures and vibrational
frequencies of carbon and silicon containing
compounds [26,27]. The calculated geometric pa-
rameters are shown in Fig. 3, and the calculated
vibrational frequencies and intensities are listed in
Table 2.
optimized bond lengths are: terminal Si–O, 1.510
ꢀ
A, terminal C–O, 1.173 A, bridged Si–O, 1.680 A,
ꢀ
ꢀ
ꢀ
and bridged C–O, 1.398 A. The calculated fre-
quencies at the optimized geometry provide good
support for the identification of this molecule. The
terminal C–O and Si–O stretching modes were
ꢀ
1
predicted at 1971.7 and 1335:3 cm , respectively,
ꢀ
1
just 36.8 and 9:2 cm from the observed values.
The two C–O stretching vibrations of the CO
3
ꢀ
1
subunit were calculated at 1075.6 and 876:2 cm ,
ꢀ
1
The SiCO
ground state in C2v symmetry with two ter-
minal O atoms and two bridging O atoms. The
4
molecule was predicted to have a
respectively, just 5.4 and 10:2 cm higher than the
observed values. As listed in Table 2, the calcu-
lated isotopic frequency shifts also matched the
1
A
1

J. Dong et al. / Chemical Physics Letters 355 (2002) 31–36
35
Table 2
Calculated isotopic vibrational frequencies ðcmꢀ Þ, intensities (km/mol) of the SiCO
1
molecule
4
Molecule
Frequency(intensity, mode)
1971.7ð582; a Þ, 1335.3ð244; a
53.6ð10; b Þ, 557.0ð31; a Þ, 510.4ð0; b
1922.1ð540Þ, 1335.3ð245Þ, 1055.5ð318Þ, 939.7ð9Þ, 872.0ð177Þ, 751.9ð29Þ, 651.5ð11Þ, 554.3ð30Þ,
05.3ð0Þ, 335.2ð48Þ, 240.2ð31Þ, 135.0ð19Þ
1971.6ð581Þ, 1334.1ð242Þ, 1066.1ð323Þ, 913.2ð11Þ, 862.7ð164Þ, 771.4ð29Þ, 638.2ð8Þ, 554.6ð33Þ,
06.4ð1Þ, 333.6ð49Þ, 239.3ð31Þ, 133.9ð18Þ
1971.7ð584Þ, 1299.9ð245Þ, 1075.5ð330Þ, 936.6ð16Þ, 874.6ð161Þ, 774.8ð29Þ, 653.4ð10Þ, 547.5ð30Þ,
10.4ð1Þ, 333.6ð46Þ, 233.6ð29Þ, 132.5ð18Þ
1971.6ð582Þ, 1298.3ð242Þ, 1065.8ð323Þ, 910.1ð18Þ, 861.2ð154Þ, 771.4ð28Þ, 638.0ð8Þ, 545.1ð31Þ,
06.4ð1Þ, 331.4ð47Þ, 232.6ð29Þ, 131.4ð18Þ
OSiðO
2
2
ÞCO
1
1
Þ, 1075.6ð331; b
2
Þ, 939.8ð10; a
1
Þ, 876.2ð172; a
1
Þ, 774.8ð29; b Þ,
1
6
2
1
2
Þ, 335.8ð48; b
1
Þ, 240.3ð31; b
2
Þ, 135.0ð19; b Þ
1
13
OSiðO
Þ CO
5
16
18
18
18 16
OSið O OÞCO
5
16
OSið O ÞCO
2
5
18 16
OSið O OÞCO
5
experimental values quite well, which add strong
support on the SiCO assignment.
reasonable agreement with previous calculations
[7–11,13]. The most stable carbon dioxide dimer is
a weakly bonded van der Waals complex with a
slipped parallel (C2h) structure. On the contrary,
the ground state of silicon dioxide dimer is con-
cluded to be a strongly covalent bonded molecule
of D2h symmetry with two terminal O atoms and
two bridging O atoms. The dimerization energy
has been calculated to be about 108 kcal/mol at the
SCF level [11,13]. This energy was predicted to be
81.6 kcal/mol at the B3LYP/6-311 + G(d) level.
4
ꢀ
1
Weak bands at 1390.1 and 2206:8 cm
creased on annealing are due to antisymmetric
in-
SiO
2
and C–O stretching vibrations of the O
2
1
ꢀ
SiCO molecule [28]. Sharp band at 1363:5 cm
produced on photolysis is due to SiO
been reported previously [29]. Weak band at
3
, which has
ꢀ
1
1
163:0 cm that appeared on photolysis was also
observed in Si þ O =Ar experiments. This band
2
cannot be assigned, and probably is due to a sili-
con oxide species.
The primary products from co-deposition of
The structure and bonding of SiCO
ferent to carbon dioxide dimer but is similar to the
silicon dioxide dimer. The SiCO molecule is also a
4
is quite dif-
laser-ablated silicon atoms with O
tures are silicon oxides: SiO and SiO, no silicon
2
=CO
2
=Ar mix-
4
covalently bonded molecule, but is not as strongly
bound as the silicon dioxide dimer. The binding
2
atom carbon dioxide reaction product was ob-
served. The isotopic substitution experiments in-
dicate that the SiCO molecules are formed by
1
þ
1
þ
energy with respect to SiO
predicted to be 9.9 kcal/mol, after a zero point
vibration energy correction.
ð R Þ þ CO
ð R Þ was
2
g
2
g
4
reaction between SiO and CO molecules in solid
2
2
argon, via reaction (1). The SiCO absorptions in-
4
Although the reaction energy for silicon dioxide
dimerization is much larger than that of reaction
creased on annealing suggest that reaction (1) re-
quires no activation energy. No obvious SiO and
2 4
(1), no obvious Si O absorptions were observed
CO
calculated the SiCO
2
reaction product was observed. We have also
species, and the optimized
under the present experimental conditions. We
note that the concentration of silicon dioxide in
the solid argon matrix is much lower than that of
carbon dioxide, and carbon dioxide molecules ex-
hibit higher mobility than that of silicon dioxide
molecules in solid argon.
3
structures are higher in energy than that of SiO þ
CO :
2
1
þ
1
þ
1
SiO
2
ð R Þ þ CO
2
ð R Þ ! SiCO
4
ð A
1
Þ
It is interesting to compare the SiCO
ð1Þ
molecule
g
g
4
with the carbon dioxide dimer and silicon dioxide
dimer, which have been studied both experimen-
tally and theoretically [1–13]. For comparison, we
have calculated the carbon dioxide and silicon di-
oxide dimers, and the results are also shown in Fig.
4. Conclusions
Reaction of silicon dioxide and carbon dioxide
molecules has been studied by matrix isolation
infrared absorption and density functional theory
3
. The optimized geometric parameters are in

36
J. Dong et al. / Chemical Physics Letters 355 (2002) 31–36
[
[
[
[
6] K.W. Jucks, Z.S. Huang, R.E. Miller, G.T. Fraser, A.S.
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form silicon dioxide and silicon monoxide as the
primary products. The SiCO molecule was pro-
2
2
(
8] R. Eggenberger, S. Gerber, H. Huber, Mol. Phys. 72 (1991)
1987) 3489.
4
duced spontaneously on matrix annealing. Isoto-
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433.
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4
2v
[
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4 2
energy of ground state SiCO with respect to SiO
1
þ
1
þ
ð R Þ þ CO
2
ð R Þ was predicted to be 9.9 kcal/
g
g
mol, after zero point energy correction.
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