Isomers of HSCO: IR absorption spectra of t-HSCO in solid Ar.

Article abstract of DOI:10.1063/1.1648634

Irradiation of an Ar matrix sample containing H2S and CO (or OCS) with an ArF excimer laser at 193 nm yields trans-HSCO (denoted t-HSCO). New lines at 1823.3, 931.6, and 553.3 cm(-1) appear after photolysis and their intensity enhances after annealing; secondary photolysis at 248 nm diminishes these lines and produces OCS and CO. These lines are assigned to C-O stretching, HSC-bending, and C-S stretching modes of t-HSCO, respectively, based on results of 13C-isotopic experiments and theoretical calculations. Theoretical calculations using density-functional theories (B3LYP and PW91PW91) predict four stable isomers of HSCO: t-HSCO, c-HSCO, HC(O)S, and c-HOCS, listed in increasing order of energy. According to calculations with B3LYP/aug-cc-pVTZ, t-HSCO is planar, with bond lengths of 1.34 A (H-S), 1.81 A (S-C), and 1.17 A (C-O), and angles angle HSC congruent with 93.4 degrees and angle SCO congruent with 128.3 degrees; it is more stable than c-HSCO and HC(O)S by approximately 9 kJ mol(-1) and more stable than c-HOCS by approximately 65 kJ mol(-1). Calculated vibrational wave numbers, IR intensities, and 13C-isotopic shifts for t-HSCO fit satisfactorily with experimental results. This new spectral identification of t-HSCO provides information for future investigations of its roles in atmospheric chemistry. (c) 2004 American Institute of Physics

Full text of DOI:10.1063/1.1648634

Isomers of HSCO: IR absorption spectra of t- HSCO in solid Ar
Wen-Jui Lo, Hui-Fen Chen, Yu-Jong Wu, and Yuan-Pern Lee
Citation: The Journal of Chemical Physics 120, 5717 (2004); doi: 10.1063/1.1648634
View online: http://dx.doi.org/10.1063/1.1648634
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JOURNAL OF CHEMICAL PHYSICS
VOLUME 120, NUMBER 12
22 MARCH 2004
Isomers of HSCO: IR absorption spectra of t-HSCO in solid Ar
Wen-Jui Loa)
Department of Nursing, Tzu Chi College of Technology, Hualien 970, Taiwan
Hui-Fen Chen and Yu-Jong Wu
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
Yuan-Pern Leeb)
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
͑Received 10 December 2003; accepted 24 December 2003͒
Irradiation of an Ar matrix sample containing H2S and CO ͑or OCS͒ with an ArF excimer laser at
193 nm yields trans-HSCO ͑denoted t-HSCO). New lines at 1823.3, 931.6, and 553.3 cmϪ1 appear
after photolysis and their intensity enhances after annealing; secondary photolysis at 248 nm
diminishes these lines and produces OCS and CO. These lines are assigned to C–O stretching,
HSC-bending, and C–S stretching modes of t-HSCO, respectively, based on results of 13C-isotopic
experiments and theoretical calculations. Theoretical calculations using density-functional theories
͑B3LYP and PW91PW91͒ predict four stable isomers of HSCO: t-HSCO, c-HSCO, HC͑O͒S, and
c-HOCS, listed in increasing order of energy. According to calculations with B3LYP/aug-cc-pVTZ,
t-HSCO is planar, with bond lengths of 1.34 Å ͑H–S͒, 1.81 Å ͑S–C͒, and 1.17 Å ͑C–O͒, and angles
ЄHSCХ93.4° and ЄSCOХ128.3°; it is more stable than c-HSCO and HC͑O͒S by ϳ9 kJ molϪ1 and
more stable than c-HOCS by ϳ65 kJ molϪ1. Calculated vibrational wave numbers, IR intensities,
and 13C-isotopic shifts for t-HSCO fit satisfactorily with experimental results. This new spectral
identification of t-HSCO provides information for future investigations of its roles in atmospheric
chemistry. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1648634͔
I. INTRODUCTION
Unlike the exothermic reaction of OH with CO,
OHϩCO→HϩOCO, ⌬H0ϭϪ104 kJ molϪ1
the reaction of HS with CO to give OCS and H,
,
͑1͒
͑2͒
Sulfate aerosol, typically produced from the oxidation of
SO2 in the atmosphere, scatters and absorbs radiation from
the Sun; it also plays an important role in heterogeneous
reactions in the atmosphere.1,2 In the stratosphere, SO2 is
either injected directly from eruptions of volcanoes, or pro-
duced via oxidation of sulfur compounds. Hydrogen sulfide
(H2S) is an important anthropogenic source of reduced sul-
fur compounds that lead to formation of SO2 in the atmo-
sphere; current estimates of its annual loading are 1–3
Tg yrϪ1 of sulfur;3 1 Tgϭ1012 g. Atmospheric oxidation of
H2S is initiated through its reaction with OH to produce HS
radical.4,5 Subsequent reactions of HS with O3 and NO2 pro-
duce HSO, which reacts further with O3 and NO2 to form
HSO2 .5,6 The hydrogen atom of HSO2 is rapidly abstracted
by O2 , yielding SO2 .
Alternative paths for oxidation of HS that might be im-
portant in the atmosphere have been investigated. Reaction
of HS with CO in air might yield carbonyl sulfide ͑OCS͒;7
this reaction is analogous to reaction of OH with CO that
yields CO2 . If this reaction is important, it provides a path-
way to convert H2S to OCS; current estimates of atmo-
spheric sources of OCS would consequently have to be
revised.8
HSϩCO→HϩOCS, ⌬H0ϭ51 kJ molϪ1
,
is endothermic and is expected to be unimportant in the
atmosphere.9 However, if the adduct HSCO were formed to
some extent via the equilibrium reaction,
HSϩCO↔HSCO, ⌬H0Х2 kJ molϪ1
,
͑3͒
a subsequent reaction of HSCO with O2 ,
HSCOϩO2→HO2ϩOCS, ⌬H0ХϪ163 kJ molϪ1
͑4͒
might produce HO2 and OCS with great exothermicity. The
energy of HSCO in trans form ͑denoted as t-HSCO) is pre-
dicted to be similar to that of reactants HS and CO, and a
small barrier ͑14 kJ molϪ1͒ for formation of t-HSCO from
HS and CO is predicted.10,11 To our knowledge, no spectral
information on HSCO exists.
The matrix isolation technique is known for its superior-
ity in trapping and preserving unstable species.12,13 Photo-
fragments produced upon photolysis of a matrix sample are
likely to be confined within a matrix cage and to react with
each other because of the cage effect; the possibility to form
various isomers of the precursor or other products from sec-
ondary reactions is hence much greater than in the gaseous
phase. Selective photodissociation with a laser avoids sec-
ondary photolysis on species of interest. Using various lasers
a͒
Author to whom correspondence should be addressed. Electronic mail:
wjl@tccn.edu.tw
b͒
Author to whom correspondence should be addressed. Electronic mail:
yplee@mx.nthu.edu.tw
0021-9606/2004/120(12)/5717/6/$22.00
5717
© 2004 American Institute of Physics
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5718
J. Chem. Phys., Vol. 120, No. 12, 22 March 2004
Lo et al.
to photodissociate matrix samples, we produced numerous
novel species that are difficult to form in the gaseous
phase.14–27 Here we report a theoretical investigation of pos-
sible isomers of HSCO and experimental production of
t-HSCO, by irradiation of matrix-isolated H2S and CO or
OCS with laser emission at 193 nm, and its infrared identi-
fication.
cmϪ1 and HSH bending (␯2) at 1180.1 cmϪ1 are consistent
with a previous report ͑maxima at 2647.8, 2630.0, and
1180.0 cmϪ1 in solid Ar͒.34 Lines at 2581.8 and 2577.6 cmϪ1
are due to dimer and trimer of H2S, respectively. A line at
2585.5 cmϪ1 was assigned to a complex of H2S and H2O.34
The IR spectrum of CO ϳ2138.2 cmϪ1 is broad and a
weaker line at 2149.3 cmϪ1 is due to a complex of CO and
H2O.35 Infrared absorption of the H2S•CO complex was
studied by Lundell et al.,36 but we found no absorption with
wave numbers 2637.3, 2611.4, 2597.5, 2143.0, and 2137.4
cmϪ1 reported by them.
II. EXPERIMENTS
The experimental setup is similar to that described
previously.15,19 A copper plate coated with platinum and
cooled to ϳ13 K serves as a substrate for a cold matrix
sample and as a mirror to reflect incident infrared ͑IR͒ beam
to the detector. Gaseous mixtures of H2S/Ar ͑typically in
proportions 1/200͒ and CO/Ar ͑or OCS/Ar, typically 1/400͒
were codeposited. Typically 10 mmol of a sample mixture
was deposited over a period of 2 h.
IR absorption spectra were recorded with an evacuable
Fourier-transform infrared ͑FTIR͒ spectrometer ͑Bomem,
DA8͒ equipped with a KBr beamsplitter and a Hg/Cd/Te
detector ͑cooled to 77 K͒ to cover the spectral range 500–
4000 cmϪ1. Typically 600 scans with resolution of 0.5 cmϪ1
were recorded at each stage of the experiment.
Partial spectra of a H2S/CO/Ar ͑2/1/800͒ matrix sample
in regions 525–600, 920–980, 1800–2200, and 2540–2660
cmϪ1 before and after laser irradiation are shown in Fig. 1.
Trace A is the spectrum recorded after deposition, and traces
B is a difference spectrum after irradiation at 193 nm for 10
min. The difference spectrum was derived on subtracting the
spectrum recorded in the preceding stage of irradiation/
annealing from a new spectrum; a positive feature indicates
production, whereas a negative feature indicates destruction.
After irradiation, lines at 2049.7, 858.5, and 520.0 cmϪ1 are
readily assigned to OCS, consistent with literature values of
OCS in the gas phase37 or in matrices.25 Lines at 2481.4,
1863.6, and 1085.6 cmϪ1 are readily assigned to HCO, con-
sistent with literature values of 2483, 1863, and 1087 cmϪ1
for HCO in solid Ar.38 Weak lines at 3602.9, 1843.7, 1211.0,
and 1064.2 cmϪ1 are due to t-HOCO.39 Intensities of new
lines at 1823.3, 931.6, and 553.3 cmϪ1 ͑marked as • in Fig.
1͒ increased slightly upon further irradiation of the sample
and increased substantially after the temperature of the ma-
trix was raised to ϳ30 K for 10 min, whereas those of other
lines remained nearly invariant, as shown in the difference
spectrum in trace C of Fig. 1. Weaker lines at 930.2 and
551.4 cmϪ1 are due to site splitting from lines at 931.6 and
553.3 cmϪ1, respectively. Further irradiation of the matrix
sample with laser emission at 248 nm for 10 min diminished
these new lines nearly completely, whereas intensities of
lines due to OCS, and CO to a less extent, were recovered, as
illustrated in the difference spectrum in trace D of Fig. 1.
Line positions of reactants and products are listed in Table I.
Similar experiments were performed with a matrix
sample of H2S/OCS/Ar ͑2/1/800͒, but the spectra appeared to
be more complex than those recorded for H2S/CO/Ar experi-
ments. Nevertheless, after irradiation at 193 nm, the three
new lines at 553.3, 931.6, and 1823.3 cmϪ1 were also ob-
served.
An ArF excimer laser ͑193 nm͒, operated at 10 Hz with
energy ϳ4 mJ pulseϪ1, was employed to photodissociate
H2S. A KrF excimer laser ͑248 nm͒, operated at 10 Hz with
energies ϳ4 mJ pulseϪ1, was used for secondary photolysis.
H2S ͑Ͼ99.5%, Scott Specialty Gases͒, CO ͑99.9%, Air
Products͒, OCS ͑99.98%, Scientific Gas Products͒, 13CO and
O
13CS ͑both from Cambridge Isotope Laboratories, isotopic
purity Ͼ99%͒ were used without further purification except
for degassing at 77 K. Ar ͑99.999%, Scott Specialty Gases͒
was used without purification.
III. COMPUTATIONAL METHOD
The equilibrium structure, vibrational frequencies, IR in-
tensities, and energies were calculated with the GAUSSIAN 98
program.28 We used density functional theory ͑DFT͒ in cal-
culations of two types, B3LYP and PW91PW91: the B3LYP
method uses Becke’s three-parameter hybrid exchange
functional,29 and a correlation functional of Lee, Yang, and
Parr,30,31 with both local and nonlocal terms; the PW91PW91
method uses exchange and correlation functionals of Perdew
and Wang.32,33 Dunning’s correlation-consistent polarized
valence triplet-zeta basis set, augmented with s, p, d, and f
functions ͑aug-cc-pVTZ͒, were used in all methods. Analytic
first derivatives were utilized in geometry optimization, and
vibrational frequencies were calculated analytically at each
stationary point.
2. 13C-isotopic experiments and assignments
An isotopic mixture containing 13CO and 12CO in nearly
equal proportion was used in one experiment. A difference
spectrum after irradiation of this matrix sample at 193 nm for
10 min, followed by annealing at 30 K is shown in trace B of
Fig. 2; trace A depicts the corresponding difference spectrum
of a natural H2S/CO/Ar matrix sample after irradiation and
annealing for comparison. Line positions of 13C-substituted
species are listed parenthetically in Table I.
IV. RESULTS AND DISCUSSION
A. Experimental observations and assignments
1. Experiments with H2S and CO in natural abundance
The IR spectrum of H2S for a sample of H2S/CO/Ar
͑2/1/800͒ at 13 K exhibits multiple lines due to rotation and
aggregation; observed lines of asymmetric H–S stretching
(␯3) at 2648.0, symmetric H–S stretching (␯1) at 2629.8
The line at 1823.3 cmϪ1 splits into two lines, with a new
line at 1784.7 cmϪ1 having a smaller intensity. Part of the
intensity of the line at 1823.3 cmϪ1 might be contributed by
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J. Chem. Phys., Vol. 120, No. 12, 22 March 2004
Isomers of HSCO
5719
FIG. 1. Partial IR absorption spectrum of a H2S/CO/Ar ͑2/1/800͒ matrix sample before irradiation ͑A͒, difference spectrum after irradiation at 193 nm for 10
min ͑B͒, difference spectrum after annealing of the matrix sample at 30 K for 10 min ͑C͒, and difference spectrum after further irradiation of the matrix at 248
nm for 10 min ͑D͒.
associated with a minor site, shifts to 930.2 and 928.8 cmϪ1
,
H 13CO that absorbs at the same wave number. The isotopic
pattern indicates that one C atom is involved in this mode.
The isotopic ratio 1784.7/1823.3ϭ0.9788, defined as a ratio
of vibrational wave numbers of the isotopically labeled spe-
cies to that of the most naturally abundant species, is similar
to the theoretical value of 0.9778 for CO. The line at 553.3
cmϪ1 splits into two lines with approximately equal intensity,
with the new line at 537.8 cmϪ1; the 13C-isotopic ratio of
537.8/553.3ϭ0.9720 is near a theoretical value of 0.9716 for
CS. The doublet line at 931.6 and 930.2 cmϪ1, with the latter
respectively; the spectrum hence appears as a triplet. The
small 13C-isotopic shift for the line at 931.6 cmϪ1 indicates
that it might be associated with either a bending mode or a
mode not directly involving the C atom.
A second isotopic sample containing equimolar O 13CS
and O 12CS in Ar was also used. Isotopically shifted lines at
1784.7, 930.2, and 537.8 cmϪ1 were also observed. A de-
tailed discussion of other reaction products of experiments
on H2S/OCS/Ar matrix samples will be reported elsewhere.
Photodissociation of H2S at 193 nm forms H and HS.40
Annealing of the matrix sample is expected to promote dif-
fusion, hence reaction between CO and HS ͑or H͒; in addi-
tion to HCO, isomers of HSCO are expected to be formed.
TABLE I. Wave numbers ͑in cmϪ1͒ of lines observed for a H2S/CO/Ar
matrix sample after deposition and after irradiation at 193 nm.
After deposition
After irradiationa
Assignment
2648.0
2629.8
1180.1
2585.5
2581.8
2577.6
2568.8
H2S, asym. stretch (␯3)
H2S, sym. stretch (␯1)
H2S, bend (␯2)
H2S•H2O
(H2S)2
(H2S)3
(H2S)n?
b
2149.3 ͑2101.9͒
2138.2 ͑2091.1͒
CO•H2O
CO
b
1823.3͑1784.7͒
931.6͑930.2͒
553.3͑537.8͒
2481.4͑2475.5͒
1863.6͑1823.3͒
1085.6͑1079.3͒
3602.9
1843.7
1211.0
1064.8
t-HSCO, C–O stretch (␯2)
t-HSCO, HSC-bend (␯3)
t-HSCO, C–S stretch (␯4)
HCO, C–H stretch (␯1)
HCO, C–O stretch (␯3)
HCO, bend (␯2)
t-HOCO, O–H stretch (␯1)
t-HOCO, C–O stretch (␯2)
t-HOCO, HOC-bend (␯3)
t-HOCO, C–O stretch (␯4)
FIG. 2. Partial difference IR absorption spectra of H2S/CO/Ar matrix
samples with isotopic variants after irradiation at 193 nm for 10 min fol-
lowed by annealing at 30 K for 10 min. ͑A͒ H2S/12CO/Ar ͑2/1/800͒ and ͑B͒
H2S/13CO/12CO/Ar ͑2/1/1/800͒.
aPhotolysis at 193 nm for 10 min.
bNumbers listed in parentheses correspond to 13C species.
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5720
J. Chem. Phys., Vol. 120, No. 12, 22 March 2004
Lo et al.
for these species are shown in Fig. 3, with those predicted
using PW91PW91 listed in parentheses. The most stable spe-
cies is t-HSCO, but c-HSCO and HC͑O͒S have energies
greater by only ϳ9 kJ molϪ1. The isomer c-HOCS, lying 65
kJ molϪ1 above t-HSCO, is the highest in energy. The
PW91PW91 method predicts a similar trend with slightly
smaller energy gaps. The energies and structures predicted in
this work are close to those predicted previously with
QCISD͑T͒ and other methods, but a fifth isomer t-HOCS
was predicted to be stable, with energy ϳ2 kJ molϪ1 below
c-HOCS.11
Both conformers of HSCO are characterized by a short
C–O bond ͑ϳ1.17 Å͒ similar to a double bond ͑cf. 1.15 Å
for OCS͒ and a C–S bond with single-bond character; the
C–S bond length ͑1.812 Å͒ of t-HSCO is slightly greater
than that of c-HSCO ͑1.787 Å͒. In contrast, c-HOCS is char-
acterized by a short C–S bond of length 1.59 Å and a long
C–O bond, 1.30 Å. HC͑O͒S has a C–S bond of length simi-
lar to that in t-HSCO, but a C–O bond of length between
those of t-HSCO and c-HOCS.
Tables II and III list vibrational wave numbers, approxi-
mate mode description, and infrared intensities ͑in parenthe-
ses͒ of four isomers of HSCO predicted with B3LYP and
PW91PW91 methods. Trend of stretching vibrational wave
numbers reflect the bond lengths discussed above, with wave
numbers of C–O stretching modes, predicted with B3LYP/
aug-cc-pVTZ, decreasing from 1881 cmϪ1 for t-HSCO,
1864 cmϪ1 for c-HSCO, 1699 cmϪ1 for HC͑O͒S, to 1418
cmϪ1 for c-HOCS. In contrast, wave numbers of C–S
stretching predicted with B3LYP increase from 480 cmϪ1 for
c-HSCO, 553 cmϪ1 for t-HSCO, 681 cmϪ1 for HC͑O͒S, to
887 cmϪ1 for c-HOCS.
FIG. 3. Geometries and relative energies ͑in kJ molϪ1͒ of isomers of HSCO
calculated with B3LYP/aug-cc-pVTZ and PW91PW91/aug-cc-pVTZ meth-
ods. Relative energies are corrected with zero-point energies; unit of bond
length is Å. Results from PW91PW91 are listed in parentheses.
Because observed isotopic shifts indicate that the species
contains a C–O bond and a C–S bond, and because observed
C–S stretching wave numbers shifted substantially from 860
cmϪ1 of OCS to 553 cmϪ1, whereas observed C–O stretch-
ing wave numbers shifted only from 2049 cmϪ1 of OCS to
1823 cmϪ1, the new species is likely HSCO rather than
HOCS or HC͑O͒S. With experimental data alone, we are
unable to identify unambiguously whether the observed spe-
cies has trans or cis conformation, but the conformation may
be determined by comparison with theoretical calculations.
Observed vibrational wave numbers of new lines at
1823.3, 931.6, and 553.3 cmϪ1 are near values predicted for
␯
͑C–O stretching͒, ␯ ͑HSC-bending͒, and ␯ ͑C–S
3 4
2
stretching͒ modes of t-HSCO. The experimental ␯ value is
2
B. Comparison with theoretical calculations
nearer the value of 1816 cmϪ1 predicted with the
We performed theoretical calculations using B3LYP and
PW91PW91 methods, both with aug-cc-pVTZ basis sets, to
find four stable isomers of HSCO: t-HSCO, c-HSCO,
HC͑O͒S, and c-HOCS. Geometries and energies predicted
PW91PW91 method than the value of 1881 cmϪ1 predicted
with the B3LYP method, whereas the experimental ␯ value
4
is closer to the value of 553 cmϪ1 predicted with the B3LYP
method than the value of 573 cmϪ1 predicted with the
TABLE II. Vibrational wave numbers ͑in cmϪ1͒ and infrared intensities of t-HSCO and c-HSCO predicted
with two DFT methods.
B3LYP/
aug-cc-pVTZ
PW91PW91/
aug-cc-pVTZ
Experiment
Ar matrix
Species
Vibrational mode
a
a
t-HSCO
2696.3 ͑2͒
2634.4 ͑3͒
␯1 , H–S stretch
␯2 , C–O stretch
␯3 , HSC-bend
␯4 , C–S stretch
␯5 , out-of-plane bend
␯6 , SCO-bend
1881.3 ͑417͒
947.8 ͑35͒
552.7 ͑60͒
392.0 ͑7͒
1816.4 ͑372͒
922.8 ͑32͒
572.7 ͑53͒
404.0 ͑8͒
1823.3
931.6
553.3
369.1 ͑12͒
371.0 ͑7͒
c-HSCO
2589.1 ͑0.4͒
1864.0 ͑357͒
872.4 ͑35͒
479.9 ͑65͒
412.9 ͑10͒
386.4 ͑3͒
2506.3 ͑2͒
1800.7 ͑319͒
839.4 ͑36͒
485.9 ͑44͒
413.9 ͑9͒
␯1 , H–S stretch
␯2 , C–O stretch
␯3 , HSC-bend
␯4 , C–S stretch
␯5 , out-of-plane bend
␯6 , SCO-bend
369.2 ͑6͒
aIR intensities ͑in km molϪ1͒ are listed in parentheses.
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J. Chem. Phys., Vol. 120, No. 12, 22 March 2004
Isomers of HSCO
5721
TABLE III. Vibrational wave numbers ͑in cmϪ1͒ and infrared intensities of HC͑O͒S and c-HOCS predicted
with two DFT methods.
Species
B3LYP/
aug-cc-pVTZ
PW91PW91/
aug-cc-pVTZ
Vibrational mode
a
a
HC͑O͒S
␯1 , C–H stretch
␯2 , C–O stretch
␯3 , HCO bend
␯4 , out-of-plane bend
␯5 , C–S stretch
␯6 , OCS bend
2934.8 ͑69͒
2941.5 ͑58͒
1699.1 ͑277͒
1339.4 ͑14͒
927.6 ͑4͒
681.1 ͑131͒
232.5 ͑31͒
1536.2 ͑54͒
1265.5 ͑11͒
894.1 ͑7͒
798.4 ͑77͒
354.5 ͑25͒
c-HOCS
3516.8 ͑9͒
1417.6 ͑396͒
1243.7 ͑151͒
886.7 ͑7͒
587.3 ͑72͒
436.5 ͑12͒
3342.1 ͑19͒
1399.8 ͑320͒
1199.8 ͑130͒
859.0 ͑9͒
580.1 ͑62͒
420.3 ͑10͒
␯1 , O–H stretch
␯2 , C–O stretch
␯3 , HOC bend
␯4 , C–S stretch ͑mixed͒
␯5 , out-of-plane bend
␯6 , OCS bend
aIR intensities ͑in km molϪ1͒ are listed in parentheses.
PW91PW91 method. The ␯ values, 1864 and 1801 cmϪ1
predicted with B3LYP and PW91PW91, respectively, for
at 30 K produced t-HSCO in substantial amount but much
less HCO indicates that H atom might have been depleted
before annealing and that formation of HSCO involves dif-
fusion of either HS or CO. The reaction for association of HS
and CO to form t-HSCO ͓reaction ͑3͔͒ is predicted at the
QCISD//UMP2/6-311ϩG(2df,2p) level to be slightly en-
2
c-HSCO are also near the experimental observation, but pre-
dicted ␯ ͑872 and 839 cmϪ1͒ and ␯ ͑480 and 486 cmϪ1
͒
3
4
are smaller than those from experiments by more than 6%
and 12%, respectively. The observed ratio of integrated in-
tensities for ␯2 :␯3 :␯4 , 1.00:0.06:0.08, agrees satisfactorily
with the ratio 1.00:0.08:0.14 predicted for t-HSCO with the
B3LYP method.
dothermic (⌬H0Х2.5 kJ molϪ1) with a small ͑14 kJ molϪ1
͒
barrier,11 but this reaction was predicted to be exothermic by
13–33 kJ molϪ1 with a barrier of 2–7 kJ molϪ1 at MP2,
B3LYP, and BLYP level.11 Our observation of t-HSCO upon
annealing of the matrix at 30 K indicates that the barrier, if it
exists, would be small and the reaction should be nearly
thermal neutral or exothermic. A small loss of OCS upon
annealing indicates that the reaction of HϩOCS might also
take place, but theoretical calculations predict a barrier Ͼ28
kJ molϪ1 for the reaction of H and OCS to form c-HSCO.
When the 193-nm irradiated H2S/CO/Ar sample was ir-
radiated further at 248 nm, lines due to t-HSCO disappeared,
whereas lines due to OCS increased and the line due to CO
increased slightly. This observation indicates that at 248 nm
t-HSCO is photodissociated to form mainly OCS; OCS fur-
ther dissociates at 248 nm and the fragments might escape
from the cage to form CO and S.41 Further investigations of
electronic absorption spectra of t-HSCO are needed to un-
derstand its photolytic behavior.
Table IV lists predicted 13C-isotopic ratios of four iso-
mers. As both B3LYP and PW91PW91 methods predict
nearly identical isotopic ratios, only those predicted with
B3LYP are listed. Predicted isotopic ratios for t-HSCO are
nearly the same as those determined experimentally ͑devia-
tions Ͻ0.0018͒; ratios predicted for other isomers of HSCO
fit less well with experimental results. Hence, based on ob-
served 13C-isotopic shifts and comparison with vibrational
wave numbers and isotopic ratios predicted with theoretical
calculations, we conclude that new absorption lines at
1823.3, 931.6, and 553.3 cmϪ1 are associated with ␯2 , ␯3 ,
and ␯ vibrational modes of t-HSCO isolated in solid Ar.
4
C. Mechanism of formation of t-HSCO
Photolysis of H2S at 193 nm produced H atom and HS
radical;40 observation of absorption lines of HCO at 2481.4,
1863.6, and 1085.6 cmϪ1 indicates that some H atoms react
with CO to form HCO. Formation of OCS is likely due to
reactions of CO with S or HS. That annealing of the matrix
On the basis of spectral information of t-HSCO obtained
in this work, further experiments in the gaseous phase at low
temperatures might be performed to investigate the adduct
formation and equilibrium of reaction ͑3͒ to assess the im-
portance of this reaction in atmospheric chemistry. Even if
only 4% of HS be converted to OCS via t-HSCO under
atmospheric conditions, it contributes about 50% of the esti-
mated total source of OCS into the atmosphere.3,8
TABLE IV. Experimental and calculated 13C-isotopic ratiosa of four isomers
of HSCO.
Species
␯
␯
␯
␯
␯
␯
6
1
2
3
4
5
Experiment
t-HSCO
c-HSCO
HC͑O͒S
0.9788 0.9985 0.9720
V. CONCLUSION
0.9999 0.9782 0.9983 0.9701 0.9911 0.9935
0.9999 0.9783 0.9928 0.9781 0.9903 0.9904
0.9971 0.9793 0.9952 0.9866 0.9777 0.9938
0.9998 0.9723 0.9936 0.9861 0.9913 0.9856
We irradiated matrix samples of H2S/CO/Ar and
H2S/OCS/Ar with an ArF excimer laser at 193 nm and ob-
served new IR absorption lines at 1823.3, 931.6, and 553.4
cmϪ1. These new features are attributed to C–O stretching
(␯2), HSC-bending (␯3), and C–S stretching (␯4) modes of
c-HOCS
aDefined as the ratio of vibrational wave numbers of a 13C isotopomer to that
of the corresponding 12C species.
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5722
J. Chem. Phys., Vol. 120, No. 12, 22 March 2004
Lo et al.
12 R. J. H. Clark and R. E. Hester, Spectroscopy of Matrix Isolated Species
͑Wiley, New York, 1989͒.
t-HSCO, respectively, based on observed 13C-isotopic shifts
and theoretical predictions of line positions, infrared intensi-
ties, and 13C/12C isotopic ratios for possible isomers of
HSCO. According to calculations t-HSCO has energy
smaller than that of isomers c-HSCO, HC͑O͒S, and
c-HOCS. The product t-HSCO was formed mainly via re-
action of HS and CO in the matrix; secondary photolysis at
248 nm depleted t-HSCO and produced mainly OCS. This
work provides spectral information for future investigations
of atmospheric reaction of HSϩCO using IR detection of
t-HSCO; formation of HSCO may have significant implica-
tion for atmospheric chemistry.
13 L. Andrews and M. Moskovits, Chemistry and Physics of Matrix-Isolated
Species ͑North-Holland, New York, 1989͒.
14 W.-J. Lo and Y.-P. Lee, J. Chem. Phys. 101, 5494 ͑1994͒.
15 W.-J. Lo, M.-Y. Shen, C.-H. Yu, and Y.-P. Lee, J. Chem. Phys. 104, 935
͑1996͒.
16 W.-J. Lo and Y.-P. Lee, Chem. Phys. Lett. 229, 357 ͑1994͒.
17 W.-J. Lo, Y.-P. Lee, J.-H. M. Tsai, H.-H. Tsai, T. P. Hamilton, J. G.
Harrison, and J. S. Beckman, J. Chem. Phys. 103, 4026 ͑1995͒.
18 W.-J. Lo, Y.-P. Lee, J.-H. M. Tsai, and J. S. Beckman, Chem. Phys. Lett.
242, 147 ͑1995͒.
19 S.-H. Jou, M.-Y. Shen, C.-H. Yu, and Y.-P. Lee, J. Chem. Phys. 104, 5745
͑1996͒.
20 L.-S. Chen, C.-I. Lee, and Y.-P. Lee, J. Chem. Phys. 105, 9454 ͑1996͒.
21 W.-J. Lo, M.-Y. Shen, C.-H. Yu, and Y.-P. Lee, J. Mol. Spectrosc. 183, 119
͑1997͒.
ACKNOWLEDGMENTS
22 C.-I. Lee, Y.-P. Lee, X. Wang, and Q.-Z. Qin, J. Chem. Phys. 109, 10446
͑1998͒.
We thank A. R. Ravishankara for bringing to our atten-
tion the importance of the reaction of HS and CO in the
atmosphere, and the National Science Council of Taiwan
͑Grant No. NSC92-2113-M-007-033͒ and MOE Program for
Promoting Academic Excellence of Universities ͑Grant No.
89-FA04-AA͒ for support. W.J.L. thanks the Institute of
Atomic and Molecular Sciences, Academia Sinica for a
short-term visiting professorship.
23 M. Bahou, Y.-C. Lee, and Y.-P. Lee, J. Am. Chem. Soc. 122, 661 ͑2000͒.
24 M. Bahou, S.-F. Chen, and Y.-P. Lee, J. Phys. Chem. A 104, 3613 ͑2000͒.
25 M. Bahou and Y.-P. Lee, J. Chem. Phys. 115, 10694 ͑2001͒.
26 W.-J. Lo, Y.-J. Wu, and Y.-P. Lee, J. Chem. Phys. 117, 6655 ͑2002͒.
27 M. Bahou, K. Sankaran, Y.-J. Wu, Y.-P. Lee, D. Rayner, and B. Simard, J.
Chem. Phys. 118, 9710 ͑2003͒.
28 M. J. Frisch, G. W. Trucks, H. B. Schlegel et al., GAUSSIAN 98, Revision
A.9, Gaussian, Inc., Pittsburgh, PA, 1998.
29 A. D. Becke, J. Chem. Phys. 98, 5648 ͑1993͒.
30 C. Lee, W. Yang, and R. G. Parr, Phys. Rev. B 37, 785 ͑1988͒.
31 B. Miehlich, A. Savin, H. Stoll, and H. Preuss, Chem. Phys. Lett. 157, 200
͑1989͒.
1 R. P. Wayne, Chemistry of Atmospheres, 3rd ed. ͑Oxford University Press,
Oxford, UK, 2000͒, pp. 409–416.
32 J. P. Perdew, K. Burke, and Y. Wang, Phys. Rev. B 54, 16533 ͑1996͒.
33 J. P. Perdew, J. A. Chevary, S. H. Vosko, K. A. Jackson, M. R. Pederson,
D. J. Singh, and C. Fiolhais, Phys. Rev. B 48, 4978 ͑1993͒.
34 E. Isoniemi, M. Pettersson, L. Khriachtchev, J. Lundell, and M. Rasanen,
J. Phys. Chem. A 103, 679 ͑1999͒.
2 O. Boucher and M. Pham, Geophys. Res. Lett. 29, 1308 ͑2002͒.
3 H. Berresheim, P. H. Wine, and D. D. Davis, ‘‘Sulfur in the atmosphere,’’
in Composition, Chemistry and Climate of the Atmosphere, edited by
H. B. Singh ͑Van Nostrand, Reinhold, 1995͒, pp. 251–307.
4 Y.-L. Lin, N. S. Wang, and Y.-P. Lee, Int. J. Chem. Kinet. 17, 1201 ͑1985͒.
5 R. Atkinson, D. L. Baulch, R. A. Cox, R. F. Hampson, Jr., J. A. Kerr,
M. J. Rossi, and J. Troe, J. Phys. Chem. Ref. Data 26, 1329 ͑1997͒.
6 G. S. Tyndall and A. R. Ravishankara, Int. J. Chem. Kinet. 23, 483 ͑1991͒
and references therein.
35 H. Abe, H. Takeo, and K. M. T. Yamada, Chem. Phys. Lett. 311, 153
͑1999͒.
36 J. Lundell, E. Nordquist, and M. Rasanen, J. Mol. Struct. 416, 235 ͑1997͒.
37 T. Shimanouchi, Tables of Molecular Vibrational Frequencies, consoli-
dated volume I ͑National Bureau of Standards, Washington, DC, 1972͒,
p. 40.
7 M. A. Kurbanov and Kh. F. Mamedov, Kinet. Katal. 36, 455 ͑1995͒.
8 S. H. Herndon, Ph.D. thesis, Department of Chemistry and Biochemistry,
University of Colorado, 1999.
38 D. E. Milligan and M. E. Jacox, J. Chem. Phys. 51, 277 ͑1969͒.
39 M. E. Jacox, J. Chem. Phys. 88, 4598 ͑1988͒.
9 M. W. Chase, Jr., NIST-JANAF Themochemical Tables, 4th ed. ͓J. Phys.
Chem. Ref. Data, Monograph 9 ͑1998͔͒.
40 L. Khriachtchev, M. Pettersson, E. Isoniemi, and M. Rasanen, J. Chem.
Phys. 108, 5747 ͑1998͒.
10 B. M. Rice and C. F. Chabalowski, J. Phys. Chem. 98, 9488 ͑1994͒.
11 B. M. Rice, S. V. Pai, and C. F. Chabalowski, J. Phys. Chem. A 102, 6950
͑1998͒.
41 N. Sivakumar, G. E. Hall, P. L. Houston, J. W. Hepburn, and I. Burak, J.
Chem. Phys. 88, 3692 ͑1988͒.
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