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

Abstract

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.

Fundamental Vibrational Frequencies and Spectroscopic Constants of cis- and trans-HOCS, HSCO, and Isotopologues via Quartic Force Fields

“…Comparisons of previously computed MP2 and B3LYP harmonic vibrational frequencies 27,28 to those computed in this study with the CcCR QFF (given in Table 5) show similar levels of correlation as the relative energies and geometrical parameters. The MP2/6-311G+(2df,2p) computations by Rice, Pai, and Chabalowski 27 yield harmonic O−H stretching frequencies within 2.0 cm −1 of the present CcCR values.…”

“…The geometrical parameters for the HOCS conformers as well as the deuterated and 34 S isotopologues are given in Table 1. The equilibrium aug-cc-pV5Z dipole moments for the most abundant isotopologues are also given in Table 1, with the largest dipole moment of the four isomers examined here belonging to trans-HOCS at 2.27 D. Comparison between previous theory and the CcCR HOCS equilibrium geometries is reasonable for the differences in the methods employed here and by Rice, Pai, and Chabalowski 27 as well as Lo et al 28 The R α vibrationally averaged zero-point geometries and rotational constants for the standard isotopologue shift from their corresponding equilibrium values and should produce more physically meaningful values, as has been observed in previous studies. 10,11,[15][16][17][18][19]25 Deuteration reduces the A 0 and C 0 rotational constants across the set.…”

“…Following from this, trans-HOCS is 15.2 kcal/mol higher in energy than the global minimum of trans-HSCO. The computational work by Rice, Pai, and Chabalowski was followed later by Lo et al, 28 who were able to assign Ar matrix reference frequencies to the C−O and C−S stretches as well as the H−S−C bend of trans-HSCO. They also report B3LYP/augcc-pVTZ harmonic vibrational frequencies for trans-HSCO, cis-HSCO, and cis-HOCS.…”

Computational Study of Carbonyl Sulphide Formation on Model Interstellar Dust Grains

“…Although this study did not investigate the energetics of OCS formation, they concluded that OCS was formed by the reaction of CO with free S, generated from the proton-induced fragmentation of the parent S-containing species. The formation of trans -HSCO, a possible intermediate in OCS formation, has also been observed in studies of the ultraviolet irradiation of H 2 S and CO in an Ar matrix …”

Chemistry in low-temperature matrices

“…Irradiation of an Ar matrix containing H 2 S and CO, again at 193 nm, gives trans-HSCO which shows IR bands at 1823.3, 931.6 and 553.3 cm À1 . 357 These bands are assigned to n(CO), d(HSC) and n(CS), respectively. Trans-HSCO is planar.…”