Theoretical Investigation on Hydrogen Abstraction Reactions of Sulfur Compounds HSX(O)H and CH3SX(O)H (X = C, S) by OH Radicals

Abstract

The kinetic and mechanistic investigation of oxidation reactions of HSC(O)H, HSS(O)H, CH3SC(O)H, and CH3SS(O)H by OH radicals is performed extensively with the help of theoretical calculations. The potential energy profiles for the titled reactions are constructed at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ level. Two isomers, cis and trans, are observed for both HSC(O)H and HSS(O)H molecules. Reaction enthalpies and reaction Gibbs free energies are calculated employing the M06-2X/aug-cc-pVTZ method. The kinetic study uses canonical variational transition state theory and small-curvature tunneling in the temperature range of 210–350 K. CVT/SCT rate coefficients are utilized for calculating branching ratios. The atmospheric lifetime of HSC(O)H is computed to be 26.76 h, 3.51 h for HSS(O)H, 1.55 years for CH3SC(O)H, and 18.20 h for CH3SS(O)H. The global warming potential (GWP) and global temperature change potential (GTP) of CH3SC(O)H are found to be significant, while cis-HSC(O)H, trans-HSC(O)H, cis-HSS(O)H, trans-HSS(O)H, and CH3SS(O)H have negligible GWPs and GTPs.