Reaction of H2S with OH and a study of the HSO and SOH isomers. High-level ab initio calculations

Abstract

The reaction between H₂S and OH radicals has been studied using ab initio molecular orbital techniques. A modified version of G-2 theory (denoted G-2* theory) has been used to examine some possible competing reaction pathways. At this level, the reaction was found to proceed via a hydrogen-abstraction mechanism, with a weakly bound hydrogen-bonded adduct possibly being formed first. The reaction was found to have ΔH²⁹⁸=–117.4 kJ mol^–1 and conventional transition-state theory calculations using the ab initio data gave values of E_a,298= 2.6 KJ mol^–1 and k₂₉₈= 6.7 × 10^–13 cm³ molecule^–1 s^–1. The Arrhenius plot between 200 and 500 K showed definite curvature, in agreement with some experiments. The isomers HSO and SOH have also been studied at the G-2* level, and values for Δ_fH²⁹⁸of –21.9 ± 2.6 and –7.7 ± 2.6 kJ mol^–1, respectively, are proposed.