High-level ab initio study of the reaction of OCS with OH radicals

Abstract

The title reaction has been studied using the high-level methods of G-2 theory. Various reaction channels on the potential surface have been identified and characterised. Formation of a carbon-bonded OCSOH adduct is found to be highly exothermic, with a modest activation barrier: ΔH(298 K)=–110.2 kJ mol^–1 and ΔH^‡(298 K)= 21.1 kJ mol^–1. Rearrangement of this adduct to form a species which can decompose into CO₂ and SH is found to be very endothemic. Formation of a sulfur-bonded adduct occurs without barrier, but the reaction is endothermic, with ΔH(298 K)= 11.3 kJ mol^–1 and ΔH^‡(298 K)= 9.7 kJ mol^–1. The implications of these results for tropospheric OCS chemistry are discussed, and a comparison with the reaction of CS₂ and OH is presented.