Selected ion flow tube studies of H 3O +(H 2O) 0.1 reactions with sulfides and thiols

Abstract

Rate coefficients and product distributions have been determined in a selected ion flow tube at 300 K for the reactions of H 3O + and the water cluster ion, H 3O +·H 2O, with the sulfur-containing compounds H 2S, CH 3SH C 2H 5SH, n-C 3H 7SH, iso-C 3H 7SH, (CH 3) 2S, CH 3SC 2H 5, and C 4H 4S. The reactions of H 3O + have high efficiency, following the trend established in reactions with other molecules, and are non-dissociative proton transfer reactions. For H 3O +·H 2O, almost all of the reactions also proceed approximately at the collision rate, with rate coefficients slightly smaller than for the analogous H 3O + reactions, consistent with the slightly larger reduced mass. The products are more varied, however. Proton transfer and/or ligand switching (presumably with internal H + transfer as, for example, in the production of CH 3SH + 2·H 2O) are observed to occur. Indeed, in some cases, proton transfer is observed where it should not be energetically possible. For example, in the cases of n- and iso-C 3H 7SH, both product channels are observed. The possibilities of neutral water dimer production, reactions being entropy driven, isomerization of the proton acceptor in the reaction, thermal dissociation of cluster ion products and uncertainties in the thermochemical data are all considered. Applications to interstellar gas clouds and the terrestrial atmosphere are discussed briefly.