Exploration of the Mechanism of the Oxidation of Sulfur Dioxide and Bisulfite by Hydrogen Peroxide in Water Clusters UsingAb InitioMethods

Abstract

Mechanisms for the oxidation of sulfur dioxide and bisulfite by hydrogen peroxide in water droplets have been explored using ab initio electronic structure methods. The large barriers that are found for bimolecular reactions are considerably reduced upon the inclusion of explicit water molecules, which provide a proton shuttle mechanism to facilitate the reaction. Further solvation of these clusters, either by a continuum model or by explicit water molecules modeled classically, has little effect on the reaction energetics. The transition state for reaction of bisulfite and hydrogen peroxide effectively involves SO2 and OH-, thus leading to acid catalysis for this reaction, analogous to the oxygen exchange in bisulfite in aqueous solution. The possibility of direct formation of sulfur(VI) species in a single step is less likely on energetic grounds.