EXPLORATION OF THE MECHANISM OF THE OXIDATION OF SULFUR-DIOXIDE AND BISULFITE BY HYDROGEN-PEROXIDE IN WATER CLUSTERS USING AB-INITIO METHODS

Mechanisms for the oxidation of sulfur dioxide and bisulfite by hydrog en peroxide in water droplets have been explored using ab initio elect ronic structure methods. The large barriers that are found for bimolec ular reactions are considerably reduced upon the inclusion of explicit water molecules, which provide a proton shuttle mechanism to facilita te the reaction. Further solvation of these clusters, either by a cont inuum model or by explicit water molecules modeled classically, has li ttle effect on the reaction energetics. The transition state for react ion 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 d irect formation of sulfur(VI) species in a single step is less likely on energetic grounds.