CHEMISTRY OF LARGE HYDRATED ANION CLUSTERS X-(H2O)N, N = 0-59 AND X = OH, O, O2, AND O3 .3. REACTION OF SO2

The kinetics and mechanisms of reactions of large hydrated anion clusters X-(H2O)n = 0-59, X = O, OH, O2, and O3, with SO2 are studied in a fast flow reactor under well-defined temperatures and pressures. All the clusters, except OH-, react with SO2 at near the collision limit; the reactions of the hydrated anions are found to proceed mainly via a ligand switching mechanism where a few water ligands are replaced by one SO2 molecule which leads to the formation of stable reaction products. At low temperatures and large cluster sizes, association eventually dominates the reaction mechanism. Interestingly, slow rate constants (k < 10(-13) cm3/s) are found for the reactions between protonated water clusters, H+(H2O)n = 1-60 and SO2, which show that different signs of charge on the hydrated clusters lead to different reaction mechanisms, and hence alter the reaction kinetics. The possible applications of the present results to atmospheric ion chemistry and aqueous solution chemistry are also briefly discussed.