Chemistry of large hydrated anion clusters X-(H2O)n, n = 0-59 and X = OH, O, O2, and O3. 3. Reaction of sulfur dioxide

Sulfur dioxide is a very important species in the atmosphere, and it is also well established that it is one of the key trace neutral reactants involved in the negative ion chemistry of the stratosphere. The kinetics and mechanisms of reactions of large hydrated anion clusters X{sup {minus}}(H{sub 2}O){sub n=0{minus}59}, X = O, OH, O{sub 2}, and O{sub 3}, with SO{sub 2} are studied in a fast flow reactor under well-defined temperatures and pressures. All the clusters, except OH{sup {minus}}, react with SO{sub 2} 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 SO{sub 2} 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{sup {minus}13} cm{sup 3}/s) are found for the reactions between protonated water clusters, H{sup +}(H{sub 2}O){sub n = 1{minus}60} and SO{sub 2}, which show that different signs of charge on the hydrated clusters lead to different reaction mechanisms, and hence alter the reaction kinetics. The possible application of the present results to atmospheric ion chemistrymore » and aqueous solution chemistry are also briefly discussed.« less