Mechanistic study on the atmospheric formation of acid rain base on the sulfur dioxide

The reaction pathways of acid rain formation from reaction of sulfur dioxide vapor and water vapor on the singlet potential energy surface have been investigated theoretically. The calculated results show that the reactants are initially associated with the adduct SO2–H2O through a barrier less process. Subsequently, via a variety of transformations of isomer SO2–H2O, three kinds of products H2SO3, SO3 + H2, and H2O2 + 3SO are obtained. The cleavage and formation of the chemical bonds in the reaction pathways have been discussed using the structural parameters. Also, by means of the transition states and their connected intermediates or products at the CCSD(T)//B3LYP level, mechanism of H2O + SO2 reaction on the singlet potential energy surface are plotted. The calculation results show that the most suitable reaction pathways are the formation of H2SO3. Finally, the rate constants have been calculated only for these suitable pathways by the RRKM and TST theories at temperature range of 250–2500 K.