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 SO(2)-H(2)O through a barrier less process. Subsequently, via a variety of transformations of isomer SO(2)-H(2)O, three kinds of products H(2)SO(3), SO(3) + H(2), and H(2)O(2) + (3)SO 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 H(2)O + SO(2) reaction on the singlet potential energy surface are plotted. The calculation results show that the most suitable reaction pathways are the formation of H(2)SO(3). 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.