Theoretical study on the atmospheric formation of sulfur trioxide as the primary agent for acid rain

The reaction mechanism of SO2 with O3 on the singlet potential energy surface has been investigated theoretically at the G3MP2B3//B3LYP/6-311+G(3df) level of theory. The reactants are initially associated with adducts IN1(O2S–OOO) and IN2(OS-cyclic O4) in a barrier-less process. Subsequently, these adducts undergo isomerization and dissociation processes to produce cis-OSOO + 3O2, SO3(C s ) + 3O2 and SO3(D 3h ) + 3O2 products. The SO3(D 3h ) + 3O2 is major product and the cis-OSOO + 3O2 and SO3(C s ) + 3O2 are minor products. No stable pathway has been found for the formation of trans-OSOO and cyclic-SOOO isomers in the reaction of SO2 + O3. For major product, the rate constant of SO2 + O3 reaction is 2.30 × 10−23 cm3 molecule−1 s−1, at room temperature and atmospheric pressure.