The reaction mechanism of CO2 with O-3 on the singlet potential energy surface has been investigated at the CBS-QB3//B3LYP/6-311++G(3df, 3pd) level of theory. The reactants are initially associated with adducts IN1 (OOO-OCO) and IN2 (OC-cyclic O-4) in a barrier-less process. Then, adducts undergo isomerization and dissociation processes to produce P-1 (CO + 2(3)O(2)) and P-2 (CO3 + O-3(2)) with two different mechanisms. The calculated results show that there is no favorable pathway for the formation of these two products in the atmospheric reaction of CO2 with O-3. (c) 2010 Elsevier B. V. All rights reserved.