Abstract: The geometries of reactants, transition states, intermediates and products on the reaction of CH3(2A′)＋O3 have been optimized at the UMP2/6-31++G** level. The transition states and intermediates of the reactions were verified by frequency analysis. The relative single-point energies were further calculated at the UQCISD(T)/6-311++G** level, based on the UMP2/6-311++G** optimized structures. The zero point energy (ZPE) corrections and reaction’s rate constants were also obtained. We used the classic transition state theory to compute the rate constants of the CH3(2A′)＋O3 reaction (k=4.73×10－14 cm3•molecule－1•s－1). Compared with the experimental values (k=2.52×10－14 cm3•molecule－1•s－1), our calculated result is in good agreement with experimental datum.

Key words: Reaction mechanism, Transition state, Reaction channel, Ab initio