Water-catalyzed gas-phase hydrogen abstraction reactions of CH3O2 and HO2 with HO2: a computational investigation

The gas-phase hydrogen abstraction reactions of CH3O2 and HO2 with HO2 in the presence and absence of a single water molecule have been studied at the CCSD(T)/6-311++G(3d,2p)//B3LYP/6-311G(2d,2p) level of theory. The calculated results show that the process for O3 formation is much faster than that for 1O2 and 3O2 formation in the water-catalyzed CH3O2 + HO2 reaction. This is different from the results for the non-catalytic reaction of CH3O2 + HO2, in which almost only the process for 3O2 formation takes place. Unlike CH3O2 + HO2 reaction in which the preferred process is different in the catalytic and non-catalytic conditions, the channel for 3O2 formation is the dominant in both catalytic and non-catalytic HO2 + HO2 reactions. Furthermore, the calculated total CVT/SCT rate constants for water-catalyzed and non-catalytic title reactions show that the water molecule doesn't contribute to the rate of CH3O2 + HO2 reaction though the channel for O3 formation in this water-catalyzed reaction is more kinetically favorable than its non-catalytic process. Meanwhile, the water molecule plays an important positive role in increasing the rate of HO2 + HO2 reaction. These results are in good agreement with available experiments.