Ab initio study of the catalytic effect of H2O on the self-reaction of HO2

The catalytic enhancement effect of H2O on the self-reaction of HO2 has been studied at the G2M//B3LYP/6-311G(d,p) level of theory. The lowest channel producing O2 (1Δ) was also calculated at the CAS(12,12)/6-311G(d,p)//CAS(2,2)/6-31G(d) level. Comparing with the results for the reaction without H2O, we note that the H2O molecule catalytically reduces the barrier for O2 (1Δ) formation by 1–3 kcal/mol and those for the formation of the ground state O2 and O3 by as much as 6–7 and 4–8 kcal/mol, respectively. Significantly, O3 formation becomes competitive with the formation of O2.