An Ab Initio Study of the Competing Reaction Channels in the Reaction of HOCO Radicals with NO and O2

The reaction between HOCO and NO, and that between HOCO and O2, have been examined using the QCISD method to locate and optimize the critical points on the PESs. Analysis of the critical points provides new insight into new intermediates and pathways by which these reactions occur and help explain recent experimental results. In the HOCO + O2 reaction, the symmetry allowed products, CO2 + HO2, can be obtained via direct H abstraction by O2 on the HOCO radical s, as well as through an adduct, HOC(O)O2, which can proceed to give the same products. The less-than-unity yield of CO2 observed in the experimental studies of the HOCO+NO reaction, as well as the lack of CO, can be explained by the formation of a stable HOC(O)NO adduct.