Ab initio/density functional theory and multichannel RRKM calculations forthe CH3O+CO reaction

The potential energy surface for the reaction of methoxy:radical with carbo n monoxide has been studied using the G2(B3LYP/MP2/CC) method. Two reaction mechanisms were revealed. The hydrogen abstraction of CH3O by CO produces CH2O + HCO via a: barrier of 24.19 kcal/mol. The addition of CH3O to CO pro ceeds to an intermediate CH3OCO via a barrier of 6.39 kcal/mol. The product s, CH3 and CO2, can be formed in two ways. One is the C-O bond cleavage of the CH3OCO radical. The other involves the isomerization of CH3OCO to the C H3CO2 radical and the subsequent C-C bond fission. CH2O and HCO can be form ed via the path CH3OCO --> TS6 --> IM4 --> TS7 --> CH2O + HCO. A radical pr oduct, CH2COOH is formed through the hydrogen rearrangement: of the CH3CO2 radical. Multichannel RRKM calculations have been carried out for the total and individual rate constants for various channels over a wide range of te mperatures and pressures using the ab initio data. At lower temperatures, t he title reaction is dominated by the stabilization of the CH3OCO radical. At higher temperatures, the CH3 + CO product channel and the direct hydroge n abstraction channels become dominant and competitive. The title reaction shows the typical falloff behavior. The calculations were compared with the :available experimental data.