Ab Initio/Density Functional Theory and Multichannel RRKM Calculations for the CH3O + CO Reaction

The potential energy surface for the reaction of methoxy radical with carbon monoxide has been studied using the G2(B3LYP/MP2/CC) method. Two reaction mechanisms were revealed. The hydrogen abstraction of CH 3 O by CO produces CH 2 O + HCO via a barrier of 24.19 kcal/mol. The addition of CH 3 O to CO proceeds to an intermediate CH 3 OCO via a barrier of 6.39 kcal/mol. The products, CH 3 and CO 2, can be formed in two ways. One is the C−O bond cleavage of the CH 3 OCO radical. The other involves the isomerization of CH 3 OCO to the CH 3 CO 2 radical and the subsequent C−C bond fission. CH 2 O and HCO can be formed via the path CH 3 OCO → TS6 → IM4 → TS7 → CH 2 O + HCO. A radical product, CH 2 COOH, is formed through the hydrogen rearrangement of the CH 3 CO 2 radical. Multichannel RRKM calculations have been carried out for the total and individual rate constants for various channels over a wide range of temperatures and pressures using the ab initio data. At lower temperatures, the title reaction is dominated by the stabilization of the CH 3 OCO radical. At higher temperatures, the CH 3 + CO product channel and the direct hydrogen abstraction channels become dominant and competitive. The title reaction shows the typical falloff behavior. The calculations were compared with the available experimental data.