Theoretical characterization of the reaction CH3+OH→CH3OH→products: The 1CH2+H2O, H2+HCOH, and H2+H2CO channels

The potential energy surface (PES) for the CH3OH system has been characterized for the 1CH2+H2O, H2+HCOH, and H2+H2CO product channels using complete-active-space self-consistent-field (CASSCF) gradient calculations to determine the stationary point geometries and frequencies followed by CASSCF/internally contracted configuration-interaction (CCI) calculations to refine the energetics. The 1CH2+H2O channel is found to have no barrier. The long range interaction is dominated by the dipole–dipole term, which orients the respective dipole moments parallel to each other but pointing in opposite directions. At shorter separations there is a dative bond structure in which a water lone pair donates into the empty a″ orbital of CH2. Subsequent insertion of CH2 into an OH bond of water involves a non-least-motion pathway. The H2+HCOH, and H2+H2CO pathways have barriers located at −5.2 and 1.7 kcal/mol, respectively, with respect to CH3+OH. From comparison of the computed energetics of the reactants and products to known thermochemical data it is estimated that the computed PES is accurate to ±2 kcal/mol.