THEORETICAL CHARACTERIZATION OF THE REACTION CH3+OH-]CH3OH-]PRODUCTS - THE (CH2)-C-1+H2O, H2+HCOH, AND H2+H2CO CHANNELS

The potential energy surface (PES) for the CH3OH system has been characterized for the (CH2)-C-1 + H2O, H-2 + HCOH, and H-2 + 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 (CH2)-C-1 + 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 H-2 + HCOH, and H-2 + 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.