Abstract

The MIND0/3-F0RCES method is applied for the calculation of the 1 CH2-1-H2 CH4 reaction. The variation of geometry is carried out in such a manner as to allow for the deviation from the Csv symmetry along the H 7 —CH, reaction coordinate. The changes in the geometric parameters of the system during the reaction are followed. It is found that the transition state of the reaction corresponds to ß = 1.8Ä and has a geometry closer to the reactants than the products. The cal-culated activation energy is 13.57 kcal/mol and the calculated reaction enthalpy 106.36 kcal/mol (118.9 kcal/mol exp.). Similar calculations for the CH4 ,+ yield a D2d structure and a AH[ value of 269.68 kcal/mol (274.0 kcal/mol exp.). The activation energy of the decomposition reaction CH4 + -> CH3 + + H -is 84.54 kcal/mol, the reaction enthalpy is 42.83 kcal/mol (38.10 kcal/mol exp.). Using both MINDO/2-and MIND0/3.F0RCES a Q>v geometry is calculated for the benzyl radical. The AHf values are 48.40 and 67.93 kcal/mol respectively. The latter calculation shows that the rotated perpendicular conformation of the methylene group is by 2 kcal/mol less stable than the planar one. The rotation transition state corresponds to the rotation angle 50°. The change in ithe geometric parameters during the rotation is followed. For he vinyl radical the MINDO/3-FORCES calculation yields a CCH angle of 151.1° and a H{ value of 69.8 kcal/mol (65 kcal/mol exp.).