INTRINSIC ACTIVATION BARRIERS FOR A PROTOTYPE HYDROGENOLYSIS REACTION D+C2H6-]DCH3+CH3 IN C-3-NU SYMMETRY

The presence of intrinsic barriers to reaction are very important to the theory of reactions, but at present accurate values of the intrinsic barriers to reaction for hydrogenolysis reactions do not appear in the open literature. In this paper we use ab initio methods to estimate the intrinsic barrier for a prototype hydrogenolysis reaction for the abstraction of a methyl group from ethane: D + CH3CH3 --> DCH3 + CH3. A potential energy surface for this reaction was calculated at the UMP2/6-31G* level of theory. Then a variety of methods up to QCISD(T)/6-311G(d,p) were used to estimate the activation barrier and intrinsic activation energy for this reaction. It was found that this reaction has an intrinsic barrier of 48 +/- 2 kcal/mol. By comparison experimental results suggest that the intrinsic barrier to hydrogen abstraction from ethane, D + CH3CH3 --> DH + CH2CH3, is only 13 kcal/mol. These results show that the intrinsic barriers to hydrogen abstraction are much lower than the intrinsic barriers to methyl abstraction, in agreement with previous experiments.