An Ab Initio Theoretical Study of the CH + H2 ⇌ Ch3 * ⇌ Ch2 + H Reactions

Abstract

Ab initio calculations of the electronic wave function and associated potential energy of CH ₃ at geometries appro priate for the title reaction described here allow charac terization of the reactants and the energetically most fa vorable routes that are followed during the reaction. The quantum mechanical description of the electronic mo tion at each molecular geometry involves the response of each electron to the average field of all other elec trons and the approximate correlated response of each electron to the instantaneous position of the other elec trons. The basic methodology for the computation of this wave function, using extensive orbital basis sets and large-scale configuration expansions, is described. This calculation is one of the largest ever attempted for the characterization of a polyatomic reaction path. However, the path description involves a fine balance of energy contributions that requires this level of sophistication. The calculated properties of the reactants, the interme diate CH₃, and the reaction paths to form CH₃ are pre sented. The computed energetics compare favorably to experimental results.