Isotopic Effects on the Dynamics of the CH3+ + H2 → CH5+ → CH3 + H2 Reaction

Diffusion Monte Carlo is used to investigate the anharmonic zero-point energy corrected energies for the CH3+ + H-2 -> CH5+ -> CH3+ + H-2 process as a function of the center of mass separation of the two fragments. In addition to the title reaction, all possible deuterated and several tritiated (CH4T+ and CH3T2+) analogues of this reaction are investigated. As anticipated, the replacement of one or more of the hydrogen atoms with deuterium or tritium atoms lowers the zero-point energy of the system. Further, in the partially deuterated or tritiated isotopologues, the lowest energy configuration generally has the heavy atoms in the CH3+ fragment. Analysis of the wave functions allows us to study how zero-point energy influences the approach geometries sampled during low-energy collisions between CH3+ and H-2, and to gain insights into how the dynamics is affected by the substitution of heavier isotopes for one or more of the hydrogen atoms. Differences between quantum and classical descriptions of the title reaction are also discussed.