Chemical accelerator studies of reaction dynamics: Ar^+ + CH4 → ArH^+ + CH3

Abstract

Chemical accelerator studies on isotopic variants of the reaction Ar+ + CH4 → ArH+ + CH3 are reported. Velocity and angular distributions of the ionic product as a function of initial translational energy have been measured over the energy range 0.39–25 eV center-of-mass (c.m.). The asymmetry of the product distribution with respect to the center of mass indicates that the reaction is predominantly direct over the energy range studied. The dynamics of the reaction are approximated by the spectator stripping model: The reaction exothermicity appears as product internal energy and product excitation increases with collision energy at the rate predicted by this model. The internal degrees of freedom of the neutral product have little effect on reactiondynamics, and product excitation appears to reside principally in the ionic product. Deviations from the spectator stripping model suggest the existence of a basin in the potential energy hypersurface for this reaction; the ArCH4 + complex which may be formed at low collision energies, however, preferentially decomposes via reaction channels other than that resulting in ArH+ formation.