Vibrational, rotational and translational effects on the OH(v, j) + CH4(v1, v2, v3, v4) dynamics reaction: a quasi-classical trajectory study

To analyze the effects of vibrational excitation and an equivalent amount of energy as translational motion on the OH(v) + CH4(v1, v2, v3, v4) gas-phase reaction, quasi-classical trajectory calculations at different collision energies in the range 3.0–30.0 kcal mol−1 were performed on a recently developed ab initio full-dimensional potential energy surface. While the OH(v) mode behaves as a spectator mode, excitation of all methane modes enhances reactivity with respect to the ground state, although when only the CH3(v = 0) coproduct is analyzed, this tendency is inverted. In addition, vibrational energy is less efficient than an equivalent amount of translational energy. Thus, this exothermic reaction with an “early” transition state holds the Polanyi’s rules and a more recent model, the sudden vector projection. The similar behavior (reaction cross section and product scattering distribution) for both CH symmetric and antisymmetric stretch modes, which differ by only 170 cm−1, rules out mode specificity for the title reaction. In addition, analysis of the rotational effects shows that both reactants inhibit reactivity, the effect of the OH reactant being greater. These theoretical results await future experimental confirmation, which is not yet available, but they do agree with previous theoretical studies, though in some cases these were performed on reduced-dimensionality potential energy surfaces.