Mode-specific and bond-selective dissociative chemisorption of CHD₃ and CH₂D₂ on Ni(111) revisited using a new potential energy surface

Abstract

Dissociative chemisorption of methane on a nickel surface is a prototypical system for studying mode-specific chemistry in gas-surface reactions. We recently developed a fifteen-dimensional potential energy surface for this system which has proven to be chemically accurate in reproducing the measured absolute dissociative sticking probabilities of CHD₃ in thermal conditions and with vibrational excitation on Ni(111) at high incident energies. Here, using this new potential energy surface, we explored mode specificity and bond selectivity for CHD₃ and CH₂D₂ dissociative chemisorption at low incidence energies down to ~50 kJ/mol via a quasi-classical trajectory method. Our calculated dissociation probabilities are consistent with previous theoretical and experimental ones with an average shift in translational energy of ~8 kJ/mol. Our results very well reproduce the C–H/C–D branching ratio upon the C–H local mode excitation, which can be rationalized by the sudden vector projection model. Quantitatively, however, the calculated dissociative sticking probabilities are systematically larger than experimental ones, due presumably to the artificial zero point energy leakage into reaction coordinate. Further high-dimensional quantum dynamics calculations are necessary for acquiring a chemically accurate description of methane dissociative chemisorption at low incident energies.