Surface reactivity of highly vibrationally excited molecules prepared by pulsed laser excitation: CH4 (2ν3) on Ni(100)

Abstract

We report state resolved sticking coefficients for highly vibrationally excited CH4 on Ni(100) at well-defined kinetic energies in the range of 12–72 kJ/mol. Incident methane molecules are prepared by pulsed laser radiation in single rovibrational levels of the first overtone of the antisymmetric stretch (2ν3) at 6004.69 cm−1 and collided at normal incidence with a clean Ni(100) single crystal. We find that the vibrational excitation enhances the reaction probability by a factor 100 at an incident translational energy of 72 kJ/mol, but this enhancement increases to more than 4 orders of magnitude at low kinetic energy. Despite this large increase in the sticking coefficient, vibrational energy in 2ν3 appears to be about 80% as effective as an equivalent amount of translational energy in promoting the chemisorption reaction.