State-Resolved Gas-Surface Reactivity of Methane in the Symmetric C-H Stretch Vibration on Ni(100)

Abstract

The state-resolved reactivity of ${\mathrm{CH}}_{4}$ in its totally symmetric C-H stretch vibration (${\ensuremath{\nu}}_{1}$) has been measured on a Ni(100) surface. Methane molecules were accelerated to kinetic energies of 49 and $63.5\text{ }\text{ }\mathrm{kJ}/\mathrm{mol}$ in a molecular beam and vibrationally excited to ${\ensuremath{\nu}}_{1}$ by stimulated Raman pumping before surface impact at normal incidence. The reactivity of the symmetric-stretch excited ${\mathrm{CH}}_{4}$ is about an order of magnitude higher than that of methane excited to the antisymmetric stretch (${\ensuremath{\nu}}_{3}$) reported by Juurlink et al. [Phys. Rev. Lett. 83, 868 (1999)] and is similar to that we have previously observed for the excitation of the first overtone ($2{\ensuremath{\nu}}_{3}$). The difference between the state-resolved reactivity for ${\ensuremath{\nu}}_{1}$ and ${\ensuremath{\nu}}_{3}$ is consistent with predictions of a vibrationally adiabatic model of the methane reaction dynamics and indicates that statistical models cannot correctly describe the chemisorption of ${\mathrm{CH}}_{4}$ on nickel.