Reactivity of Vibrationally Excited Methane on Nickel Surfaces
L Halonen, S Bernasek, David Nesbitt
Four-Dimensional variational calculations have been performed for modeling energy flow between CH2 stretching vibrational energy statesas the molecule adiabatically approaches a nickel surface. The model is based on a local mode Hamiltonian for isolated CH4 and LEPS potentialdescribing surface-molecule interactions. The results suggest the possibility of mode specific effects on chemical reactivity. Specifically, thesymmetric A1 stretch fundamental adiabatically correlates with the localized excitation in the unique CH bond pointinc, toward the Ni surface.Conversely, the antisymmetric F2 stretch fundamental excitation correlates with A and E vibrations in the CH3 radical, and therefore this decreeof freedom is localized away from the reactive CH bond. Landau-Zener semiclassical analysis of non-adiabatic curve crossings predicts asignificant velocity dependence to the state specific energy flow dynamics. As excitation localized in active vs spectator bonds is expected to be more efficient in accelerating CH bond cleavage and adsorption reactivity, these results offer insight in interpreting velocity and vibrationally mediated reaction dynamics of CH4 at nickel surfaces.