Quantum and classical dynamics of methane scattering

Abstract

The dissociation of methane on transition metals is an important reaction in catalysis. It is the rate limiting step in steam reforming to produce syngas. Molecular beam experiments have shown that the energy in the internal vibrations are about as effective as the translational energy in inducing dissociation. The published wave packet simulations on the methane dissociation reaction on transition metals have treated the methane molecule always as a diatomic up to now. Besides the C-H bond and molecule surface distance, a combination of other coordinates were included, like (multiple) rotations and some lattice motion. None of them have looked at the role of the internal vibrations. We were not able yet to simulate the dissociation including all internal vibrations. Instead we simulated the scattering of methane in fixed orientations, for which all internal vibrations can be included, and used the results to deduce consequences for the dissociation. Furthermore we studied the isotope effect, and the role of vibrational excitations. We ended with classical trajectory calculations of the rotational vibrational scattering of a non-rigid methane molecule from a Ni(111) surface. Energy dissipation and scattering angles have been studied as a function of the translational kinetic energy, the incident angle, the (rotational) nozzle temperature, and the surface temperature.