Energy distribution analysis of the wavepacket simulations of CH4 and CD4 scattering

The isotope effect in the scattering of methane is studied by wavepacket simulations of oriented CH4 and CD4 molecules from a flat surface including all nine internal vibrations. At a translational energy up to 96 kJ/mol we find that the scattering is still predominantly elastic, but less so for CD4. Energy distribution analysis of the kinetic energy per mode and the potential energy surface terms, when the molecule hits the surface, are used in combination with vibrational excitations and the corresponding deformation. They indicate that the orientation with three bonds pointing towards the surface is mostly responsible for the isotope effect in the methane dissociation.Comment: 20 pages LaTeX, 1 figure (eps), to be published in Surf. Sc

Bond breaking in vibrationally excited methane on transition metal catalysts

The role of vibrational excitation of a single mode in the scattering of methane is studied by wave packet simulations of oriented CH4 and CD4 molecules from a flat surface. All nine internal vibrations are included. In the translational energy range from 32 up to 128 kJ/mol we find that initial vibrational excitations enhance the transfer of translational energy towards vibrational energy and increase the accessibility of the entrance channel for dissociation. Our simulations predict that initial vibrational excitations of the asymmetrical stretch (nu_3) and especially the symmetrical stretch (nu_1) modes will give the highest enhancement of the dissociation probability of methane.Comment: 4 pages REVTeX, 2 figures (eps), to be published in Phys. Rev. B. (See also arXiv:physics.chem-ph/0003031). Journal version at http://publish.aps.org/abstract/PRB/v61/p1565