  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.
