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. 
R. Milot and A. P. J. Jansen