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

The isotope effect in the scattering of methane is studied by wavepacket si mulations of oriented CH4 and CD4 molecules from a flat surface including a ll nine internal vibrations. At a translational energy of up to 96 kJ mol(- 1) we find that the scattering is still predominantly elastic, but less so for CD4. Energy distribution analysis of the kinetic energy per mode and th e potential-energy surface terms, when the molecule hits the surface, are u sed in combination with vibrational excitations and the corresponding defor mation. They indicate that the orientation with three bonds pointing toward s the surface is mostly responsible for the isotope effect in methane disso ciation. (C) 2000 Elsevier Science B.V. All rights reserved.