Collision of a diatomic molecule with a solid surface

The collision of a diatomic molecule with a solid surface (neglecting phonon excitation and molecular fragmentation) is formulated as a set of coupled linear, second-order differential equations. A model potential for the collision of H2 with the (001) face of LiF is proposed. Scattering intensities are computed including 29 diffraction processes for the ν = 0, J = 0 internal state and 5 diffraction processes for the ν = 0, J = 2 internal state (34 channels in all). By comparing with a calculation omitting rotationally excited states (that is, the 29 channels for ν = 0, J = 0), it is observed that most of the 0 → 2 rotational excitation occurs at the expense of the 0 → 0 specular reflection. The 29 channel basis set includes all diffractions through third order and some fourth-order diffractions as well. Based on previous calculations of He+LiF scattering, it is concluded that this basis is sufficiently large to provide an accurate description of all rotationally elastic diffraction processes, but must be augmented to take proper account of rotation excitation. Calculations are also carried out for D2+LiF collisions, and several of the trends observed experimentally for these two isotopes are also observed here.