Rotational transitions in the scattering of a beam of light diatomic molecules from a surface

The quantum mechanical theory of Jackson and Howarth for the interaction of diatomic molecules with solid surfaces is extended to allow the incident molecules to have a general orientation relative to the surface and to include an attractive potential well. The theory is used to calculate the outgoing translational and rotational states of a molecular beam of a light diatomic gas scattered from a solid surface. The analysis is applied specifically to the case of a beam of H2 incident with thermal energy on a cold surface. For this situation a separate scattering peak away from the specular angle and containing about 2 per cent of the incident molecules is predicted, consisting entirely of molecules in the same excited rotational energy state.