Grazing incidence scattering of vibrationally excited H2 molecules from metal surfaces

We have studied the scattering of vibrationally excited H₂ molecules from metal surfaces under fast grazing incidence conditions, by means of quasi-classical calculations based on six-dimensional potential energy surfaces. We show that, in spite of the fast parallel motion, the reorientation of the molecule along the trajectory plays a fundamental role on the scattering, being responsible for the nonmonotonic behavior observed as a function of the normal incidence energy, similar to that observed under slow normal incidence conditions. The present study has allowed us to further prove that the interaction between a H₂ molecule and an ordered metal surface under fast grazing incidence conditions is, in general, governed by the normal momentum of the molecule.