Rovibrationally inelastic scattering of (v=1, j=1) H2 from Cu(100): Experiment and theory

A comparison between experiment and theory is performed for the scattering of (v=1, j=1) H2 from Cu(100) at normal incidence. Experimentally, this system was studied using molecular beam techniques, with stimulated Raman pumping employed to overpopulate (v=1, j=1) in the incident beam, and resonance enhanced multi-photon ionization used to detect the H2 scattered in two (v=1, j) states, and two (v=0, j) states. Theoretically, six-dimensional wave packet calculations were performed, employing a new, extended potential energy surface that was computed with density functional theory, using the generalized gradient approximation and a slab representation of the metal surface. Theory and experiment are in good agreement for the survival probability, i.e., the probability for rovibrationally elastic scattering. However, the theory overestimates the probabilities for rotationally inelastic scattering (to v=1, j=3) and for rovibrationally inelastic scattering (to v=0, j=5 and 7) for channels that could be determined experimentally. The cause of these discrepancies is discussed, as are possibilities for future improvements in the theory as well as the experiment.