Translation-to-rotational energy transfer in scattering of H2 molecules from Cu(111) surfaces

This work investigates rotational transitions of H-2 scattering from Cu(111). A notable feature of this study is the application of simple classical dynamics to reveal mechanisms of rotational transitions. This methodology is justified for the H-2/Cu system by remarkable agreement between quantum wavepacket calculations and classical trajectory simulations for both dissociation and re-vibrational transitions. A vibrational sudden approximation is proposed which interprets rotational transitions in terms of an effective gas-surface potential energy surface for a molecule having a distended bond. The validity of the approximation is verified by the close correlation between molecular trajectories and this effective potential. The vibrational sudden analysis comprehensively explains the mechanism of strong translation-to-rotational energy transfer for H-2 scattering from Cu(111), observed experimentally. (C) 2000 Elsevier Science B.V. All rights reserved.