NONADIABATIC EFFECTS IN THE FRAGMENTATION OF H2 AT SURFACES

A model calculation is presented using time-dependent quantum wavepackets that examines the fragmentation of H-2 on a metal surface using two diabatic potentials. We include two spatial dimensions in the calculation, the molecule-surface distance and the vibrational coordinate. In particular we have focussed upon the dependence of the atomic fragmentation on the initial translational energy and vibrational state of the molecule for differing potential topologies. It is found that strong quantum interferences can occur which give rise to oscillations in the fragmentation probabilities. These distributions depend critically on the topology of the crossing seam between the two diabatic potentials. The results of the two-dimensional calculation are compared to a one-dimensional calculation using the Landau-Zener model. The calculations are performed with an efficient grid cutting method which gives results over a wide energy range within one propagation thereby reducing the computational time.