NONADIABATIC EFFECTS IN THE FRAGMENTATION OF H2 AT SURFACES

A model calculation is presented using time-dependent quantum wavepack ets that examines the fragmentation of H-2 on a metal surface using tw o diabatic potentials. We include two spatial dimensions in the calcul ation, the molecule-surface distance and the vibrational coordinate. I n particular we have focussed upon the dependence of the atomic fragme ntation on the initial translational energy and vibrational state of t he molecule for differing potential topologies. It is found that stron g quantum interferences can occur which give rise to oscillations in t he fragmentation probabilities. These distributions depend critically on the topology of the crossing seam between the two diabatic potentia ls. The results of the two-dimensional calculation are compared to a o ne-dimensional calculation using the Landau-Zener model. The calculati ons are performed with an efficient grid cutting method which gives re sults over a wide energy range within one propagation thereby reducing the computational time.