THE ENERGETICS AND DYNAMICS OF H-2 DISSOCIATION ON AL(110)

We present a modeling of the sticking dynamics of H-2 on Al(110). The modeling is based on an ab initio calculation of the H-2/Al(110) poten tial energy surface. The calculation is done both within the local den sity approximation (LDA) and using non-local corrections via the gener alized gradient correction (GGA). We find that the GGA increases the b arrier for dissociation substantially, and that the inclusion of gradi ent corrections greatly influences the dissociation dynamics. The diss ociation dynamics is simulated by first doing a full quantum mechanica l calculation of the dynamics in two of the six H-2 coordinates, the d istance of the molecule from the surface and the intra-molecular bond length. The other four degrees of freedom are then included using the hole model. This implies that these coordinates are treated classicall y, and in the sudden approximation. Test calculations in three dimensi ons, where full quantum calculations are feasible, show the hole model to work well for the onset of sticking. Finally, the full six-dimensi onal sticking calculations are compared to the results of molecular be am experiments, both for pure and seeded beams.