Density functional theory and an approximate instanton method have been applied to calculate absolute rate constants of ammonia dissociation on a model Si(100) surface. It is shown that the dissociation is dominated by hydrogen atom tunneling even at room temperature, and that high coverage of the surface, when two ammonia molecules adsorb on the nearest-neighbour Si dimers occupying the same row, speeds up the dissociation process. This auto-catalytic effect is attributed to the modification of the buckling of the two Si dimers in the presence of a second ammonia molecule.
EPL (Europhysics Letters)
- Pub Date:
- August 2003
- Ab initio calculations of adsorbate structure and reactions;
- Decomposition reactions;
- Surface and interface chemistry;
- heterogeneous catalysis at surfaces