Auto-catalytic effect in ammonia dissociation on

Density functional theory and an approximate instanton method have been applied to calculate absolute rate constants of ammonia dissociation on a model $\chem{Si(100)}$ 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 $\chem{Si}$ 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 $\chem{Si}$ dimers in the presence of a second ammonia molecule