Ab initio quantum dynamics of H-2/Si(100) adsorption desorption on a 3-D potential

Hydrogen adsorption on the Si(100)2 x 1 transforms the buckled Si dimers of the reconstructed surface into symmetric monohydride units. The dynamics of adsorption is therefore coupled to lattice dynamics. Based on the results of ab initio calculations, we study the dynamics of both adsorption and desorption for the coupled molecule + surface system in a coupled channel approach. We find that the desorption barrier is not only reflected in the energy of the desorbing molecules, but also transferred to lattice excitations. In adsorption thermal excitations of the surface help to overcome the barrier and thus increase the sticking coefficient at elevated surface temperatures. As has been pointed out earlier, a dynamical mechanism with such features could help to understand discrepancies between experimental results for the H-2/Si(100) system that are hard to reconcile otherwise.