STEERING EFFECTS IN NONACTIVATED ADSORPTION

Classical and quantum calculations of the dissociation dynamics of H-2 on W(100) have been performed on an ab initio PES. The results show c onclusively that at Low translational energies the dissociation is dom inated by strong steering in an essentially direct process. Starting f rom a value near unity, the dissociation falls with increasing energy because the steering has less time to operate and is therefore less ef fective. No precursor state is involved in the process. By examining t he quantum flux we see that molecules oriented with their axes perpend icular to the surface reflect at high translational energy, but not at low translational energy. Some molecular trapping occurs as a result of rotational excitation which gives rise to sharp peaks in the quantu m dissociation probability.