Effects of H coverage on the dynamics of H abstraction from Cu(1 1 1)

We study the dynamics of H abstraction from Cu(1 1 1) by performing quantum dynamics calculations. We introduce a new theoretical approach that considers both quantum mechanically direct (the impinging H directly abstracts an adsorbed H) and indirect (the impinging H diffuses on the surface before it abstracts an adsorbed H) processes for H abstraction, and investigate how the coverage of adsorbed H on Cu(1 1 1) affects the vibrational and surface-parallel translational energy distribution of product H2. We expect that the H abstraction dynamics would depend on the coverage, because the shape of the corrugation depends on the coverage. Our results, calculated for the case when the kinetic energy of the incident H Et=0.1 (eV), confirm this expectation. The normalised mean vibrational energies of product H2 decrease with decreasing coverage. On the other hand, the normalised mean surface-parallel translation energies of product H2 increase with decreasing coverage. These results indicate that for the low coverage case, H abstraction occurs mainly through the indirect process, where the vibrational excitation of product H2 is suppressed, and the excitation for the surface-parallel translational motion of product H2 is enhanced, as compared with those for the high coverage case, where the H abstraction can occur through both direct and indirect processes.