ENERGY-TRANSFER AND VIBRATIONAL EFFECTS IN THE DISSOCIATION AND SCATTERING OF D(2) FROM CU(111)

ACTIVATED surface dissociation of adsorbed molecules is of basic importance to surface chemistry, but in only a few systems are details of the molecule-surface potential-energy surface well understood. Central to this problem are the processes of energy disposal and transfer during the molecule-surface collision and the manner in which molecular motions (translational, rotational and vibrational) are channelled into the dissociative coordinate. The dissociation of hydrogen and deuterium molecules on a copper surface provides a prototypical system for studying these processes. Here we describe measurements of the scattering of D2 from a Cu(111) surface as a function of incident translational energy, angle and vibrational state of the incoming molecules. Molecules in the ground and first excited vibrational levels show very different translational-energy thresholds for removal (0.6 and 0.35 eV respectively). At higher incident energies, efficient transfer of translational to vibrational energy occurs in those ground-state D2 molecules that survive the collision without dissociating. These data will allow a better test of the various potential-energy curves that have been proposed for this system in the dissociative region.