Energy transfer and vibrational effects in the dissociation and scattering of D₂ from Cu (111)

Abstract

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.