ROTATIONAL EFFECTS IN THE DISSOCIATIVE ADSORPTION OF H-2 ON CU(111)

Experimental studies show that the dissociation probability of H-2 mol ecules impinging on a Cu(111) surface is strongly affected by the init ial rotational state. Increasing the angular momentum slightly suppres ses the dissociation at low J, but strongly enhances it at high J. We show that this is due to two competing effects; one is essentially ori entational, and results in the decrease in dissociation probability, w hile the increased dissociation is due to the transfer of energy from the rotational coordinates into the reaction coordinate (R-T transfer) . Quantum-mechanical wavepacket calculations are used to illustrate th ese effects, focussing in particular on the close connection between R -T and vibrational-translational (V-T) coupling.