Effects of Rotational State Excitations on the Dissociative Adsorption Dynamics of D₂/Cu(111)

Abstract

Recent time-of-flight experiments show a non-monotonous dependence of the dissociative adsorption/sticking^* probability of D₂(H₂)/Cu(111) on the initial rotational state. There is an observed decrease in the sticking probability with a slight increase in the initial rotational state quantum number j. As j is increased further, the sticking probability eventually increases. We show that, to account for this interesting behaviour, there are two opposing factors working for and against the adsorption process: STEERING EFFECT and ENERGY TRANSFER EFFECT. The first is dueto a dynamical reorientation of the molecule, and the latter is due to the coupling of therotational motion to the translational motion along the reaction path. To illustrate these two effects, we performed quantum mechanical model calculations using a variation of the coupled-channel method, a physically realistic model potential based on available potential energy (hyper-) surface plots for D₂(H₂)/Cu for two different orientations-parallel and perpendicular to the surface, and the concept of a reaction path.