N-2 dissociative adsorption on Ru(0001): The role of energy loss

New molecular beam experiments on the dissociation probability S-0 for N-2 on Ru(0001) are presented. These are in general agreement with prior measur ements and exhibit very unusual behavior; a very slow increase of S-0 with incident kinetic energy E and the fact that S-0 is still only similar to 10 (-3) at incident energies considerably above the barrier. A simple dynamica l model is developed to describe this unusual sticking behavior. The key as pect is that there is considerable energy loss Delta from E upon initial im pact with the surface (principally to the lattice) and only E-Delta is then available to surmount the activation barrier in the exit channel. Using ex perimentally measured values of Delta from scattering experiments gives goo d qualitative agreement of this model with the measured S-0. One implicatio n of the strong energy loss is that there is an apparent violation of detai led balance when comparing only the reactive fluxes of activated adsorption and associative desorption. (C) 2001 American Institute of Physics.