Inelastic effects in dissociative sticking of diatomic molecules on metals

Abstract

A quantum mechanical model for the dissociative sticking, and scattering of a diatomic molecule on a potential surface containing both elastic and inelastic couplings is solved exactly. The inelastic potential can be due to the excitation of either electron–hole pairs, or phonons. The model is parametrized for vibrationally cold H2 on copper assuming that electron–hole pairs are the source of the inelastic potential. The main effect is a dynamical polarization of the adiabatic electron system, which increases the sticking coefficient over that calculated with the elastic potential alone, for most couplings. It is a no-loss contribution. Within this model the real energy loss contributes little to the sticking coefficient because a negligible fraction of reaction exothermicity is dissipated before the two atoms are separated on the surface. If the electron–hole pair coupling is very strong and highly localized within the molecule bond, the effect of inelasticity is to act as a reflection barrier reducing the sticking coefficient compared to the elastic calculation. The mass dependence of these effects is also discussed.