Precursor dynamics in dissociative hydrogen adsorption on W (100)

Abstract

A study of the dynamics of dissociative adsorption on H 2 of W (100) has been carried out using a supersonic molecular beam source. For beam energies in the range 200–13 meV, a 30% increase in the initial sticking probability s 0 is observed with decreasing translational energy. At low beam energies, a complex incident angular dependence of s 0 is also observed. The sticking probability s exhibits a linear decrease with hydrogen coverage at higher energies, however in the lower energy regime a more complex coverage dependence is exhibited, manifested in an initial independence, or increase, in s with increasing coverage. This behaviour is also associated with the contribution of an indirect route to dissociation at lower energies, in addition to a direct channel which predominates above ≈ 150 meV. The value of s 0 at a beam energy of 13 meV, where the contribution of the indirect channel should be greatest, appears to be independent of surface temperature within the accessible range 150 < T s(K) < 370. We suggest that the probability that the precursor will go on to dissociate rather than desorb depends on the surface structure.