SCATTERING AND DISSOCIATION OF H-2 D(2) AT FE(110)/

The dissociative chemisorption of H-2/D2 at an Fe(110) surface has bee n studied as a function of the translational energy of the incident mo lecules. The sticking probability shows an activated behaviour, increa sing with translational energy, similar to that previously reported1 b ut with a rather higher dissociation probability. The sticking coeffic ients for H-2 and D2 are the same within experimental error. Seeding e xperiments at a constant translational energy indicate that adsorption on a clean surface is insensitive to the internal state distribution P(v, J) of the incident molecules, in contrast to measurements reporte d for the Fe(100) surface.2 The sticking probability does not depend o n the surface temperature and deviates significantly from a normal ene rgy scaling, momentum parallel to the surface inhibiting dissociation. Sticking is dramatically inhibited by low concentrations of adsorbed O and dissociation becomes sensitive to the internal energy of the inc ident molecules. Under these conditions the scattered flux of H-2(v, J ) shows a steady change in reflectivity with translational energy, sim ilar to the steady variation in the overall sticking coefficient. Ther e is no sign of any abrupt translational energy threshold for removal of this vibrational level. The sticking on the clean and O precovered surfaces is discussed in the light of the recent results showing the i nfluence of internal energy on dissociation.