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

The dissociative chemisorption of H-2/D2 at an Fe(110) surface has been studied as a function of the translational energy of the incident molecules. The sticking probability shows an activated behaviour, increasing with translational energy, similar to that previously reported1 but with a rather higher dissociation probability. The sticking coefficients for H-2 and D2 are the same within experimental error. Seeding experiments 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 reported for the Fe(100) surface.2 The sticking probability does not depend on the surface temperature and deviates significantly from a normal energy 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 incident molecules. Under these conditions the scattered flux of H-2(v, J) shows a steady change in reflectivity with translational energy, similar to the steady variation in the overall sticking coefficient. There 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 influence of internal energy on dissociation.