DISSOCIATIVE CHEMISORPTION OF H2(D2) AT Fe(110)

The dissociative chemisorption of H2(D2) at a Fe(110) surface has been studied as a function of translational energy ET, internal energy Ei, incident angle θi, and surface temperature Ts. Adsorption is activated, the sticking probability increasing steadily with translational energy with no evidence of a threshold for dissociation. Within experimental error there is no isotope effect or surface temperature dependence (180 K s<400 K). Using seeded beams at constant translational energy, sticking on a clean surface is insensitive to the internal state distribution of the incident molecules, consistent with a barrier to dissociative chemisorption in the entrance channel. For translational energies below 0.2 eV sticking deviates from normal energy scaling, momentum parallel to the surface strongly inhibiting dissociative chemisorption. Dissociaton is interpreted in terms of a localised surface site for dissociative chemisorption at low energies.