Adsorption dynamics for CO and H2 on an NiAl(110) surface

Abstract

We have used nozzle beams to investigate the energy and angle dependence of the initial sticking coefficient for CO and H₂ on an NiAl(110) surface. CO exhibits two adsorption paths, one non-activated, precursor-assisted path and one activated path. A mean activation barrier of ca. 0.67 eV is obtained; such a high barrier has never before been observed for CO adsorption. Saturation coverage is 0.39 ML expressed in terms of surface particle densities. Molecular hydrogen, which is not adsorbed at room temperature, can be adsorbed dissociatively at beam energies above 0.15 eV. A saturation coverage of 0.5 ML (ratio of surface atoms) is seen, accompanied by a work function decrease of 550 meV. Seeded-beam experiments demonstrate a major contribution of vibrational energy in the adsorption dynamics of H₂ and D₂. State-resolved sticking coefficients could be obtained, indicating an activation barrier of 0.72 eV to dissociation of both isotopes.