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Abstract

The adsorption of H₂ on a series of gas-phase transition metal (scandium, vanadium, iron, cobalt, and nickel) clusters containing up to 20 metal atoms is studied using IR-multiple photon dissociation spectroscopy complemented with density functional theory based calculations. Comparison of the experimental and calculated spectra gives information on hydrogen bonding geometries. The adsorption of H₂ is found to be exclusively dissociative on ScnO⁺, Vn⁺, Fen⁺, and Con⁺, while both atomic and molecularly chemisorbed hydrogen is present in NinHm+ complexes. It is shown that hydrogen adsorption geometries depend on the elemental composition as well as on the cluster size and that the adsorption sites are different for clusters and extended surfaces. In contrast to what is observed for extended metal surfaces, where hydrogen has a preference for high coordination sites, hydrogen can be
both two- or three-fold coordinated to cationic metal clusters.