Sequential attachment of hydrogen molecules to niobium cluster cations

The reactivity of niobium cluster cations Nbn+ (n=6–12) towards molecular hydrogen was studied using an FT-ICR mass spectrometer combined with a laser-ablation/supersonic-jet external ion source. The reaction rate patterns for the sequential adsorption of hydrogen on niobium cluster cations as well as the H2 saturation coverage pattern were measured. It was found that for the Nb8+ and Nb11+ clusters, the adsorption of an H2 molecule can increase the reactivity of the cluster toward another H2 molecule. This suggests that the adsorption of a hydrogen molecule can substantially change the electronic configuration and/or geometric structure of a niobium cluster and therefore supports the chemisorption mechanism for H2 adsorption on Nbn+ clusters.