Guided ion beam studies of the reactions of Vn+ (n=2–13) with D2: Cluster–deuteride bond energies as a chemical probe of cluster electronic structure

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The kinetic energy dependencies of the reactions of Vn+ (n=2–13) with D2 are studied in a guided ion beam tandem mass spectrometer. Products observed are VnD+ for all clusters and VnD2+ for n=4–13. All reactions are observed to exhibit thresholds, except for formation of VnD2+ for n=4,5,7,9,11–13. The enhanced reactivity of the odd-sized clusters towards D2 chemisorption is nicely correlated with the D0(Vn+–V) bond energies. The odd-number clusters are less stable and more reactive, suggesting that they are open shell, whereas the even-number clusters, which are more stable and less reactive, appear to be closed shell. Threshold analyses of the endothermic reactions lead to Vn+–D binding energies (n=1–13), which reach values comparable to the bulk phase for larger clusters. The Vn+–D bond energies show odd–even oscillations anticorrelated with D0(Vn+–V) for n<5, but roughly parallel with D0(Vn+–V) for n>5. Magnitude differences in the two series of bond energies suggest that the metal–metal bonding has appreciable 3d–3d contributions. The variation in the Vn+–D bond energies with cluster size is explained using promotion energy arguments.