Guided ion beam studies of the reactions of V_n~+(n=2-13) with D_2: Cluster-deuteride bond energies as a chemical probe of clster electronic structure

摘要

The kinetic energy dependencies of the reactions of V_n~+ (n = 2-13) with D_2 are studied n a guided ion beam tandem mass spectrometer. Products observed are V_nD~+ for all clusters and V_nD_2~+ for n = 4-13. All reactions are observed to exhibit thresholds, except for formation of V_nD_2~+ for n=4,5,7,9,11-13. THe enhanced reactivity of the odd-sized clusters towards D_2 chemisorption is nicely correlated with the D_0(V_n~+-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 shelel. Threshold analyses of the endothermic reactions lead to V_n~+-D binding energies (n = 1-13), which reach values comparable to the bulk phase for larger clusters. The V_n~+-D bond energies show odd-even oscillations anticorrelated with D_0(V_n~+-V) for n<5, but roughly parallel with D_0(V_n~+-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 V_n~+-D bond energies with cluster size is explained using promotion energy arguments.