Photoelectron spectra and geometric structures of small niobium cluster anions

Photoelectron spectroscopy measurements and density functional theory calculations are combined to determine structures of Nb-n(-) (n = 3-8) clusters. A detailed comparison between observed and calculated electronic binding energies shows that the clusters have low-symmetry compact 3D structures and the lowest possible total spin, except for the three- and five-atom clusters which are in triplet states. We find evidence for the coexistence of two isomers of Nb-8(-) under some experimental conditions. This approach shows great promise for structural characterization of small clusters.