Photoelectron spectroscopy measurements and density functional theory calculations are combined to determine structures of ${\mathrm{Nb}}_n^{-}$ ( $n=3\mathrm{}–8$) 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 ${\mathrm{Nb}}_8^{-}$ under some experimental conditions. This approach shows great promise for structural characterization of small clusters.

• Received 22 August 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.4528