Electronic and geometric structures of vanadium cluster ions, V⁺_n (n = 3-5), studied by optical absorption spectroscopy

Optical absorption spectra of vanadium cluster ions, V⁺_n, (n = 3-5) were obtained in the IR-UV region by measuring photodissociation action spectra of their argon-atom complexes. The spectra were analyzed with the aid of the density functional theory to obtain their most probable geometric and electronic structures. V⁺₃ was shown to be an isosceles triangular structure with bond lengths of 2.5 Å and the apex angle of 42°. On the other hand, V⁺₅ was found to have a trigonal bipyramid structure with an isosceles basal triangle (two bond lengths of 2.6 Å and the other of 2.2 Å) and a pair of three legs (two of 2.4 Å and the other of 2.2 Å). Analysis of the spin configuration indicates that V⁺₃ and V⁺₅ exhibit high-spin characters (triplet), where the spin magnetic moments at each atomic site couples in an anti-parallel manner. They are in contrast to V⁺₄, which has been shown in our previous study to be in the lowest spin state.