Electronic structure of vanadium tetramer ion studied by optical absorption spectroscopy

The optical absorption spectrum of a vanadium tetramer ion, V₄⁺, was obtained by measuring a photodissociation efficiency of an ion complex, V₄⁺Ar, as a function of the photon energy of the laser pulse used for the photodissociation. The optical absorption spectrum thus obtained was simulated by a density functional calculation to search for the most probable geometric structure which reproduces the measured spectrum. The analysis showed that V₄⁺ is most likely to have a "distorted" tetrahedral structure with C_2v symmetry. The ground electronic state of V₄⁺ was found to be a low spin state, ²A₁. The relatively broad spectral profile is explained in terms of the distortion related to a low-energy vibration. Geometry optimization of the Amsterdam density functional (ADF) calculation also predicts C_2v symmetry for the structure of V₄⁺.