The bond length and electronic structure of V2

Abstract

We report of the first gas-phase electronic spectrum of V2. The dimer was generated in an expansion cooled molecular beam by laser vaporization of vanadium metal. Using the technique of resonant two photon ionization spectroscopy a strong band system with origin near 7000 Å was observed. Rotationally resolved spectra of this band system conclusively demonstrate that the transition is of the type 3Πu(a)←3Σ−g(a), and we assign the 3Σ−g state as the ground electronic state of V2. The short ground state bond length re″=1.77 Å and high vibrational frequency ωe″=535 cm−1 are indicative of extensive 3d-orbital participation in the bonding of this molecule. The unusual case (a) coupling and large second-order spin-orbit splitting observed in the 3Σ−g state implies that the ground state electronic configuration contains a half-filled π(3d) or δ (3d) orbital. The most plausible valence configuration consistent with the data is σg(3d)2πu(3d)+σg(4s)2δg(3d)2. In the excited state there is strong evidence of predissociation occuring for levels higher than 14 872 cm−1 above the ground state, thus providing an upper bound of 1.85 eV for the dissociation energy of V2.