A new electronic transition in vanadium fluoride, VF

The red-degraded [12.7]5Δ-X5Δ (0-0) band of gas-phase vanadium fluoride at 789 nm has been recorded by laser excitation spectroscopy and represents only the second reported rotational analysis of an electronic transition of VF. A hollow cathode discharge source was employed, with laser-induced fluorescence detected via the [12.7]5Δ-X5Δ (0-1) band. All five main (∆Ω = 0) subbands were identified, each containing only P and R branches, as expected in a parallel (∆Λ = 0) transition. The upper state displays the effects of strong local perturbations. Molecular constants describing the X5Δ (v = 0 and 1) levels and the [12.7]5Δ (v = 0) level were determined from least-squares fits using an effective Hamiltonian written in a Hund's case (a) basis. The equilibrium rotational constant of the ground state was determined to be Be = 0.38324(89) cm-1, which yields a molecular bond length of Re = 1.7829(21) Å.