First detection and analysis of an electronic spectrum of vanadium hydride: The D⁵Π-X⁵Δ (0,0) band

The D⁵Π-X⁵Δ (0,0) band of vanadium hydride at 654 nm has been recorded by laser excitation spectroscopy and represents the first analyzed spectrum of VH in the gas phase. The molecules were generated using a hollow cathode discharge source, with laser-induced fluorescence detected via the D⁵Π-A⁵Π (0,0) transition. All five main (ΔΩ = ΔΛ) subbands were observed as well as several satellite ones, which together create a rather complex and overlapped spectrum covering the region 15 180-15 500 cm^-1. The D⁵Π state displays the effects of three strong local perturbations, which are likely caused by interactions with high vibrational levels of the B⁵Σ^- and c³Σ^- states, identified in a previous multiconfigurational self-consistent field study by Koseki et al. [J. Phys. Chem. A 108, 4707 (2004)]. Molecular constants describing the X⁵Δ, A⁵Π, and D⁵Π states were determined in three separate least-squares fits using effective Hamiltonians written in a Hund's case (a) basis. The fine structure of the ground state is found to be consistent with its assignment as a σπ²δ, ⁵Δ electronic state. The fitted values of its first-order spin-orbit and rotational constants in the ground state are A=36.537815cm^-1 and B = 5.7579(13) cm^-1, the latter of which yields a bond length of R₀=1.72122 Å. This experimental value is in good agreement with previous computational studies of the molecule and fits well within the overall trend of decreasing bond length across the series of 3d transition metal monohydrides.