A new electronic transition of vanadium hydride: The C′5Δ–X5Δ (1,0) band

We report the observation and analysis of a new electronic transition in gas-phase vanadium hydride (VH), identified as the C′⁵Δ–X⁵Δ (1,0) band with an origin at 14,015 cm⁻¹ (714 nm). The spectrum was recorded by laser excitation spectroscopy, with laser-induced fluorescence detected to the X⁵Δ (v = 1) level. Dispersed fluorescence measurements enabled a detailed characterization of the vibrationally excited ground state, yielding a vibrational interval of ΔG_1/2 = 1606.6(2) cm⁻¹. Despite the presence of significant local perturbations—particularly in the Ω = 0 and 1 spin components of the C′⁵Δ state—a full rotational analysis of the spectrum using a Hund's case (a) Hamiltonian was achieved. Spectroscopic constants including rotational, spin–orbit, spin–rotation, and Λ-doubling parameters are reported for both the new C′⁵Δ state and the X⁵Δ (v = 1) level. Additionally, we observed a small local perturbation in the X⁵Δ₁ (v = 1) level near J = 9, attributed to homogeneous spin–orbit and heterogeneous L-uncoupling interactions with the previously analyzed A⁵Π (v = 0) state. An X⁵Δ ∼ A⁵Π coupled Hamiltonian was used to model this perturbation and yielded interaction parameters roughly consistent with semi-empirical estimates. This work represents only the second analyzed spectroscopic transition of gas-phase VH.