Resolved hyperfine structure in the C–X electronic transition of VO. An internal hyperfine perturbation in the C4Σ− state

New grating and laser excitation spectra of VO show resolved nuclear hyperfine structure in the lines of the F1 and F4 electron spin components in the C4Σ−–X4Σ−electronic transition. It is shown that the C4Σ− state has a sizeable hyperfine structure, with the Fermi contact parameter bF (the coefficient of I∙S in the magnetic hyperfine Hamiltonian) equal to −0.00773 cm−1. Another internal hyperfine perturbation, of the type described by Richards and Barrow for the ground state, occurs in the C4Σ−state near N = 5; the line doublings are consistent with the Fermi contact parameter derived from the F1 and F4 lines.