A novel electronic-hyperfine perturbation in the C4Σ− state of VO

The hyperfine structure of the level N = 37, $\text{J = 38}\text{1}\text{2}$ in the C⁴Σ^?, v = 0 state of VO is anomalous as a result of an electronic perturbation. Because of the high nuclear spin of ⁵¹V ($\text{I =}\text{7}\text{2}$), the hyperfine pattern has a sufficient number of lines that it can be analyzed in detail just as if it were a rotational branch fragment containing an avoided crossing. It is shown how the coefficient of F(F + 1) in the hyperfine energy expression for the perturbing state and the perturbation matrix element can be obtained very accurately, though because the nature of the perturbing state is unknown it has not been possible to interpret the coefficient in terms of conventional hyperfine parameters in this case. The conditions for the appearance of perturbations of this type and the results to be obtained from them are discussed.