Rotational and Hyperfine Structure in the B4Π-X4Σ− (0,0) Band of VO at 7900 Å: Perturbations by the a2Σ+, v = 2 Level

Abstract

The (0,0) band of the B4Π-X4Σ− system of VO near 7900 Å has been analyzed from Doppler-limited Fourier transform emission spectra, together with wavelength-resolved laser-induced fluorescence and sub-Doppler intermodulated fluorescence spectra. The B4Π, ν = 0 level is heavily perturbed by the a2Σ+, ν = 2 level. Because the 3dδ2 4sσ a2Σ+ and 3dδ2 3dπ B4Π states have very different hyperfine parameters, the hyperfine patterns of the rotational lines vary dramatically with J at the perturbations. The observed hyperfine structure of the band, including the lowest-J perturbation, near J = 3812, could be explained in detail by a model Hamiltonian that takes the interactions into account: 3211 hyperfine line frequencies have been fitted with an rms error of 11 MHz. The b parameter (the coefficient of I·S in the magnetic hyperfine Hamiltonian) is well determined for the a2Σ+ state and provides the evidence for its electron configuration. The hyperfine structure of the B4Π state shows no effects of spin-orbit distortion and is well explained by the standard case (aβJ) model. Only the spin-orbit operator is needed to describe the interaction between the a and B states; the parameter for the direct dipolar interaction between them is too small to be determined. A fit to the higher-J rotational data showed that the spin-orbit interaction matrix element, which arises as a result of configuration interaction in the two states, has an apparent J dependence; this presumably means that the mixing is r dependent. Improved values for the ground state hyperfine parameters have been obtained from the new data, supplemented by the three very precise microwave frequencies measured by Suenram et al. (J. Mol. Spectrosc.148, 114, 1991).