ROTATIONAL AND HYPERFINE-STRUCTURE IN THE B(4)PI-X(4)SIGMA(-) (0,0) BAND OF VO AT 7900 ANGSTROM - PERTURBATIONS BY THE A(2)SIGMA(+), V=2 LEVEL

The (0,0) band of the (BII)-I-4-X(4) Sigma(-) system of VO near 7900 Angstrom has been analyzed from Doppler-limited Fourier transform emission spectra, together with wavelength-resolved laser-induced fluorescence and sub-Doppler intermodulated fluorescence spectra. The (BII)-I-4, v = 0 level is heavily perturbed by the a(2) Sigma(+), v = 2 level. Because the 3d delta(2) 4s sigma a(2) Sigma(+) and 3d delta(2) 3d pi B4II 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 = 381/2, 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 a(2) Sigma(+) state and provides the evidence for its electron configuration. The hyperfine structure of the (BII)-I-4 state shows no effects of spin-orbit distortion and is well explained by the standard case (a(beta J)) 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 el al. (J. Mel. Spectrosc. 148, 114, 1991). (C) 1995 Academic Press, Inc.