The (0,0) and (0,1) bands of the C 4 R À -X 4 R À electronic transition of VS (near 809 and 846 nm, respectively) have been recorded at high resolution by laser-induced fluorescence, following the reaction of laser-ablated vanadium atoms with CS 2 under supersonic free-jet conditions. A least squares fit to the resolved hyperfine components of the rotational lines gives the rotational constants and bond lengths as
The electron spin parameters for the two states show that there are some similarities between the states of VS and those of VO, but the hyperfine parameters show that the compositions of the partly filled molecular orbitals are by no means the same. The ground state Fermi contact parameter of VS, bðX 4 R À Þ, is only 58% of that of the ground state of VO, which implies that the r orbital of the ground rd 2 electron configuration has less than 50% vanadium 4s character. Similarly, the excited state Fermi contact parameter, bðC 4 R À Þ, is very much smaller than that of VO. No local rotational perturbations have been found in the C 4 R À state of VS, though an internal hyperfine perturbation between the F 2 and F 3 electron components at low N confuses the hyperfine structure and induces some forbidden (DJ ¼ AE2) rotational branches.