PERTURBATIONS OF THE FINE AND HYPERFINE STRUCTURE IN THE PURE ROTATIONAL SPECTRUM OF VCl (X$^{5}\Delta_{r}$)

Author Institution: Department of Chemistry, Department of Astronomy, and Steward Observatory, University of Arizona, Tucson, AZ, 85721The pure rotational spectrum of the VCl (X$^{5}\Delta_{r}$) radical has been measured using millimeter/sub-mm-wave direct absorption methods. This work is the first pure rotational study of this molecule. Vanadium chloride was produced in a plasma created by an AC discharge of gas-phase VCl$_4$ and argon. Ten rotational transitions each of the $^{35}$Cl and $^{37}$Cl isotopomers have been measured for all five spin-orbit components, confirming the $^{5}\Delta_{r}$ ground state. Lambda doubling is observed in four of the five $\Omega$ ladders, including the $\Omega$ = 0 ladder, which had not been observed previously. Each fine structure component was found to exhibit hyperfine splittings due to the $^{51}$V nuclear spin (I = 7/2). The fine structure pattern of the spin-orbit ladders suggests that the ground state is perturbed with the $\Omega$ = 1 ladder significantly shifted with respect to the overall pattern. In addition, the hyperfine structure of the $\Omega$ = 1 and 2 ladders becomes highly irregular for certain rotational transitions. Rotational, spin-orbit, spin-spin, lambda-doubling, and hyperfine parameters have been determined from the spectra, and the results will be discussed