Knowledge Bank

The pure rotational spectrum of the VCl (X$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}\Delta r$) 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}$Cl and $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}$Cl isotopomers have been measured for all five spin-orbit components, confirming the $\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}\Delta r$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">51</mrow>}$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.