Fourier transform microwave spectroscopy of ScS (X ²Σ ⁺) and YS (X ²Σ ⁺)

The pure rotational spectra of the transition metal sulfide radicals ScS and YS in their ²Σ ⁺ ground states have been measured in the range 8-48 GHz using Fourier transform microwave (FTMW) spectroscopy. The radicals were synthesized from the reaction of metal vapor, produced by laser ablation, and H ₂S gas, heavily diluted in argon. A DC discharge was needed in the case of ScS. Four rotational transitions were recorded for each molecule, in which multiple fine and hyperfine components were resolved. The spectra were analyzed with a case (b) Hamiltonian, and rotational, fine, and hyperfine constants were determined for both molecules, improving the precision of previous parameters established from optical and double resonance data. The quadrupole coupling constant eQq has been accurately established for ScS for the first time, as well. From the rotational constants, the bond lengths were determined to be 2.1288 Å for ScS and 2.2614 Å for YS. The hyperfine parameters suggest that, although ScS and YS are principally ionic molecules, they are more covalent than their oxygen analogs.