The millimeter/sub-millimeter spectrum of the LiS radical in its 2Πi ground state

The pure rotational spectrum of LiS (X2Πi) has been recorded in the v=0 and v=1 states in the region 130–540 GHz using millimeter/sub-millimeter direct absorption methods. This radical was synthesized from lithium vapor and CS2 in a DC discharge. Transitions arising from the two orbit components were measured, both which exhibited lambda-doubling and, for the Ω=1/2 ladder, hyperfine interactions. Rotational, lambda-doubling, and hyperfine parameters have subsequently been determined. These data prove unambiguously that the ground state of LiS is 2Πi and suggest that the A2Σ+ state lies ∼4300 cm−1 higher in energy. The bonding in this radical appears to be predominantly ionic.