Rotational spectroscopy of LiCCH (X̃ 1Σ) in its ground and v5 vibrational states

The pure rotational spectrum of LiCCH (X̃ 1Σ) in its ground and v5 vibrational states has been recorded using direct absorption, millimeter/sub-millimeter spectroscopy in the range of 105–538 GHz. For the main isotopomer, 21 transitions were measured for the ground state and 10 transitions each for the excited levels v5=1, 2, and 3, where ℓ-type doubling was resolved. Several transitions were also recorded for 6LiCCH, Li13CCH, LiC13CH, and LiCCD. All were observed in their natural abundances except for LiCCD. Rotational, ℓ-type doubling and vibration–rotation constants were determined for LiCCH, as well as rs and ro structures.