Millimeter-wave spectroscopy of vibrationally-excited NaCCH (X̃ 1Σ+) and MgCCH (X̃ 2Σ+): the v5 bending mode

Pure rotational spectra of NaCCH (X̃1Σ+) and MgCCH (X̃ 2Σ+) have been recorded in their ground state and v5 vibrational level, the metal–C–C bend, in the range 315–525 GHz using millimeter-wave direct absorption techniques. This data set complements previous measurements. For NaCCH, rotational transitions were recorded for v5l=00, 11, 22, 20, 33, and 44 levels, and for the 00 states of NaCCD and Na13CCH. Transitions originating in the 11, 20, and 22 states of MgCCH were additionally observed. Rotational, l-type doubling, and vibration–rotation parameters have been determined for both species, as well as estimates of the ω5 bending frequency.