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The sodium sulfide radical NaS has been observed in the laboratory for the first time using millimeter/submillimeter direct absorption spectroscopy. Twelve rotational transitions originating in both the Ω = 1/2 and 3/2 sublevels of this species in its X2Πi ground state were recorded in the frequency range 200-400 GHz. Splittings arising from lambda-doubling interactions were resolved in both spin-orbit components and were particularly large (~2.9 GHz) in the Ω = 1/2 substate. The data were analyzed using a2Π Hamiltonian, and rotational, spin-orbit, and lambda-doubling parameters were determined. NaS may be detectable in the late-type star IRC +10216, given the observation of CS, SiS, NaCl, and NaCN in this object.

Sodium monoacetylide has been observed in the laboratory for the first time using millimeter/submillimeter direct absorption techniques. The species was produced by the reaction of sodium vapor and acetylene under DC discharge conditions. Nineteen rotational transitions of NaCCH in its X1Σ ground state and 14 lines of the deuterium isotopomer NaCCD were recorded in the range 270-510 GHz. From these data, highly accurate rotational constants were determined. The detection of NaCN and NaCl in the envelope of the evolved carbon star IRC +10216 suggests that other sodium-bearing species may be present in this object.