Laboratory detection and submillimeter spectrum of the NaS radical (X-2 Pi(i))

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 Ohm = 1/2 and 3/2 sublevels of this species in its X-2 Pi(i) 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 (similar to 2.9 GHz) in the Ohm = 1/2 substate. The data were analyzed using (2) Pi Hamiltonian, and rotational, spinorbit, 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.