Laboratory detection and pure rotational spectrum of the NaCH radical (X̃ ³Σ^-)

The sodium methylidyne radical, NaCH, has been detected in the laboratory for the first time using submillimeter direct absorption spectroscopy. The species was created in the gas phase in a DC discharge by the reaction of sodium vapor and CH₄. Nine rotational transitions of this molecule were recorded in the frequency range 339-520 GHz, and five transitions of its deuterium isotopomer, NaCD. Each transition of sodium methylidyne was found to consist of triplets resulting from fine structure interactions, identifying the ground state of the molecule to be X̃ ³Σ^-. The data were analyzed with a ³Σ^- Hamiltonian in a case b basis, and rotational, spin-spin, and spin-rotation constants have been accurately determined. NaCH may be formed in the envelopes of AGB stars from the reaction of sodium with photodissociation products of methane.