Accurate Laboratory Measurement of the Complete Fine Structure of the N = 1 - 0 Transition of 15NH

The imidogen radical is an important molecule of the chemistry of nitrogen in the interstellar medium and is thought to be a key intermediate in the gas-phase synthesis of ammonia. The full fine structure of the N = 1 ← 0 rotational transition of 15NH has been observed for the first time by pure rotational spectroscopy around 1 THz. The radical has been produced by means of low-pressure glow discharge of H2 and 15N-enriched nitrogen. A number of hyperfine components have been observed and accurately measured. The analysis of the data provided very precise spectroscopic constants, which include rotational, centrifugal distortion, electron spin-spin interaction, and electron spin-rotation terms in addition to the hyperfine parameters relative to the isotropic and anisotropic electron spin-nuclear spin interactions for 15N and H and to the nuclear spin-rotation for 15N. The efficiency of the discharge system allowed us to observe several components of the same rotational transition in the excited vibrational state v=1, for which a set of spectroscopic constants has also been determined.