Laboratory submillimeter-wave observation of the N = 1-0 transition of the ND(3Sigma-) radical

Three fine-structure components of the N = 1-0 rotational transition of the ND radical in its ground vibronic (X 3Sigma-) state were observed by laboratory submillimeter-wave spectroscopy using a source-modulated system combined with a hollow cathode free-space cell. The ND radical was generated by a dc glow-discharge in pure ND3 gas. Six hyperfine resolved components were observed for N, J = 1, 0-0, 1 transition at 492 GHz, 22 components for N, J = 1, 2-0, 1 at 522 GHz, and 12 components for N, J = 1, 1-0, 1 at 546 GHz. The molecular constants, including the rotational constant, the spin-spin coupling constant with its centrifugal distortion term, and the hyperfine coupling constants associated with the nitrogen and deuterium nuclei were precisely determined by least-squares fitting to the observed spectral lines. The precise line frequency determined by laboratory spectroscopy should be useful for future astronomical searches.