The rotational spectrum of the NH+ radical in its X²∏ and a4∑- states

Transitions between the spin-rotational levels of the 14NH+ radical in the υ=0 levels of its X ²∏ and α 4Σ- states have been studied by the technique of laser magnetic resonance at far-infrared wavelength. The data have been combined with a previous zero-field measurement of the J=1½-½ transition frequencies at 1.01 THz to determine much improved set of molecular parameters for NH+ in the X ²∏ state; the major parameters for the α 4Σ- state also been determined. A full determination of the hyperfine parameters for both 14N and 1H nuclei has been achieved for the first time. Accurate predictions of the transition frequencies between the low-lying levels of the radical in the absence of a magnetic field have also been made, including lambda-doubling frequencies for use by radio astronomers