The far-infrared spectrum of the 14NH radical in its X3Σ- state

Pure rotational transitions of the (NH)-N-14 radical in the v = 0 level of the X(3)Sigma(-) ground state have been detected using tunable far-infrared radiation generated by third-order mixing of radiation from two CO2 lasers with that front a microwave Source. The NH radical was formed in a cooled dc electric discharge through ammonia gas in helium. The rotational transitions from N = 1-0 up to 5-4 inclusive were detected. The nuclear hyperfine splittings become progressively less well resolved as N increases. These measurements have been combined with previous, more accurate measurements of the N = 1-0 transition [Astron. Astrophys. 322 (1997) L1] to determine all improved set of molecular parameters for (NH)-N-14. (C) 2004 Elsevier Inc. All rights reserved.