PURE ROTATIONAL SPECTRA OF HNCO IN THE FAR-INFRARED - GROUND-STATE ANALYSIS

The pure rotational spectrum of the quasilinear molecule HNCO and some of its isotopomers was measured with the Giessen high-resolution Four ier transform spectrometer in the far infrared. In addition to a-type transitions with high rotational quantum number, b-type transitions fr om K-a = 1 <-- 0 to K-a = 8 <-- 7 for HNCO and DNCO, and from K-a = 1 <-- 0 to K-a = 5 <-- 4 for (HNCO)-C-13 were identified. Several rotati onal transitions near 600 GHz were also measured using the Cologne sub millimeter-wave spectrometer with a high-frequency backward wave oscil lator as source. Rotational parameters were determined using both Wats on's S-reduced asymmetric rotor Hamiltonian and for comparison a linea r molecule Hamiltonian. The centrifugal distortion resonance between t he ground state and the lowest excited bending vibration was clearly o bserved and analyzed by a second-order perturbation treatment. The obs erved K dependence of the rotational parameter B(K) is caused by the c ombined effects of centrifugal distortion resonance and quasilinearity . (C) 1995 Academic Press, Inc.