Laser induced fluorescence measurements of NCO formed in the reaction CN+O2rarr;NCO+O in a free jet expansion are reported. The rotational temperature achieved in the experiments was typically 10ndash;15 K and absorption from vibrationally excited levels was very much reduced in intensity. Two bands in theAtilde;ndash;Xtilde; system, thev1,v2,v3=200ndash;000 and 120ndash;000, of the radical were rotationally resolved for the first time, and wavelength resolved laser excited fluorescence measurements have been used to characterize many ground state vibronic energy levels below 6000 cmminus;1in energy. Stimulated emission pumping experiments were carried out on vibronic levels associated with the ngr;3vibration with 1le;v3le;3 in the electronic ground state. Harmonic and anharmonic constants were determined, together with the spinndash;orbit coupling parameters and rotational constants for these levels.
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