STIMULATED EMISSION PUMPING SPECTROSCOPY OF JET COOLED NCO

Author Institution: Department of Chemistry, Brookhaven National LaboratoryStimulated emission pumping has been used to measure vibration-rotation levels in the ground electronic state of NCO at energies of up to $ 6500 cm^{-1}$. The radicals were formed in the reaction of $CN + O_{2}$ in the throat of a supersonic free jet expansion of a mixture of cyanogen and oxygen in nitrogen carrier gas. The expansion mixture was excited by an excimer laser at 193 nm immediately after the nozzle orifice causing the cyanogen to dissociate. The reaction and susequent cooling of the NCO product radicals occurs as the expansion proceeds and the radicals were probed in the collision free region of the expansion some $12-15$ mm from the nozzle. Many of the rovibronic levels probed have never before been observed and will provide interesting tests of approximate treatments of the combined effects of Renner-Teller and spin-orbit coupling and Fermi-resonance interactions in the radical. We have made a systematic study of the $(v_{1}, v_{2}, v_{3}) = (00v_{3})$ levels up to $v_{3} = 3$ and many examples of $(v_{1}, v_{2}, 0)$ and $(v_{1}, v_{2}, 1)$ Fermi-resonant multiplets with both $\Pi$ and $\Sigma$ vibronic symmetries