The vibronic state distribution of the NCO(X2Π) product from the CN+O2 reaction

The vibronic state distribution of the NCO product from the CN+O2 reaction has been extracted from a laser fluorescence experiment in a cell at a total pressure of 140 mTorr. The CN reagent was prepared by 193 nm photolysis of cyanogen, and individual NCO vibronic levels were interrogated by fluorescence excitation in its à 2Σ+−X̃ 2Π band system after a variable delay. A finite induction time was observed for the formation of the NCO product in all detected vibronic levels, indicative of the necessity to moderate the translational and rotational energy of the CN photolysis fragment before appreciable reaction can occur. The NCO product was observed in 80 different vibronic levels, with energies up to 51.5 kJ/mol. A nascent vibronic state distribution among the various (v1,v2) Renner–Teller components was estimated from the relative intensities of the various bands. While it was not possible to determine the distribution in the v3 levels because of insufficiently accurate spectroscopic data, it is nevertheless clear that the NCO product from CN+O2 is formed with considerable vibrational excitation. These results are consistent with previous kinetic studies which suggest that the reaction occurs on an attractive potential energy surface, with no activation barrier.