The production of vibrationally excited NCO(X̃ 2Π) in the reaction between CN radicals and O2

Experiments of two kinds have been performed to determine the vibronic state distribution in NCO(X̃ 2Π) produced in the radical—radical reaction CN+O2→NCO+O; ΔH00=−29±6 kJ mol−1. In both experiments, CN radicals are produced by photolysis of NCNO using a frequency-doubled Nd:YAG laser. NCO radicals are observed as products of the reaction with O2, either by recording laser excitation spectra at short times after the initiation of reaction, or by fixing the probe laser frequency and recording the variation of laser-induced fluorescence with the time delay between photolysis and probe lasers. NCO is produced in a wide range of vibronic levels. Insufficient information about band intensities is available to transform the spectra into relative populations. However, the ν2 bending vibration is highly excited and this mode absorbs ∼ 50–60% of the energy available to the products. The stretching modes absorb ≈ 15–20% of the energy. The implications of these results for the dynamics of reactive collisions between CN and O2 are discussed.