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

Abstract

Experiments of two kinds have been performed to determine the vibronic state distribution in NCO(X̃ 2Π) produced in the radical—radical reaction CN+O 2→NCO+O; Δ H 0 0=−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 O 2, 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 ν 2 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 O 2 are discussed.