Association reaction of CH3 and NO: evidence for the involvement of the triplet surface

Abstract

The rate constant for the CH₃+ NO reaction has been measured by laser flash photolysis/absorption spectroscopy over the temperature range 296–509 K and at pressures of 25–600 Torr. The data have been analysed using a global variant of the Troe factorisation technique which provides parameters for the representation of k₁(P, T) over the experimental range. In addition, a further global technique for analysing the experimental data, based on inverse Laplace transformation of k^∞₁(T), coupled with a master equation treatment, has been developed. The advantage of this approach is that it emphasises the relationship between the limiting high-pressure rate coefficient and the energy-dependent lifetime of the adduct. In the present reaction system, this approach enables the lowest triplet state to be implicated in the reaction; it is proposed that, following its formation, the triplet undergoes rapid intersystem crossing to the ground singlet state. The limiting rate parameters returned from the analysis are k^∞₁= 1.5 × 10^–11 exp(–60 K/T) cm³ molecule^–1 s^–1, k⁰₁= 6.9 × 10^–32 exp(1430 K/T) cm⁶ molecule^–2 s^–1, 〈ΔE〉_down= 235 cm^–1, for Ar as the diluent gas.