ASSOCIATION REACTION OF CH3 AND NO - EVIDENCE FOR THE INVOLVEMENT OF THE TRIPLET SURFACE

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 K1 infinity(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 k1 infinity = 1.5 x 10(-11) exp(-60 K/T) cm3 molecule-1 s-1, k1o = 6.9 x 10(-32) exp(1430 K/T) cm6 molecule-2 s-1, <DELTA-E>down = 235 cm-1, for Ar as the diluent gas.