Kinetics of free radicals produced by infrared multiphoton-induced decomposition. 2. Formation of acetyl and dichlorofluoromethyl radicals and their reactions with nitrogen dioxide

Abstract

A versatile, indirect method of producing polyatomic free radicals under conditions which are suitable for quantitative studies of their gas-phase reactions has been developed. Cl atoms are homogeneously generated in a flow reactor by the infrared multiple-photon-induced decomposition (IRMPD) of CF/sub 2/Cl/sub 2/ or C/sub 6/F/sub 5/Cl and then rapidly reacted with an organic precursor to produce the desired free radical. Reactions of this free radical can then be monitored in a time-resolved manner using photoionization mass spectrometry. In this study we have produced the acetyl radial and studied its reaction with NO/sub 2/ under photoionization mass spectrometry. In this study we have produced the acetyl radical and studied its reaction with NO/sub 2/ under pseudo-first-order conditions in order to determine not only the rate constant but also to verify the mechanism of this oxidation reaction. Modeling of reactant and product ion signal profiles indicates that the products produced and rate constants (k/sub 4/) are CH/sub 3/CO + NO/sub 2/ ..-->.. CH/sub 3/CO/sub 2/ + NO, with k/sub 4/= 2.5 (+- 0.6) x 10/sup -11/ cm/sup 3/ molecule/sup -1/ s/sup -1/ at 295 K. In addition, the rate and mechanism of the reaction of CF/sub 2/Cl (produced by the directmore » IRMPD of CF/sub 2/Cl/sub 2/) with NO/sub 2/ have also been determined. The products produced and rate constants (k/sub 5/) are CF/sub 2/Cl + NO/sub 2/ ..-->.. CF/sub 2/Cl0 + NO with k/sub 5/ = 9.6 (+- 1.9) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/.« less