Kinetics of the reactions of methyl, ethyl, isopropyl, and tert-butyl radicals with molecular chlorine

The gas-phase kinetics of the reactions of four alkyl radicals (CH/sub 3/, C/sub 2/H/sub 5/, i-C/sub 3/H/sub 7/, and t-C/sub 4/H/sub 9/) with molecular chlorine have been studied over limited temperature ranges. The reactions were isolated for quantitative study in a tubular reactor coupled to a photoionization mass spectrometer. The radicals were homogeneously generated in the reactor by pulsed photolysis of suitable precursor molecules at 193 nm. The subsequent decays of the radical concentration in the presence of different molecular chlorine concentrations were monitored in real-time experiments. For each reaction studied, rate constants (k) were measured at a minimum of five temperatures. The temperature-dependent expressions for log k derived from these studies for the four R + Cl/sub 2/ ..-->.. RCl + Cl reactions and the temperature ranges covered are as follows: R = CH/sub 3/ (-11.3 + (-116/T)), 296 - 712 K; R = C/sub 2/H/sub 5/ (-10.9 + (66/T)), 295 - 498 K; R = i-C/sub 3/H/sub 7/ (-10.6 + (106/T)), 298-498 K; R = t-C/sub 4/H/sub 9/ (-10.4 + (2/T)), 298-498 K. Units are cm/sup 3/ molecule/sup -1/ s/sup -1/. The measured rate constants, their closeness to those of corresponding R + O/sub 3/ rate constants, and the results of a prior study of the dynamics of the CH/sub 3/ + Cl/sub 2/ reaction indicate that the reactivity of alkyl radicals with molecular chlorine is determined largely by long-range attractive forces.