ChemInform Abstract: Rate Constants for the Elementary Reactions Between CN Radicals and CH4, C2H6, C2H4, C3H6, and C2H2 in the Range: 295 ≤ T/K ≤ 700

Abstract

Pulsed laser photolysis, time-resolved laser-induced fluorescence experiments have been carried out on the reactions of CN radicals with CH4, C2H6, C2H4, C3H6, and C2H2. They have yielded rate constants for these five reactions at temperatures between 295 and 700 K. The data for the reactions with methane and ethane have been combined with other recent results and fitted to modified Arrhenius expressions, k(T) = A′(298) (T/298)n exp(−θ/T), yielding: for CH4, A′(298) = 7.0 × 10−13 cm3 molecule−1 s−1, n = 2.3, and θ = −16 K; and for C2H6, A′(298) = 5.6 × 10−12 cm3 molecule−1 s−1, n = 1.8, and θ = −500 K. The rate constants for the reactions with C2H4, C3H6, and C2H2 all decrease monotonically with temperature and have been fitted to expressions of the form, k(T) = k(298) (T/298)n with k(298) = 2.5 × 10−10 cm3 molecule−1 s−1, n = −0.24 for CN + C2H4; k(298) = 3.4 × 10−10 cm3 molecule−1 s−1, n = −0.19 for CN + C3H6; and k(298) = 2.9 × 10−10 cm3 molecule−1 s−1, n = −0.53 for CN + C2H2. These reactions almost certainly proceed via addition-elimination yielding an unsaturated cyanide and an H-atom. Our kinetic results for reactions of CN are compared with those for reactions of the same hydrocarbons with other simple free radical species. © John Wiley & Sons, Inc.