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The pulsed laser photolysis (PLP), laser-induced fluorescence (LIF) technique for the study of the kinetics of free-radical reactions is applied to reactions of CH radicals both in the ultralow-temperature environment of a Cinétique de Réaction en Ecoulement Supersonique Uniforme (CRESU) apparatus, as well as in a conventional heated cell. The combined techniques provide kinetic data over an extremely wide temperature range. Rate coefficients are reported for the reactions of CH with O2 (T = 13−708 K), NO (T = 13−708 K), and NH3 (T = 23−295 K). All three reactions remain very rapid down to the lowest temperatures at which measurements were made and display differing temperature dependences. The results are discussed in the light of previous work on these systems and of the reaction mechanisms.

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Pulsed laser photolysis, time-resolved laser-induced fluorescence experiments have been carried out on the reactions of CN radicals with CH,, CZHs, 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) = "98) (T/298)" exp(-O/T), yielding: for CH,, A'(298) = 7.0 X cm3 molecule-' s-', n = 2.3, and 6 = -16 K; and for C2&, A'(298) = 5.6 x lo-'' cm3 molecule-' s-', n = 1.8, and 6 = -500 K. The rate constants for the reactions with C2H4, C3H6, and CzHz all decrease monotonically with temperature and have been fitted to expressions of the form, k(T) = k(298) (T/298)" with k(298) = 2.5 X lo-'' cm3 molecule-' s-', n = -0.24 for CN + CzH4; h(298) = 3.4 X lo-'' cm3 molecule-' s -I , n = -0.19 for CN + C3H6; and k(298) = 2.9 X lo-'' cm3 molecule-' s-', n = -0.53 for CN + C2H2.These reactions almost certainly proceed via addition-elimination yielding a n unsaturated cyanide and a n 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. 0 1992 John Wiley & Sons, Inc.