Temperature and pressure dependence of the absolute rate constant for the reactions of NH2 radicals with acetylene and ethylene

Absolute rate constants for reaction of the NH2 free radical with acetylene and ethylene have been measured as a function of pressure and temperature using the technique of flash photolysis combined with time resolved detection of NH2 via laser induced fluorescence. NH2 radicals were produced by flash photolysis of ammonia highly diluted in argon and the decay of fluorescent NH2 photons was measured by multiscaling techniques. At each temperature employed in the study, the observed pseudo‐first‐order rate constants were independent of flash intensity (i.e., initial [NH2]) and were a linear function of [C2H2] or [C2H4]. The bimolecular rate constant for the reaction NH2+C2H2 (1) increased with an increase in pressure at 373 and 459 K but not at lower temperatures. Results at or near the high pressure limit are well represented by the Arrhenius expression k∞1 =(1.11±0.36)×10−13 exp[−(1852±100)/T] cm3 molecule−1 s−1 over the temperature range 241–459 K. For the reaction NH2+C2H4 (2), a smaller increase in th...