A Kinetic Study About the Reactions of NH2(X̄2B1) Radicals with Saturated Hydrocarbons in the Gas Phase

The reactions of NH 2 (X 2 B 1 ) with the hydrocarbons ethene (1), propene (2) and acetylene (3) were investigated behind incident shock waves at temperatures between 1500 K and 2000 K. The decay of NH 2 was measured by laser absorption. NH 2 was formed by the thermal decomposition of hydrazine. The following rate constants were obtained for the temperature range mentioned: k 1 = (5.3±0.5).10 12 exp (-(43.0±4.1) kJ/mol/RT)cm 3 mol -1 s -1 k 2 = (7.5±0.6).10 12 exp (-(39.7±3.7) kJ/mol/RT) cm 3 mol -1 s -1 k 3 = (3.7±0.4).10 12 exp (-(47.4±4.4) kJ/mol/RT) cm 3 mol -1 s -1 . These measurements extend the results obtained at low temperatures by Bosco et al. (240 K-460 K) and by Khe and Lesclaux (300K-500K) into the range of interest for combustion processes. The apparent energies of activation correlate well with the ionisation potentials of the unsaturated hydrocarbons and can therefore be used for the extrapolation to the addition reactions of the higher alkenes. For the reaction of propene with NH 2 a contribution of an abstraction reaction channel besides electrophilic addition cannot be excluded at high temperatures.