A kinetic study about the reactions of NH(X3Σ−) with hydrocarbons part 1: Saturated hydrocarbons and acetaldehyde

The reactions of NH in its electronic ground state with the hydrocarbons methane (1), ethane (2), propane (3) and with acetaldehyde (4) were investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ−). The experiments were performed with very low initial concentrations of HN3 which was used as NH source to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reactions of NH(X3Σ−) with hydrocarbons directly. The following rate constants were obtained: k1 = (9±3)·1013 exp (−(84±5) kJ mol−1/RT) cm3/ mol s ( 1150 K < T < 1500 K) k2 = (7±3)·1013 exp (−(70±5) kJ mol−1/RT) cm3/ mol s ( 1010 K < T < 1170 K) k3 = (6±3)·1013 exp (−(61±5) kJ mol−1/RT) cm3/ mol s ( 980 K < T < 1150 K) k4 = (5±3)·1013 exp (−(48±5) kJ mol−1/RT) cm3/ mol s ( 1000 K < T < 1200 K) The apparent energies of activation fit rather well into an Evans Polanyi plot. They correlate with the energies of activation of the corresponding reactions of O(3P) and therefore also with (CH2(X̃3B1) radicals.