Kinetics of OH reactions with N2H4, CH3NHNH2and (CH3)2NNH2in the gas phase

Abstract

AbstractThe gas phase reaction kinetics of OH with three di‐amine rocket fuels—N2H4, CH3NHNH2, and (CH3)2NNH2—was studied in a discharge flow tube apparatus and a pulsed photolysis reactor under pseudo‐first‐order conditions in [OH]. Direct laser‐induced fluorescence monitoring of the [OH] temporal profiles in a known excess of the [diamine] yielded the following absolute second‐order OH rate coefficient expressions;k1= (2.17 ± 0.39) × 10−11e(160±30)/T,k2= (4.59 ± 0.83) × 10−11e(85±35)/Tandk3= (3.35 ± 0.60) × 10−11e(175±25)/Tcm3molec−1s−1, respectively, for reactions with N2H4, CH3NHNH2and (CH3)2NNH2in the temperature range 232–637 K. All three reactions did not show any discernable pressure dependence on He or N2buffer gas pressure of up to 530 torr. The magnitude of the weak temperature and the lack of pressure effects of the OH + N2H4reaction rate coefficient suggest that a simple direct metathesis of H‐atom may not be important compared to addition of the OH to one of the N‐centers of the diamine skeleton, followed by rapid dissociation of the intermediate into products. Our findings on this reaction are qualitatively consistent with a previousab initiostudy [3]. However, in the alkylated diamines, direct H‐abstraction from the methyl moiety cannot be completely ruled out. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 354–362, 2001