Reaction Kinetics of O(3P) and OH With Diamine Rocket Fuels

Abstract

Abstract : The gas phase kinetics of O((sup 3)P) and OH reactions with the three diamine fuels; N2H4, CH3NHNH2 and (CH3)2NNH2 has been studied in a discharge flow-tube apparatus. The reactions were studied in 2 torr of He under pseudo-first-order conditions in the transient species concentration with a known excess of diamine concentration. The steady-state concentration temporal profiles of the transient species were directly monitored by fluorescence techniques to deduce the absolute second-order reaction rate coefficients. The Arrhenius expressions; (7.35 +/- 2.16) x 10(exp -13) e(640 +/- 60)/T, (2.71 +/- 0.04) x 10(exp -11) e-(190 +/- 50)/T and (1.96 +/- 0.29) x 10(exp -11) e(20 +/- 40)/T cu cm/molec/s in the temperature range 252-640 K were obtained for reactions of O((sup 3)P) with N2H4, CH3NHNH2 and (CH3)2NNH2, respectively. The corresponding expressions; (1.25 +/- 0.19) x 10 (exp -11) e(315 +/- 55)/T, (2.88 +/- 0.04) x 10(exp -11) e(210 +/- 55)/T and (2.00 +/- 0.30) x 10(exp -11) e(330 +/- 80)/T cu cm/molec/s in the range 232-374 K were determined for the OH reactions. Our recent measurement of the total yield of OH(X(sup 2)II) formation in the O +/- N2H4 reaction of (0.15 +/- 0.05) at 298 K (of which ^50% was found to be produced hot with vibrational excitation up to the limit of reaction exothermicity) and the present observed experimental kinetic trends suggest that the initial addition of O((sup 3)P) and OH to the hydrazine molecule followed by rapid dissociation to products is an important process. Alkylation in the diamine molecule also allows direct H-abstraction mechanism to operate in these reaction systems.