The explosive oxidation of ammonia and hydrazine studied by kinetic spectroscopy

Abstract

The explosive oxidation of ammonia and hydrazine are studied by the method of flash photolysis and kinetic spectroscopy. The propagating reactions describing the oxidation of ammonia are concluded to be NH 2 + O 2 = HNO + OH and OH + NH 3 = NH 2 + H 2 O, nitric oxide being the main product and resulting from the breakdown of HNO. The oxidation of hydrazine is described by two mechanisms for the two separate overall reactions. It is concluded that the minor reaction yielding nitric oxide as the product results from the splitting of N 2 H 3 into NH and NH 2 , the propagating reactions being NH + O 2 = NO + OH and OH + N 2 H 4 = N 2 H 3 + H 2 O. The major reaction giving rise to nitrogen as the product is described in terms of a mechanism which does not involve the fission of the N—N bond. A successive dehydrogenative mechanism is considered though a scheme analogous to that in the ammonia oxidation involving nitrosamine, NH 2 NO, via the reaction N 2 H 3 + O 2 = NH 2 NO + OH is favoured in the light of the evidence. A general scheme for the oxidation of non-metal hydrides is considered. Preliminary experiments were carried out on the photolyses of ammonia and hydrazine. The thermal nature of the decomposition of ammonia has been illustrated, a strong NH spectrum being observed when the conditions for a temperature rise were chosen. Hydrazine has been detected as a product in this system. A mechanism in agreement with that postulated by Ramsay is reported for the photolysis of hydrazine, the first step being the splitting of the N—N bond followed by abstraction reactions on the parent molecule, fission of the hydrazyl radical occurring to a small extent only when explosion takes place. These preliminary studies served as a basis for the investigation of the combustion reactions.