The O + NH3 reaction: A review

Experimental data for the reaction of O atoms with NH3 have been reviewed with particular attention to the possible effects of secondary reactions on the deduced rate coefficient. A reaction mechanism was assembled and computer calculations carried out to simulate several sets of experiments. The sensitivity of the calculations to uncertainties in the various rate coefficients was assessed. Transition-state theory calculations were carried out on the rate coefficient k1 for the O + NH3 → OH + NH2 reaction. These studies suggest that the reaction stoichiometry is dependent on temperature, initial reagent ratios, and extent of reaction; that available data are not sufficient to determine whether the initial step is H-atom abstraction (producing OH and NH2 radicals) or O-atom addition (producing an NH3O* complex): and that the low temperature values of k1 (T ⩽ 400 K) are not consistent with values deduced at higher temperatures if the reaction proceeds by H-atom abstraction. Taking all the evidence into account, it is recommended that the expression 1.1 × 103 T2.1 exp(−2620/T) L mol−1 s−1 be used for k1 until more definitive experimental measurements are made at low temperatures.