Fourier transform infrared spectrometry has been used to study the products of the photooxidation of ammonia in the presence of oxygen at 296 K. The data have been used to derive an upper limit of 6¿10-21 cm3 molecule-1 s-1 for the reaction of NH2 radicals with O2 to produce NOx at 296 K. This upper limit, which is 3 orders of magnitude lower than previous estimates based on the kinetics of NH2 loss, rules out the importance of this reaction in the atmosphere and suggests that NH2 will be oxidized by O3 or NO2. The effect on the NOx and N2O budgets depends critically on the products of the NH2+O3 reaction. Simulations of the experimental product yields also allow an evaluation of possible product channels for the reaction of NH2 with HO2. ¿ American Geophysical Union 1991