The rate constant for the NH3 + NO2 rlhar2; NH2 + HONO reaction (1) has been kinetically modeled by using the photometrically measured NO2 decay rates available in the literature. The rates of NO2 decay were found to be strongly dependent on reaction (1) and, to a significant extent, on the secondary reactions of NH2 with NOX and the decomposition of HONO formed in the initiation reaction. These secondary reactions lower the values of k1 determined directly from the experiments. Kinetic modeling of the initial rates of NO2 decay computed from the reported rate equation, - d[NO2]/dt = k1[NH3][NO2] based on the conditions employed led to the following expression: This result agrees closely with the values predicted by ab initio MO [G2M//B3LYP/6-311 G(d,p)] and TST calculations. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 245–251, 1997.