The rate and equilibrium constants for the reaction NO3. + Cl-reversible arrow NO3 + Cl-. in aqueous solutions were measured by pulse radiolysis. The formation and decay of the nitrate radical, NO3. and the dichloride radical anion, Cl-2(.-), in irradiated aqueous solutions containing nitric acid and chloride ions were followed under various conditions. Because of the complexity of the system, the forward rate constant and the equilibrium constant were derived from modeling the experimental results, including secondary formation and decay reactions. The modeling study results in an equilibrium constant of K-eq = (3.5 +/- 0.5) at an ionic strength between 0.1 and 1 mol L-1 and a forward rate constant kl = (3.5 +/-0.5) x 10(8) L mol(-1) s(-1). in contrast with previous reports, no effect of ionic strength (up to 2 mol L-1) on the forward rate constant was observed.