Abstract Spectrokinetic studies of the gas-phase equilibrium F+ O 2⇌ FO 2 have been undertaken at six temperatures between 295 and 359 K. F atoms were produced by pulse radiolysis of Ar/F 2/O 2 mixtures. The yield of FO 2 radicals and the rates of formation and decay were studied as a function of the oxygen concentration, and the temperature dependences of both the forward and reverse rate constants, k 1 and k− 1, were obtained. ...