AbstractThe photochemistry of basic aqueous solutions containing hydrogen peroxide and oxygen has been investigated by the flash photolysis method. The decay of O3−was followed at 4300 Å over the pH range 13 – 13.7 as a function of hydrogen peroxide and oxygen concentrations. The decay was found to be of the first order under all conditions −[d(O3)−/dt] = kobs[O3−]. The pseudo first‐order rate constant kobswas found to be dependent on H2O2and O2concentrations. A mechanism which is consistent with the experimental results