ESR study of ClO<inf>2</inf> and O<inf>3</inf>^- centres in single crystals of Ba(ClO<inf>4</inf>)<inf>2</inf>.3H<inf>2</inf>O and Ba(ClO<inf>4</inf>)<inf>2</inf>.3D<inf>2</inf>O γ-irradiated at 300K

As well as ClO3 paramagnetic defect centres of ClO2 and O3- are identified in Ba(ClO4) 2.3H2O and Ba(ClO4)2.3D2O single crystals gamma -irradiated at 300K O3- radicals are found to be trapped at two chemically inequivalent sites. One of them is supposed to be at an interstitial site, the other being at the anion site. The O3- radical trapped at the anion site is perturbed by a chlorine-containing radiation damage fragment which has been identified as ClO- from the nature of the chlorine hyperfine interaction and this radical can best be described as O3-...ClO-. The O3- radical trapped at the interstitial site exhibits an isotropic spectrum and is supposed to be undergoing molecular rotation. The ClO2 radicals are trapped at the anion site and exhibit proton superhyperfine interaction. The orientation, the effect of thermal and UV light bleaching and radiation damage mechanisms under different conditions of irradiation are discussed.