HYDROPEROXYL RADICAL GENERATION BY GAMMA-IRRADIATION OF GLASSY WATER AT 77 K

ESR spectroscopy has been used to identify the paramagnetic species tr apped at 77 K upon gamma-irradiation of glassy water prepared by hyper quenching of liquid water at cooling rates exceeding 10(5) K/s. Beside s OH radicals, which are the only paramagnetic intermediates of water radiolysis stabilized at 77 K in hexagonal ice prepared by slow coolin g of liquid water, comparable amounts of HO2 radicals were found in gl assy water. The ESR spectra for trapped OH radicals were typical of su ch radicals in a glass. Neither trapped electrons nor trapped hydrogen atoms were detected. The contributions of OH and HO2 radicals to the ESR spectra of glassy water do not depend on irradiation dose in the r ange 0.8-18 kGy. We stress that HO2 radicals are not detected in irrad iated hexagonal ice under these conditions. They are formed as seconda ry products after annealing to destroy the OH radicals, but the yields are tiny relative to the remarkably high yields observed in the glass y water. Possible mechanisms for HO2 radical formation in the early st ages of water radiolysis in the glassy state are discussed.