Muoniated free radicals have been detected in muon-irradiated aqueous solutions at high temperatures and pressures. Results are presented for the cyclohexadienyl radical, formed by muonium addition to benzene, and for tert-butyl, formed by reaction of muonium with isobutene, itself formed in situ from the dehydration of the starting material, tert-butanol. This is the first report of the direct identification of organic free radicals in near critical and supercritical water.
