Muonium-substituted organic free radicals in liquids. Isomer distribution and end-of-track radiolytical processes determined from studies of cyclohexadienyl radicals derived from substituted benzenes

Abstract

Muonium-substituted free radicals are observed by muon spin rotation when positive muons are stopped in liquid substituted benzenes. From muon precession frequencies in high external magnetic fields the isotropic muon-electron hyperfine coupling constants Aμ are determined. 66 radicals are assigned to ortho-, meta- and para-substituted cyclohexadienyl-type radicals. Formally they are produced by addition of the light hydrogen isotope muonium to 24 mono-substituted benzenes. The distribution of muons between radicals and diamagnetic molecules is suggested to be governed by radiolytical processes near the end-of-track of the thermalizing muon.