ELECTRON SPIN RESONANCE STUDIES ON GAMMA-IRRADIATED FERROCENE

The aim of this study was to determine the nature of the free radicals induced in ferrocene by 50Co gamma rays. The irradiations were carried out on the powder at 77°K, the temperature at which crystals have burst into powder form, and on the single crystals at 193°K. At 77°K two radicals are formed, I and II; I transforms itself into a third radical, III, on annealing at temperatures above 145°K. In the single crystals irradiated at 193°K, only radicals II and III are formed. When the single crystals were not too damaged, the disappearance of the radical III with concommitant appearance of a fourth radical, IV, which presents a hyperfine structure of five lines was observed. Taking into account the anisotropies of the g tensors, change in spectra upon deuterium substitution of the cyclopentadienyl protons, and behavior on annealing, the spectra of radicals I-IV were attributed tentatively as follows: I to a straight moleculeferricinium ion, II to a protonated ferrocene radical, III to a bent molecule-ferricinium ion, IV to a C5H5-Fe-C5H4·radical. Mechanisms are given for the formation of these radicals as well as for their disappearance on annealing.