Brookhaven National Laboratory Report BNL-6472

The object of this study was to determine the nature of the free radicals induced in ferrocene by Co60 gamma rays. The irradiations were carried out on the powder at 77°K and on the single crystals at 193°K. The variation of the splitting factor, g, of the signals observed when the single crystals were oriented at different angles relative to the external magnetic field direction, indicated the existence of three types of resonance peaks. It was possible to correlate these variations with the molecular orientations in the crystal unit cell and with the spatial arrangement of the molecular orbitals. Taking into account the spectral changes observed after thermal annealing of the crystal, the existence of the following free radicals has been suggested: 1) a straight molecule-ferricinium ion, 2) a bent molecule-ferricinium ion, and 3) a cyclopentadienyl radical with four protons, the fifth having been transferred to the iron atom. A signal with a cylindrically symmetric g tensor, observed at 77°K, has been assigned to another radical but its nature was not fully established