EPR and ENDOR studies of self(α)-irradiation effects in Pu(VI) oxalate: evidence for participation of 5f electrons of 239Pu in chemical bonding with CO2−

EPR and ENDOR investigations have been carried out on polycrystalline samples of self(α)-irradiated PuO2C2O4·3H2O (cumulative dose = 1 MGy). The 239Pu (I=1/2) hyperfine structure on the EPR signal of the CO2− radical ion has given clear evidence for participation of 5f electrons of 239Pu in chemical bonding. The ENDOR spectra were used to identify unambiguously the hyperfine interaction between the unpaired electron on the CO2− radical ion and the nuclear spin of 239Pu. In addition to the CO2− radical ion, EPR evidence was also obtained for the formation of O2− during the autoradiolysis of PuO2C2O4·3H2O.