Chemical Kinetics for the Oxidation of Californium(III) Ions with Select Radiation-Induced Inorganic Radicals (Cl₂^•– and SO₄^•–)

Abstract

Despite the availability of transuranic elements increasing in recent years, our understanding of their most basic and inherent radiation chemistry is limited and yet essential for the accurate interpretation of their physical and chemical properties. Here, we explore the transient interactions between trivalent californium ions (Cf 3+ ) and select inorganic radicals arising from the radiolytic decomposition of common anions and functional group constituents, specifically the dichlorine (Cl 2•− ) and sulfate (SO 4•− ) radical anions. Chemical kinetics, as measured using integrated electron pulse radiolysis and transient absorption spectroscopy techniques, are presented for the reactions of these two oxidizing radicals with Cf 3+ ions. The derived and ionic strength-corrected second-order rate coefficients (k) for these radiation-induced processes are k() = (9.50 ± 0.43) × 10 8 M −1 s −1 under ambient temperature conditions (22 ± 1 °C).

Generation and study of Am(iv) by temperature-controlled electron pulse radiolysis

“…The ambient temperature rate for eqn (8) is consistent with those reported for the few other measured trivalent actinides: plutonium (2.50 × 10 8 M −1 s −1 ), 45 curium ((4.83 ± 0.09) × 10 7 M −1 s −1 ), 41 and californium ((1.78 ± 0.06) × 10 8 M −1 s −1 ). 42,46 Comparison of these values with the associated IV/III redox couples (ESI, Fig. S13†) 2 demonstrates that single electron transfer to NO 3 ˙ becomes less energetically favourable with increasing reduction potential, as expected.…”

“…40 That said, more recent studies have shown that NO 3 ˙ is capable of transiently oxidizing trivalent actinides with formally higher IV/III couples, such as curium ( E ° = 3.1 V SHE ) and californium ( E ° = 3.2 V SHE ). 24,41,42 Consequently, NO 3 ˙ may have the capacity to transiently generate Am( iv ), providing the opportunity to study this non-equilibrium oxidation state under conditions more frequently encountered in fundamental and applied americium manipulations.…”