DETERMINING THE KINETICS OF DISCRETE AQUEOUS REDOX REACTION SUB-STEPS USING COMPUTATIONAL METHODS: APPLICATION TO REACTIONS OF PLUTONYL (PuO2+/2+) WITH Fe2+, Fe3+, AND HYDROXYL RADICAL (center dot OH)

摘要

The solubility and mobility of actinides, such as plutonium, are highlydependent on their oxidation state, with the penta-and hexavalent species forming soluble actinyl ions (for example, PuO2+/2+). While significant data exist on the equilibrium thermodynamics of these species, the kinetic datasets for actinide reactions are less robust. To understand these reactions in greater detail, this study assesses the degree to which different sub-steps affect the overall rate of an aqueous reaction. In this approach, reactions are broken into three steps: (1) the diffusion of reactants toward each other in solution to form an outer-sphere complex, (2) the transition from outer-to inner-sphere complex, and (3) the transfer of an electron. We address encounter frequency using collision theory and the last two steps using quantummechanical modeling to analyze the energy, as well as atomic charges and spins, as a function of distance between the two reactants.