Ligand effect on uranium isotope fractionations caused by nuclear volume effects: An ab initio relativistic molecular orbital study

Abstract

We have calculated the nuclear volume term (ln Knv) of the isotope fractionation coefficient (ε) between 235U - 238U isotope pairs by considering the effect of ligand coordination in a U(IV)-U(VI) reaction system. The reactants were modeled as [UO2 Cl3]- and [UO2 Cl4]2- for U(VI), and UCl4 for U(IV). We adopted the Dirac-Coulomb Hartree-Fock method with the Gaussian-type finite nucleus model. The result obtained was ln Knv =0.001 90 at 308 K, while the experimentally estimated value of ln Knv is 0.002 24. We also discuss how the ligand affects the value of ln Knv, especially for the various structures of different compounds, and different ligands within the halogen ion series (F, Cl, and Br). © 2010 American Institute of Physics.