Energy-Degeneracy-Driven Covalency in Actinide Bonding.

Evaluating the nature of chemical bonding for actinide elements represents one of the most important and long-standing problems in actinide science. We directly address this challenge and contribute a Cl K-edge X-ray absorption spectroscopy and relativistic density functional theory study that quantitatively evaluates An-Cl covalency in AnCl (An = Th, U, Np, Pu). The results showed significant mixing between Cl 3p- and An 5f- and 6d-orbitals (t*/t* and t*/e *), with the 6d-orbitals showing more pronounced covalent bonding than the 5f-orbitals.