Characterization of pentavalent and hexavalent americium complexes in nitric acid using X-ray absorption fine structure spectroscopy and first-principles modeling

The speciation of pentavalent and hexavalent americium (Am) complexes in nitric acid have been studied by X-ray absorption fine structure spectroscopy, UV–visible spectroscopy, and density functional theory. Calculated bond distances for the Am(VI) complex are in reasonable agreement with EXAFS data and suggest the presence of a mixture of AmO2 + and AmO2 2+ as well as a slightly higher kinetic stability for Am(VI) compared to Am(V).