New spectroscopic studies of plutonium (IV) nitrate complex formation in solution

Spectrophotometric titrations of Pu(IV) with HNO{sub 3} were conducted in a series of aqueous HClO{sub 4} solutions ranging ionic strength from 2 to 19 mol/kg on the molality scale. The Pu f-f absorption spectra in the visible and near IR range were deconvoluted into spectra of Pu{sup 4+}(aq), Pu(NO{sub 3}){sup 3+} and Pu(NO{sub 3}){sub 2}{sup 2+} complexes and their formation constants as functions of ionic strength. When corrected for the incomplete dissociation of nitric acid, these formation constants exhibit smooth increases with ionic strength from 5 to 19 mol/kg