Infrared Spectra and Structure of Uranyl and Transuranium (V) and (VI) Ions in Aqueous Perchloric Acid Solution

Infrared spectra of aqueous solutions of U(VI), Np(VI), Pu(VI), and Am(VI) show conclusively that these ions exist as symmetrical and linear, or nearly linear, XO2++. The spectra of Np(V) and Am(V) show that they are probably XO2+ ions. Force constants and estimated distances are given for the X—O bonds. For the XO2++ series, the X—O force constant is expressed as a parabolic function of atomic number, with the maximum occurring at NpO2++. This is contrary to behavior expected if there were a regular contraction in ionic radii for the series XO2++.