Figure 2.

L _III-edge XANES spectra collected on frozen solutions of (a) Pu(III)-343-HOPO and (b) Bk(III)-343-HOPO (purple traces). The vertical dashed lines in (a) highlight the white-line position (E _WL) for oxidation-state references Pu(III) and Pu(IV) in 1 M HClO₄ solutions (Conradson et al., 2004 ▸), which have been calibrated to the Zr K-edge (Kraft et al., 1996 ▸). The XANES data for Bk(III)-DTPA (blue trace) is plotted in (b) for comparison, along with the Bk(III)-DTPA E _WL position (vertical dashed line). In addition, an estimated E _WL position of a hypothetical Bk(IV)-DTPA complex (vertical dashed line) is shown as a Bk(IV) oxidation state reference. The estimate of the Bk(IV)-DTPA E _WL was calculated as a +5.5 eV shift from the Bk(III)-DTPA white line as was observed in the electrochemical oxidation of Bk(III) to Bk(IV) in 1 M HClO₄ acidic solution (Antonio et al., 2002 ▸).