PNNL

Abstract

Two-Dimensional (2D) Correlation Spectroscopy was used to resolve the positions and correlations among U4f primary peaks and satellite structures that evolved as UVI was progressively reduced by a constant high flux of monochromatic Al K? X-rays during X-ray photoelectron spectroscopy (XPS). Synchronous and asynchronous 2D maps of these results are consistent with previous assignments to UIV, UV and UVI components of the solid. The synchronous spectra confirmed the negative correlation between UVI and UIV components. The asynchronous spectra displayed cross-peaks that were characteristic of peak shift and confirmed the role of UV as a reactive intermediate in the reduction reaction of UVI to UIV. Simulations of 2D correlation maps using synthetic spectra of the primary peaks showed that the presence of highly overlapped peaks centered within 2 eV cannot be distinguished without the presence of additional cross-peaks. The maps have therefore confirmed the existence of three dominant oxidation states, and identified positions of UIV, UV, and UVI U4f primary peaks and satellite structures that are consistent with previous peak-fitting efforts. Satellite structures also showed out-of-phase correlations among the different oxidation states, confirming previous assignments.