LOW AND AMBIENT-TEMPERATURE XAFS STUDY OF U(VI) IN SOLIDS AND AQUEOUS-SOLUTION

To evaluate the ability of XAFS spectroscopy to elucidate the structural environment of U(VI) at the solid-water interface, we have carried out an in-depth analysis of XAFS data from U(VI) solid and solution model compounds. Using the ab initio XAFS code FEFF 6, we have calculated phase-shift (phi) and amplitude (A) functions for fitting low (10K) and ambient temperature data. FEFF 6 does a good job of reproducing experimental data, and is particularly valuable for providing phi and A functions for backscattering atoms whose spectral contributions are difficult to isolate from experimental data due to overlap of Fourier transform (FT) features. In solid-phase model compounds at ambient temperature, we are able to fit single-scattering (SS) contributions from neighbors out to 5.2 Angstrom. Multiple-scattering (MS) was assessed and found not to be significant above k = 3 Angstrom(-1). The use of shell-dependent disorder parameters (sigma(2)) is essential and values have been constrained.