Abstract
Inelastic neutron scattering (INS) is uniquely sensitive to hydrogen due to its comparatively large thermal neutron scattering cross-section (82 b). Consequently, the inclusion of water in real samples presents significant challenges to INS data analysis due directly to the scattering strength of hydrogen. Here, we investigate uranyl fluoride (UO2F2) with inelastic neutron scattering. UO2F2 is the hydrolysis product of uranium hexafluoride (UF6), and is a hygroscopic, uranyl-ion containing particulate. Raman spectral signatures are commonly used for inferential understanding of the chemical environment for the uranyl ion in UO2F2, but no direct measurement of the influence of absorbed water molecules on the overall lattice dynamics has been performed until now. To deconvolute the influence of waters on the observed INS spectra, we use density functional theory with full spectral modeling to separate lattice motion from water coupling. In particular, we present a careful and novel analysis of the Q-dependent Debye–Waller factor, allowing us to separate spectral contributions by mass, which reveals preferential water coupling to the uranyl stretching vibrations. Coupled with the detailed partial phonon densities of states calculated via DFT, we infer the probable adsorption locations of interlayer waters. We explain that a common spectral feature in Raman spectra of uranyl fluoride originates from the interaction of water molecules with the uranyl ion based on this analysis. The Debye–Waller analysis is applicable to all INS spectra and could be used to identify light element contributions in other systems.
| Original language | English |
|---|---|
| Article number | 10476 |
| Journal | Scientific Reports |
| Volume | 9 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 1 2019 |
Funding
A portion of this research used resources at the Spallation Neutron Source, a Department of Energy, Office of Science User Facility operated by the Oak Ridge National Laboratory. This research also used resources of the Compute and Data Environment for Science (CADES) at Oak Ridge National Laboratory, which is supported by the U.S. Department of Energy, Office of Science under contract number DE-AC05-00OR22725. A.E.S. would like to thank the Department of Homeland Security Domestic Nuclear Detection Office National Technical Nuclear Forensics Center for the fellowship funding. The authors would like to thank an anonymous reviewer for significantly improving the spectral assignment based on their comments.
| Funders | Funder number |
|---|---|
| Department of Homeland Security Domestic Nuclear Detection Office National Technical Nuclear Forensics Center | |
| U.S. Department of Energy | |
| Office of Science | DE-AC05-00OR22725 |
| Oak Ridge National Laboratory |