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Title: Vibrational Properties of Anhydrous and Partially Hydrated Uranyl Fluoride

Abstract

Uranyl fluoride (UO 2F 2) is a hygroscopic powder with two main structural phases: an anhydrous crystal and a partially hydrated crystal of the same R¯3m symmetry. The formally closed-shell electron structure of anhydrous UO 2F 2 is amenable to density functional theory calculations. We use density functional perturbation theory (DFPT) to calculate the vibrational frequencies of the anhydrous crystal structure and employ complementary inelastic neutron scattering and temperature-dependent Raman scattering to validate those frequencies. As a model closed-shell actinide, we investigated the effect of LDA, GGA, and non-local vdW functionals as well as the spherically-averaged Hubbard +U correction on vibrational frequencies, electronic structure, and geometry of anhydrous UO 2F 2. A particular choice of U eff = 5.5 eV yields the correct U Oyl bond distance and vibrational frequencies for the characteristic Eg and A1g modes that are within the resolution of experiment. Inelastic neutron scattering and Raman scattering suggest a degree of water coupling to the lattice vibrations in the more experimentally accessible partially hydrated UO 2F 2 system, with the symmetric O-U-O stretching vibration shifted approximately 47 cm -1 lower in energy compared to the anhydrous structure. Evidence of water interaction with the uranyl ion is presentmore » from a two-peak decomposition of the uranyl stretching vibration in the Raman spectra and anion hydrogen stretching vibrations in the inelastic neutron scattering spectra. A first-order dehydration phase transition temperature is definitively identified to be 125 °C using temperature-dependent Raman scattering.« less

Authors:
 [1];  [2];  [2];  [2];  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1340443
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 146; Journal Issue: 2; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY

Citation Formats

Anderson, Brian B., Kirkegaard, Marie C., Miskowiec, Andrew J., Steill, Jeffrey D., and Langford, John F. Vibrational Properties of Anhydrous and Partially Hydrated Uranyl Fluoride. United States: N. p., 2017. Web. doi:10.1063/1.4973430.
Anderson, Brian B., Kirkegaard, Marie C., Miskowiec, Andrew J., Steill, Jeffrey D., & Langford, John F. Vibrational Properties of Anhydrous and Partially Hydrated Uranyl Fluoride. United States. doi:10.1063/1.4973430.
Anderson, Brian B., Kirkegaard, Marie C., Miskowiec, Andrew J., Steill, Jeffrey D., and Langford, John F. Mon . "Vibrational Properties of Anhydrous and Partially Hydrated Uranyl Fluoride". United States. doi:10.1063/1.4973430. https://www.osti.gov/servlets/purl/1340443.
@article{osti_1340443,
title = {Vibrational Properties of Anhydrous and Partially Hydrated Uranyl Fluoride},
author = {Anderson, Brian B. and Kirkegaard, Marie C. and Miskowiec, Andrew J. and Steill, Jeffrey D. and Langford, John F.},
abstractNote = {Uranyl fluoride (UO2F2) is a hygroscopic powder with two main structural phases: an anhydrous crystal and a partially hydrated crystal of the same R¯3m symmetry. The formally closed-shell electron structure of anhydrous UO2F2 is amenable to density functional theory calculations. We use density functional perturbation theory (DFPT) to calculate the vibrational frequencies of the anhydrous crystal structure and employ complementary inelastic neutron scattering and temperature-dependent Raman scattering to validate those frequencies. As a model closed-shell actinide, we investigated the effect of LDA, GGA, and non-local vdW functionals as well as the spherically-averaged Hubbard +U correction on vibrational frequencies, electronic structure, and geometry of anhydrous UO2F2. A particular choice of Ueff = 5.5 eV yields the correct U Oyl bond distance and vibrational frequencies for the characteristic Eg and A1g modes that are within the resolution of experiment. Inelastic neutron scattering and Raman scattering suggest a degree of water coupling to the lattice vibrations in the more experimentally accessible partially hydrated UO2F2 system, with the symmetric O-U-O stretching vibration shifted approximately 47 cm-1 lower in energy compared to the anhydrous structure. Evidence of water interaction with the uranyl ion is present from a two-peak decomposition of the uranyl stretching vibration in the Raman spectra and anion hydrogen stretching vibrations in the inelastic neutron scattering spectra. A first-order dehydration phase transition temperature is definitively identified to be 125 °C using temperature-dependent Raman scattering.},
doi = {10.1063/1.4973430},
journal = {Journal of Chemical Physics},
number = 2,
volume = 146,
place = {United States},
year = {2017},
month = {1}
}

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