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Title: The effect of symmetry on the U L3 NEXAFS of octahedral coordinated uranium(vi)

Abstract

We describe a detailed theoretical analysis of how distortions from ideal cubic or Oh symmetry affect the shape, in particular the width, of the U L3-edge NEXAFS for U(VI) in octahedral coordination. The full-width-half-maximum (FWHM) of the L3-edge white line decreases with increasing distortion from Oh symmetry due to the mixing of symmetry broken t2g and eg components of the excited state U(6d) orbitals. The mixing is allowed because of spin-orbit splitting of the ligand field split 6d orbitals. Especially for higher distortions, it is possible to identify a mixing between one of the t2g and one of the eg components, allowed in the double group representation when the spin-orbit interaction is taken into account. This mixing strongly reduces the ligand field splitting, which, in turn, leads to a narrowing of the U L3 white line. However, the effect of this mixing is partially offset by an increase in the covalent anti-bonding character of the highest energy spin-orbit split eg orbital. At higher distortions, mixing overwhelms the increasing anti-bonding character of this orbital which leads to an accelerated decrease in the FWHM with increasing distortion. Additional evidence for the effect of mixing of t2g and eg components is that themore » FWHM of the white line narrows whether the two axial U-O bond distances shorten or lengthen. Our ab initio theory uses relativistic wavefunctions for cluster models of the structures; empirical or semi-empirical parameters were not used to adjust prediction to experiment. A major advantage is that it provides a transparent approach for determining how the character and extent of the covalent mixing of the relevant U and O orbitals affect the U L3-edge white line.« less

Authors:
ORCiD logo [1];  [2];  [3]
  1. Department of Chemistry, University of North Texas, Denton, Texas 76203-5017, USA
  2. Consultant, Austin, Texas 78730, USA
  3. Pacific Northwest National Laboratory, Richland, Washington 99352, USA
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1372961
Report Number(s):
PNNL-SA-123334
Journal ID: ISSN 0021-9606; KC0302060
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 146; Journal Issue: 11; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English

Citation Formats

Bagus, Paul S., Nelin, Connie J., and Ilton, Eugene S. The effect of symmetry on the U L3 NEXAFS of octahedral coordinated uranium(vi). United States: N. p., 2017. Web. doi:10.1063/1.4978481.
Bagus, Paul S., Nelin, Connie J., & Ilton, Eugene S. The effect of symmetry on the U L3 NEXAFS of octahedral coordinated uranium(vi). United States. doi:10.1063/1.4978481.
Bagus, Paul S., Nelin, Connie J., and Ilton, Eugene S. Tue . "The effect of symmetry on the U L3 NEXAFS of octahedral coordinated uranium(vi)". United States. doi:10.1063/1.4978481.
@article{osti_1372961,
title = {The effect of symmetry on the U L3 NEXAFS of octahedral coordinated uranium(vi)},
author = {Bagus, Paul S. and Nelin, Connie J. and Ilton, Eugene S.},
abstractNote = {We describe a detailed theoretical analysis of how distortions from ideal cubic or Oh symmetry affect the shape, in particular the width, of the U L3-edge NEXAFS for U(VI) in octahedral coordination. The full-width-half-maximum (FWHM) of the L3-edge white line decreases with increasing distortion from Oh symmetry due to the mixing of symmetry broken t2g and eg components of the excited state U(6d) orbitals. The mixing is allowed because of spin-orbit splitting of the ligand field split 6d orbitals. Especially for higher distortions, it is possible to identify a mixing between one of the t2g and one of the eg components, allowed in the double group representation when the spin-orbit interaction is taken into account. This mixing strongly reduces the ligand field splitting, which, in turn, leads to a narrowing of the U L3 white line. However, the effect of this mixing is partially offset by an increase in the covalent anti-bonding character of the highest energy spin-orbit split eg orbital. At higher distortions, mixing overwhelms the increasing anti-bonding character of this orbital which leads to an accelerated decrease in the FWHM with increasing distortion. Additional evidence for the effect of mixing of t2g and eg components is that the FWHM of the white line narrows whether the two axial U-O bond distances shorten or lengthen. Our ab initio theory uses relativistic wavefunctions for cluster models of the structures; empirical or semi-empirical parameters were not used to adjust prediction to experiment. A major advantage is that it provides a transparent approach for determining how the character and extent of the covalent mixing of the relevant U and O orbitals affect the U L3-edge white line.},
doi = {10.1063/1.4978481},
journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 11,
volume = 146,
place = {United States},
year = {2017},
month = {3}
}

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