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Title: Intermediate coupling for core-level excited states: Consequences for X-Ray absorption spectroscopy

Abstract

The origin of the complex NEXAFS features of X-Ray Absorption, XAS, spectra in transition metal complexes is analyzed and interpreted in terms of the angular momentum coupling of the open shell electrons. Especially for excited configurations where a core-electron is promoted to an open valence shell, the angular momentum coupling is intermediate between the two limits of Russell- Saunders, RS, coupling where spin-orbit splitting of the electron shells is neglected and j-j coupling where this splitting is taken as dominant. The XAS intensities can be understood in terms of two factors: (1) The dipole selection rules that give the allowed excited RS multiplets and (2) The contributions of these allowed multiplets to the wavefunctions of the intermediate coupled levels. It is shown that the origin of the complex XAS spectra is due to the distribution of the RS allowed multiplets over several different intermediate coupled excited levels. The specific case that is analyzed is the L2,3 edge XAS of an Fe3+ cation, because this cation allows a focus on the angular momentum coupling to the exclusion of other effects; e.g., chemical bonding. Arguments are made that the properties identified for this atomic case are relevant for more complex materials. Themore » analysis is based on the properties of fully relativistic, ab initio, many-body wavefunctions for the initial and final states of the XAS process. The wavefunction properties considered include the composition of the wavefunctions in terms of RS multiplets and the occupations of the spin-orbit split open shells; the latter vividly show whether the coupling is j-j or not.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1244802
Report Number(s):
PNNL-SA-108070
Journal ID: ISSN 0368-2048; 47824; KC0302060
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Electron Spectroscopy and Related Phenomena
Additional Journal Information:
Journal Volume: 200; Journal ID: ISSN 0368-2048
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
XAS; NEXAFS; Intermediate Coupling; Dipole Selection Rules; Environmental Molecular Sciences Laboratory

Citation Formats

Bagus, Paul S., Sassi, Michel J., and Rosso, Kevin M. Intermediate coupling for core-level excited states: Consequences for X-Ray absorption spectroscopy. United States: N. p., 2015. Web. doi:10.1016/j.elspec.2015.04.021.
Bagus, Paul S., Sassi, Michel J., & Rosso, Kevin M. Intermediate coupling for core-level excited states: Consequences for X-Ray absorption spectroscopy. United States. https://doi.org/10.1016/j.elspec.2015.04.021
Bagus, Paul S., Sassi, Michel J., and Rosso, Kevin M. 2015. "Intermediate coupling for core-level excited states: Consequences for X-Ray absorption spectroscopy". United States. https://doi.org/10.1016/j.elspec.2015.04.021.
@article{osti_1244802,
title = {Intermediate coupling for core-level excited states: Consequences for X-Ray absorption spectroscopy},
author = {Bagus, Paul S. and Sassi, Michel J. and Rosso, Kevin M.},
abstractNote = {The origin of the complex NEXAFS features of X-Ray Absorption, XAS, spectra in transition metal complexes is analyzed and interpreted in terms of the angular momentum coupling of the open shell electrons. Especially for excited configurations where a core-electron is promoted to an open valence shell, the angular momentum coupling is intermediate between the two limits of Russell- Saunders, RS, coupling where spin-orbit splitting of the electron shells is neglected and j-j coupling where this splitting is taken as dominant. The XAS intensities can be understood in terms of two factors: (1) The dipole selection rules that give the allowed excited RS multiplets and (2) The contributions of these allowed multiplets to the wavefunctions of the intermediate coupled levels. It is shown that the origin of the complex XAS spectra is due to the distribution of the RS allowed multiplets over several different intermediate coupled excited levels. The specific case that is analyzed is the L2,3 edge XAS of an Fe3+ cation, because this cation allows a focus on the angular momentum coupling to the exclusion of other effects; e.g., chemical bonding. Arguments are made that the properties identified for this atomic case are relevant for more complex materials. The analysis is based on the properties of fully relativistic, ab initio, many-body wavefunctions for the initial and final states of the XAS process. The wavefunction properties considered include the composition of the wavefunctions in terms of RS multiplets and the occupations of the spin-orbit split open shells; the latter vividly show whether the coupling is j-j or not.},
doi = {10.1016/j.elspec.2015.04.021},
url = {https://www.osti.gov/biblio/1244802}, journal = {Journal of Electron Spectroscopy and Related Phenomena},
issn = {0368-2048},
number = ,
volume = 200,
place = {United States},
year = {Wed Apr 01 00:00:00 EDT 2015},
month = {Wed Apr 01 00:00:00 EDT 2015}
}