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Title: Analysis of the crystal-field spectra of the actinide tetrafluorides. II. AmF[sub 4], CmF[sub 4], Cm[sup 4+]:CeF[sub 4], and Bk[sup 4+]:CeF[sub 4]

Abstract

We report a systematic analysis of the crystal-field spectra of four fluoride compounds containing tetravalent actinide ions. The first part of this work [J. Chem. Phys. [bold 95], 7194 (1991)] provided interpretation of the absorption spectra of UF[sub 4], NpF[sub 4], and PuF[sub 4]. To extend our analysis to heavier elements of the series, low-temperature absorption spectra of AmF[sub 4] and CmF[sub 4], and site selective laser-induced emission and excitation spectra of Cm[sup 4+]:CeF[sub 4] and Bk[sup 4+]:CeF[sub 4] were obtained. A model energy level calculation was found to be in good agreement with the experimental results. It is shown that the crystal-field interaction in combination with spin--orbital coupling results in significant [ital J] mixing in the excited states, but ground state wave functions are still relatively pure in [ital J] character for the tetravalent actinide ions Am[sup 4+], Cm[sup 4+], and Bk[sup 4+]. Trends in the parameters of the effective operator Hamiltonian are compared with those of a Hartree--Fock free-ion model. Interpretation of the ground-state splitting of the nominal [ital S]-state ion Bk[sup 4+] in CeF[sub 4] and color center formation in AmF[sub 4] are also discussed.

Authors:
; ; ;  [1]
  1. (Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States))
Publication Date:
Research Org.:
Argonne National Laboratory (ANL), Argonne, IL
OSTI Identifier:
6841563
DOE Contract Number:
W-31109-ENG-38
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; (United States); Journal Volume: 101:10
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AMERICIUM FLUORIDES; CRYSTAL FIELD; CERIUM FLUORIDES; CURIUM FLUORIDES; BERKELIUM IONS; COLOR CENTERS; CURIUM IONS; DOPED MATERIALS; ENERGY LEVELS; EXCITED STATES; FREQUENCY MIXING; GROUND STATES; HAMILTONIANS; ION IMPLANTATION; L-S COUPLING; MATHEMATICAL MODELS; WAVE FUNCTIONS; ACTINIDE COMPOUNDS; AMERICIUM COMPOUNDS; CERIUM COMPOUNDS; CHARGED PARTICLES; COUPLING; CRYSTAL DEFECTS; CRYSTAL STRUCTURE; CURIUM COMPOUNDS; FLUORIDES; FLUORINE COMPOUNDS; FUNCTIONS; HALIDES; HALOGEN COMPOUNDS; INTERMEDIATE COUPLING; IONS; MATERIALS; MATHEMATICAL OPERATORS; POINT DEFECTS; QUANTUM OPERATORS; RARE EARTH COMPOUNDS; TRANSPLUTONIUM COMPOUNDS; TRANSURANIUM COMPOUNDS; VACANCIES 360606* -- Other Materials-- Physical Properties-- (1992-)

Citation Formats

Liu, G.K., Carnall, W.T., Jursich, G., and Williams, C.W. Analysis of the crystal-field spectra of the actinide tetrafluorides. II. AmF[sub 4], CmF[sub 4], Cm[sup 4+]:CeF[sub 4], and Bk[sup 4+]:CeF[sub 4]. United States: N. p., 1994. Web. doi:10.1063/1.468093.
Liu, G.K., Carnall, W.T., Jursich, G., & Williams, C.W. Analysis of the crystal-field spectra of the actinide tetrafluorides. II. AmF[sub 4], CmF[sub 4], Cm[sup 4+]:CeF[sub 4], and Bk[sup 4+]:CeF[sub 4]. United States. doi:10.1063/1.468093.
Liu, G.K., Carnall, W.T., Jursich, G., and Williams, C.W. 1994. "Analysis of the crystal-field spectra of the actinide tetrafluorides. II. AmF[sub 4], CmF[sub 4], Cm[sup 4+]:CeF[sub 4], and Bk[sup 4+]:CeF[sub 4]". United States. doi:10.1063/1.468093.
@article{osti_6841563,
title = {Analysis of the crystal-field spectra of the actinide tetrafluorides. II. AmF[sub 4], CmF[sub 4], Cm[sup 4+]:CeF[sub 4], and Bk[sup 4+]:CeF[sub 4]},
author = {Liu, G.K. and Carnall, W.T. and Jursich, G. and Williams, C.W.},
abstractNote = {We report a systematic analysis of the crystal-field spectra of four fluoride compounds containing tetravalent actinide ions. The first part of this work [J. Chem. Phys. [bold 95], 7194 (1991)] provided interpretation of the absorption spectra of UF[sub 4], NpF[sub 4], and PuF[sub 4]. To extend our analysis to heavier elements of the series, low-temperature absorption spectra of AmF[sub 4] and CmF[sub 4], and site selective laser-induced emission and excitation spectra of Cm[sup 4+]:CeF[sub 4] and Bk[sup 4+]:CeF[sub 4] were obtained. A model energy level calculation was found to be in good agreement with the experimental results. It is shown that the crystal-field interaction in combination with spin--orbital coupling results in significant [ital J] mixing in the excited states, but ground state wave functions are still relatively pure in [ital J] character for the tetravalent actinide ions Am[sup 4+], Cm[sup 4+], and Bk[sup 4+]. Trends in the parameters of the effective operator Hamiltonian are compared with those of a Hartree--Fock free-ion model. Interpretation of the ground-state splitting of the nominal [ital S]-state ion Bk[sup 4+] in CeF[sub 4] and color center formation in AmF[sub 4] are also discussed.},
doi = {10.1063/1.468093},
journal = {Journal of Chemical Physics; (United States)},
number = ,
volume = 101:10,
place = {United States},
year = 1994,
month =
}
  • An interpretation of the low-temperature absorption spectra of AnF{sub 4} (An=U, Np, Pu) is presented. Using an effective operator Hamiltonian with orthogonalized free-ion operators and initializing crystal-field parameter values based on a superposition model calculation for An{sup 4+} sites with {ital C}{sub 2} symmetry, good agreement between the model calculations and experimentally observed absorption band structure could be obtained. Correlations with published magnetic and heat capacity measurements are discussed.
  • We have used neutron diffraction on polycrystalline samples of AnF[sub 4] (An=Th, U, and Np) to examine the structures. All are isostructural with monoclinic space group [ital C]2/[ital c]. The structure of UF[sub 4] has been examined in some detail as a function of temperature. The volume of the unit cell has a minimum not at lowest temperature (15 K) examined, but rather at [similar to]350 K. ThF[sub 4] also has a larger volume at low rather than room temperature; suggesting that this effect is caused by structural rather than electronic (as ThF[sub 4] has no 5[ital f] electrons) interactions.more » An examination of the coordination around the two independent An sites in UF[sub 4] shows that the fluorine configuration changes appreciably around An2 as a function of temperature. At low temperatures the distorted cubic antiprism structure is considerably more puckered'' than at higher temperatures. This puckering requires more volume for the molecule, thus causing the volume to [ital expand] as the temperature is lowered. The temperature factors and the interatomic distances vary smoothly with temperature and show no unusual behavior.« less
  • With our measurements of the 4/ital f/ binding energies of NpF/sub 4/ and PuF/sub 4/, values for all the light-actinide dioxides and tetrafluorides (Th--Pu, except Pa) are available. In spite of the fact that the electronegativities of these elements are nearly constant, the chemical shifts for each series show a regular increase, relative to the metals. Using the results of previously reported band-structure and molecular-orbital calculations, we show that the shifts result from increasing differences in 5/ital f/ occupation and, to a lesser extent, increases in the 5/ital f/--core-level Coulombic interaction. Recently reported /ital L//sub 3/ x-ray-absorption and renormalized-atom calculationsmore » are employed to assess the importance of final-state screening energies in both the metals and the insulating compounds.« less