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Optical absorption spectroscopy in geosciences: Part II: Quantitative aspects of crystal fields

By
Michael Andrut
Michael Andrut
1
Institut für Mineralogie & Kristallographie, Universität Wien, Althanstr. 14, A-1090 Wien, Austria
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Manfred Wildner
Manfred Wildner
1
Institut für Mineralogie & Kristallographie, Universität Wien, Althanstr. 14, A-1090 Wien, Austria
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Czesław Z. Rudowicz
Czesław Z. Rudowicz
2
Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Tong, Hong Kong SAR, People's Republic of China
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Published:
January 01, 2004

Abstract

In Part I (Chapter 3 in this volume - Wilder et al., 2004) we described the basic principles of crystal field theory (CFT) based on group theory and symmetry. The usefulness of CFT resides in the fact that it can predict the type and number of electronic transitions and their relative energies for transition metal ions in crystals. Hence CFT enables interpretation of the optical absorption spectra. The crystal (or ligand) field induced on the central ion depends on the type and positions of the ligands (i.e., bond angles and distances R) and on the point symmetry of the resulting coordination polyhedron. The number of exited crystal field (CF) states and the type of the ground state arising from a given free-ion dN configuration depends solely upon molecular symmetry, i.e. the site symmetry in case of crystals, and is independent of any model used to describe the metal-ligand bonds. Although the exact energies cannot be calculated ab initio, it is possible to extract empirical parameters from experimental electronic absorption spectra which describe the interaction between metal and ligand. For a given dNX6 complex with an ideal octahedral coordination (symmetry Oh), the cubic CF splitting parameter 10Dq, together with Racah parameters B and C, provide basis for a reasonably complete description of the electronic spectra (Lever, 1984). In most crystals the site symmetry is, however, lower than Oh. This requires introduction of additional, so-called distortion parameters to describe the lower symmetry CF components

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Contents

European Mineralogical Union Notes in Mineralogy

Spectroscopic methods in mineralogy

Anton Beran
Anton Beran
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Eugen Libowitzky
Eugen Libowitzky
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Mineralogical Society of Great Britain and Ireland
Volume
6
ISBN electronic:
9780903056519
Publication date:
January 01, 2004

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