International Tables for Crystallography

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Pre-edge structure, selection rules and quadrupole contributions
Takashi Yamamoto. International Tables for Crystallography (2022). Vol. I [ doi:10.1107/S157487072000751X ]

Abstract

The features and origin of pre-edge peaks in K-edge XANES spectra of 3d transition-metal compounds are reviewed from the viewpoints of the coordination environment of a central atom, the oxidation state and the selection rule of an electric dipole transition. The contribution of the electric dipole and quadrupole transition is discussed based on group theory. The pre-edge peak intensity of four-coordinated species with Td symmetry are much larger than those of six-coordinated species for all 3d elements, and the remarkable intense pre-edge peak is confirmed for d0 compounds. The peak intensity is closely related to the number of 3d electrons and is almost independent of the element. The electric dipole transition is the main component of the intense pre-edge peak, and its possibility is strictly regulated by the selection rules. The probability of transition between s and d orbitals by the electric quadrupole transition is much lower than that for sp transition. An electric dipole transition between an s orbital and the p component of a dp orbital would be possible if the d orbital hybridizes with the p orbital, and the availability can be qualitatively evaluated using character tables from group theory. Polarized and/or high-energy resolution experiments and their theoretical calculation could give useful information for their interpretation.


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About International Tables for Crystallography

International Tables for Crystallography is the definitive resource and reference work for crystallography. The multi-volume series comprises articles and tables of data relevant to crystallographic research and to applications of crystallographic methods in all sciences concerned with the structure and properties of materials.