The K absorption edge of pure Fe and the pre-edge Fe K absorption of FeS, (pyrite), Fe20, (hematite), and FeCO, (siderite) are investigated with single crystal absorbers of these materials using linearly polarized synchrotron X-radiation. From the angular dependence of the pre-edge K absorption the existence of predominantly ligand-field-induced dipole transitions in Fe,O, and of quadrupole transitions in FeCO, is concluded. The multipole character and the mechanism of the pre-edge K absorption are discussed.Die K-Absorptionskante von reinem Fe und die Fe K-Vorkantenabsorption von FeS, (Pyrit), Fe,O, (Hamatit) und FeCO, (Siderit) werden a n einkristallinen Absorbern dieser Materialien mit linear polarisierter Synchrotron-Rontgenstrahlung untersucht. Aus der Winkelabhangigkeit der K-Vorkantenabsorption wird auf das Aaftreten von iiberwiegend ligandenfeldinduzierten Dipolubergangen im Fe,O, und von Quadrupoliibergangen im FeCO, geschlossen. Der Multipolcharakter und der Mechanismus der K-Vorkantcnabsorption werden diskutiert.

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Polarized Cu K x-ray absorption near-edge structure spectra of CuO are measured and analyzed with the aim of extracting quadrupole and dipole partial spectral components. Theoretical spectral components are calculated within the framework of real-space multiple-scattering technique, relying on a non-self-consistent muffintin potential. A local coordinate system xЈyЈzЈ suitable for polarization analysis is defined by the sides of the CuO 4 quasirectangle rather than by directions of the Cu-O bonds. An exclusively quadrupole nature of the prepeak is established both experimentally and theoretically. By analyzing the experimental data, we find that those states which give rise to the prepeak lie within the CuO plane, and have mainly a d x Ј y Ј character. The theory correctly reproduces gross features of the polarized structure generated by dipole transitions, apart from a spurious peak at 8983 eV for the p z Ј component. A partial agreement between theory and experiment in the shoulder region suggests that this structure may arise partly from one-electron states and partly from manybody processes.

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