Issue 11, 2022

High resolution off resonant spectroscopy as a probe of the oxidation state

Abstract

Currently, chemistry and physics are strongly dependent on the concept of the oxidation state. While the formal oxidation state is easily evaluated, the real physical oxidation state value is often difficult to determine and significantly varies from the formal values. Determination of the ionization threshold in X-ray absorption spectroscopy (XANES) relies on the absorption edge position and sometimes poses limitations, mainly due to the edge resonances. Moreover, the lower energy states can be probed only within x-soft or XUV photons providing only surface state information of probed materials. Here, we employ high energy resolution off-resonant spectroscopy to determine both 1s and 3p binding energies of Fe-based materials and therefore correlate to their physical oxidation state. The results are compared to the ones obtained with classical X-ray absorption, X-ray emission, and photoelectron spectroscopies. The observed differences in binding energies are discussed in a frame of initial and final state interactions with the atom's electronic configurations. The presented methodology is discussed towards potential use to single-shot experiments and application at X-ray free-electron lasers. Alternatively, core level X-ray emission spectroscopy can be used, but the emission line positions are strongly affected by spin-orbit interaction. However, due to the energy transfer from the photon to the excited core electron, the same information as in XANES is probed in high energy resolution off-resonant spectroscopy (HEROS). Based on the Kramers–Heisenberg theory, we propose a new approach for ionization threshold determination which is free of the limitations encountered in XANES-based determination of the core state energy. Namely, the value of core state energy can be determined analytically using a few HEROS spectra recorded with significantly higher spectral resolution. This approach provides a basis for the universal physical oxidation state determination method.

Graphical abstract: High resolution off resonant spectroscopy as a probe of the oxidation state

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
05 Jūl. 2022
Accepted
26 Sept. 2022
First published
29 Sept. 2022
This article is Open Access
Creative Commons BY-NC license

J. Anal. At. Spectrom., 2022,37, 2383-2391

High resolution off resonant spectroscopy as a probe of the oxidation state

M. Nowakowski, A. Kalinko, J. Szlachetko, R. Fanselow and M. Bauer, J. Anal. At. Spectrom., 2022, 37, 2383 DOI: 10.1039/D2JA00232A

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