HERFD-XAS and valence-to-core-XES: new tools to push the limits in research with hard X-rays?

Abstract

In this perspective, the HERFD-XANES (high energy resolution fluorescence detected X-ray absorption near edge structure) and Kβ2,5- or V2C-XES (valence-to-core X-ray emission spectroscopy) methods are discussed as new and powerful tools for chemical research with hard X-rays. This includes a brief survey of the underlying physical processes and the introduction of experimental issues. The potential of both methods to overcome limitations of conventional XAS (X-ray absorption spectroscopy) and to push the limits for obtaining new information about the electronic and geometric structures of metal centers, in the solid state structure or heterogeneous catalysts, but also in metal complexes and homogeneous catalysts, is discussed by presenting a survey of representative references and recent own studies, rounded off by a conclusion and outlook.

Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions

“…Finally, the concept of hard X‐ray techniques has been extended to further photon‐in/photon‐out techniques (e.g. HERFD‐XANES, X‐ray emission techniques like V2C‐XES),83, 84 and X‐ray microscopic techniques 18…”

High‐Energy Resolution Fluorescence Detected X‐Ray Absorption Spectroscopy: A Powerful New Structural Tool in Environmental Biogeochemistry Sciences

“…The main advantages of measuring fluorescence‐XAS with CAS instead of SSD (or SDD) are: XAS (including extended x‐ray absorption fine structure [EXAFS] and X‐ray absorption near edge structure [XANES]) measurements can be achieved on complex and/or diluted systems where the detection limit is determined by the fluorescence of the main constituents of the matrix and/or the scattering signals; Energy resolution of HERFD‐XANES spectra can be sharper than what could be achieved conventionally (Hämäläinen et al, 1991; de Groot et al, 2002; Bauer, 2014), which improves the accuracy of XANES quantitative analyses; Energy position of the fluorescence lines (and especially the Kβ ones for the K‐edges) is sensitive to the spin state (Kβ 1,3 ) and to the ligands (Kβ 2,5 and its satellite lines) of the probed element. The XAS spectra obtained by measuring these lines are then spin or ligand sensitive (Bergmann et al, 1999; Rovezzi and Glatzel, 2014), Other spectroscopic techniques such as XES can be performed.…”

“…The XAS spectra obtained by measuring these lines are then spin or ligand sensitive (Bergmann et al, 1999; Rovezzi and Glatzel, 2014), Other spectroscopic techniques such as XES can be performed. For example, valence‐to‐core XES allows discrimination between the different ligands in the first coordination sphere of the probed element (Safonov et al, 2006; Bauer, 2014; Gallo and Glatzel, 2014). …”

“…Detailed explanations of the XAS and XES theories fall outside the scope of this paper and can be found in numerous recent reviews, on core‐level spectroscopy generality (de Groot and Kotani, 2008), XANES (Henderson et al, 2014; Joly and Grenier, 2016), EXAFS (Newville, 2014), XAS (Rehr and Albers, 2000; Ortega et al, 2012; Milne et al, 2014), XES (DeBeer and Bergmann, 2016), and HERFD (Bauer, 2014; Kowalska et al, 2016) applied to bioionorganic chemistry, and applications in environmental sciences (Gräfe et al, 2014). We will briefly recall the main principles of the core‐level spectroscopy techniques with special attention to effects that can be better analyzed with CAS.…”

Probing Transient Valence Orbital Changes with Picosecond Valence-to-Core X-ray Emission Spectroscopy

“…5−10 The features in this hard X-ray spectral region stem from radiative transitions from occupied valence orbitals to an inner core-hole vacancy generated, for instance, through X-ray absorption by a core electron. The transition probability can be about 3 orders of magnitude lower than that of the main emission lines (e.g., 2p → 1s) and is therefore challenging to measure.…”