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Abstract: We report the first experimental discovery of Hidden Satellites within the Kemission lines of manganese metal (Mn, ) with a total integrated statistical significance exceeding 270 (standard error), far beyond the discovery threshold. Experimental data were collected at the I20-Scanning beamline at the Diamond Light Source using our new eXtended-Range High-Energy-Resolution Fluorescence Detection (XR-HERFD) technique. The Hidden Satellites, embedded in the core emission structure, represent novel quantum many-body processes that evolve systematically as the incident photon energy increases. Principal Component Analysis (PCA) was applied to extract the major separable physical processes and validate the significance of the observed Hidden Satellites. The application of physical insight to the PCA method allowed us to isolate the satellites, and measure the evolutionary profile. Our paper reveals that the total intensity of shake-off satellites can reach as high as 20–25%. Although these are hidden, they are very significant. These results directly challenge the traditional treatment of the many-body reduction factor, , as a constant in the standard XAFS equation. Our findings demonstrate that this term must be modelled as an energy-dependent function, reflecting its variation with incident photon energy and highlighting its role in many-body interactions. This deeper understanding of fundamental atomic processes directly impacts relativistic quantum mechanics, in theory and application. Also, this develops the two most popular experimental techniques at synchrotrons: X-ray absorption and X-ray emission spectroscopy, responsible for some 12,000 papers per annum, and all applications of these techniques in chemistry, physics, and biology. It offers insights into the evolution of satellites and underscores the broader implications of hidden features in X-ray spectra.

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Abstract: We employ several X-ray based techniques, including X-ray diffraction, X-ray absorption spectroscopy and resonant inelastic X-ray scattering, to disentangle the contributions of individual chemical species to the structural, electronic and magnetic properties of high-entropy oxides. In the benchmark compound Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O and related systems, we unambiguously resolve a sizable Jahn–Teller distortion at the Cu sites, more pronounced in the absence of Ni2+ and Mg2+, suggesting that these ions promote positional order, whereas Cu2+ ions act to destabilize it. Moreover, we detect magnetic excitations and estimate the strength of the interactions between pairs of different magnetic elements. Our results provide valuable insights into the role of various chemical species in shaping the physical properties of high-entropy oxides.

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Abstract: Diorganozinc reagents (ZnR2, e.g. R = Et, Ph, C6F5) are widely used as Lewis acid catalysts or Lewis base reagents in their own right. However, descriptors for predicting the influence of the R substituent on ZnR2 Lewis acidity/basicity are very sparse. This is because ZnR2 liquid-phase speciation and electronic structure are unknown to date due to zinc’s ‘spectroscopically quiet’ nature and inability to measure ‘at zinc’. Here, we identify the geometric structures of ZnR2 in weakly coordinating solvents, demonstrating that electronic structure factors will dominate reactivity. We quantify the electronic structure properties that dictate ZnR2 Lewis acidity/basicity using three newly developed zinc-specific descriptors by combining the results from three zinc-specific X-ray spectroscopy methods and calculations. We provide accessible methods to pre-screen ZnR2 reactivity. Furthermore, our X-ray spectroscopy toolkit offers opportunities to develop liquid-phase descriptors that dictate reactivity for other zinc species, e.g. zinc bis-amides, battery electrolytes and enzymes.

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Abstract: The release of geogenic arsenic into groundwater, driven by reductive dissolution of Fe(III)/As(V) oxide phases, poses a severe health risk to millions in South and Southeast Asia. However, the microbes and electron donors responsible for the reductive dissolution remain unclear, due to complex a(biotic) interactions in sediments (traditionally used in microcosm incubation studies). In this study, indigenous microbial communities were sampled from arsenic-prone aquifers in Kandal Province, Cambodia, by filtering groundwater through sands coated with Fe(III)/As(V) minerals. This provided a streamlined inocula to study fundamental Fe(III)/As(V) reduction processes in controlled laboratory experiments. Anoxic incubations with contrasting electron donors suggested that biolabile organics are the main drivers of Fe(III) and As(V) reduction in the sampled aquifers, but methane can also contribute to Fe(III) reduction (at a slower rate) in the absence of labile organics. Known Fe(III)-reducing bacteria (e.g. Geobacter and Geothrix) were implicated in Fe(III)/As(V) reduction. Methane-driven Fe(III) reduction appeared to be mediated by proteobacterial methanotrophs (e.g., Methylomonas and Methylosinus), either directly or via symbiotic interactions with Geobacter through labile organic intermediates (suggested by acetate generation) highlighting the flexibility of proteobacterial methanotrophs under anoxic conditions. No methane-driven As(V) reduction was implicated in this study, while nominal As(V) reduction driven by aquatic organics (sorbed from the groundwater during filtration) was evident in control incubations suggesting some decoupling between Fe(III) and As(V) reduction. Furthermore, the sand filtration approach offers a promising method for producing simplified inocula for further studies of microbe-organic-mineral interactions in arsenic-prone aquifers and other complex biogeochemical systems.

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Abstract: The discovery of the novel n = 2 satellite transition in the Kβ emission spectrum of manganese and its evolution with incident photon energy are presented. Using the XR-HERFD (extended-range high-energy-resolution fluorescence detection) technique, we conclusively demonstrate the existence of this phenomenon with a statistical significance corresponding to 652 σse across the measured spectrum, far above the discovery threshold of 3–6 σse. We apply principal component analysis (PCA) to the XR-HERFD data to extract advanced structural insights. The evolution of this novel spectral feature and physical process are quantified by incorporating regression, revealing the increase in intensity over a wide range of incident photon energies. We validate these findings through independent test data. These results directly challenge the conventional treatment of the many-body reduction factor S02 as a constant independent of incident photon energy in the standard XAFS (X-ray absorption fine structure) equation. Thereby, these results present compelling evidence that S02 should be modelled as a varying function of incident photon energy, marking the first observation of this behaviour in Kβ spectra. This facilitates a greater quantitative understanding of HERFD spectra and a comprehensive representation of many-body effects in condensed matter systems.