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With the help of newly developed X-ray free-electron laser (XFEL) sources, creating double core holes (DCHs) simultaneously at the same or different atomic sites in a molecule has now become possible. DCH X-ray emission is a new form of X-ray nonlinear spectroscopy that can be studied with a XFEL. Here, we computationally explore the metal K-edge valence-to-core (VtC) X-ray emission spectroscopy (XES) of metal/metal and metal/ligand DCH states in a series of transition metal complexes with time-dependent density functional theory. The simulated DCH VtC-XES signals are compared with conventional single core hole (SCH) XES signals. The energy shifts and intensity changes of the DCH emission lines with respect to the corresponding SCH-XES features are fingerprints of the coupling between the second core hole and the occupied orbitals around the DCHs that contain important chemical bonding information of the complex. The difference between delocalized/localized core hole models on DCH VtC-XES is also briefly discussed. We theoretically demonstrate that DCH XES provides subtle information on the local electronic structure around metal centers in transition metal complexes beyond conventional linear XES. Our predicted changes from calculations between SCH-XES and DCH-XES features should be detectable with modern XFEL sources. [ABSTRACT FROM AUTHOR]

L'identification des composés à base de carbone, bien que difficile, est une source d'information essentielle dans de nombreuses études archéologiques et paléontologiques. La diffusion Raman de rayons X est une méthode de spectroscopie sur synchrotron qui permet d'identifier des signatures organiques, de retracer l'origine chimique des systèmes étudiés et de comprendre l'altération des composés organiques dans le temps. Cette technique, conduite de manière non destructive, dans l'air, avec une sensibilité en profondeur afin de fournir des informations non compromises par la contamination superficielle, surmonte ainsi plusieurs contraintes fondamentales à la caractérisation des matériaux organiques anciens. [ABSTRACT FROM AUTHOR]

We report the nearest-neighbor oxygen-oxygen radial distribution function (NN O–O RDF) of room temperature liquid water and polycrystalline ice Ih (-16.8 °C) obtained by x-ray Raman based extended x-ray absorption fine structure (EXAFS) spectroscopy. The spectra of the two systems were taken under identical experimental conditions using the same procedures to obtain the NN O–O RDFs. This protocol ensured a measurement of the relative distance distribution with very small systematic errors. The NN O–O RDF of water is found to be more asymmetric (tail extending to longer distances) with longer average distance (2.81 Å for water and 2.76 Å for ice) but a slightly shorter peak position (2.70 Å for water and 2.71 Å for ice). The refinement also showed a small but significant contribution from the linear O–H–O multiple scattering signal. The high sensitivity to short range distances of the EXAFS probe will set further restrictions to the range of possible models of liquid water. [ABSTRACT FROM AUTHOR]

The layered nickel manganese oxide of LiNi0.5Mn0.5O2 is a technologically important and promising cathode material for lithium-ion batteries. A study of the structural perturbation, charge compensation mechanism, and the valence of the constituent transition metal elements (Ni and Mn) during electrochemical cycling was performed using x-ray absorption spectroscopy (XAS) employing an in situ technique with an electrochemical cell designed for long term x-ray experiments. We present the changes in the oxidation state, bond distance, and coordination number of the Ni and Mn absorbers as a function of the state of charge of the material during electrochemical cycling at moderate rate through a typical Li-ion battery operating voltage range (2.9–4.7 V). The oxidation states of the transition metals in LiNi0.5Mn0.5O2 are Mn4+ and Ni2+. The x-ray absorption near edge spectra reveal that on delithiation of Li1-xNi0.5Mn0.5O2 the Mn is electrochemically inactive and remains at Mn4+ whereas the Ni is oxidized from Ni2+ to almost Ni4+ through an intermediate stage of Ni3+. A quantitative picture of the Ni valence during the charging process was obtained employing Faraday’s law calculations in combination with the XAS results. The Faraday’s law calculation indicated that at the end of the charge Ni is at Ni3.91+ in close agreement with the XAS results where Ni is found to be at Ni3.88+ at the end of the charge. Analysis of the extended x-ray absorption fine structure shows that during cycling the material retains its crystallographic symmetry and good structural short-range order which should lead to stable cycling. [ABSTRACT FROM AUTHOR]

The layered LiNi1/3Co1/3Mn1/3O2 system has recently drawn considerable interest for use as a cathode material for rechargeable lithium batteries. In order to investigate the charge-compensation mechanism and structural perturbations occurring in the system during cycling, in situ x-ray absorption spectroscopy (XAS) measurements were performed utilizing a novel electrochemical in situ cell specifically designed for long term x-ray experiments. The cell was cycled at a moderate rate through a typical Li-ion battery operating voltage range (2.9–4.7 V). The electrode contained 2.025 mg of LiNi1/3Co1/3Mn1/3O2 on a 25-μm Al foil and had an area of 0.79 cm2. The x-ray absorption spectroscopy (XAS) measurements were performed at the Ni, Co, and the Mn edges at different states of charge (SOC) during cycling, revealing details about the response of the cathode to Li insertion and extraction processes. Changes of bond distance and coordination number of Ni, Co, and Mn absorbers as a function of the state of charge of the material were obtained from the extended x-ray-absorption fine structure (EXAFS) region of the spectra. The x-ray absorption near-edge structure (XANES) region was studied in order to characterize the oxidation states of the 3d transition metals during cycling (Li extraction/insertion). We found that oxidation states of transition metals in LiNi1/3Co1/3Mn1/3O2 are Ni2+, Co3+, and Mn4+, whereas during charging Ni2+ is oxidized to Ni4+ through an intermediate stage of Ni3+, Co3+ is oxidized almost to Co4+ and, utilizing Faraday’s calculation and XAS results, the Co was found to be at Co3.92+ at the end of the charge, while Mn was found to be electrochemically inactive and remains as Mn4+. The EXAFS data that were collected continuously during cycling revealed details about the response of the cathode to Li insertion and extraction. These measurements on the LiNi1/3Co1/3Mn1/3O2 cathode confirmed that the material retains its symmetry and good structural short-range order leading to superior cycling. [ABSTRACT FROM AUTHOR]

The essay discusses a manuscript of the Qurān dating from the first half of the seventh century AD. The text does not belong to the Utmānic textual tradition, making this the only known manuscript of a non-Utmānic text type. The essay compares this text type with those of the Utmānic and other Companion textual traditions in order to shed light on the Prophetic prototype. [ABSTRACT FROM AUTHOR]

Abstract: Fe K-edge X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) have been performed on electrodes containing LiFePO4 to determine the local atomic and electronic structure and their stability with electrochemical cycling. A versatile electrochemical in situ cell has been constructed for long-term soft and hard X-ray experiments for the structural investigation on battery electrodes during the lithium-insertion/extraction processes. The device is used here for an X-ray absorption spectroscopic study of lithium insertion/extraction in a LiFePO4 electrode, where the electrode contained about 7.7mg of LiFePO4 on a 20μm thick Al-foil. Fe K-edge X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) have been performed on this electrode to determine the local atomic and electronic structure and their stability with electrochemical cycling. The initial state (LiFePO4) showed iron to be in the Fe2+ state corresponding to the initial state (0.0mAh) of the cell, whereas in the delithiated state (FePO4) iron was found to be in the Fe3+ state corresponding to the final charged state (3mAh). XANES region of the XAS spectra revealed a high spin configuration for the two states (Fe (II), d6 and Fe (III), d5). The results confirm that the olivine structure of the LiFePO4 and FePO4 is retained by the electrodes in agreement with the XRD observations reported previously. These results confirm that LiFePO4 cathode material retains good structural short-range order leading to superior cycling capability. [Copyright &y& Elsevier]

The creation of a 1s core hole in a 3d transition metal ion gives rise to an emission spectrum that can be recorded using a crystal analyzer. K shell X-ray spectroscopy using an analyser energy bandwidth of ∼1 eV is sensitive to electron–electron interactions and orbital splittings and preserves the advantages of the hard X-ray probe. We review recent developments in Kα and Kβ spectroscopy and show how the chemical sensitivity of the fluorescence lines can be exploited for selective X-ray absorption studies. When the photo excitation energy is tuned close to the K edge threshold, the phenomenon known as X-ray resonant Raman or resonant inelastic X-ray scattering (RIXS) occurs. RIXS spectroscopy on 3d transition metals at the 1s resonances with lowest incident energies (K pre-edge) is a very recent technique. We discuss basic aspects and demonstrate with several examples its potential as a future routine spectroscopic tool. [Copyright &y& Elsevier]

The extraction and insertion of lithium in LiFePO4 has been investigated in practical Li-ion intercalation electrodes for Li-ion batteries using Fe K-edge X-ray absorption spectroscopy (XAS). A versatile electrochemical in situ reaction cell was utilized, specifically designed for long-term X-ray experiments on battery electrodes during the lithium-extraction/insertion process in electrode materials for Li-ion batteries. The electrode contained about 7.7 mg of LiFePO4 on a 20 µm-thick Al foil. In order to determine the charge compensation mechanism and structural perturbations occurring in the system during cycling, in situ X-ray absorption fine-structure spectroscopy (XAFS) measurements were conducted on the cell at a moderate rate using typical Li-ion battery operating voltages (3.0-4.1 V versus Li/Li+). XAS studies of the LiFePO4 electrode measured at the initial state (LiFePO4) showed iron to be in the Fe(H) state corresponding to the initial state (0.0 mAh) of the battery, whereas in the delithiated state (FePO4) iron was found to be in the Fe(III) state corresponding to the final charged state (3 mAh) of the battery. The X-ray absorption near-edge structure (XANES) region of the XAS spectra revealed a high-spin configuration for the two states [Fe(II), d6 and Fe(III), d5]. The XAFS data analysis confirmed that the olivine structure of the LiFePO4 and FePO4 is retained by the electrodes, which is in agreement with the X-ray diffraction observations on these compounds. The XAFS data that were collected continuously during cycling revealed details about the response of the cathode to Li insertion and extraction. These measurements on the LiFePO4 cathode show that the material retains good structural short-range order leading to superior cycling. [ABSTRACT FROM AUTHOR]

Resonant inelastic X-ray scattering (RIXS) was used to collect Mn K pre-edge spectra and to study the electronic structure in oxides, molecular coordination complexes, as well as the S1 and S2 states of the oxygen-evolving complex (OEC) of photosystem II (PS Il). The RIXS data yield two-dimensional plots that can be interpreted along the incident (absorption) energy or the energy transfer axis. The second energy dimension separates the pre-edge (predominantly is to 3d transitions) from the main K-edge, and a detailed analysis is thus possible. The 1s2p RIXS final-state electron configuration along the energy transfer axis is identical to conventional L-edge absorption spectroscopy, and the RIXS spectra are therefore sensitive to the Mn spin state. This new technique thus yields information on the electronic structure that is not accessible in conventional K-edge absorption spectroscopy. The line splittings can be understood within a ligand field multiplet model, i.e., (3d,3d) and (2p,3d) two-electron interactions are crucial to describe the spectral shapes in all systems. We propose to explain the shift of the K pre-edge absorption energy upon Mn oxidation in terms of the effective number of 3d electrons (fractional 3d orbital population). The spectral changes in the Mn 1s2p3/2 RIXS spectra between the PS II S1 and S2 states are small compared to that of the oxides and two of the coordination complexes (Mn111(acac) 3 and MnIV(sal) 2(bipy)). We conclude that the electron in the step from S1 to S2 is transferred from a strongly delocalized orbital. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are essential components in numerous natural and man made organic compounds. In asphaltenes, knowledge of the electronic structure of both its aromatic and aliphatic components is of crucial importance, when trying to understand and predict its macroscopic properties. Theoretical studies of complex PAHs have led to simple rules to describe their π electron distribution, but systematic experimental support is still needed. A novel approach to directly probe carbon type in PAHs is described here, namely the technique of X-ray Raman spectroscopy (XRS). Conventional X-ray absorption spectroscopy (XAS) has been used for many years for element specific characterization of local structure and chemistry. However, in the soft X-ray region (relevant for light elements) its application to numerous carbonaceous systems including asphaltenes encounters problems. Most of the difficulties, including surface sensitivity and restricted sample environments, stem from the submicron path lengths of soft X-rays and/or electrons. XRS provides a means for obtaining the information content of soft X-ray absorption spectra while maintaining the experimental benefits of hard X-ray techniques (˜mm path length). In the XRS process an incident photon is inelastically scattered and part of its energy is transferred to excite an inner shell electron into an unoccupied state. Under the dipole approximation, the resulting features are identical to the corresponding XAS spectrum. In the past, the extremely low cross-section of XRS has made this technique impractical, but intense new X-ray facilities and improvements in X-ray optics have helped to advance this unique spectroscopic tool. We have applied XRS to a series of PAHs and several asphaltenes. The results directly support the simple ideas contained in the “sextet-double bond” description of PAHs. Furthermore, we show that XRS can probe the geometrry of aromatic ring systems in asphaltenes, as well as its ratio of aromatic and aliphatic constituents. [ABSTRACT FROM AUTHOR]

The nature and distribution of electron density in polycyclic aromatic hydrocarbons (PAHs) determines PAH properties. Theoretical investigations have yielded simple heuristics to describe the π electron distribution in complex PAHs, but systematic experimental support is lacking. Here, we show that using the novel approach of carbon K-edge X-ray Raman spectroscopy (XRRS), carbon type in PAHs can be probed directly. Our unique detector has enabled application of XRRS on PAHs and asphaltenes. XRRS results directly support the powerful ‘aromatic sextet’ description of PAHs. Also, XRRS is shown to establish geometries of aromatic ring systems in asphaltenes, a complex natural carbonaceous material. [Copyright &y& Elsevier]

Introduces an approach to high-resolution imaging of radio-labeled agents. Limitations of scintillation cameras with pinhole collimators; Advantages of Bragg diffraction optics over conventional pinhole cameras; Fundamentals of Bragg optics.

X-Ray absorption spectroscopy (XAS) is a powerful tool for element-specific characterization of local structure and chemistry. Although application of XAS in the hard X-ray region is now routine, the soft X-ray region (containing light-element K-edges) presents a number of experimental problems. Most of the difficulties, including surface sensitivity, restricted sample environments, and radiation damage, stem from the submicron path lengths of soft X-rays and/or electrons. X-Ray Raman scattering (XRS) provides a means for obtaining the information content of soft X-ray spectra while maintaining the experimental benefits of hard X-ray techniques. In the XRS process, an incident photon is inelastically scattered and part of its energy is transferred to excite an inner shell electron into an unoccupied state. Under the dipole approximation, the resulting features are identical to the corresponding XAS spectrum. In the past, the extremely low cross-section of XRS has made this technique impractical, but intense new X-ray facilities and improvements in X-ray optics have helped to put XRS on the brink of becoming a routine spectroscopic tool. At present, high-quality X-ray Raman spectra can be obtained in minutes to hours. X-Ray Raman spectroscopy thus represents a hard X-ray alternative to conventional XAS techniques in the study of systems with light elements, including C, N and O. In this review we describe the technique, present examples of recent work, and discuss the prospects for the future. [Copyright &y& Elsevier]

Reports that x-ray Raman spectra of the carbon K-edge have been recorded using radiation for a petroleum asphaltene. Comparison with coronene, graphite and paraffin standards; Composition of the asphaltene spectrum; Potential of x-ray Raman spectroscopy in the characterization of light elements in fuels, catalysts and other complex materials.

A correction to the article "Nearest-neighbor oxygen distances in liquid water and ice observed x-ray Raman based extended x-ray absorption fine structure," by Uwe Bergmann and colleagues, is presented.

X-ray absorption spectroscopy measured in transmission mode was used to study the effect of alkali and halide ions on the hydrogen-bonding (H-bonding) network of water. Cl- and Br- are shown to have insignificant effect on the structure of water while I- locally weakens the H-bonding, as indicated by a sharp increase of the main-edge feature in the x-ray absorption spectra. All alkali cations act as structure-breakers in water, weakening the H-bonding network. The spectral changes are similar to spectra of high density ices where the 2nd shell has collapsed due to a break-down of the tetrahedral structures, although here, around the ions, the breakdown of the local tetrahedrality is rather due to non-directional H-bonding to the larger anions. In addition, results from temperature-dependent x-ray Raman scattering measurements of NaCl solution confirm the H-bond breaking effect of Na+ and the effect on the liquid as similar to an increase in temperature. [ABSTRACT FROM AUTHOR]

We use hard x-ray resonant inelastic x-ray scattering (RIXS) and density functional theory (DFT) calculations to characterize charge transfer excitations in K3Mn(CN)6. The combination of RIXS measurements and DFT calculations allows us to characterize the strength of the ligand-metal electronic interaction and assign the Raman resonances in the RIXS spectra to charge transfer excitations. With x-ray excitation energies resonant with the T2g and Eg pre-edge peaks derived predominantly from the Mn 3d orbitals, we observe Raman resonances in the energy transfer range from 2 to 12 eV, which results from the filling of the 1s core-hole from T1u-symmetry occupied orbitals. DFT calculations indicate that these orbitals exhibit primarily ligand character, supporting the assignment of the energy transfer resonances to ligand-to-metal charge transfer excitations. Our RIXS measurements and DFT calculations also indicate that the Eg-orbital spin-splits by roughly 0.8 eV, though we do not cleanly resolve the two absorption peaks in the RIXS spectra. We also see evidence for a metal-to-ligand charge transfer (MLCT) excitation when exciting with a 6545.0 eV incident photon, roughly 4 eV above the Eg absorption peaks. The 6545.0 eV resonant emission spectrum shows a 6.0 eV energy transfer resonance, which corresponds to a final state hole in the T2g partially occupied orbital. DFT calculations indicate that excitation at 6545.0 eV populates an unoccupied T1u-symmetry orbital of primarily ligand character. Given the predominantly metal character of the final state hole, we assign the 6.0 eV Raman resonance to a MLCT excitation. These measurements demonstrate the ability of hard x-ray RIXS to characterize the valence electronic structure of coordination compounds. [ABSTRACT FROM AUTHOR]

X-ray crystallography and X-ray spectroscopy using X-ray free electron lasers plays an important role in understanding the interplay of structural changes in the protein and the chemical changes at the metal active site of metalloenzymes through their catalytic cycles. As a part of such an effort, we report here our recent development of methods for X-ray absorption spectroscopy (XAS) at XFELs to study dilute biological samples, available in limited volumes. Our prime target is Photosystem II (PS II), a multi subunit membrane protein complex, that catalyzes the light-driven water oxidation reaction at the Mn4CaO5 cluster. This is an ideal system to investigate how to control multi-electron/proton chemistry, using the flexibility of metal redox states, in coordination with the protein and the water network. We describe the method that we have developed to collect XAS data using PS II samples with a Mn concentration of <1 mM, using a drop-on-demand sample delivery method. [ABSTRACT FROM AUTHOR]

Highlights the workshop "Inelastic X-ray Scattering and Advanced Spectroscopy Facility for SPEAR3" in conjunction with the 30th Annual Stanford Synchrotron Radiation Laboratory Users' Meeting held on October 8, 2003. Speakers; Perspective on structure and bonding in water using X-ray absorption spectroscopy and X-ray Raman scattering; Needs for advanced X-ray microprobes to study crystal and electronic structures of solids at high pressure.

Presents observation of Fe-H/D modes by nuclear resonant vibrational spectroscopy. Effect of nuclear resonant inelastic X-ray scattering; Frequencies and motion.

Examines the electronic structure of nickel coordination complexes using 1s2p X-ray resonance Raman spectroscopy. Electronic ground state; Valence electron excitations; Sensitivity of the spectroscopy.

We present the X-FAST (XUV Femtosecond Absorption Spectroscopy Tabletop) instrument at the University of Wisconsin-Madison. The instrument produces femtosecond extreme ultraviolet photon pulses via high-harmonic generation in the range of 40–72 eV, as well as optical pump pulses for transient-absorption experiments. The system implements a gas-cooled sample cell that enables studying the dynamics of thermally sensitive thin-film samples. This paper provides potential users with specifications of the optical, vacuum, data acquisition, and sample cooling systems of the X-FAST instrument, along with performance metrics and data of an ultrafast laser-induced phase transition in a Ni2MnGa Heusler thin film. [ABSTRACT FROM AUTHOR]

Water in aerosol OT reverse micelles has been extensively studied as a model system for nanoconfined water. Results from previous vibrational studies suggest that water confined this way has slower dynamics compared to bulk water; however, the effects on the hydrogen bonding network are unclear. From our study of the structure of water hydrogen bonding using x-ray Raman spectroscopy, we found an increased fraction of weakened hydrogen bonds upon confinement, similar to the effect seen in temperature increase and NaCl solvation, as evidenced by the changes in specific spectral features. [ABSTRACT FROM AUTHOR]

Ever since the discovery that Mn was required for oxygen evolution in plants by Pirson in 1937 and the period‐four oscillation in flash‐induced oxygen evolution by Joliot and Kok in the 1970s, understanding of this process has advanced enormously using state‐of‐the‐art methods. The most recent in this series of innovative techniques was the introduction of X‐ray free‐electron lasers (XFELs) a decade ago, which led to another quantum leap in the understanding in this field, by enabling operando X‐ray structural and X‐ray spectroscopy studies at room temperature. This review summarizes the current understanding of the structure of Photosystem II (PS II) and its catalytic centre, the Mn4CaO5 complex, in the intermediate Si (i = 0–4)‐states of the Kok cycle, obtained using XFELs. [ABSTRACT FROM AUTHOR]

A chart is presented that lists the pages and cross-references for the codex of the companion of the prophet and the Qur'an of the prophet.

This paper provides a review of the characterization of organic systems via X‑ray Raman scattering (XRS) and a step-by-step guidance for its application. We present the fundamentals of XRS required to use the technique and discuss the main parameters of the experimental set-ups to optimize spectral and spatial resolution while maximizing signal-to-background ratio. We review applications that target the analysis of mixtures of organic compounds, the identification of minor spectral features, and the spatial discrimination in heterogeneous systems. We discuss the recent development of the direct tomography technique, which utilizes the XRS process as a contrast mechanism for assessing the three-dimensional spatially resolved carbon chemistry of complex organic materials. We conclude by exposing the current limitations and provide an outlook on how to overcome some of the existing challenges and advance future developments and applications of this powerful technique for complex organic systems. [ABSTRACT FROM AUTHOR]

Here, we describe a new synchrotron X-ray Fluorescence (XRF) imaging instrument with an integrated High Energy Fluorescence Detection X-ray Absorption Spectroscopy (HERFD-XAS) spectrometer at the Stanford Synchrotron Radiation Lightsource at beamline 6-2. The X-ray beam size on the sample can be defined via a range of pinhole apertures or focusing optics. XRF imaging is performed using a continuous rapid scan system with sample stages covering a travel range of 250 × 200 mm2, allowing for multiple samples and/or large samples to be mounted. The HERFD spectrometer is a Johann-type with seven spherically bent 100 mm diameter crystals arranged on intersecting Rowland circles of 1 m diameter with a total solid angle of about 0.44% of 4π sr. A wide range of emission lines can be studied with the available Bragg angle range of ∼64.5°–82.6°. With this instrument, elements in a sample can be rapidly mapped via XRF and then selected features targeted for HERFD-XAS analysis. Furthermore, utilizing the higher spectral resolution of HERFD for XRF imaging provides better separation of interfering emission lines, and it can be used to select a much narrower emission bandwidth, resulting in increased image contrast for imaging specific element species, i.e., sparse excitation energy XAS imaging. This combination of features and characteristics provides a highly adaptable and valuable tool in the study of a wide range of materials. [ABSTRACT FROM AUTHOR]

Solenopora jurassica is a fossil calcareous alga that functioned as an important reef-building organism during the Palaeozoic. It is of significant palaeobiological interest due to its distinctive but poorly understood pink and white banding. Though widely accepted as an alga there is still debate over its taxonomic affinity, with recent work arguing that it should be reclassified as a chaetetid sponge. The banding is thought to be seasonal, but there is no conclusive evidence for this. Other recent work has, however demonstrated the presence of a unique organic boron-containing pink/red pigment in the pink bands of S. jurassica. We present new geochemical evidence concerning the seasonality and pigmentation of S. jurassica. Seasonal growth cycles are demonstrated by X-ray radiography, which shows differences in calcite density, and by varying δ13C composition of the bands. Temperature variation in the bands is difficult to constrain accurately due to conflicting patterns arising from Mg/Ca molar ratios and δ18O data. Fluctuating chlorine levels indicate increased salinity in the white bands, when combined with the isotope data this suggests more suggestive of marine conditions during formation of the white band and a greater freshwater component (lower chlorinity) during pink band precipitation (δ18O). Increased photosynthesis is inferred within the pink bands in comparison to the white, based on δ13C. Pyrolysis Gas Chromatography Mass Spectrometry (Py-GCMS) and Fourier Transform Infrared Spectroscopy (FTIR) show the presence of tetramethyl pyrrole, protein moieties and carboxylic acid groups, suggestive of the presence of the red algal pigment phycoerythrin. This is consistent with the pink colour of S. jurassica. As phycoerythrin is only known to occur in algae and cyanobacteria, and no biomarker evidence of bacteria or sponges was detected we conclude S. jurassica is most likely an alga. Pigment analysis may be a reliable classification method for fossil algae. [ABSTRACT FROM AUTHOR]

For thousands of years, the unique physicochemical properties of plant exudates have defined uses in material culture and practical applications. Native Australian plant exudates, including resins, kinos, and gums, have been used and continue to be used by Aboriginal Australians for numerous technical and cultural purposes. A historic collection of well-preserved native Australian plant exudates, assembled a century ago by plant naturalists, gives a rare window into the history and chemical composition of these materials. Here we report the full hierarchical characterization of four genera from this collection, Xanthorrhoea, Callitris, Eucalyptus, and Acacia, from the local elemental speciation, to functional groups and main molecular markers. We use high-resolution X-ray Raman spectroscopy (XRS) to achieve bulk-sensitive chemical speciation of these plant exudates, including insoluble, amorphous, and cross-linked fractions, without the limitation of invasive and/or surface specific methods. Combinatorial testing of the XRS data allows direct classification of these complex natural species as terpenoid, aromatic, phenolic, and polysaccharide materials. Differences in intragenera chemistry was evidenced by detailed interpretation of the XRS spectral features. We complement XRS with Fourier-transform infrared (FT-IR) spectroscopy, gas chromatography--mass spectrometry (GC-MS), and pyrolysis-GC-MS (Py-GC-MS). This multimodal approach provides a fundamental understanding of the chemistry of these natural materials long used by Aboriginal Australian peoples. [ABSTRACT FROM AUTHOR]

Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics and the flux limitations of ultrafast X-ray sources. Such a situation exists for archetypal polypyridyl iron complexes, such as [Fe(2,2′-bipyridine)3]2+, where the excited-state charge and spin dynamics involved in the transition from a low- to a high-spin state (spin crossover) have long been a source of interest and controversy. Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, can elucidate the spin crossover dynamics of [Fe(2,2′-bipyridine)3]2+ on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate that these capabilities will make our method a valuable tool for mapping in unprecedented detail the fundamental electronic excited-state dynamics that underpin many useful light-triggered molecular phenomena involving 3d transition metal complexes. [ABSTRACT FROM AUTHOR]

The end-Cretaceous Chicxulub impact triggered Earth's last mass-extinction, extinguishing ~ 75% of species diversity and facilitating a global ecological shift to mammal-dominated biomes. Temporal details of the impact event on a fine scale (hour-to-day), important to understanding the early trajectory of mass-extinction, have largely eluded previous studies. This study employs histological and histo-isotopic analyses of fossil fish that were coeval with a unique impact-triggered mass-death assemblage from the Cretaceous-Paleogene (KPg) boundary in North Dakota (USA). Patterns of growth history, including periodicity of ẟ18O and ẟ13C and growth band morphology, plus corroborating data from fish ontogeny and seasonal insect behavior, reveal that the impact occurred during boreal Spring/Summer, shortly after the spawning season for fish and most continental taxa. The severity and taxonomic symmetry of response to global natural hazards are influenced by the season during which they occur, suggesting that post-impact perturbations could have exerted a selective force that was exacerbated by seasonal timing. Data from this study can also provide vital hindsight into patterns of extant biotic response to global-scale hazards that are relevant to both current and future biomes. [ABSTRACT FROM AUTHOR]

A systematic study of 12 ferric and ferrous Kβ X-ray emission spectra (XES) is presented. The factors contributing to the Kβ main line and the valence to core region of the spectra are experimentally assessed and quantitatively evaluated. While the Kβ main line spectra are dominated by spin state contributions, the valence to core region is shown to have greater sensitivity to changes in the chemical environment. A density functional theory (DFT) based approach is used to calculate the experimental valence spectra and to evaluate the contributions to experimental intensities and energies. The spectra are found to be dominated by iron np to 1s electric dipole allowed transitions, with pronounced sensitivity to spin state, ligand identity, ligand ionization state, hybridization state, and metal-ligand bond lengths. These findings serve as an important calibration for future applications to iron active sites in biological and chemical catalysis. Potential applications to Compound II heme derivatives are highlighted. [ABSTRACT FROM AUTHOR]

X-ray absorption spectroscopy (XAS) has become an indispensable tool in catalysis research. The instrumentation at synchrotron radiation sources as well as analysis and calculation of XAS has reached such a high level that this technique is now attractive to a very large user community. Standard XAS, however, cannot answer all questions and complementary techniques that address the electronic structure in more detail and help to investigate low Z elements as ligand or absorber add to the repertoire of hard X-ray techniques. We discuss in this contribution how energy analysis of the scattered photons [1] in addition to control of the incident photon energy (cf. Figure 1) extends the range of applications of XAS and addresses some problems that XAS cannot solve [2]. [ABSTRACT FROM AUTHOR]

Abstract: A study of the Mn K absorption pre-edges in oxides using resonant inelastic X-ray scattering (RIXS) spectroscopy is presented. The energy transfer dimension enhances the separation of the pre-edge (predominantly 1s to 3d transitions) from the main K-edge and a detailed analysis is thus possible. The RIXS spectra are sensitive to the Mn spin state. The technique thus yields detailed information on the electronic structure that is not accessible in conventional K-edge absorption spectroscopy. The line splittings can be understood within a ligand field multiplet model, showing the importance of (2p,3d) two-electron interactions that give rise to the spin-sensitivity. [Copyright &y& Elsevier]

Determines the use of high-resolution fluorescence in determining the site-selective iron (Fe) absorption spectra of Prussian Blue. Importance of mixed-valence metals in copper oxide superconductors; Detection of Fe cluster in methane monooxygenase; Crystallographic distances of the Fe site.

Investigates the oxidation states of manganese in each of the intermediate S-states using K(beta) x-ray emission spectroscopy and x-ray absorption near-edge structure. S-state composition of samples given 0-6 flashes; S[sub 2]-state multiline electron paramagnetic resonance signal oscillation pattern; Second-derivative inflection point energy values for various S-states.

Investigates the influence of oxidation-state changes and ligand environment on two structurally homologous manganese (Mn) compounds. Analysis of Mn K-edge X-ray absorption near-edge structures and Mn KBeta X-ray emission spectroscopy data. Implications of Mn-Mn backscatter Fourier peak in all spectra; Effect of ligand changes on energy shift.

Hard X-ray spectroscopy is an element specific probe of electronic state, but signals are weak and require intense light to study low concentration samples. Free electron laser facilities offer the highest intensity X-rays of any available light source. The light produced at such facilities is stochastic, with spikey, broadband spectra that change drastically from shot to shot. Here, using aqueous ferrocyanide, we show that the resonant X-ray emission (RXES) spectrum can be inferred by correlating for each shot the fluorescence intensity from the sample with spectra of the fluctuating, self-amplified spontaneous emission (SASE) source. We obtain resolved narrow and chemically rich information in core-to-valence transitions of the pre-edge region at the Fe K-edge. Our approach avoids monochromatization, provides higher photon flux to the sample, and allows non-resonant signals like elastic scattering to be simultaneously recorded. The spectra obtained match well with spectra measured using a monochromator. We also show that inaccurate measurements of the stochastic light spectra reduce the measurement efficiency of our approach. X-ray absorption and X-ray free electron lasers are important tools to study chemical and structural dynamics, but spectral details like pre-edge features are inherently hard to detect. Here, the authors show that stochastic spectroscopy can yield similar spectral information to monochromatic spectroscopies, while increasing signal yield and reducing acquisition time. [ABSTRACT FROM AUTHOR]

The structure of bulk liquid water was recently probed by x-ray scattering below the temperature limit of homogeneous nucleation (TH) of ~232 K [J. A. Sellberg et al., Nature 510, 381-384 (2014)]. Here, we utilize a similar approach to study the structure of bulk liquid water below TH using oxygen K-edge x-ray emission spectroscopy (XES). Based on previous XES experiments [T. Tokushima et al., Chem. Phys. Lett. 460, 381-400 (2008)] at higher temperatures, we expected the ratio of the 1b1' and 1b1" peaks associated with the lone-pair orbital in water to change strongly upon deep supercooling as the coordination of the hydrogen (H-) bonds becomes tetrahedral. In contrast, we observed only minor changes in the lone-pair spectral region, challenging an interpretation in terms of two interconverting species. A number of alternative hypotheses to explain the results are put forward and discussed. Although the spectra can be explained by various contributions from these hypotheses, we here emphasize the interpretation that the line shape of each component changes dramatically when approaching lower temperatures, where, in particular, the peak assigned to the proposed disordered component would become more symmetrical as vibrational interference becomes more important. [ABSTRACT FROM AUTHOR]

The iron-molybdenum cofactor (FeMoco) of nitrogenase contains a biologically unprecedented μ6-coordinated C4- ion. Although the role of this interstitial atom in nitrogenase catalysis is unknown, progress in understanding its biosynthetic origins has been made. Here we report valence-to-core Fe Kβ X-ray emission spectroscopy data to show that this C4- ion is present in the Fe8S9 "L-cluster," which is the immediate precursor to FeMoco prior to the insertion of molybdenum and coordination by homocitrate. These results accord with recent evidence supporting a role for the S-adenosylmethionine-dependent enzyme NifB in the incorporation of carbon into the FeMoco center of nitrogenase. [ABSTRACT FROM AUTHOR]

X-ray Raman spectroscopy (XRS) combined with small-angle x-ray scattering (SAXS) were used to study aqueous solutions of HCl and NaOH. Hydrated structures of H+ and OH- are not simple mirror images of each other. While both ions have been shown to strengthen local hydrogen bonds in the hydration shell as indicated by XRS, SAXS suggests that H+ and OH- have qualitatively different long-range effects. The SAXS structure factor of HCl (aq) closely resembles that of pure water, while NaOH (aq) behaves similar to NaF (aq). We propose that protons only locally enhance hydrogen bonds while hydroxide ions induce tetrahedrality in the overall hydrogen bond network of water. [ABSTRACT FROM AUTHOR]

Oscillators are at the heart of optical lasers, providing stable, transform-limited pulses. Until now, laser oscillators have been available only in the infrared to visible and near-ultraviolet (UV) spectral region. In this paper, we present a study of an oscillator operating in the 5- to 12-keV photon-energy range. We show that, using the Kα1 line of transition metal compounds as the gain medium, an X-ray free-electron laser as a periodic pump, and a Bragg crystal optical cavity, it is possible to build X-ray oscillators producing intense, fully coherent, transform-limited pulses. As an example, we consider the case of a copper nitrate gain medium generating ∼ 5 × 1010 photons per pulse with 37-fs pulse length and 48-meV spectral resolution at 8-keV photon energy. Our theoretical study and simulation of this system show that, because of the very large gain per pass, the oscillator saturates and reaches full coherence in four to six optical-cavity transits. We discuss the feasibility and design of the X-ray optical cavity and other parts of the oscillator needed for its realization, opening the way to extend X-ray–based research beyond current capabilities. [ABSTRACT FROM AUTHOR]

Ancient stromatolites can provide key insights into the early evolution of life on Earth. Neoarchean fenestrate stromatolites from the ∼2520 Ma Upper Nauga Formation (Transvaal Supergroup, South Africa) preserve cuspate morphologies. They possess clearly delineated support and drape structures interpreted as dolomitized microbial mat material. Petrographic observations show that the biogenic structures are composed of planar-s to non-planar ferroan dolomite, encased in ferroan calcite, including herringbone calcite textures. The cuspate stromatolites were analyzed using Synchrotron Rapid Scanning X-Ray Fluorescence (SRS-XRF) and more conventional techniques to determine: (i) whether element distributions could be distinguished in ancient stromatolites at both cm to dm scales, (ii) whether element distributions show variation between biogenic and abiogenic textures, and (iii) the sample's paragenesis. The distributions of Ca, Fe, Mn, Pb, Cu, As, Br, Al, Si, P, and S directly correspond to dolomitized stromatolitic structures and show trace element distributions are principally controlled by calcite and dolomite occurrence. Dolomite formation was mainly driven by seawater-derived fluids given the high concentrations of Fe and retention of marine shale-normalized rare earth element and yttrium (REY SN) patterns, however the spatial association of dolomite to stromatolite structures may reflect microbially-influenced mineral nucleation. Given the complexity of this sample's paragenetic evolution, trace metal distributions cannot be conclusively tied to specific metabolic pathways, bioaccumulation or passive binding, however, the results show SRS-XRF can be used for quantifiable, spatial, in-situ investigation of ancient microbialites. [ABSTRACT FROM AUTHOR]

This work has demonstrated that X‐ray absorption spectroscopy (XAS), both Mn XANES and EXAFS, of solutions with millimolar concentrations of metal is possible using the femtosecond X‐ray pulses from XFELs. Mn XAS data were collected using two different sample delivery methods, a Rayleigh jet and a drop‐on‐demand setup, with varying concentrations of Mn. Here, a new method for normalization of XAS spectra based on solvent scattering that is compatible with data collection from a highly variable pulsed source is described. The measured XANES and EXAFS spectra of such dilute solution samples are in good agreement with data collected at synchrotron sources using traditional scanning protocols. The procedures described here will enable XFEL‐based XAS on dilute biological samples, especially metalloproteins, with low sample consumption. Details of the experimental setup and data analysis methods used in this XANES and EXAFS study are presented. This method will also benefit XAS performed at high‐repetition‐rate XFELs such as the European XFEL, LCLS‐II and LCLS‐II‐HE. [ABSTRACT FROM AUTHOR]

Aqueous solutions of acetonitrile (MeCN) have been studied with oxygen K-edge x-ray Raman scattering (XRS) which is found to be sensitive to the interaction between water and MeCN. The changes in the XRS spectra can be attributed to water directly interacting with MeCN and are reproduced by density functional theory calculations on small clusters of water and MeCN. The dominant structural arrangement features dipole interaction instead of H-bonds between the two species as revealed by the XRS spectra combined with spectrum calculations. Small-angle x-ray scattering shows the largest heterogeneity for a MeCN to water ratio of 0.4 in agreement with earlier small-angle neutron scattering data. [ABSTRACT FROM AUTHOR]

X-ray Raman scattering (XRS) spectroscopy and small angle x-ray scattering (SAXS) are used to study water in aqueous solutions of NaCl, MgCl2, and AlCl3 with the particular aim to provide information about the structure of the hydration shells of the cations. The XRS spectra show that Na+ weakens the hydrogen bonds of water molecules in its vicinity, similar to the effect of increased temperature and pressure. Mg2+ and Al3+, on the other hand, cause the formation of short and strong hydrogen bonds between the surrounding water molecules. The SAXS data show that Mg2+ and Al3+ form tightly bound hydration shells that give a large density contrast in the scattering data. From the form factors extracted from the SAXS data, we found that Mg2+ and Al3+ have, respectively, an equivalent of one and one and a half stable hydration shells that appear as a density contrast. In addition, we estimated that the density of water in the hydration shells of Mg2+ and Al3+ is, respectively, ∼61% and ∼71% higher than in bulk water. [ABSTRACT FROM AUTHOR]