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Mixed anion compounds afford considerable compositional diversity and tunability of function. A challenging aspect of anion control of properties of periodic solids is to preserve the crystal lattice while substituting for different anions of widely varying size and hardness. Post-synthetic modification routes that place cations or anions in non-equilibrium configurations represent a promising means of decoupling composition and crystal structure and for accessing metastable solids; however, such methods remain relatively unexplored for anion placement. Here, we report the synthesis of LaOI nanocrystals by a non-hydrolytic sol-gel condensation reaction and their transformation into LaOBr, LaOCl, and LaOF nanocrystals along hard-soft-acid-base principles using post-synthetic metathesis reactions with ammonium halides. Anion displacement proceeds along halide planes preserving the tetragonal matlockite structure. Energy-variant X-ray excited optical luminesce signatures of alloyed Tb3+-ions serves as a sensitive quantum reporter of the preservation of the cation sublattice and hardening of the crystal structure upon anion replacement.

The unstable solid–electrolyte interphase (SEI) on Li anodes is the origin of major performance challenges in Li batteries, namely, insufficient Coulombic efficiency (CE) and cycle life. While it i...

Transformations between different atomic configurations of a material oftentimes bring about dramatic changes in functional properties as a result of the simultaneous alteration of both atomistic a...

Rare-earth scheelites represent a diverse family of compounds with multiple degrees of freedom, which enables the incorporation of a wide range of lanthanide color centers. Precise positioning of quantum objects is attainable by the choice of alkali cations and lattice connectivity of polyanion units. Herein, we report the structure-dependent energy transfer and lattice coupling of optical transitions in La3+- and Dy3+-containing scheelite-type double and quadruple molybdates NaLa1-xDyx(MoO4)2 and Na5La1-xDyx(MoO4)4. X-ray excitation of La3+ core states generates excited-state electron-hole pairs, which, upon thermalizing across interconnected REO8 polyhedra in double molybdates, activate a phonon-coupled excited state of Dy3+. A pronounced luminescence band is observed corresponding to optical cooling of the lattice upon preferential radiative relaxation from a "hot" state. In contrast, combined X-ray absorption near-edge structure and X-ray-excited optical luminescence studies reveal that such a lattice coupling mechanism is inaccessible in quadruple molybdates with a greater separation of La3+-Dy3+ centers.

The inner-valence Auger electron spectra after the chlorine 2p ionization in the gas phase CHCl3 molecule were investigated both theoretically and experimentally. The total ion yield spectrum exhibits a broad structure at 217 eV, above the Cl 2p ionization threshold, which can be attributed to either a shape resonance or a shake-up. In addition, we have performed a series of high-level ab initio quantum mechanical calculations at the density functional theory level to compute the Auger lines.

The uneven consumption of anions during the lithium (Li) deposition process triggers a space charge effect that generates Li dendrites, seriously hindering the practical application of Li-metal batteries. We report on a cobalt phthalocyanine electrolyte additive with a planar molecular structure, which can be tightly adsorbed on the Li anode surface to form a dense molecular layer. Such a planar molecular layer cannot only complex with Li ions to reduce the space charge effect, but also suppress side reactions between the anode and the electrolyte, producing a stable solid electrolyte interphase composed of amorphous lithium fluoride (LiF) and lithium carbonate (LiCO3 ), as verified by X-ray absorption near-edge spectroscopy. As a result, the Li|Li symmetric cell exhibits excellent cycling stability above 700 h under a high plating capacity of 3 mAh cm-2 . Moreover, the assembled Li|lithium iron phosphate (LiFePO4 , LFP) full-cell can also deliver excellent cycling over 200 cycles under lean electrolyte conditions (3 μL mg-1 ).

Transformations between different atomic configurations of a material oftentimes bring about dramatic changes in functional properties as a result of the simultaneous alteration of both atomistic and electronic structure. Transformation barriers between polytypes can be tuned through compositional modification, generally in an immutable manner. Continuous, stimulus-driven modulation of phase stabilities remains a significant challenge. Utilizing the metal-insulator transition of VO

No. 2019-A0010806820 UIDB/00068/2020 PTDC/FIS-AQM/31281/2017 Abstract: We present novel results of the analysis of the electronic structure of two aliphatic esters: methyl butyrate and methyl valerate. High-resolution photoabsorption spectra were collected and analyzed over the energy range 4.0–10.8 eV and showed for both the molecules not only a clear band of the HOMO to LUMO transition, but also vibronic structure associated with the first Rydberg-valence transition. Photoelectron spectra recorded from 9 to over 28 eV revealed many ionization states with the first adiabatic ionization energies found to be 9.977 eV and 9.959 eV for methyl butyrate and methyl valerate, respectively. Ab initio calculations have been performed in order to help assign the photoabsorption and photoelectron features. Photolysis life times in the atmosphere were calculated revealing that photolysis is not competitive over hydroxyl radical scavenging in the process of removal of these esters from the atmosphere. Graphical abstract: [Figure not available: see fulltext.] publishersversion published

The conversion of biomass waste into valuable carbon composites as efficient non-precious metal oxygen-reduction electrocatalysts is attractive for the development of commercially viable fuel-cell and metal-air battery technologies. Herein, a highly active and robust Si-contained Fe/N/C catalyst is prepared based on the porous carbon deriving from waste reed stalk after carbonization and KOH corrosion. Reed waste is a natural, abundantly available, and yearly renewable source, acting as the single precursor for Si containing-carbon substrate. The typical product (Si-Fe20/N/C1_6 in this work) possesses a high BET specific surface area, porous structure with high pyridinic-N and pyrrolic-N content. The X-ray absorption near edge structure (XANES), Raman, X-ray photoelectron spectroscopy (XPS) measurements and electrochemical measurements show that Si facilitates incorporation of more N to coordinate with Fe in the porous carbon and induces more graphitic carbon in the catalyst. The sample Si-Fe20/N/C1_6 exhibits better activity and superior stability than the Fe20/N/C counterpart and commercial Pt/C catalyst for the oxygen reduction reaction (ORR) in 0.1 M KOH electrolyte. The results suggest a promising route based on economical and sustainable biomass towards the development and engineering of value-added carbon materials as robust catalysts for oxygen reduction.

We present the first Li K-edge XANES study of a varied suite of lithium silicate (LS) and lithium alkaline-earth silicate (LMS) glasses. The LS series contains three glasses with compositions LS4 (20 Li2O–80 SiO2), LS2 (33 Li2O–67 SiO2) and LS1.5 (40 Li2O–60 SiO2) and the LMS series is comprised of four glasses of compositions 20 Li2O–20 M2O–60 SiO2 where M = Mg, Ca, Sr and Ba. The spectra were compared to those of known salts and minerals, particularly to lithium metasilicate (Li2SiO3) and lithium carbonate (Li2CO3). Crystalline lithium metasilicate has a sharp, strong intensity absorption edge whereas the lithium silicate glasses all have a weak intensity edge feature, similar to that of lithium carbonate (Li2CO3). The intensity of the edge is governed by the existence of a 2p electron and can be correlated with the ionicity of the Li O bond. Therefore, the bonding environment in LS glasses differs considerably from their crystalline counterparts. The area of the absorption edge peak increases with the lithium content of the LS glasses. As for the LMS glasses the edge peak changes drastically depending on the alkaline-earth present. The peak area of the LMS glasses decreases with increasing charge density (Z/r2) from barium to magnesium. The area of the absorption edge peak in the LS glasses is larger than that of the LMS glasses. Thus, the addition of alkaline-earth elements to lithium silicate glasses modifies the glass network differently depending on the specific element, which in turn creates an altered lithium bonding environment as evidenced by their Li K-edge XANES spectra.

The conversion and numerical amplification of X-ray photons to visible light is at the heart of numerous technological applications spanning the range from X-ray detectors and scintillators to radiographic medical imaging devices. The need for increased sensitivity and spatial resolution to reduce radiation exposure and provide better differentiation of specimens presenting an X-ray contrast has been a strong driving force in the search for novel X-ray phosphors. However, the current palette of X-ray phosphors is rather sparse. The development of color tunable phosphors necessitates the incorporation of multiple dopants, which in turn interact through complex sensitization mechanisms that are poorly understood for high-energy excitation. In this work, we describe the stabilization of multiply alloyed LaOCl nanocrystals incorporating Tb3+ cations in conjunction with either divalent or trivalent europium ions, yielding phosphors emitting in the blue–green and green–red regions of the electromagnetic spectru...

A solution method was developed to synthesize reduced graphene oxide (RGO) – red phosphorous (RP) composites. The uniform distribution of RP particles into three-dimensional conductive RGO network was obtained. Due to both improved electronic structure and mechanical properties, the hybrids delivered a high lithium storage capacity with superior rate performance. For the first time, the electronic structure, as revealed by phosphorous (P) L-edge and lithium (Li) K-edge X-ray absorption near-edge structure (XANES), provides spectroscopic evidence to identify the lithiated products and solid electrolyte interphase. Charge distribution in between RP and RGO was also found by XANES, facilitating the anchoring of active RP into RGO surface.

The thermally driven orders-of-magnitude modulation of resistance and optical transmittance observed in VO2 makes it an archetypal first-order phase transition material and underpins functional applications in logic and memory circuitry, electromagnetic cloaking, ballistic modulation, and thermochromic glazing to provide just a few representative examples. VO2 can be reversibly switched from an insulating to a metallic state at an equilibrium transition temperature of 67 °C. Tuning the phase diagram of VO2 to bring the transition temperature closer to room temperature has been a longstanding objective and one that has tremendous practical relevance. Substitutional incorporation of dopants has been the most common strategy for modulating the metal—insulator transition temperature but requires that the dopants be incorporated during synthesis. Here we demonstrate a novel postsynthetic diffusive annealing approach for incorporating interstitial B dopants within VO2. The postsynthetic method allows for the tr...

The dynamics of the photofragmentation pathways of tetrachloroethylene with photon energies from 15 up to 250 eV encompassing the Cl 2p edge is presented. In order to distinguish the fragmentation channels, the ionic fragments were separated according to their mass-to-charge ratio, measured in coincidence with the photoelectrons, and collected as a function of the incident photon energy. Distinct minima or maxima are found in the partial ion yield in the region between 40 and 50 eV. These features are believed to be associated with the Cooper minimum which results from a molecular orbital with a strong atomic 3p subshell character. In the shallow core region, some fragmentation patterns are considered in terms of fast fragmentation of the C2Cl4 molecule, despite the heavy mass of its fragments. In the present case, the fast fragmentation is favored by the very strong antibonding character of the LUMO, understandable in the frame of the core equivalent model for halogen-containing molecules. In addition, a...

Lithium ion batteries (LIB) have achieved great success as energy supply systems in portable devices and in electrical vehicles. Identifying the local chemical structures of elemental lithium in lithium compounds is beneficial for improving understanding of battery components and performance. Herein, a library of Li K-edge X-ray absorption near edge structure (XANES) of lithium compounds relevant to Li-ion batteries is reported. Materials described include lithium metals (anode), Li-containing cathodes, electrolytes and solid electrolyte interphase (SEI). The results illustrate the characteristic spectral features stemming from the various electronic structures and chemical environment of lithium atoms for each and every possible battery component. XANES spectra of Sn based anode after discharging reveal the appearance of Li 2 CO 3 on electrode surface. X-ray damage on sensitive lithium species is also assessed; the results reveal that more attention should be paid to irradiation effects to conduct XANES measurements for battery materials properly.

An EUV Stokes polarimeter designed for operation up to 150 eV photon energy has been fabricated and commissioned (with red, green and violet light). The polarimeter consists of two identical 4-mirror optical groups acting as a phase retarder and analyser respectively. Each group is capable of independent azimuthal rotation about the beam without deviating the beam. The mirrors are gold coated and operating at 80° angle of incidence. Such an instrument can determine both the full Stokes vector of the incoming light and the optical constants (polarizance and phase delay) of the optical elements of the polarimeter, which are then translated into the optical constants (n and k) for gold and compared to the literature values.

The Auger electron spectra after the chlorine 2p excitation and ionization in the gas phase CH2Cl2 and CD2Cl2 molecules were investigated both theoretically and experimentally. A series of high-level ab initio quantum mechanical calculations have been performed at multiconfigurational self-consistent field (MCSCF) and multireference configuration interaction (MRCI) levels of theory to compute the Cl L2,3VV Auger lines. Calculations were compared with the corresponding experimental photoexcited and photoionized spectra.

A wide range of methods are used to estimate the plant-availability of soil phosphorus (P). Published research has shown that the diffusive gradients in thin films (DGT) technique has a superior correlation to plant-available P in soils compared to standard chemical extraction tests. In order to identify the plant-available soil P species, we combined DGT with infrared and P K- and L2,3-edge X-ray adsorption near-edge structure (XANES) spectroscopy. This was achieved by spectroscopically investigating the dried binding layer of DGT devices after soil deployment. All three spectroscopic methods were able to distinguish between different kinds of phosphates (poly-, trimeta-, pyro- and orthophosphate) on the DGT binding layer. However, infrared spectroscopy was most sensitive to distinguish between different types of adsorbed inorganic and organic phosphates. Furthermore, intermediates of the time-resolved hydrolysis of trimetaphosphate in soil could be analyzed Refereed/Peer-reviewed

The instability of the solid electrolyte interphase (SEI) on the lithium (Li) metal anode is a major challenge towards improving the Coulombic efficiency (CE) and cycle life of Li batteries. In classical SEI models with mosaic and layered structures, ionic phases (e.g., Li2O and LiF) are enriched closest to the Li|SEI interface, while the outer SEI are highly dependent on electrolytes and typically assigned to less-reduced species, such as semi-carbonates and organic Li salts.1, 2 The formation of SEI on Li is often interpreted as a consequence of reactivity between Li metal and electrolytes; however, there remains a lack of understanding about the interplay between electrolytes and specific SEI phases once they are formed. Some recent computational studies have shed light on the chemical reactivity between thin (~1 nm) single-phase inorganic SEI (Li2O, LiOH, and Li2CO3) on Li metal and DME electrolytes containing LiTFSI or LiFSI salts, using ab initio molecular dynamics (AIMD) calculations;3, 4 experimental insights are still much-needed. Herein, we study two ionic SEI phases, Li2O (Fig. 1a-b) and LiF (Fig. 1c-d), that are nearly ubiquitously found across many native SEIs, and investigate their stability at the SEI|electrolyte interface. We find, by using a combination of electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and non-destructive X-ray absorption near-edge spectroscopy (XANES), that the ionic SEI|electrolyte interfaces can undergo significant chemical evolution as a function of electrolyte. As shown in Fig. 1a, distinctive lower-frequency semicircles emerged in the Nyquist plots of EIS when 1 M LiTFSI EC/DEC and 1 M LiPF6 EC/DEC were used, indicating significant changes at the interface between the ionic Li2O SEI and carbonate-based electrolytes, especially in the presence of LiPF6 salt. The surface atomic concentration of F also increased significantly from 4 at.% in 1 M LiTFSI DOL/DME to 44 at.% in 1 M LiPF6 EC/DEC, suggesting that a F-rich Li2O|electrolyte interface leads to an additional charge transfer barrier. Non-destructive Li K-edge XANES of the Li2O SEI soaked in 1 M LiPF6 EC/DEC electrolyte displayed a dominant LiF peak at 62.3 eV with an evident blue shift compared with the standard LiF peak at 62.0 eV (Fig. 1b),5 which could be attributed to the solvation of F-rich species at the interface by organic phases from carbonates decomposition, forming an “organic/F-rich” outer SEI layer. Similar organic/F-rich outer SEI was also observed on the LiF SEI soaked in 1 M LiPF6EC/DEC electrolyte, as evidenced by EIS (Fig. 1c), XPS (Fig. 1d) and XANES results. The organic/F-rich outer SEI induced by reactivity between ionic SEI phases and carbonate-based electrolytes can significantly exacerbate the subsequent plating overpotentials. Our experimental results suggest that electrolyte solvent and salt selection is of great importance to optimize transport in ionic-rich Li interfaces, which can have important implications ultimately for SEI stability and thus CE. Figure 1. (a) Nyquist plot of EIS spectra of Li|Li2O SEI in the three different electrolytes, where the thickness L and conductivity σ of the Li2O SEI were acquired by fitting the higher-frequency semi-circle (or the sole semi-circle in the case of DOL/DME).6 (b) Li K-edge XANES fluorescence yield (FLY) of Li|Li2O interface after soaking in EC/DEC solvent or 1 M LiPF6 EC/DEC electrolyte for 20 hours. (c) Nyquist plot of EIS spectra of Li|LiF SEI in the three different electrolytes. (d) C1s and F1s XPS of the surface layer on Li|LiF SEI after soaking in each electrolyte. References: 1. E. Peled, D. Golodnitsky, and G. Ardel, J. Electrochem. Soc., 144 (8), L208-L210 (1997). 2. A. Schechter, D. Aurbach, and H. Cohen Langmuir, 15 (9), 3334-3342 (1999). 3. E. P. Kamphaus, S. Angarita-Gomez, X. P. Qin, M. H. Shao, M. Engelhard, K. T. Mueller, V. Murugesan, and P. B. Balbuena, ACS Appl. Mater. Interfaces, 11 (34), 31467-31476 (2019). 4. E. P. Kamphaus, S. A. Gomez, X. Qin, M. Shao, and P. B. Balbuena, ChemPhysChem, 21 (12), 1310-1317 (2020). 5. D. Wang and L. Zuin, J. Power Sources, 337, 100-109 (2017). 6. R. Guo and B. M. Gallant, Chem. Mater., 32 (13), 5525-5533 (2020). Figure 1

Dust deposition is an important source of phosphorus (P) to many ecosystems. However, there is little evidence of dust-derived P-containing minerals in soils. Here we studied P forms along a well-described climatic gradient on Hawaii, which is also a dust deposition gradient. Soil mineralogy and soil P forms from six sites along the climatic gradient were analyzed with bulk (X-ray diffraction and P K-edge X-ray absorption near edge structure) and microscale (X-ray fluorescence, P K-edge X-ray absorption near edge structure, and Raman) analysis methods. In the wettest soils, apatite grains ranging from 5 to 30 µm in size were co-located at the micro-scale with quartz, a known continental dust indicator suggesting recent atmospheric deposition. In addition to co-location with quartz, further evidence of dust-derived P included backward trajectory modeling indicating that dust particles could be brought to Hawaii from the major global dust-loading areas in central Asia and northern Africa. Although it is not certain whether the individual observed apatite grains were derived from long-distance transport of dust, or from local dust sources such as volcanic ash or windblown fertilizer, these observations offer direct evidence that P-containing minerals have reached surface layers of highly-weathered grassland soils through atmospheric deposition., Geoderma, 381, ISSN:0016-7061, ISSN:1872-6259

Design rules for X-ray phosphors are much less established as compared to their optically stimulated counterparts owing to the absence of a detailed understanding of sensitization mechanisms, activation pathways and recombination channels upon high-energy excitation. Here, we demonstrate a pronounced modulation of the X-ray excited photoluminescence of Tb(3+) centers upon excitation in proximity to the giant resonance of the host Gd(3+) ions in solid-solution Gd1-xTbxOCl nanocrystals prepared by a non-hydrolytic cross-coupling method. The strong suppression of X-ray excited optical luminescence at the giant resonance suggests a change in mechanism from multiple exciton generation to single thermal exciton formation and Auger decay processes. The solid-solution Gd1-xTbxOCl nanocrystals are further topotactically transformed with retention of a nine-coordinated cation environment to solid-solution Gd1-xTbxF3 nanocrystals upon solvothermal treatment with XeF2. The metastable hexagonal phase of GdF3 can be stabilized at room temperature through this topotactic approach and is transformed subsequently to the orthorhombic phase. The fluoride nanocrystals indicate an analogous but blue-shifted modulation of the X-ray excited optical luminescence of the Tb(3+) centers upon X-ray excitation near the giant resonance of the host Gd(3+) ions.

Glasses with the mol% composition of 51.9SiO2/21.2Al2O3/21.2MgO/5.7ZrO2 without and with the addition of 2.5 mol% Y2O3 were melted and subsequently transformed into glass-ceramics via annealing. Both glass-ceramics show strong differences in the microstructure and in the phase composition after crystallization at 950 °C for 5 h and subsequently at 1060 °C for different annealing times. In the glass without Y2O3, the main crystal phase is a quartz solid solution accompanied by the precipitation of ZrO2 and spinel. By contrast, glass-ceramics without the presence of a quartz solid solution were observed after the crystallization of the Y2O3-containing glass, using the same heat treatment. This is confirmed by analytical scanning transmission electron microscopy analysis and X-ray absorption near-edge structure spectroscopy data gathered at the Zr L2-, Y L2,3-, Si K- and Al L-edges. Furthermore, using X-ray absorption spectroscopy the coordination of the respective elements is analysed, and changes of the coordination during crystallization are monitored.

In the present work, we use tunable synchrotron radiation to investigate experimentally and theoretically the dissociation of a chlorinated methane, the CHCl3 molecule, by exciting a chlorine 2p core electron into the LUMO and LUMO + 1 orbitals. The Auger electron energy distribution measured at the Cl 2p3/2 → 10a1 resonance shows narrow lines which energies correspond to the Cl* → Cl+ atomic decay, a clear evidence that the Auger decay takes place after consummation of the dissociation, when the moieties were already far away from each other. Our experimental data are endorsed theoretically by a series of high-level ab initio quantum mechanical calculations. The excited states are calculated to be strongly repulsive in the Franck–Condon region (−dE/dy ∼ 0.15 a.u.) along the C–Cl bond direction.

The development of an expanded palette of X-ray phosphors is a critical imperative for applications in medical imaging, radiation detection, and scientific instrumentation. The rational design of X-ray phosphors has been stymied by the absence of fundamental understanding of activation channels, sensitization mechanisms, and recombination pathways induced upon high-energy excitation of luminescent centers. In this article, we describe the preparation of Eu-doped LaOCl nanocrystals based on the condensation of molecular precursors. The synthetic route allows for control of the oxidation state of the incorporated Eu-atoms based on ligand-induced oxidation or reduction of the Eu-precursors. Nanocrystals exhibiting blue and red X-ray excited optical luminescence are developed by tuning the oxidation state of europium ions incorporated within the LaOCl nanocrystal matrix. Pronounced modulation of the intensity of the optical luminescence is evidenced at and near the giant resonance absorption of the host matrix as a result of distinctly divergent recombination channels. Resonant excitation results in recombination via Auger electron ionization and relaxation of a single electron-hole pair, whereas excitation away from the giant resonance results in thermalization of "hot" electron-hole pairs, while launching cascades of energy transfer, excitation, and radiative recombination events at the Eu-luminescent centers. Mechanistic elucidation and the development of a generalizable synthetic route starting from molecular precursors paves the way to an expanded palette of X-ray phosphors.

To decrease environmental impacts from usage of mineral P fertilizers based on rock phosphate, alternative P fertilizers are urgently necessary but have to be critically evaluated for their characteristics and behaviour or effects in soil. For this reason, bone char (BC) and S-enriched BC (BCplus), original and after one vegetation period in soil, were analysed by wet chemical analyses and XANES spectroscopy. According to X-ray absorption near edge structure (XANES) spectroscopy, both chars were dominated by P bound in hydroxyapatite, which was well reflected by wet chemical P fractionation, where Ca-P was the dominant fraction. Sulfur fractionation of both chars confirmed low percentages of sulfate-S according to XANES analysis but failed to detect elemental S in BCplus. Because S concentrations in BCplus were comparable to that of activated carbon used for biogas desulfurization and sorbed S was dominantly elemental S, BC seems to be well suited for biogas desulfurization. After one year in soil the disappearance of more easily soluble Ca(H2PO4)·2H2O and strongly reduced proportions of sulfates and sulfonates in soil-BCplus compared to BCplus pointed to considerable advantages of BCplus over BC. Taking into consideration the acidic pH of BCplus, the high Ca, P, and S concentrations and the expected microbial induced "in situ digestion" of BC by oxidation of elemental S, it can be concluded that a cascade usage of BC as biogas adsorber and following subsequent usage of BCplus as S/P/Ca/Mg (multi-element) fertilizer could be an alternative to mineral fertilizers based on rock phosphate. The agronomic efficiency and detailed application guidelines must be derived from established and currently running longer-term plot and field experiments.

The electronic state and photoionization spectroscopy of a series of acetate esters: methyl acetate, isopropyl acetate, butyl acetate and pentyl acetate as well as two propionates: methyl propionate and ethyl propionate, have been determined using vacuum-ultraviolet photoelectron spectroscopy. These experimental investigations are complemented by ab initio calculations. The measured first adiabatic and vertical ionization energies were determined as: 10.21 and 10.45 eV for methyl acetate, 9.99 and 10.22 eV for isopropyl acetate, 10.07 and 10.26 eV for butyl acetate, 10.01 and 10.22 eV for pentyl acetate, 10.16 and 10.36 eV for methyl propionate and 9.99 and 10.18 eV for ethyl propionate. For the four smaller esters vibrational transitions were calculated and compared with those identified in the photoelectron spectrum, revealing the most distinctive ones to be a C–O stretch combined with a C[dbnd]O stretch. The ionization energies of methyl and ethyl esters as well as for a series of formates and acetates were compared showing a clear dependence of the value of the ionization energy on the size of the molecule with very little influence of its conformation.

The first comprehensive LiK-edge XANES study of a varied suite of Li-bearing minerals is presented. Drastic changes in the bonding environment for lithium are demonstrated and this can be monitored using the position and intensity of the main LiK-absorption edge. The complex silicates confirm the assignment of the absorption edge to be a convolution of triply degeneratep-like states as previously proposed for simple lithium compounds. The LiK-edge position depends on the electronegativity of the element to which it is bound. The intensity of the first peak varies depending on the existence of a 2pelectron and can be used to evaluate the degree of ionicity of the bond. The presence of a 2pelectron results in a weak first-peak intensity. The maximum intensity of the absorption edge shifts to lower energy with increasing SiO2content for the lithium aluminosilicate minerals. The bond length distortion of the lithium aluminosilicates decreases with increasing SiO2content, thus increased distortion leads to an increase in edge energy which measures lithium's electron affinity.

Biochar application to agricultural land has been proposed as a means for improving phosphorus (P) availability in soil. The purpose of the current study was to understand how pyrolysis temperature affects P speciation in biochar and how this affects availability of P in the amended soil. Biochar was produced at different temperatures from digestate solids. The primary species of P in digestate solids were simple calcium phosphates. However, a high co-occurrence of magnesium (Mg) and P, indicated that struvite or other magnesium phosphates may also be important species. At low temperatures, pyrolysis had little effect on P speciation; however, as the temperature increased above 600 °C, the P gradually became more thermo-dynamically stable in species such as apatite. At very high temperatures above 1000 °C, there were indications of reduced forms of P. Biochar production decreased the immediate availability of P in comparison with the original digestate solids. However, for biochar produced at low temperatures, availability quickly increased to the same levels as in the digestate solids. For biochar produced at higher temperatures, availability remained depressed for much longer. The low availability of P in the biochar produced at high temperatures can probably be explained by the formation of less soluble P species in the biochar. In contrast, the transient decrease of availability of the P in the biochar produced at low temperatures can be explained by mechanisms, such as sorption on biochar, which gradually decreases because of oxidation of the biochar surfaces or changes in pH around the biochar particles. Refereed/Peer-reviewed

The nature of the chemical bonding in an amorphous Si-coated carbon nanotube (Si-CNT) anode, and its evolution upon electrochemical cycling, have been investigated using comprehensive X-ray absorption spectroscopy (XANES) at the Si L- and K-edges, along with the C and O K-edges. The Si nanolayer on the CNT is found to be anchored to the CNT via Si–O–C bonding. This bond weakens upon electrochemical cycling, accompanied by the generation of Li2CO3 on the surface of the Si-CNT. These findings are crucial in designing further improved Si–C composite anodes for lithium ion batteries.

In this study the brominated derivative of pyrimidine, 2-bromopyrimidine, was investigated by photoelectron spectroscopy. Outer valence photoelectron spectra recorded at 21.22, 45 and 100 eV photon energy for this compound are presented. The recorded spectra have a higher resolution than that previously reported in the literature. The bromine 3d and 3p edge photoelectron spectra have also been recorded in a photon impact experiment at 100 and 225 eV. All measurements were performed using Double Toroidal Coincidence Spectrometer showing its potential as a versatile apparatus for spectroscopic studies.

The pyridine molecule has been examined by the means of photoelectron and threshold photoelectron spectroscopies. Ionization energies were determined for both outer and inner valence orbitals and new adiabatic values were also resolved. Vibronic structure associated with several states was assigned mainly to be due to C-C stretches and ring bends. Additionally a Rydberg state converging to 7b2 state was ascribed. The data shown here are in a good agreement with previous results and brings some new insights into the electronic structure of this biologically and astrochemically relevant and important molecule.

X-ray absorption near-edge structure (XANES) spectroscopy has been used to investigate the local structural environments around each of the elements within the haplobasaltic system. The XANES results reveal both, linear changes in Ca, O and Si whereas non-linear changes are also observed for Si as well as Al and Mg. Unexpectedly, both Si and Al spectra show complex edge structure that varies non-linearly across the join. The Si L 2,3 -edge results suggest that the Si environment in An100 is very similar to that in crystalline anorthite whereas the Di100 and diopside spectra show large offsets. The L 3 and L 2 peaks display a linear behavior whereas peak B of the Si L 2,3 spectra displays a non-linear behavior displaying a maximum position at the Di40 and Di100 compositions and decreasing in between. We estimate the Si O bond length from shift in the peak B position which suggests a change in bond length between 1.58 and 1.66 A across the join. The Al K -edge spectra suggests that there is a constant decrease in the inter-tetrahedral angle as Al is added. The local Mg environment displays non-linear changes in intensity and for compositions with An content greater than Di40 it appears that [4] Mg plays an important role whereas [5] Mg is dominant in diopside-rich melts, though octahedral coordinated Mg cannot be ruled out. The oxygen environment appears similar to crystalline anorthite in the haplobasaltic system. Calcium is present in highly distorted sites that are dominantly [7] Ca in anorthite-rich glasses whereas [8] Ca is more important in diopside-rich glasses. These results provide additional independent constraints on the atomic structure of haplobasaltic silicate melts and highlight the need for further investigation into the relationships between network formers, modifiers and the oxygen to which they are bound.

Photoelectron asymmetry parameters (β) of the gerade and ungerade C 2s−1 derived states of ethyne, ethene and ethane as a function of photon energy have been calculated and experimentally measured, to extend the search of interference effects on angular distributions to polyatomic molecules. The calculations cover the electron energy range from 0 to 1100 eV while the experimental measurements cover the electron energy range from 30 to 220 eV. Clear oscillations are interpreted in terms of interference of the photoelectron wave emitted from the two possible C 2s centres, or equivalently from the gerade and ungerade states associated with them. This is a microscopic analog of Young's double-slit experiment. The effect is however quite small and requires very high experimental accuracy to be detected. It is best evidenced in the behaviour of β difference between the two channels. The connection between β trends and structural parameters shows the expected inverse correlation between oscillation period and distance between the carbon atoms, but do not simply parallel the analogous behaviour found in cross sections.

We report considerable chemical and morphological changes of reaction products in binder-free, vertically aligned carbon nanotube (VACNT) electrodes during Li–O2 battery cycling with a 1,2-dimethoxyethane (DME)-based electrolyte. X-ray absorption near edge structure (XANES) of discharged oxygen electrodes shows direct evidence for the formation of Li2CO3-like species at the interface between VACNTs and Li2O2 but not significantly on the Li2O2 surfaces exposed to the electrolyte. Although Li2O2 and Li2CO3-like species were largely removed upon first charge, the oxidation kinetics became increasingly difficult during Li–O2 cycling, which is accompanied by the accumulation of Li2CO3 in the discharged and charged electrodes as evidenced by selected area electron diffraction (SAED) and transmission electron microscopy (TEM). Together, these results indicate that the irreversibility during Li–O2 cycling in DME can be attributed largely to the growth of Li2CO3-like species associated with the reactivity between ...

Bioglass®45S5 was co-sintered with hydroxyapatite at 1200 °C. When small amounts ( Si L2,3-edge spectra of sintered bioceramic compositions indicates that the primary silicates present in these compositions are sodium silicates in the amorphous state. From Si K-edge spectra, it is shown that the silicates are in a similar structural environment in all the sintered bioceramic compositions with 4-fold coordination. Using P L2,3-edge it is clearly shown that there is no evidence of sodium phosphate present in the sintered bioceramic compositions. In the P K-edge spectra, the post-edge shoulder peak at around 2155 eV indicates that this shoulder to be more defined for calcium phosphate compounds with decreasing solubility and increasing thermodynamic stability. This shoulder peak is more noticeable in hydroxyapatite and β-TCP indicating greater stability of the phosphate phase. The only spectra that does not show a noticeable peak is the composition with Na3Ca6(PO4)5 in a silicate matrix indicating that it is more soluble compared to the other compositions.

Autoionization spectra of CH2Cl2 and CD2Cl2 molecules after Cl 2p excitation are studied. The two molecular and atomic Auger transitions are examined and assigned. The contribution of atomic Auger transitions is lower in the deuterated molecule. In addition, to support the presence of the ultrafast dissociation mechanism in the dichloromethane molecule, a series of high-level ab initio quantum mechanical calculations were performed at multiconfigurational self-consistent field (MCSCF) and multireference configuration interaction (MRCI) levels of theory. Minimum energy pathways for the dissociation of the dichloromethane molecule have been calculated by taking into account the spin-orbit splitting between the singlet and triplet transitions in the Cl 2p edge.

Nonaqueous lithium-oxygen batteries have a much superior theoretical gravimetric energy density compared to conventional lithium-ion batteries, and thus could render long-range electric vehicles a reality. A molecular-level understanding of the reversible formation of lithium peroxide in these batteries, the properties of major/minor discharge products, and the stability of the nonaqueous electrolytes is required to achieve successful lithium-oxygen batteries. We demonstrate that the major discharge product formed in the lithium-oxygen cell, lithium peroxide, exhibits a magnetic moment. These results are based on dc-magnetization measurements and a lithium-oxygen cell containing an ether-based electrolyte. The results are unexpected because bulk lithium peroxide has a significant band gap. Density functional calculations predict that superoxide-type surface oxygen groups with unpaired electrons exist on stoichiometric lithium peroxide crystalline surfaces and on nanoparticle surfaces; these computational results are consistent with the magnetic measurement of the discharged lithium peroxide product as well as EPR measurements on commercial lithium peroxide. The presence of superoxide-type surface oxygen groups with spin can play a role in the reversible formation and decomposition of lithium peroxide as well as the reversible formation and decomposition of electrolyte molecules.

Soft X-rays (90-173 eV) from the 3rd generation Canadian Light Source have been used in conjunction with a multi coincidence time and position sensitive detection apparatus to observe the dissociative ionization of OCS. By varying the X-ray energy we can compare dynamics from direct and Auger ionization processes, and access ionization channels which result in two or three body breakup, from 2+ to 4+ ionization states. We make several new observations for the 3+ state such as kinetic energy release limited by photon energy, and using Dalitz plots we can see evidence of timescale effects between the direct and Auger ionization process for the first time. Finally, using Dalitz plots for OCS$^{4+}$ we observe for the first time that breakup involving an O$^{2+}$ ion can only proceed from out of equilibrium nuclear arrangement for S(2p) Auger ionization., 24 pages, 8 figures, 1 table, 77 references

Dissociative photoionization (DPI) of randomly oriented H2 molecules has been studied using linearly polarized synchrotron radiation at selected photon energies of 31, 33, and 35 eV. Large amplitude oscillations in the photoelectron asymmetry parameter β, as a function of electron energy, have been observed. The phase of these β oscillations are in excellent agreement with the results of recent close coupling calculations [Fernández and Martín, New J. Phys. 11, 043020 (2009)]. We show that the oscillations are the signature of interferences between the 1Q1 Σu+1 and 1Q2 Πu1 doubly excited states decaying at different internuclear distances. The oscillations thus provide information about the classical paths followed by the nuclei. The presence of such oscillations is predicted to be a general phenomenon in DPI, We acknowledge NSERC, CLS, and UoW for their support. We thank Mare Nostrum BSC and CCC-UAM for allocation of computer time. Work partially supported by the MICINN Projects No. FIS2010-15127, No. ACI2008-0777, and No. CSD 2007-00010, the European MC-ITN CORINF, and the COST Action CM0702

The photoelectron asymmetry parameter for single photon ionization of H2 between hν = 31 eV and 35 eV has been measured. At these photon energies the doubly excited Q1 and Q2 states are energetically accessible and lie within the Franck-Condon absorption range. For electron energies greater than ~6 eV, the β parameter oscillates strongly, mainly due to interferences in autoionization decay of the Q1 1Σu+ and Q2 1Πu doubly excited states. The experimental results are compared with close coupling calculations.

The distinct optical emission from ZnO materials, nanoneedles and microcrystallites synthesized with different sizes and morphologies by a flow deposition technique, is investigated with X-ray excited optical luminescence (XEOL) and time-resolved Xray excited optical luminescence (TR-XEOL) from a synchrotron light source at the O K and Zn L3,2 edges. The innovative use of XEOL, allowing site-specific chemical information and luminescence information at the same time, is fundamental to provide direct evidence for the different behaviour and the crucial role of bulk and surface defects in the origin of ZnO optical emission, including dynamics. XEOL from highly crystalline ZnO nanoneedles is characterized by a sharp band-gap emission (about 380 nm) and a broad red luminescence (about 680 nm) related to surface defects. Luminescence from ZnO microcrystallites is mostly dominated by green emission (about 510 nm) associated with defects in the core. TR-XEOL experiments show considerably faster decay dynamics in nanoneedles compared to microcrystallites for both band-gap emission and visible luminescence. Herein we make a fundamental step forward correlating for the first time the interplay of size, crystallinity, morphology and excitation energy with luminescence from ZnO materials.

Little is known about P species in agro-industrial byproducts from developing countries, which may be either pollutants or valuable soil amendments. The present study speciated P in dry (COD) and wet (COW) coffee, sisal (SIS), barley malt (BEB) and sugar cane processing (FIC) byproducts, and filter cakes of linseed (LIC) and niger seed (NIC)with sequential fractionation, solution (31)P nuclear magnetic resonance (NMR) spectroscopy, and P K- and L(2,3)-edge X-ray absorption near-edge structure (XANES) spectroscopy. The sequential P fractionation recovered 59% to almost 100% of total P (P(t)), and more than 50% of P(t) was extracted by H(2)O and NaHCO(3) in five out of seven samples. Similarly, the NaOH + EDTA extraction for solution (31)P NMR recovered 48-94% of P(t). The (31)P NMR spectra revealed orthophosphate (6-81%), pyrophosphate (0-10%), and orthophosphate monoesters (6-94%). Orthophosphate predominated in COD, COW, SIS, and FIC, whereas BEB, UC, and NIC were rich in orthophosphate monoesters. The concentrations of P(i), and P(o) determined in the sequential and NaOH + EDTA extractions and (31)P NMR spectra were strongly and positively correlated (r = 0.88-1.00). Furthermore, the P K- and L(2,3)-edge XANES confirmed the H(2)SO(4)--P(i) detected in the sequential fractionation by unequivocal identification of Ca--P phases in a few samples. The results indicate that the combined use of all four analytical methods is crucial for comprehensive P speciation in environmental samples and the application of these byproducts to soil.