Phosphorus L2,3‐edge XANES: overview of reference compounds

Synchrotron‐based X‐ray absorption near‐edge structure (XANES) spectroscopy is becoming an increasingly used tool for the element speciation in complex samples. For phosphorus (P) almost all XANES measurements have been carried out at the K‐edge. The small number of distinctive features at the P K‐edge makes in some cases the identification of different P forms difficult or impossible. As indicated by a few previous studies, the P L_2,3‐edge spectra were richer in spectral features than those of the P K‐edge. However, experimentally consistent spectra of a wide range of reference compounds have not been published so far. In this study a library of spectral features is presented for a number of mineral P, organic P and P‐bearing minerals for fingerprinting identification. Furthermore, the effect of radiation damage is shown for three compounds and measures are proposed to reduce it. The spectra library provided lays a basis for the identification of individual P forms in samples of unknown composition for a variety of scientific areas.     

Fully relativistic calculations of the L2,3-edge XANES spectra for vanadium oxides

Fully relativistic multielectron method based on the numerical solution of the Dirac equation was used to calculate the L_2,3-edge X-ray absorption near edge structure (XANES) spectra of VO₂, V₂O₃, and V₂O₅ crystals. The key-points of the method are: i) usage of the molecular orbitals (MO); ii) absence of any fitting parameters; iii) wide area of application: to any ion in any symmetry; iv) possibility of numerical analysis of the MO composition. The calculated spectra are in a satisfactory agreement with experimental data available in the literature, including the absolute values of the transitions energy, the shape of the absorption bands, and polarization dependence. The assignment of the absorption bands in terms of the electronic configurations was done. The structure of the absorption bands is attributed to the splitting of the vanadium p- and d-orbitals; the magnitude of this splitting is estimated from the spectra. Covalency effects were considered for all hosts; it was shown that the contribution of the oxygen wave functions increases with increasing the vanadium oxidation state. Dependence of the relative positions of the vanadium 3d and oxygen 2p levels and energies of the “ligand–metal” charge transfer transitions on the vanadium oxidation state was analysed.     

Ru L2,3 XANES theoretical simulation with DFT: A test of the core-hole treatment

Density functional theory (DFT)-based relativistic calculations were performed to model the Ru L-edge X-ray absorption near edge structure (XANES) spectra of the hexaammineruthenium complex [Ru(NH₃)₆]³⁺ and “blue dimer” water oxidation catalyst, cis,cis- [(bpy)₂(H₂O)Ru^IIIORu^III(OH₂)(bpy)₂]⁴⁺ (bpy is 2,2-bipyridine). Two computational approaches were compared: simulations without the core-hole and by modeling of the core-hole within the Z+1 approximation. Good agreement between calculated and experimental XANES spectra is achieved without including the core-hole. Simulations with algorithms beyond the Z+1 approximation were only possible in a framework of the scalar relativistic treatment. Time-dependent DFT (TD-DFT) was used to compute the Ru L-edge spectrum for [Ru(NH₃)₆]³⁺ model compound. Three different core-hole treatments were compared in a real-space full multiple scattering XANES modeling within the Green function formalism (implemented in the FEFF9.5 package) for the [Ru(Mebimpy)(bpm)(H₂O)]²⁺ complex. The latter approaches worked well in cases where spin–orbit treatment of relativistic effects is not required.     

Density functional theory simulation of the L<Subscript>2,3</Subscript> XANES spectra

A method for the theoretical simulation of X-ray absorption near edge structure (XANES) spectra at the Ru L_2,3 edges has been developed using relativistic density functional theory (DFT) calculations. The effect of the parameters of DFT calculations on the shape of theoretical curves has been comparatively analyzed for XANES spectra of a water oxidation catalyst and hexaammineruthenium complexes. Recommendations for the choice of the best parameters ensuring good agreement with the experimental data, including the most correct exchange-correlation potential, have been made.     

Level crossing investigations in the 4d 2 D 5/2,3/2-states of the A1 I-spectrum

The level crossing technique with combined electric and magnetic fields was used to investigate the hyperfine structure, the Stark effect, and the mean life time of the 4d ² D _5/2,3/2-states in the Al I-spectrum. The experimental values are discussed in connection with interconfiguration mixing.     

Electrical resistivity and band gap of marcasite (FeS2)

For a natural crystal of marcasite, an energy gap of 0.34 eV and an acceptor level at 0.052 eV are determined from temperature-dependent (53–370 K) electrical resistivity measurements. Magnetic susceptibilities and dielectric constants of marcasite and pyrite are compared in view of the large difference in their energy gaps.     

Comparison of pyrite thin films obtained from Fe and natural pyrite powder

Pyrite thin films have been prepared by two different procedures: by sulphurating thermally evaporated iron films and by flash evaporating natural FeS₂ powder. The structural, morphological, electrical and optical properties of both kinds of films are compared and the influence of the sulphuration conditions studied. The films directly evaporated from pyrite powder show higher absorption coefficients and better photoactive response than those prepared from iron. Sulphuration of the films is always required in order to improve the crystallinity and decrease the density of sulphur vacancies generated by these methods.     

XANES and EXAFS study of some metal-metalloid glasses

XANES and EXAFS techniques are proving very popular in the study of local environment in disordered systems. Results of such studies in a large number of metal (Fe, Co, Ni, etc)-metalloid (B, Si, C, etc) glasses are reported. Experiments were done with synchrotron radiation as well as an x-ray tube. The values of bond lengths and co-ordination numbers computed from one-electron single scattering Fourier transform method turn out substantially smaller. The values of bondlength determined from the other EXAFS calculation method and the multiple-scattering computation scheme show good agreement. Importance of choice of suitable reference materials for analysis of data is emphasized. The experimental work was done at EXAFS 5.1 Station at Daresbury Laboratory, U.K.     

Exploration on laminar flame propagation of 3,3-dimethyl-1-butene, 2,3-dimethyl-1-butene and 2,3-dimethyl-2-butene

Laminar flame propagation of branched hexene isomers/air mixtures including 3,3-dimethyl-1-butene (NEC₆D3), 2,3-dimethyl-1-butene (XC₆D1) and 2,3-dimethyl-2-butene (XC₆D2) was investigated using a high-pressure constant-volume cylindrical combustion vessel at 1–10 atm, 373 K and equivalence ratios of 0.7–1.5. The measured laminar burning velocity (LBV) decreases in the order of NEC₆D3, XC₆D1 and XC₆D2, which indicates distinct fuel molecular structure effects. A kinetic model was constructed and examined using the new experimental data. Modeling analyses were performed to reveal fuel-specific flame chemistry of branched hexene isomers. In the NEC₆D3 and XC₆D1 flames, the allylic CC bond dissociation reaction plays the most crucial role in fuel decomposition under rich conditions, while its dominance is replaced by H-abstraction reactions under lean conditions. The H-abstraction and H-assisted isomerization reactions are concluded to govern fuel consumption in the XC₆D2 flame under all investigated conditions. Both C₀C₃ reactions and fuel-specific reactions are found to be influential to the laminar flame propagation of the three branched hexene isomers. Fuel molecular structure effects were analyzed with special attentions on key intermediates distributions and fuel-specific reactions in all flames. Due to the formation selectivity of key intermediates such as 2-methyl-1,3-butadiene and 2,3-dimethyl-1,3-butadiene, the production of reactive radicals especially H follows the order of NEC₆D3 > XC₆D1 > XC₆D2, which results in the same order of fuel reactivities and LBVs.     

A complex first-principles study of the L2,3-edge XANES spectra and crystal field effects for divalent 3d ions in cubic ZnS

A detailed first-principles analysis of the L_2,3 X-ray absorption near edge structure (XANES) spectra, crystal field strength 10Dq, covalent effects and molecular orbitals (MO) position for all divalent 3d ions from Sc²⁺ to Cu²⁺ in cubic ZnS is performed in the present paper. The calculations were done in the framework of the first-principles fully relativistic discrete variational multi-electron (DVME) based on numerical solution of the Dirac equation with the local density approximation. As a result of the performed calculations, the L_2,3 XANES spectra for all considered ions were calculated and assigned in terms of the electron configurations involved into the absorption transitions; fairly good agreement with available experimental data for Ti²⁺, Mn²⁺, Fe²⁺, Co²⁺ and Ni²⁺ is demonstrated. Experimental XANES spectra for Sc²⁺, V²⁺, Cr²⁺, Cu²⁺ not reported previously were also calculated for the sake of completeness of the present study to enable a systematic analysis of all calculated results for the whole series considered. It was shown that the L₃ and L₂ bands shift to the higher energies on increasing a 3d ion atomic number. In addition, the separation between the L₃ and L₂ bands, the crystal field strength 10Dq and mixture between the 3d ion and sulfur wave functions increase along the considered series, from Sc²⁺ to Cu²⁺. On the other hand, all orbitals of the 3d ions systematically lower down in the same direction. The above formulated trends were confirmed by the experimental data on the crystal field splittings and nephelauxetic effect.     

Vibrational Analysis of 2,3-Dimethyl-1-Butene

Infrared and Raman spectra were obtained for 2,3-dimethyl-1-butene. The spectra showed the presence of two stable conformations. Vibrational assignments were made for both conformers with the aid of normal coordinate calculations. Values for the force constants that were obtained will be used in the future as the initial values for other substituted 1-alkenes, such as 2-isopropyl-3-methyl-1-butene.     

Luminescence,vibrational and XANES studies of AlN nanomaterials

The paper reports comparative studies on synthesized aluminium nitride nanotubes, nanoparticles and commercially available micron-sized AlN powder using different spectroscopic techniques: cathodoluminescence measurements (CL), X-ray absorption near edge spectroscopy (XANES) and Fourier-transform infrared spectroscopy (FTIR). Crucial distinctions in CL spectra are observed for nano- and microsized aluminium nitride powders; systematic shift of the IR absorption maximum has been detected for nanostructured aluminium nitride as compared to commercial samples. Through XANES experiments on Al K-edge structural differences between nano- and bulk AlN are revealed, intensity of features in absorption spectra has been found to be a function of wurtzite and zincblend phases amount in nanostructured samples.     

The calculation of X-ray emission L2,3 bands of Ge,GaAs and ZnSe

Profiles and integral intensities of the L_2,3 emission bands are predicted in the series of semiconductors Ge, GaAs and ZnSe. Partial densities of s and d-symmetry valence states are computed.