Mn Kβ Research Articles

Mn K-edge XANES and Kbeta XES studies of two Mn-oxo binuclear complexes: investigation of three different oxidation states relevant to the oxygen-evolving complex of photosystem II.

Two structurally homologous Mn compounds in different oxidation states were studied to investigate the relative influence of oxidation state and ligand environment on Mn K-edge X-ray absorption near-edge structure (XANES) and Mn Kbeta X-ray emission spectroscopy (Kbeta XES). The two manganese compounds are the di-mu-oxo compound [L'2Mn(III)O2Mn(IV)L'2](ClO4)3, where L' is 1,10-phenanthroline (Cooper, S. R.; Calvin, M. J. Am. Chem. Soc. 1977, 99, 6623-6630) and the linear mono-mu-oxo compound [LMn(III)OMn(III)L](ClO4)2, where L- is the monoanionic N,N-bis(2-pyridylmethyl)-N'-salicylidene-1,2-diaminoethane ligand (Horner, O.; Anxolabéhère-Mallart, E.; Charlot, M. F.; Tchertanov, L.; Guilhem, J.; Mattioli, T. A.; Boussac, A.; Girerd, J.-J. Inorg. Chem. 1999, 38, 1222-1232). Preparative bulk electrolysis in acetonitrile was used to obtain higher oxidation states of the compounds: the Mn(IV)Mn(IV) species for the di-mu-oxo compound and the Mn(III)Mn(IV) and Mn(IV)Mn(IV) species for the mono-mu-oxo compound. IR, UV/vis, EPR, and EXAFS spectra were used to determine the purity and integrity of the various sample solutions. The Mn K-edge XANES spectra shift to higher energy upon oxidation when the ligand environment remains similar. However, shifts in energy are also observed when only the ligand environment is altered. This is achieved by comparing the di-mu-oxo and linear mono-mu-oxo Mn-Mn moieties in equivalent oxidation states, which represent major structural changes. The magnitude of an energy shift due to major changes in ligand environment can be as large as that of an oxidation-state change. Therefore, care must be exercised when correlating the Mn K-edge energies to manganese oxidation states without taking into account the nature of the ligand environment and the overall structure of the compound. In contrast to Mn K-edge XANES, Kbeta XES spectra show less dependence on ligand environment. The Kbeta1,3 peak energies are comparable for the di-mu-oxo and mono-mu-oxo compounds in equivalent oxidation states. The energy shifts observed due to oxidation are also similar for the two different compounds. The study of the different behavior of the XANES pre-edge and main-edge features in conjunction with Kbeta XES provides significant information about the oxidation state and character of the ligand environment of manganese atoms.

Valence electronic structure of Mn in undoped and doped lanthanum manganites from relative K X-ray intensity studies

Relative K X-ray intensities of Mn in Mn, MnO 2, LaMnO 3 and La 0.7B 0.3MnO 3 (B = Ca, Sr and Ce) systems have been measured following excitation by 59.54 keV γ-rays from a 200 mCi 241Am point-source. The measured results for the compounds deviate significantly from the results of pure Mn. Comparison of the experimental data with the multi-configuration Dirac–Fock (MCDF) effective atomic model calculations indicates reasonable agreement with the predictions of ionic model for the doped manganites except that the electron-doped La 0.7Ce 0.3MnO 3 and hole-doped La 0.7Ca 0.3MnO 3 compounds show some small deviations. The results of MnO 2 and LaMnO 3 deviate considerably from the predictions of the ionic model. Our measured Kβ/Kα ratio of Mn in La 0.7Ca 0.3MnO 3 cannot be explained as a linear superposition of Kβ/Kα ratios of Mn for the end members which is in contrast to the recent proposal by Tyson et al. from their Mn Kβ spectra.

Mn K-edge XANES spectra of manganites measured by Kbeta emission.

The electronic state of Mn atoms in mixed valence manganites has been studied by means of X-ray absorption spectroscopy at the Mn K-edge. Higher resolution than in conventional measurements has been achieved by measuring the Mn Kbeta fluorescence line. We have found a unique resonance at the edge in the XANES spectra of intermediate composition RE1-xCa(x)MnO3 samples. The features of these XANES spectra do not depend on small changes in the local structure around the Mn atom. However, the spectra of the intermediate composition samples can not be reproduced by a linear combination of REMnO3 and CaMnO3 spectra. Accordingly, the electronic state of Mn atoms in these compounds can not be considered as a mixture of Mn3+ and Mn4+ pure states.

Spin State Analysis of Epitaxial Mn Compound Films Using High Resolution X-Ray Fluorescence

We have determined the spin states of Mn compounds by using Mn Kα1 peak widths and relative Mn Kβ′ peak intensities of high-resolution X-ray fluorescence (HRXRF) spectra. The number of unpaired 3d electrons for molecular beam epitaxy (MBE)-grown MnAs films was calculated to be 2.8, which is in good agreement with that determined from the experimental value of magnetic moments. We think this technique is very promising for microbeam analysis and in situ analysis of spin states during crystal growth.

Chemical dependence of interatomic X-ray transition energies and intensities – a study of Mn Kβ″ and Kβ 2, 5 spectra

A study of ligand (N, O, F) 2s to metal (Mn) 1s `interatomic' or `crossover' X-ray transitions is reported. We show that the energy of the Kβ″ feature is related to the ligand 2s binding energy and can be used to identify the type of ligand. For oxygen-ligated Mn compounds, the strength of the Kβ″ transition decreases exponentially with increasing Mn–O distance. This can be used to predict distances to ∼0.1 Å. The Kβ 2, 5 energy shows shifts of ∼1 eV per unit oxidation state. Kβ″ and Kβ 2, 5 transitions are a promising tool for structural characterization of transition-metal complexes.

Using Quantitative Iteration to Correct for Pathological Spectral Interferences

Abstract A number of problematic analytical situations are known to exist in electron probe microanalysis (EPMA) where characteristic x-ray spectral overlaps are not only severe, but are also of the “self-interfering” or “cascade” variety. The “self-interfering” variety is exemplified by the innocuous Ba Lα ↔ Ti Kα; to the fearsome Pb Lα↔As Kα binaries, while “cascade” interferences are often seen among the transition metal series as in Ti Kβ → V Kα - V Kα Cr Kα or as seen with a secondary fluorescence interference effect as in Ni K ⇒ Fe Kα - Fe Kβ → Co Kα. Unlike simple interferences of the type Mn Kβ → Fe Kα, both of these types of spectral interferences are often quite troublesome for the analyst to correct for, especially for Si(Li) and Ge energy dispersive spectrometers (EDS) where the analytical peaks are often so overlapped as to prevent graphical deconvolution, and even for the higher resolution wavelength dispersive spectrometers (WDS) along with the yet to come bolometric energy dispersive detectors (based on projected resolution), the task can still be formidable.

Determination of L 3 subshell fluorescence yield of Nd with a Si(Li) detector

The L 3 subshell fluorescence yield of Nd has been measured using the photoionisation by Mn Kβ X-rays (6.492 keV) emitted from a 55Fe radioisotope annular source. The present results have been found in good agreement with the theoretical values.

Theory of X-Ray Photoemission and X-Ray Emission Spectra in Mn Compounds

We analyze theoretically X-ray photoemission spectra (XPS) from Mn 2 p and 3 p core-levels in Mn compounds and Mn Kβ X-ray emission spectra (XES) by means of an MX 6 cluster model. In the calculation of 3 p -XPS and Kβ-XES, we take into account the effect of the term-dependent lifetime of the Mn 3 p core-hole due to the 3 p -3 d 3 d super-Coster-Kroning decay. The Kβ-XES is treated as a coherent second-order optical process, and the excitation spectra of Kβ-XES, which reflect the spin-dependent Mn 1 s absorption, are also calculated. It is shown that the effect of the core-hole potential plays an essential role in the excitation spectra of MnF 2 and MnO. The importance of the term-dependent lifetime of the final states is also pointed out.

Chemical effects in X‐ray fluorescence analysis

AbstractEnergy‐dispersive x‐ray fluorescence (EDXRF) analysis of manganese compounds has been carried out. A significant dependence of the Mn Kα and Kβ x‐ray yields per incident photon and of the Kβ/Kα ratio on the valence state of manganese in these compounds was observed. The measurement of attenuation coefficients of these compounds, which are used in absorption corrections in XRF analysis, also showed similar effects. These results imply that the EDXRF elemental analysis results have inherent inaccuracies of the order of 10%.

Contribution de la spectrometrie X à l'étude du manganèse dans les oxydes mixtes de structure spinelle: Analyse du spectre Mn Kβ et du seuil d'absorption K

Chemical shifts of Kβ 1,3 and Kβ 5 emission bands and X-ray absorption spectra near the K edge have been measured in several manganese spinel oxides with the metal in the formal oxidation states +2, +3, and +4. The position of line Mn Kβ 1,3 is determined mainly by the valence of manganese. The relative intensity of Kβ′ satellite with respect to the Kβ 1,3 line gives qualitative information about the presence of Mn(II) in mixed oxides. Mn(IV) oxides are characterized by a small chemical shift of the Kβ 5 band unlike Mn(II) and Mn(III) compounds. The first high resolution XANES spectra for these materials were performed at the DCI storage ring at LURE (Orsay, France). The chemical shifts ΔE ( K absorption discontinuty) and ΔE max (main peak) are correlated with the oxidation state of metal. Spectra of Mn 3+ and Mn 4+ ions in the octahedral environment are characterized by the splitting of 1 s → 3 d transitions (2 eV). In mixed oxides, the first Mn(II) 1 s → 4 s-4 p transition is observed as a peak (or shoulder) located at 7 eV above the 1 s → 3 d transition. The study of the X-ray absorption fine structure in the near edge region can be used for qualitative solid-state analysis of mixed oxides such as NiMn 2O 4 or CuMn 2O 4.