X-ray K-absorption edge of niobium in some of its niobates

The position and extended fine structure of X-ray K-absorption edge of niobium in its various niobates has been investigated using 400-mm bent crystal (mica, 100 planes) spectrograph. The shift of the K-absorption edge of niobium in its various niobates is related to the size of the next nearest cation; large the size, smaller the shift of the absorption edge towards higher energy side.     

X-ray K-absorption studies of molybdenum sulphide,selenides and tellurides

X-ray K-absorption studies of molybdenum sulphide, selenides and tellurides have been carried out using 400-mm bent crystal (mica) spectrograph. K-absorption edge of molybdenum in its selenides, tellurides and sulphide lies on the higher energy side with respect to that in the molybdenum metal; the shift in higher selenide and telluride, namely MoSe₂ and MoTe₂ being smaller than that in the lower selenide and telluride, Mo₃Se₄ and Mo₃Te₄ respectively. On the other hand selenium K-absorption edge changes from low energy side in Mo₃Se₄ to higher energy side in MoSe₂ with respect to that in the selenium metal.     

K-absorption spectral investigations on some dimeric copper(II) carboxylate complexes

The X-ray K-absorption edge position and the extended fine structure of copper in some copper(II) carboxylate complexes involving metal-metal exchange interaction have been investigated using a 40 cm bentcrystal spectrograph. It has been found that the edge position in these complexes shifts towards the higher energy side as the pK_a value of the corresponding acids increases. Sharp and narrow main peaks have been observed in all these complexes except the monomeric complex, copper(II) trichloroacetate. Estimates of metal-ligand average bond distances have also been made.     

X-ray K-absorption studies ofsome ruthenium compounds

X-ray K-absorption studies of ruthenium in ruthenium metal,RuO₂, K₂(RuCl₆) and K₄[Ru(CN)₆]: 3H₂O have been carried out using 400 mm bent crystal (mica) spectrograph. K-absorption edge of ruthenium in these compounds lies on the higher energy side with respect to that in the ruthenium metal; the divalent K₄[Ru(CN)₆]·3H₂O gives the shift in the range of tetravalent compounds RuO₂ and K₂[RuCl₆]. This discrepancy has been explained on the basis of molecular orbital picture.     

Determination of ionicity in zinc chalcogenides by X-ray absorption study

K-absorption edges and associated extended fine structure is recorded for zinc and zinc chalcogenides using a 40 cm, automatic scanning, Cauchois type X-ray spectrometer. It is observed that there is a correlation between the positive X-ray K-absorption edge chemical shift and Phillips' electronegativity difference C for zinc chalcogenides. The bond lengths for these compounds are determined using Lytle, Chivate et al. and Levy's methods. These bond lengths are observed to tally well with X-ray crystallographic data. The covalent energy gaps in Phillips' theory are determined using bond lengths determined by Chivate et al.'s method. Values of ionicities are obtained from X-ray spectroscopically determined values of C and E_h and are compared with Phillips' spectroscopically determined ionicities for zinc chalcogenides. It is shown that X-ray spectroscopically determined values of ionicities for these compounds show a more correct chemical trend.     

X-ray K-absorption edge shifts in transition elements

It has been found that a striking correlation exists between the plasman energy in solids and the chemical shifts of the X-ray K-absorption edges of the transition elements Cr, Cu, Ni, Co, Zn and their compounds. Fairly good agreement between the calculated values of the plasmon energies and the observed values of the chemical shifts has been obtained.     

X-ray absorption spectral investigations on mixed-valence copper complexes of penicillamine and cysteamine

The X-ray K-absorption spectra of copper in some of its complexes involving ligands like penicillamine (known detoxicating agent for heavy metal poisoning) and cysteamine (a known radiation protector) have been investigated using a 40 cm curved crystal spectograph. These complexes are described in the literature as being mixed-valence [1, 2]. The copper-penicillamine complex shows two distinct edges, K₁ and K₂, indicating mixed-valency in the complex. The cysteamine complexes do not show any splitting of the edges. In one of the cysteamine complexes, which is said to involve molecular oxygen, the magnitudes of shifts of the main edge and principal absorption maximum fall close to copper (II) compounds whereas in the other complex, these shifts are in the range of copper (I) compounds. The probable reasons for the observed deviations have been discussed.     

Determination of ionicity in zinc phosphide and zinc arsenide by X-ray absorption method

K-absorption edges and associated extended fine structure is recorded using a 40 cm, automatic scanning X-ray spectrometer for zinc in zinc phosphide and zinc arsenide. The bond lengths for these compounds are determined using Lytle and Chivate et al.'s method. The convalent energy gaps in Phillips' theory are evaluated on the basis of Levine's extension to Phillips theory for these complex compounds. The X-ray absorption edge shifts for zinc in both of these compounds and the ionic energy gap determined using Levine's method are in good agreement. Hence, ionicities for these compounds were determined. The ionicity value for zinc phosphide comes out to be 0.17 and for zinc arsenide 0.16.     

X-ray spectroscopic investigation of some spinel structures

K-absorption edges of cations in the manganites of magnesium, nickel, copper, zinc and cadmium and ferrite samples of composition, Mg_1?x Mn_x Fe₂O₄ (x=0, 0·25, 0·50, 0·75, 1·0), have been recorded employing a 40 cm curved mica crystal spectrograph of transmission type. It is observed that the absorption edges for the specimen shift towards the shorter wavelength side of the metal edge position. Shifts of both the absorption edges and the main absorptoin peaks for ferrites and manganites have been compared with compounds in which the oxidation state of the cation is well known. It is found that the manganese ions in these ferrites and manganites exist in valence states two and three respectively while iron in the ferrite samples is present in oxidation state three. An attempt has been made to interpret the observed absorption edge features in the light of neutron and X-ray diffraction studies on the same ferrite and manganite samples.     

Chemical shifts of X-ray K or L-absorption edges of solids

A very simple method for the calculation of the chemical shifts of X-ray K or L-absorption edges of metals when they undergo chemical combination, is proposed. It has been found that the major contribution to the chemical shifts comes from the change in the Fermi energy when the metal forms a compound. Fairly good agreement in the nature and the numerical magnitude of the chemical shifts between the observed and calculated values has been obtained.     

X-ray absorption near edge structure in some Mn compounds

The shapes of the manganese K-absorption edge in the compounds MnSO₄H₂O, MnF₂, MnCO₃, MnO and MnS have been studied using a Cauchois type X-ray spectrograph. Three peaks A, B and C observed in the main edges have been assigned the electronic transitions ls → 3d, ls → 4s and ls → 4p respectively. The transitions have been explained on the basis of the Z + 1 analogy. It has also been shown that the 3d → 4s and 4s → 4p orbital separations depend on the partial charge of an ion in its compound.     

Effective ionic charges and chemical bonding in GaSe and GaTe from chemical shifts of X-ray K absorption discontinuities

Chemical shifts in the X-ray K absorption edges of gallium and selenium in some of their binary compounds have been studied using a bent crystal X-ray spectrograph. The shifts are found to be governed by the effective charges on the absorbing ions, which have been calculated using Suchet's theory. For the compounds GaSe and GaTe, however, the effective ionic charges cannot be calculated for want of data on the divalent radius of gallium. The plot of the chemical shift, δE, against the theoretically calculated effective ionic charge, q, has been used to determine the charges on the ions in these two compounds. The effective charges, thus determined, provide information about the chemical bonding in the compounds.     

The nature of a selective peak in the BK-absorption edge spectrum and the electronic energy band structure of the crystal 3C BN0.99

A new interpretation of the nature of the resonance in the quantum-yield K spectra of boron in the crystal 3C BN is proposed. This interpretation is based on calculation of the electronic energy band structure of the nonstoichiometric boron nitride 3C BN_0.99, which is carried out by the local coherent potential method in the multiple-scattering approximation. The tops of the valence band and of the XANES range of nonstoichiometric and perfect crystals of boron nitride are compared with the x-ray photoelectron spectrum of 3C BN and the BK-absorption edge spectrum. The electronic states near the BK-absorption edge are modeled and discussed for the relaxed and metastable states caused by the formation of vacancies in the nitrogen sublattice.     

Potassium and titaniumKX-ray de-excitation induced by ion bombardment

KX-ray de-excitation spectra have been produced for K and Ti by proton, alpha and oxygen ion beam bombardment. These spectra have been measured with a crystal spectrometer of resolution (FWHM) of 10 and 13 ev for theKα_1,2 line in K and Ti respectively. The additional lines not found in the normal X-ray spectra are attributed to multiple inner shell ionization. The energy shifts and relative intensities of these lines are compared to theoretical predictions.     

Co-ordination stoichiometry,edge shift and effective nuclear charge: A novel correlation

Summary K-absorption edge shifts of the absorbing atom in its complexes have been correlated with the effective nuclear charge on the central metal ion, overall electronegativity difference between the nearest neighbours in the complexes and the ionic radius of the central metal ion; a linear correlation has been observed among them, the data subjected to the method of least squares indicated that the correlation is genuine.

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Riassunto Gli slittamenti dell’orlo di assorbimentoK dell’atomo assorbente nei suoi complessi sono stati correlati con la carica nucleare efficacie sullo ione metallico centrale, con la differenza di elettronegatività generale tra vicini prossimi nei complessi e col raggio ionico dello ione metallico centrale; una correlazione lineare è stata osservata tra loro, i dati soggetti al metodo dei minimi quadranti hanno indicato che la correlazione è genuina.

     

Determination of effective atomic charge,extra-atomic relaxation and madelung energy in chemical compounds on the basis of X-ray photoelectron and auger transition energies

A new method is proposed for the determination of effective atomic charge, extra-atomic relaxation, and Madelung energy in chemical compounds, based on the experimentally measured energies of X-ray photoelectron and Auger transitions. The method has been applied to solid compounds of the elements from Na to Cl, and to a number of free sulfur-, phosphorus-, silicon-, and chlorine-containing molecules. The experimental energies are represented as consisting of two parts. The first part is determined by the ionization energy of a free ion with a given effective charge, and includes the intra-atomic relaxation. The second part is determined by the Madelung energy and the extra-atomic relaxation. The first contribution is calculated by using the Hartree-Fock method. The effective atomic charges required have been found from the shifts of Kα-lines in the X-ray spectra. The extra-atomic relaxations are obtained as the differences between experimental and theoretical Auger parameters, and the values calculated are the additive functions of ligands of the atom studied. The increments of the additive scheme correlate with the ligand refractions. The effective charges, extra-atomic relaxation energies and Madelung potentials obtained from ESCA and AES data agree well with both calculated and direct experimental results.     

KLL auger and core level (1s and 2p) photoelectron shifts in a series of gaseous sulfur compounds

Core (1s and 2p) X-ray photoelectron shifts and KLL (¹D₂) Auger shifts for 22 sulfur compounds have been measured. The values have been correlated by means of atomic charge plus remote potential or central atom potential models. Either approach is equally effective tor binding energy correlations. The relaxation corrected and transition state models are in general superior to ground state models. Auger shift predictions are however poor in all cases. Absolute total static relaxation and extra-atomic relaxation values have been assessed by using the Auger parameter of Lang and Williams and relativistic atomic calculations for the free atom and its ions. These extra-atomic relaxation components are not additive but rather obey an average contribution behavior. The relaxation shift values have been compared with those obtained from the original Auger parameter (α) of Wagner. The correlation of 1s and 2p binding energies suggested a revised relationship for the Wagner Auger parameter and an equivalent simple form of the Lang and Williams parameter which can be used with satisfactory results when only the usual experimental binding energy (2p) is available in conjunction with the Auger shift.     

Spectroscopic fingerprints of valence and spin states in manganese oxides and fluorides

We performed a systematic study of soft X-ray absorption spectroscopy in various manganese oxides and fluorides. Both Mn L-edges and ligand (O and F) K-edges are presented and compared with each other. Despite the distinct crystal structure and covalent/ionic nature in different systems, the Mn-L spectra fingerprint the Mn valence and spin states through spectral lineshape and energy position consistently and evidently. The clear O- and F-K pre-edge features in our high resolution spectra enable a quantitative definition of the molecular orbital diagram with different Mn valence. In addition, while the binding energy difference of the O-1s core electrons leads to a small shift of the O-K leading edges between trivalent and quadrivalent manganese oxides, a significant edge shift, with an order of magnitude larger in energy, was found between divalent and trivalent compounds, which is attributed to the spin exchange stabilization of half-filled 3d system. This shift is much enhanced in the ionic fluoride system. This work provides the spectroscopic foundation for further studies of complicated Mn compounds.     

X-ray absorption study of effective coordination charges of iron in crystals and amorphous solids

The positions of the K-absorption edges of iron are recorded for five crystals: Fe_0.885O, Fe_0.905O, Fe₃O₄, Fe₂O₃ and Fe metal, and for two amorphous solids: oxide glass ([Na₂O · 2SiO₂]_0.8 [Fe₂O₃]_0.2) and metallic glass (Fe₃₆Cr₃₂Ni₁₄P₁₂B₆). It is observed that there is a correlation between the positive X-ray K- absorption edge chemical shift and the effective coordination charge. The ionic state of iron in oxide glass is identical to the ferric iron in Fe₂O₃ as shown by the same positions of iron K-absorption edges in this glass and Fe₂O₃. The K-edge of the metallic glass appears 6.5 eV higher than that of the pure iron edge, which suggests that the bonding of iron in metallic glass is different from the pure iron metal.     

DasK-Röntgenemissionsspektrum des Chlors in freien Molekülen

TheKα andKβ spectra of chlorine in free molecules were studied using a special fluorescence X-ray tube and a high resolving curved crystal spectrograph with photoelectric registration. It was found that the wavelength shifts of ClKα₁ obtained for various gaseous compounds do not show the regularities observed with solid compounds of other 3rd period elements. — TheKβ spectrum consists of discrete lines the most intense of which result from transitions of the lonely pair electrons of the chlorine atoms. The spectra of HCl, Cl₂ and CH₃Cl can be explained using optical and betaspectroscopical data and MO calculations. The general structure of ClKβ of organic compounds seems to be determined by the hybridisation type of the carbon atoms bound to the chlorine atoms. Evidence is found for a contribution of molecular vibrational energy to the energies of the X-ray transitions.