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1.
The L spectra of the elements 14 ≤ Z ≤ 22 were reinvestigated. Because of the limited energy resolution of the multilayer reflectors neither Ll and Lη nor Lα and Lβ1 could be resolved. Nevertheless, the line Lβ3,4 = L1M2,3 was observed for all elements Z ≥ 16, but not for 14Si and 15P. Exceptions to this are 18Ar and 22Ti. For 18Ar no suitable sample is available. In the case of 22Ti the Lβ3,4 line is overlapped by the O Kα line which has its origin in the oxide surface layer of the Ti standard. In all cases the Lβ3,4 line was observed near to the expected position which was determined by means of the known electron binding energies. The L spectrum of 21Sc was studied for various energies of the incident electrons, E0. These measurements show that Lβ3,4 is much more strongly absorbed in Sc than Ll,η and Lα,β1. From these measurements approximate mass absorption coefficients (m.a.c.) were deduced. The relative net peak height I(Lβ3,4)/I(Lα,β1) decreases from 15% at E0 = 4 keV to 4% at E0 = 20 keV, whereas I(Ll,η)/I(Lα,β1) remains nearly constant at 90%. The peak to background ratio of Ll,η is greater than that of Lα,β1.  相似文献   

2.
The intensities of the Fe L lines/bands l = L3M1, η = L2M1, α1,2 = L3M4,5, β1 = L2M4, and β3,4 = L1M2,3 were measured for pure Fe and Fe3O4 using a TAP crystal as the dispersing element. The energy of the exciting electrons, E0, was varied in the range 5 ≤ E0 ≤ 25 keV. For pure Fe the following results were obtained. The net peak height ratio Ll/Lα remains relatively constant with varying E0 at approximately 14%. The E0 dependence of Lη is similar to that of Ll, although Lη is less intense than Ll by a factor of 7. Lβ1/Lα decreases from 20% for E0 = 5 keV to about 5% for 25 keV. Lβ3,4 behaves like Lβ1 but is weaker by a factor of 15. For Fe3O4 a much weaker intensity of Lα was observed which can be partially explained by its stronger absorption. Again, the E0 dependence of Ll and Lη is similar with Ll/Lα = 19% and Lη/Lα = 4%. Lβ1 and Lβ3,4 show a comparable E0 dependence. Lβ1/Lα decreases from 50% for E0 = 5 keV to 34% for 25 keV. Lβ3,4 is weaker than Lβ1 by a factor of about 25. The observed E0 dependence of the different lines was used to estimate a set of mass absorption coefficients. Our value for Lα in Fe agrees well with other data which were deduced from variable E0 measurements but differs considerably from data given by Heinrich and Henke.  相似文献   

3.
The effect of chemical composition and external magnetic field on the / intensity ratio and line-shape of some chromium compounds have been investigated using the energy dispersive X-ray fluorescence analysis. The measurements were done using the 22.69 keV photon energy and energy dispersive Si(Li) semiconductor detector. The samples are located in the external magnetic field of intensities 0.6 T and 1.2 T. The experimental results obtained for B = 0 are compared with other experimental and theoretical values. The results have shown that the X-ray / intensity ratios, chemical shifts, asymmetry indices and full widths at half maximum (FWHM) values can change when irradiation is conducted in a magnetic field.  相似文献   

4.
Chemical shifts and full widths at half maximum intensity (FWHM) of Kα and Kβ1,3 X-ray emission lines and differences of full widths at half maximum intensity (ΔFHWM) using metallic element as reference for these emission lines were measured for oxygen compounds of elements in the range 22≤Z≤29 with a Wavelength-Dispersive X-Ray Fluorescence Spectrometer (WDXRF). It was also found larger chemical shifts and FWHM for Kβ1,3 lines than those of Kα ones. It should be noted that the magnitude of the chemical shifts increases with increasing number of ligand atom.  相似文献   

5.
A reinvestigation was undertaken in order to obtain reliable data of the relative intensities of the L spectra for the elements 24 ≤ Z ≤ 33. A TAP crystal with a periodicity of 25.757 ? was used as the dispersing element. With this crystal one is able to resolve the lines/bands Ll = L3M1, Lη = L2M1, Lα1,2 = L3M4,5, Lβ1 = L2M4, and Lβ3,4 = L1M2,3. Among the investigated elements 33As is the only one for which the energy of the lines Lα1,2 and Lβ1 is below the L3 absorption edge. For all the other elements the lines Ll, Lη, and Lα1,2 are below the L3 edge, whereas Lβ1 and Lβ3,4 are above this edge. This difference leads to effects of differential absorption, where the absorption is stronger for decreasing line energy. For the net peak height ratio β1/α we obtained results which are of the same order of magnitude as those given by White and Johnson (W&J) in their popular tables. But for l/α and β3,41 our results show an atomic number dependence which is completely different from those given by W&J.  相似文献   

6.
 β-sialon ceramics sintered with yttria additives have been studied with the use of an electron probe X-ray analysis (EPMA). Sialon ceramics were prepared from a carbothermally derived β-sialon powder and then sintered in a nitrogen atmosphere with yttria admixture. The above process was followed by annealing in flowing nitrogen. Scanning electron microscope (SEM) observations have shown that the sintered material contains a glassy phase (Y-Si-Al-O-N) on the grain boundaries. X-ray diffraction (XRD) after annealing in nitrogen revealed the presence of a considerable amount of yttrium aluminium garnet (YAG). The higher voltage of 30 kV was used in order to excite the yttrium Kα radiation (14.96 keV) at an appropriate overvoltage ratio because in some phases of the material, the disappearance of the yttrium Lα line has been observed during EPMA examination at an accelerating voltage of 15 kV in energy dispersive spectra (EDS). The intensity of the yttrium Kα line was sufficiently high, while the Y Lα line was not seen in the ED spectrum. Because the position of the yttrium Lα line (1.922 keV) is very close to the Si (K) absorption edge (1.84 keV), the strong absorption at this edge is probably responsible for the effect. This result should be considered as a serious warning in the case of EPMA (EDS) studies on compounds or mixtures suspected to contain both silicon and yttrium, because at electrons energies lower than 15 keV, the presence of yttrium in materials can go unnoticed. In wavelength dispersive spectra (WDS) obtained at 15 keV the intensity of the yttrium Lα line was also very low but measurable.  相似文献   

7.
The fluorescence and photochemical properties of crystalline β-diketonatoboron difluorides (DBD) RCOCHCOR1BF2 were studied. These compounds are characterized by relatively high photochemical stability. The introduction of electron-donating groups into the aromatic α-substituent of the chelate ring increases and the introduction of electron-withdrawing groups decreases the fluorescence intensity of DBD. Anisoylbenzoylmethanotoboron difluoride was found to exhibit the highest fluorescence intensity. The substituents were shown to influence the relative arrangement of singlet and triplet ηπ* and ππ* levels and luminescence properties of compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1030–1033, June, 2000.  相似文献   

8.
The K/K X-ray intensity ratios were measured for pure Cr, Mn, Co and Cu belonging to the 3 d shell as well as in their compounds, to look for the influence of the chemical environment on the fluorescence yield ratios. The vacancies in the K shell created by 59.5 keV -rays from an241Am source and the X-rays were measured using a Ge(Li) detector. A steady increase of the K/K intensity ratio was observed with increasing oxidation. The present results agree with previously published experimental data.  相似文献   

9.
Expressions for calculating the cation vacancy contents of MnZn ferrites from thermogravimetric curves are presented together with some experimental data. In a single-phase MnZn ferrite synthesized by conventional ceramic procedures, the O2 evolution accompanying ferrite formation follows the formal equation. Mn2+ σα Znσβ Fe3+ 2σ(1–γ) [V ]σ/4(1–2γ) O4 =σ'/σ Mn2+ σ(α–2ϕ) Znσβ Fe2+ 2σθ Mn3+ 2σϕ Fe3+ 2σ(1–γ–θ) [V ]σ/4(1–2γ–3ϕ) O4 +σ'φ/2O2 (g) where α and β denote the MnO and ZnO mole fractions in the primary mixture γ=α+β, θ and ϕ depend on the quantities of Fe2+ and Mn3+ formed, respectively, φ=θ–ϕ and σ'/σ is a function of the former parameters. Even though the relative amounts of Fe2+ /Fe3+ and Mn2+ /Mn3+ remain uncertain, the vacancy content [V ] of the ferrite can be determined because it depends on φ alone, which is related to the change in mass of the sample as the synthesis takes place through the equation φ=(1.5–γ) μβO2 (1–m f /m i ) Here, m i and m f are the masses of the sample before and after O2 evolution, μB is the formula mass of the ferrite and μO2 is the O2 molar mass. Practically vacancy-free single-phase MnZn ferrite samples were obtained by sintering in air at 1250°C and cooling in pure N2 . This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
Kβ/Kα X-ray intensity ratios of some K and Ca compounds were studied. The samples were excited by 5.96 keV γ-rays emitted from (50 mCi 55Fe filtered annular) radioisotope source and characteristic K X-ray from the samples were measured by a Si(Li) detector, with a resolution of 0.16 keV at 5.9 keV. The experimental values were compared with the calculated theoretical values for K and Ca.  相似文献   

11.
Existing experimental data on positional selectivity in electrophilic substitution reactions of π-excessive heterocycles are classified. These data are discussed basing on the results of the authors' quantum-chemical calculations [RHF/6-31G(d), MP2/6-31G(d), and B3LYP/6-31G(d)] of the σ-complexes formed during attack of electrophiles such as H+, Me+, Me3Si+, Br+, NO2 +, MeCO+, and SO3 at the α- and β-positions of furan, thiophene, selenophene, pyrrole and its N-substituted derivatives, N-R-pyrroles (R = Me, t-Bu, SiMe3, Si(i-Pr)3, C6H4(p-NO2), SO2Ph, CHO, CO2Me), and the corresponding α- and β-substituted electrophilic substitution products. The differences in energies of the α-and β-isomers of the σ-complexes characterize the preferred direction of electrophilic attack, while the differences in the energies of the isomeric products make it possible to assess the energy preference of one of them. Analysis of the obtained data demonstrates the effects of the studied heterocycles' structure, the nature of the electrophile, and the thermal and steric factors on the positional selectivity (α/β ratio) in electrophilic substitution reactions of π-excessive five-membered heteroaromatic compounds.  相似文献   

12.
Experimental, relative intensities for the components of L X-rays have been collected from the literature, and the atomic number dependence has been found for the Lβ/Lα, Lγ/Lα, L/Lα and Lη/Lα ratios. Among the L X-ray components Lα is predominant if Z<40, Lβ/Lα≈1.0 if 50≤Z≤90, Lγ/Lβ≈1.0 if 94≤Z≤100, and Lγ/Lα>1.0 if Z≈100.  相似文献   

13.
Unlike theE HOMO energies, the first vertical ionization potentials (I 1) of monosubstituted ethylenes dependen not only on both the inductive and resonance effects but also on the polarizability of the substituents, which can be characterized by the σα parameters. The σ R + , σ p + , and σα parameters for 12 silicon-, germanium-, and tin-containing groups were determined using the equations relating theI 1 values and the σI, σ R + , σ p + and σα parameters of the substituents in the molecules of organic compounds. The conjugation of organoelemental substituents with the double bond is stronger than that with benzene ring; the σ R + parameters in the ethylene and benzene series are related by a linear dependence. Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 9, pp. 1626–1631, September, 1997.  相似文献   

14.
Guest-host interactions of haloperidol (Halo) with β-cyclodextrin (β-CD) have been investigated using several techniques including phase solubility diagrams (PSD), proton nuclear magnetic resonance (1H-NMR), X-ray powder diffractometry (XRPD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and molecular mechanical modeling (MM+). From an analysis of the PSDs, both protonated and neutral Halo (pK a=8.5) form soluble 1:1 and 1:2 Halo/β-CD complexes, while the insoluble complex has 1:2 (Halo:β-CD) stoichiometry (BS-type PSD). Ionization of Halo reduces its tendency to complex with β-CD, where the protonated species at pH=4.6 and 6.0 have K 11 values of 100 L⋅mol−1 and 298 L⋅mol−1, respectively, compared with 2000 L⋅mol−1 for neutral species at pH=10.6. The hydrophobic character of Halo was found to provide 32% of the driving force for complex stability, whereas other factors including specific interactions contribute −15 kJ⋅mol−1. 1H-NMR and MM+ studies indicate the formation of isomeric 1:1 and 1:2 complexes, where the chlorophenyl, flurophenyl, piperidine and butanone moieties become included into separate β-CD cavities. The dominant driving force for complexation is evidently van der Waals with very little electrostatic contribution. PSD, 1H-NMR, XRPD, DSC and SEM studies indicate the formation of inclusion complexes in solution and in the solid state.  相似文献   

15.
The cross sections for the 118Sn (n, α)115Cd, 120Sn (n, α)117gCd and 120Sn (n, α)117mCd reactions have been measured in the neutron energy range of 13.5–14.6 MeV using the activation technique and a coaxial HPGe γ-ray detector. The fast neutrons were produced by the T (d, n) 4He reaction. The neutron energies in the measurements were determined by cross section ratios for 93Nb(n,2n)92mNb and 90Zr(n, 2n)89m+gZr reactions. The results of present work were discussed and compared with theoretical calculation data, measurement results found in the literature and with the comprehensive evaluation data in ENDF/B-VII.0, CENDL-3.1, JENDL-4.0 libraries.  相似文献   

16.
Several host–guest inclusion compounds of eugenol as a guest molecule and cyclodextrins (α-,β-,γ-CD) and heptakis (2,6-di-O-methyl)-β-cyclodextrin (DMβ-CD) as hosts were investigated in the solid state and in aqueous solution. The one-to-one solid inclusion compounds of eugenol and β-CD or γ-CD were prepared, but those of eugenol with α- or DMβ-CD were not obtained under the same condition. However, the UV-visible absorption spectroscopy data indicated that the liquid guest could form a 1:1 inclusion compound with all four hosts respectively in aqueous solution. The two solid inclusion compounds were characterized by powder X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). The association constants (K), calculated from the modified Benesi–Hidebrand equation, of eugenol with α-, β-, γ- and DMβ-CD is 4.95 × 104, 3.96 × 105, 1.47 × 105 and 9.33 × 104 mol−1 dm3, respectively.  相似文献   

17.
Chances for estimating the FeO/Fe2O3tot ratio in rocks by the K and L series of X-ray fluorescence spectra are studied. The errors in the determination of FeO/Fe2O3tot by the intensity ratio of the Kβ2,5/Kβ1,3 and Lβ/Lα1,2 lines are compared. The relative standard deviation of determining FeO using a set of 49 standard samples of eruptive rocks varies in the range 5–16%, depending on the ratio FeO/Fe2O3tot and the concentration of FeO. The better precision is attainable for a ratio above 0.45 at a FeO concentration in the range 5–15%. For samples of andesites and basalts, the relative standard deviation is better than 4%, for rocks of the granite family it is 23% at FeO concentrations below 3%. For samples of metamorphic and sedimentary rocks, the error of FeO determination is higher than that for the eruptive ones. For samples with the ratio FeO/Fe/Fe2O3tot < 0.25, the deviation may exceed 30 rel %. In contrast to chemical analysis, the X-ray fluorescence method appears advantageous in time and cost of sample preparation and can be used for routine analysis in geochemical research.  相似文献   

18.
The interaction of two benzocycloheptanes namely, pizotifen (Pizo) and ketotifen (Keto), with cyclodextrins (CDs: α-, β-, γ-, and HP-β-CDs) has been investigated by several techniques including phase solubility, X-ray powder diffractometry, 1H-nuclear magnetic resonance and molecular mechanical modeling. The effects of CD type, pH, ionic strength and temperature on complex stability were also explored. The complex formation constant (K 11) values for the Pizo/CD system follows the decreasing order β-CD > γ-CD > HP-β-CD > α-CD. However, for the Keto/CD system it follows the decreasing order γ-CD > β-CD > HP-β-CD > α-CD. The tendency of Pizo and Keto to complex with β-CD is driven to the extent of 70% by the hydrophobic effect. Complex formation of Keto and Pizo was substantially driven by entropy (>100 J⋅mol−1⋅K−1) but slightly retarded by enthalpy (3–8 kJ⋅mol−1). 1H-NMR and MM+ studies indicate multimodal inclusion of the methylpiperadine, thiophene and phenyl moieties into the β-CD cavity.  相似文献   

19.
The study aimed to determine the chemical effects on the K and L X-ray intensity ratios and the K and L X-ray production cross sections for gold compounds. The K shell fluorescence yields and L shell average yields were also investigated. The samples were excited by 59.5 keV γ-rays from an 241Am annular radioactive source and 123.6 keV γ-rays from a 57Co annular radioactive source. K and L X-rays emitted from samples were counted by an Ultra-LEGe detector with a resolution of 0.150 keV at 5.9 keV. The experimental values were compared with theoretical, the semi-empirical and other experimental values.  相似文献   

20.
Hemoglobin (Hb) is a tetrameric noncovalent complex consisting of two α- and two β-globin chains each associated with a heme group. Its exact assembly pathway is a matter of debate. Disorders of hemoglobin are the most common inherited disorders and subsequently the molecule has been extensively studied. This work attempts to further elucidate the structural properties of the hemoglobin tetramer and its components. Gas-phase conformations of hemoglobin tetramers and their constituents were investigated by means of traveling-wave ion mobility mass spectrometry. Sickle (HbS) and normal (HbA) hemoglobin molecules were analyzed to determine whether conformational differences in their quaternary structure could be observed. Rotationally averaged collision cross sections were estimated for tetramer, dimer, apo-, and holo-monomers with reference to a protein standard with known cross sections. Estimates of cross section obtained for the tetramers were compared to values calculated from X-ray crystallographic structures. HbS was consistently estimated to have a larger cross section than that of HbA, comparable with values obtained from X-ray crystallographic structures. Nontetrameric species observed included apo- and holo- forms of α- and β-monomers and heterodimers; α- and β-monomers in both apo- and holo- forms were found to have similar cross sections, suggesting they maintain a similar fold in the gas phase in both the presence and the absence of heme. Heme-deficient dimer, observed in the spectrum when analyzing commercially prepared Hb, was not observed when analyzing fresh blood. This implies that holo-α-apo-β is not an essential intermediate within the Hb assembly pathway, as previously proposed.  相似文献   

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