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.     

A computational NICS and 13C NMR characterization of the substitution patterns of C70−2x(BN)x fullerenes (x=1–25)

A density functional study has been performed to investigate the electronic and magnetic properties of BN substituted fullerenes C_70?2x(BN)_x (x=1, 2, 3, 6, 9, 12, 15, 17, 19, 21, 23 and 25) based on the NMR parameters and NICS index. The calculated ¹³C chemical shielding (CS) tensors are found to be perturbed at the first and second neighbors of the doped atoms while the other distant carbon atoms not to be influenced significantly. ¹³C Chemical shifts (δ_iso) of the second neighbors of nitrogen and boron are significantly shifted to upfield and downfield (the second neighboring effects), respectively. Besides, chemical shifts are also affected by the curvature of the corresponding sites; for example, the perturbed sites at the caps yield smaller absolute values of chemical shifts than those located at the equator. Nucleus independent chemical shifts (NICS) at the cage centers of heterofullerenes (from ?25.29 to ?8.80) demonstrate that all the substituted species are aromatic, but less than C₇₀ (?27.29). The predicted NICS values may be useful for identification of the heterofullerenes through their endohedral ³He NMR chemical shifts.     

Calculation of Chemical Shifts of X-Ray-Emission Spectra of Niobium in Niobium(V) Oxides Relative to Metal

Chemical shifts of the K_α1 and K_β1 lines of X-ray-emission spectra of niobium in oxides (Nb₂O₅)_n, n = 1–4, relative to metal Nb have been calculated. Stoichiometric clusters (Nb2O5)n the electronic structure of which was calculated using accurate relativistic pseudopotentials and two-component version of the density functional theory are considered as prototypes for modeling different crystal forms of niobium(V) oxide. The chemical shifts were calculated using the method based on using the property of approximate proportionality of valence spinors in the core region of the heavy atom [11]. Corrections to values of chemical shifts have been determined with allowance for deviations from the abovementioned proportionality. Rapid convergence of results with respect to the size of the niobium oxide cluster has been demonstrated.     

X-ray K-absorption edge shifts due to chemical combination

A possible explanation is given of the chemical shifts of x-ray K-absorption edges of metals when they undergo a chemical combination and form compounds. It is proposed that when a metal forms a compound its Fermi edge changes. It explains the numerical order as well as the nature of the chemical shifts. A fairly good agreement between the calculated and observed values has been obtained.     

Solving the differential Yakubovsky equations for p 3He scattering by the cluster-reduction method

The cluster-reduction method has been used to solve numerically the differential equations for the s-wave Yakubovsky components in the nppp system. Proton scattering on a ³He nucleus has been considered for energies below the three-body threshold in the singlet and triplet spin states of the system. Nucleon-nucleon interaction has been simulated by the MT I–III potential, and the Coulomb interaction between the protons has been taken into account. Effective equations that describe the relative motion of clusters have been derived. The low-energy behavior of phase shifts has been analyzed. The values of ¹ A=8.2 fm and ³ A=7.7 fm have been obtained for, respectively, the singlet and triplet scattering lengths. The calculated phase shifts agree well with experimental data.     

NMR chemical shifts in cuprous salts: The magnetic moment of Cu

An extensive study has been made of chemical shifts of the ⁶³Cu resonance in a number of cuprous salts. The observed trend in chemical shifts for the cuprous halides is in disagreement with theoretical ionicity estimates of either Pauling or Phillips. This trend has been explained by taking into account the relative importance of π bonding for the different halides. On the basis of the present data, CuBr is the most suitable Knight shift reference compound. The measurements indicate μ = 2.2206 nm for ⁶³Cu and μ = 2.3791 nm for ⁶³Cu for reference moment, without diamagnetic correction.     

Chemical shifts of the copper and cobalt K absorption discontinuities in some ternary compounds

The present paper reports the chemical shifts of the K X-ray absorption discontinuities of copper and cobalt in ternary compounds. Relationships between the chemical shifts ΔE of the discontinuities and the various bond parameters (C, E_g, and f_i) calculated from Levine's theory have been established. It is found that distinctly separate curves can be drawn for different valencies (Cu¹⁺ and Cu²⁺, Co²⁺ and Co³⁺) of the absorbing ions. Making use of Levine's method for calculating bond charges, the effective charges q on the absorbing ions have been evaluated. The dependence of ΔE on q has been confirmed.     

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.     

Hyperfine structure in the 6p5d configuration and isotope shifts in transitions between the 6s5d and the 6p5d configurations in Ba I

High-resolution laser fluorescence spectroscopy, using a single-mode dye laser acting on a collimated atomic beam, has been performed to determine the hyperfine-structure (hfs) constants in six states of the 6p 5d configuration of¹³⁵Ba and¹³⁷Ba. Isotope shifts (IS) for eleven transitions between the 6s 5d and the 6p 5d configurations have also been measured. From an analysis of the energy levels, intermediate angular wavefunctions have been deduced. The wavefunctions are used to evaluate experimental hyperfine parameters from the experimental hfs constants. The parameters are, for the magnetic-dipole interaction compared with theoretical values, and for the electricquadrupole interaction used to estimate the nuclear quadrupole moments for the odd isotopes. The IS in the measured transitions are analysed using a King-plot, with the first resonance line in Ba II as the reference. Specific mass and field shifts are evaluated for the measured transitions. The field shifts have been used to determine the change in mean-square radius between the natural abundant Ba-isotopes.     

Some regularities within the Stark widths and shifts of resonance ion lines from Li to Ca

A periodic dependence of the Stark widths and shifts of resonance lines, for singly- and doubly-ionized elements, has been found on nuclear charge number Z. These periodicities were found for Griem's theoretical values of the Stark parameters of resonance lines of some singly charged ions from Li to Ca; for other singly- and doubly- charged ions, this parameter was calculated from Griem's semiempirical formula. The dependence of the Stark parameters of the resonance lines on atomic polarizability X has been determined and used to estimate Stark widths and shifts for other singly-charged ions. These values are compared with estimates derived form Griem's semiempirical formula for the Gaunt factor g = 0.2.     

平衡电负性与烷烃核磁共振碳谱位移

定义了烷烃分子中碳原子的平衡电负性(AEE),用平衡电负性和Nⁱ_H(em=0, α, β, γ)和N^j_C(j=α, β, γ)结构信息参数研究了烷烃的¹³C NMR化学位移模型.结果表明,烷烃¹³C NMR化学位移(CS)可用下式来定量描述：
CS=-1736.776+755.118AEE+5.2539N⁰_H+1.8837N^β_H-0.2066N^γH
用上式估算了99个碳原子的化学位移,标准差为0.9861ppm,平均绝对误差0.78ppm,预测值与实验值十分吻合.     

Volumetric, acoustic and spectroscopic studies for binary mixtures of ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) with alkoxyalkanols at T = (288.15 to 318.15) K

Densities and speeds of sound have been measured for the binary mixtures of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF₆] with ethylene glycol monoethyl ether (EGMEE), diethylene glycol monoethyl ether (Di-EGMEE), triethylene glycol monoethyl ether (Tri-EGMEE) over the whole composition range at atmospheric pressure. Experimental densities have been used to estimate excess molar volumes, V^E. Changes in isentropic compressibility, Δκ_s have been estimated by using experimental speed of sound and density values. Excess properties were fitted to the Redlich-Kister polynomial equation to obtain the binary coefficients and the standard errors. The molecular scale interactions between ionic liquid and alkoxyalkanols have been investigated through ¹H NMR spectroscopy. NMR chemical shifts for hydroxyl group of alkoxyalkanols and their deviations show hydrogen bonding interactions of varying strengths between ionic liquid and alkoxyalkanol in their binary mixtures.     

Systematic discrepancy of theoretical predictions of NMR chemical shifts for chlorinated aromatic carbons using the GIAO DFT method

Theoretical calculations of carbon-13 NMR chemical shifts using the gauge including atomic orbitals (GIAO) DFT approach with a moderately large set of basis functions usually yield quite satisfactory results. In the case of chlorinated aromatic carbons, however, abnormally large differences between experimental and calculated values have been noticed. This discrepancy has been proven not to be caused by improper referencing, or the basis set effect, and probably not by neglect of vibrational corrections. One of the possible sources of the chlorine effect could be the impact of relativistic phenomena on electrons moving about the chlorine nucleus. The second, probably more important factor is the influence of electron correlations, ignored in Hartree–Fock SCF and only partially included in DFT calculations. Surprisingly, however, the observed divergence has been significantly larger for DFT than for Hartree–Fock results. In the latter case the observed divergence between theoretical and experimental ¹³C NMR chemical shifts of chlorine-bonded carbons is systematic but rather small (3.4–4.4ppm).     

Photoemission studies of a clean and oxidized niobium-aluminum alloy using synchrotron radiation

The alloy formation and oxidation of a Nb-rich Nb-Al alloy has been studied using core level photoemission in combination with synchroton radiation as a surface sensitive probe. Exactly the same chemical shifts were observed from both the Nb-Al alloy and an Al-evaporated Nb surface, indicating similar structural arrangements. It is found that the oxidation rate of Nb in these structures is drastically decreased in comparison to either pure Nb metal or Nb₃Sn. Two stages in the oxidation of the Nb-Al alloy are clearly distinguished by chemical shifts of the Al_2p, Nb_4p and O_2p levels.     

Optical isotope shifts in neodymium

Isotope shifts have been measured in Nd II from which the shifts between pure configurations 4f ⁴ 6s and 4f ⁴ 5d can be determined. The specific mass shift for such a “transition” was estimated to be + 3 mK for a change of two neutrons. By comparison with electronic X-ray isotope shifts the following values were obtained for the change in the nuclear charge distributionδ〈r ²〉 [fm²]: (142, 144) 0.277; (144, 146) 0.257; (146, 148) 0.286; (148, 150) 0.381; (142, 143) 0.130; (144, 145) 0.111. Field shifts in several optical transitions have been compared with values of ¦ψ(0)¦² obtained from Hartree-Fock wave functions; agreement is good. Other specific mass shifts have been estimated 4f ⁴ 6s? 4f ⁴ 6p, ?1 mK; 4f ⁴ 6s? 4f ³ 5d ², ?30 mK. These values are in good agreement with calculated values of ?1.1 and ?30.6 mK.     

R-matrix formulation and phase shifts for n-He and p-He scattering for energies up to 20 MeV

An R-matrix formulation for a single level with a background approximation has been used to analyse n-⁴He and p-⁴He elastic scattering data below the inelastic thresholds near 22 MeV. For every partial wave a single level and a distant pole contribution constant with energy has been employed. Simple relations between neutron and proton scattering parameters have been sought to possibly derive more dependable values for neutron phase shifts and analysing powers at energies where little experimental information exists. The R-matrix parameters corresponding to ⁵He and ⁵Li ground and 1st excited states, phase shifts up to 20 MeV and neutron analysing powers up to 15 MeV are given in tabular form and are compared to results of earlier analyses. Differences in n-⁴He phase shifts are discussed and shown to be due to a scarcity of accurate neutron scattering data above 11 MeV. Some typical fits to n-⁴He scattering data are shown.     

NMR chemical shifts of129Xe dissolved in liquid ethers, secondary amines, and alkyl sulfides

Xenon-129 NMR spectra have been measured for solutions containing Xe dissolved in a variety of linear aliphatic ethers, secondary amines, and alkyl sulfides. The chemical shifts obtained from these data are found to be linearly related to the composition of the solvent molecules expressed as volume fraction of the constituent methyl groups, methylene groups, and the respective oxygen, nitrogen, and sulfur atoms. These results support a model used previously to interpret chemical shifts measured for¹²⁹Xe dissolved in a variety ofn-alkanes and their terminally substituted derivatives. This model treats dispersion force contributions to the chemical shift as resulting from pairwise additive interactions between each dissolved Xe atom and the individual constituent groups of each solvent molecule.     

Absorption edge shift in ZnO thin films at high carrier densities

The optical absorption edge has been measured as a function of carrier concentration for thin films of zinc oxide prepared by organometallic chemical vapour deposition and reactive R.F. magnetron sputtering. Large shifts of the absorption edge have been observed which are only a function of the carrier concentration. Below n = 3 × 10¹⁹ cm^-3 the shifts are well described by the Burstein-Moss model. For carrier concentrations between 3–5 ×10¹⁹cm^-3, the shift decreases very rapidly, finally increasing again with further increases in the carrier density. These effects are consistent with a merging of the donor band with the conduction band following a semiconductor-metal transition.     

Interpretation of apparent chemical shifts in XP spectra from oxide—GaP interfaces

The cause of the apparent chemical shifts (ACS's) of XPS peaks between oxide and substrate GaP has been studied. The ACS's for Ga 3d, P 2p and GaLMM change significantly depending on the conditions of oxidation. The changes in the ACS's are considered in terms of not only the chemical structure of the oxide, but also other possible causes, such as charging effects, electric dipole moment, extra-atomic relaxation energy, Fermi-level pinning position, etc. The change of the Fermi-level position at the surface of substrate GaP is revealed to be a dominant factor causing the changes in the ACS's.