Charge transfer and chemical shifts in zincblende compounds

Charge transfer and chemical shifts for some zincblende compounds are calculated using the electrostatic model of Shevchik et al.^3,4. A comparison of the results obtained from Phillips ionicities, the bond orbital model of Harrison and ionicities, recently proposed⁹, is performed. The predictions from the latter scale are in sufficient agreement with the experimental data. Additionally chemical shifts for some zincblende compounds are predicted, for which experimental data are not available.     

Charge transfer from chemical shifts at (110) surfaces of III–V compound semiconductors

Surface charge-transfer are calculated from surface core-level shifts determined by Eastman et al. and Taniguchi et al. by using soft X-ray photoemission spectroscopy. A simple electrostatic model which was first applied by Shevchik et al. to the analysis of bulk data is adapted for surfaces of compound semiconductors. The charge transferred from cations to anions is found to be the same in the bulk and at the (110) surfaces of GaP, GaAs, GaSb, and InSb.     

Photoelectron-spectroscopic determination of lattice self-potentials in lanthanide trifluorides

Since the photoelectron spectroscopically measured binding energies probe the potentials at the cation and anion sites separately in solids, they should be a direct determination of the lattice self-potentials at these sites through comparisons with the respective ionization potentials of the gaseous ions. In a study of the photoionization of the 1s orbital electrons on the fluoride ion and of the outer 5p or 4f orbital electrons on the cations of the lanthanide trifluorides, it is found that the so determined lattice self-potentials at the anion sites deviate from those calculated from the electrostatic interactions in the point charge model by an amount which can be explained in terms of ionicity. For the cations, however, the deviations for all except La³⁺ and perhaps Gd³⁺ exceed those expected for ionicity in the point charge model by as much as 2.3 eV in the case of the maximum at Pr³⁺. These deviations are discussed in terms of crystal field interactions, covalency, polarization, and complication caused by final state relaxation during photoionization.     

Ionicity scale and piezoelectricity of crystals with zincblende- and wurtzite-type structure

We have tried to determine the ionicity of crystals with a dynamical effective ionic charge defined by the observed TO-LO splitting. We find excellent agreement between our results and the ionicity scale derived by Phillips from band gap theory. We confirm that the observed piezoelectric constants can be well accounted for on the basis of the Born lattice-dynamical treatment by adding the concept of charge transfer, and we have made an estimate of the latter.     

Chemical shift of the Ga and As Kα1,2 and Kβ1,3 X-ray emission lines

By means of a double crystal spectrometer and a computer the chemical shifts of the Ga Kα_1,2, As Kα_1,2 and Kβ_1,3 lines were determined with high accuracy. An interpretation of the results obtained with a free ion model and a calculation according to the Hartree method shows agreement of the values calculated for the effective atomic charges with those based on chemical experience, and also the presence of a charge transfer from the A atom to the B atom in A^IIIB^V compounds. The existence of binding charges is one of the reasons for the fact that |q_A| ≠ |q_B|. The interpretation of the Kβ_1,3 and Lα shifts shows the limitations of the free ion model.     

Solvatochromic and Preferential Solvation Studies on Schiff Base 1,4-Bis(((2-Methylthio)Phenylimino)Methyl) Benzene in Binary Liquid Mixtures

The solvatochromic behavior of the 1,4-bis(((2-methylthio) phenylimino)methyl) benzene [BMTPMB] in single solvents and binary mixtures were investigated. Fluorescence spectra show the dual emission due to twisted intramolecular charge transfer (TICT) state. The preferential solvation parameters: local mole fraction, X₂^L, solvation index δ_s2, exchange constant K₁₂ were calculated for the binary mixtures, ACN+MEOH, DMSO+CCl₄ and CCl₄+1,2 DCE. The dipole moment ratios between ground and excited states were deduced using the solvatochromic shifts of absorption and fluorescence spectra as a function of dielectric constant (ε), refractive index (n) and it was found to be 1.25.     

Isomer shifts of sp impurities in metallic hosts

Isomer shifts for¹¹⁹Sn and¹²¹Sb impurities in different metallic hosts are compared. In the frame of the Miedema and van der Woude model three contributions to the isomer shifts due to the charge transfer, electron density mismatch and volume adjustment are calculated.     

离子性指数、立体效应参数与膦类化合物31P NMR δP的关系

利用离子性指数(INI)和立体效应参数（α、β、γ）对100个膦化合物中磷原子进行结构表征，并与其核磁共振磷谱(³¹P NMR)建立了优良的定量构谱相关(QSSR)模型：δ_P=-163.695 3-1.003 1INI+34.632 7α+13.892 9β-3.331 7γ. 建模的计算值、留一法(Leave-One-Out, LOO)交互校验(Cross-Validation, CV)预测值的复相关系数(R)分别为0.976 5和0.973 9. 所建模型不仅在一定程度上阐明了膦类化合物³¹P NMR谱化学位移与其分子结构信息之间的关系，同时也提供了一种从理论上计算膦类化合物³¹P NMR谱化学位移的新方法，并对深入了解膦类化合物结构与性能的关系及解析、预测其³¹P NMR谱提供了一定的理论依据.     

13C NMR Chemical Shift of β-Alkoxyvinylketones: II. Empirical Substituent Effects in β-Aryl-β-Methoxyvinyltrihalomethylketones

Evaluation by empirically derived equations for the substituent effect (α,β,γ,δ) on the ¹³C NMR chemical shifts for C-1, C-2, C-3 and C-4 in β-aryl-β-methoxyvinylhalomethylketones 1a-g to 2a-g [R³C(O)-CH=C(Ar)-OMe, where R³ = CCl₃, CF₃ and Ar = p-YC₆H₄ (Y = H, Me, MeO, F, Cl, Br, NO₂)], taking as reference the β-ethoxyvinyltrichloromethylketone (3), is reported. From the calculated values for the α,β,γ,δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1,2. The ¹³C chemical shifts of the C-1, C-2, C-3, C-4 of these compounds, can be estimated with good to rasoable precision: 84% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm. The Y-Effects on C-3 and C-4 are compared with carbon charge densities (qr).     

Electron structure of interstitial hydrogen inα-Zr

The impurity-induced charge density in jellium is calculated by solving the Schr?dinger equation self-consistently. The resulting phase shifts have been used to estimate the value of residual resistivity for dilute Zr-H system, which comes out to be 0.50 μΘ cm/at.%. An alternative form of one-parameter-screened Coulomb potential, which is more suitable than the customary Thomas-Fermi potential, is suggested. The calculated self-energy by using new potential is found close to its value obtained by Darbyet al.     

Resonant charge transfer in grazing atom-metal surface collisions: effect of the presence of steps on the surface

The resonant charge transfer process between an atom and a metal surface is studied in the case of a stepped surface. A sudden approximation is introduced to model the effect of steps in the dynamics of the charge transfer process for grazing angle collisions. It is applied to the problem of H⁻ formation by scattering on Al(111) surfaces. The final H⁻ fractions are demonstrated to be very sensitive to the density of steps on the surface. A large difference between the effect of steps up and down is found. The analysis of this phenomenon is performed. The results are compared with the experimental results of Wyputta et al. [Nucl. Instrum. Methods B 58 (1991) 379].     

Doubly charged clusters - neutral atom charge transfer: the role of the Coulombic repulsion

We have studied experimentally the collisional charge transfer between a neutral atom and a multicharged metal-atom cluster. The charge transfer cross section measured for Na ₃₁ ^{+ +} + Cs is in the range of 400 ?². The time-of-flight mass analysis of the singly charged collision products demonstrates that an energy of about 0.5 eV is deposited in the cluster fragment during the charge transfer collision. This effect can be interpreted as a charge transfer to an excited state of the metal cluster. The measured cross section for Na ₃₁ ^{+ +} + Cs is larger than the one for Na ₃₁ ⁺ + Cs collisions. This difference between these two systems is due to the existence, for the first one, of a Coulombic repulsion term in the collision output channel. Received 24 October 2000     

Ionicities of boron-boron bonds in B(12) icosahedra

First-principles calculations are used to investigate ionicities of boron-boron bonds in B(12) icosahedra. It is observed that the geometrical symmetry breaking of B(12) icosahedra results in the spatial asymmetry of charge density on each boron-boron bond, and further in the ionicity of B(12) icosahedra. The results calculated by a new ionicity scale, a population ionicity scale, indicate that the maximum ionicity among those boron-boron bonds is larger than that of boron-nitrogen bonds in the III-V compound cubic BN. It is of great importance that such an ionicity concept can be extended to boron-rich solids and identical atom clusters.     

Auger kinetic energies and electronic relaxation phenomena in atoms and solids

A semi-empirical theory has been developed to calculate the kinetic energy of Auger electrons resulting from radiationless transitions in both free atoms and metals. Experimental electron binding energies and calculated two-electron interaction and relaxation energies are used. Relaxation energies are determined by means of hyper-Hartree—Fock hole-state calculations. To account for extra-atomic relaxation phenomena in metals, it is assumed that conductionband electrons occupy free-atom-like screening orbitais. The relationship of the present theory to recent work of Shirley et al., Larkins, Kim et al. and Watson et al. is discussed. The dependence of the Auger cross-relaxation energy on the ionicity of compounds is briefly 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.     

Esca. results versus other physical and chemical data

X-ray photoemission spectra yield quantities of very direct interest in physics and chemistry. In this paper the relations of these spectra to other data and concepts are discussed. Both initial-state and final-state properties may be studied: the former are treated first. Charge distributions in molecules alter the effective (Coulomb plus exchange) potential experienced by core electrons in molecular ground states, there by shifting their binding energies. The shifts can be calculated by $\text{ab}$$\text{initio}$ methods or more directly by using potential models based on intermediate-level molecular-orbital theories such as INDO. One version, the ground-state potential model (GPM) yields good predictions of core-level shifts among atoms in similar environments. Alternatively, the measured shifts may be used to derive charges on individual atoms in molecules. It is more difficult to derive charges in solids in this way, but a characteristic splitting in the more tightly-bound valence bands yields a direct measure of ionicity in simple binary compounds of the zinc-blende and rocksalt structures. Atomic orbital composition of molecular orbitals can be deduced from photoemission spectra. In solids such as diamond and graphite comparison of photoemission spectra with x-ray emission spectra yields the atomic-orbital composition of the valence bands. Turning to final-state properties, the spectra are dominated by relaxation effects. Again a simple approach—the relaxation potential model (RPM)—predicts core-level shifts well for cases in which the atomic environments are varied substantially. Among ammonia and the methylamines, for example, the N(ls) shifts are predicted correctly by RPM, while GPM reverses the order. For paramagnetic molecules RPM predicts electron charge transfer toward the positive hole but usually spin transfer away, in agreement with experiment. Extra-atomic relaxation in metals, a many-body effect, is manifest both as a contribution to the binding energy and as line-shape asymmetry. Delocalized valence electrons also show relaxation shifts that can be understood as polari zation of the electron gas toward the “Coulomb hole”. Auger lines show larger relaxation shifts. Comparison of core-level or Auger shifts in nonmetallic solids separately is questionable because there is no reference level, but intercomparison of the two is meaningful. Finally, core-level binding-energy trends in series of simple alcohols, etc., agree quantitatively with proton affinities and core-level shifts in other functional groups. This suggests extending the concept of Lewis basicity to include lone pairs of core electrons. Thus, core-level shifts measure the chemical reactivity—a quantity of great chemical importance that depends on both initial- and final-state properties—rather directly. Rela xation energies are shown to be the dominant cause of trends in the lowest ionization potentials of simple alcohols and amines.     

Electronic structure of hydrogen and muonium in Al,Mg and Cu

The electronic structure of hydrogen and muonium in simple metals is investigated. The spherical solid model potential is used for the discrete lattice and the Blatt correction for lattice dilation. The proton and muon are kept at the octahedral sites in the fcc and hcp lattices and self-consistent non-linear screening calculations are carried out. The scattering phase shifts, electronic charge density, effective impurity potential, self-energy, charge transfer, residual resistivity and Knight shift are calculated. The spherical solid potential changes the scattering character of impurity. The phase shifts are found slowly converging. The scattering is more prominent in Al than in Mg and Cu. The virtual bound states of proton and muon are favoured in all the three metals. The calculated value of residual resistivity for CuH is in good agreement with the experimental value. The results for Knight shift forμ ⁺ in Cu and Mg are in reasonable agreement with the experimental values while those forμ ⁺ in Al are lower than the experimental value. The analytical expressions for effective impurity potential and electronic charge density are suggested.