Electronic band structure of TiCl3

Energy bands for the 3d? electrons of Ti³⁺ in the high temperature structure of TiCl₃ have been calculated by the tight-binding approximation. Cubic symmetry around each Ti³⁺ is assumed and transfer between the 3p atomic orbitals of Cl^? and 3d? atomic orbitals of Ti³⁺ is considered. Two singlet bands and two doublet bands with no dispersion have been obtained. The dispersionless character is discussed by constructing Wannier functions.     

Identification of two types of F centres in BaClF by endor

By means of an ENDOR investigation we have shown beyond doubt, that the optical bands at 2.83 and 2.25 eV belong to electrons trapped at Cl^?-vacancies (F(Cl^?)-centres)), whereas the bands at 2.33 and 2.82 eV are due to electrons at F^? vacancies (F(F^?)-centres)). The current F-centre theory fails to explain the spin densities at nearest neighbour sites by one (F(Cl^?)) and two orders of magnitude (F(F^?)), respectively.Mit Hilfe einer ENDOR-Untersuchung haben wir eindeutig gezeigt, daβ die optischen Banden bei 2,83 und 2,25 eV zu Elektronen in Cl^?-Leerstellen (F(Cl^?)-Zentren)), die Banden bei 2,33 und 2,82 eV zu Elektronen in F^?-Leerstellen (F(F^?)-Zentren)) gehören. Theoretische Werte für die Spindichte der nächsten Nachbarn aufgrund der gegenwärtigen F-Zentren-theorie ergeben Diskrepanzen um eine (F(Cl^?)) bzw. zwei (F(F^?)) Gröβenordnungen.     

Triple resonance investigation of F centres in BaFCl

Abstract

In BaFCl two types of F centres can be produced, where the electron occupies a Cl^? vacancy [F(Cl^?)-centres] or an F^? vacancy [F(F^?)-centres]. When producing F(F^?)-centres the simultaneous production of F(Cl^?)-centres cannot be avoided. Both ESR spectra overlap strongly. The ENDOR spectra contain very many lines of both centres and have a very complicated angular dependence. It is shown that the angular dependence of the ENDOR spectra of both F centres can be measured separately by applying a double ENDOR technique (called also Triple Resonance). The ratio of the signal heights of the ENDOR lines compared to the double ENDOR lines is characteristic for the neighbour shell to which the nuclei involved belong. The use of this effect for the analysis of the spectra and its explanation are discussed.     

The reactions of Cl+ (3P) and Cl+ (1D) with hydrogen sulphide. A G2 molecular orbital study

G2 ab initio molecular orbital calculations have been performed to study the potential energy surfaces (PESs) associated with the reactions of Cl⁺ in its ³P ground state and in its ¹D first excited state with hydrogen sulphide. [H₂, Cl, S]⁺ singlet and triplet state cations present very different bonding characteristics. The latter are systematically ion-dipole or hydrogen-bonded weakly bound species, while the former are covalent molecular ions. As a consequence, although the Cl⁺(³P) is 34.5 kcal mol^?1 more stable than Cl⁺(¹D), the global minimum of the singlet PES lies 37.3 kcal mol^?1 below the global minimum of the triplet PES. Both singlet and triplet potential energy surfaces show significant differences with respect to those associated with Cl⁺ + H₂O reactions as well as with SH₂ reactions with F⁺. In both cases, the major product should be SH⁺ ₂; SH⁺ and HCl⁺ being the minor products, in agreement with the experimental evidence. The estimated heat of formation for the most stable H₂SCl⁺ singlet state species is 198 ± 1 kcal mol^?1.     

Dielectric-field effect correction on i.r. band shapes in the liquid phase

The dielectric-field correction on i.r. band shape in the liquid has been studied by using the Lorentz internal field. The deformation of the band shape is inappreciable for a weak absorption band that becomes measurable only at a sample thickness larger than 10μ. The shapes of the strong singlet and doublet bands of hexafluorobenzene at 1530 cm^?1 and near 1000 cm^?1, respectively, and also of the doublet band of carbon tetrachloride near 790 cm^?1 have been measured in dilute solutions and compared with those for the pure liquid.     

Optical absorption spectrum of Cr3+ ion doped in zinc cesium sulphate hexahydrate

Optical absorption spectrum of Cr³⁺ ion doped in zinc cesium sulphate hexahydrate single crystal has been studied both at room and liquid nitrogen temperatures. From the nature and position of the bands a successful interpretation of all the bands could be made assuming octahedral symmetry for the Cr³⁺ ion in the crystal. The observed bands are assigned to the transitions from the ground ⁴A_2g(F) state to the excited ²E_g(G), ²T_1g(G), ⁴T_2g(F) and ⁴T_1g(F) states.The crystal field parameters Dq = 1735 cm^?1, B = 635 cm^?1 and C = 4.75 B are found to give a good fit to the observed band positions.     

Mössbauer spectroscopy of exchangeable ions

In this paper Mössbauer spectroscopy is used to study anion exchange processes. In β-FeOOH the effect of the exchangeable ions OH^?, Cl^? and F^? on lattice iron is studied. For the anion exchangers ZrO₂ and the resins amberlite IRA 400, Dowex MSA-1 and Dowex MWA-1, Fe(II)- and Fe(III) hexacyanides are used as Mössbauer probes. The confirmation of a third doublet in F^?-exchanged β-FeOOH and the perturbation of redox equilibrium in the other exchangers are the main observations.     

X-ray structure refinement and ionic conductivity of Na6.69Ca3.355(SO4)6Cl0.77F0.63

The structure of Na_6.69Ca_3.355(SO₄)₆Cl_0.77F_0.63, isostructural with fluorapatite, was determined by X-ray powder diffraction methods. The results of Rietveld refinement revealed a space group P6₃/m with lattice parameters of a?=?9.477 (2) Å, c?=?6.865 (5) Å. Final refinement led to R _F?=?1.83 % and R _B?=?7.64 %. The location of Na⁺ ions in the M (2) sites surrounding the channels was related particularly to the high polarizability of the Ca²⁺. The ionic conductivity over a wide range of temperature was investigated according to the complex impedance method. The highest overall conductivity values were found at σ _500 °C?=?1.03?×?10^?5?S?cm^?1 and E_a?=?0.70 eV.     

Ultraviolet photoemission study of LiF

Photoemission from evaporated films of LiF were measured at photon energies of 10-27 eV. The photoelectron spectra exhibit features that can be identified as density-of-states structures in the valence and conduction bands of LiF. Regions of high density of states can be seen at ca. 3.3 and 7.8 eV above the vacuum level. The valence-band spectrum shows a doublet structure similar to the calculated density of states for the F^?2p band of LiF. The base width of this structure is found to be 4.6 ± 0.3 eV. The photoelectron spectra for photon energies > 15 eV indicate that the highest occupied states of the F^?2p band are located at 11.8 ± 0.3 eV below the vacuum level. The photoelectron spectra in the exciton region, however, show photo-emission from higher occupied states.     

First far-infrared high-resolution analysis of the ν2 and ν4 bands of phosgene 35Cl2CO and 35Cl37ClCO

ABSTRACT

A Fourier transform spectrum of phosgene (Cl₂CO) has been recorded in the 17.3-μm spectral region at a temperature of 180 K and at a resolution of 0.00102 cm^?1 using a Bruker IFS125HR spectrometer coupled to synchrotron radiation, leading to the observation of the ν₂ and ν₄ vibrational bands of the two isotopologues ³⁵Cl₂CO and ³⁵Cl³⁷ClCO. The corresponding upper-state ro-vibrational levels were fit using a Hamiltonian model accounting for the A-type Coriolis interaction linking the rotational levels of the 2¹ and 4¹ vibrational states. In this way, it was possible to reproduce the upper-state ro-vibrational levels to within the experimental uncertainty, i.e. ～0.30 × 10^?3 cm^?1. Very accurate rotational and centrifugal distortion and interaction constants were derived from the fit, together with the following band centres: ν₀(ν_2, ³⁵Cl₂CO) = 572.526299(30) cm^?1, ν₀(ν_4, ³⁵Cl₂CO) = 582.089026(30) cm^?1, ν₀(ν_2, ³⁵Cl³⁷ClCO) = 568.951791(35) cm^?1 and ν₀(ν₄, ³⁵Cl³⁷ClCO) = 581.758279(35) cm^?1.     

High-resolution analysis of the ν1 and ν5 bands of phosgene 35Cl2CO and 35Cl37ClCO

Fourier transform spectra of phosgene (Cl₂CO) have been recorded in the 11.75 and 5.47 μm spectral regions using a Bruker IFS125HR spectrometer at resolutions of 0.00102 and 0.0015 cm^?1, respectively, leading to the observation of the ν₅ and ν₁ vibrational bands of the two isotopologues ³⁵Cl₂CO and ³⁵Cl³⁷ClCO. The corresponding upper state ro-vibrational levels were fit using Watson-type Hamiltonians and/or a Hamiltonian matrix accounting for resonance effects when necessary. In this way, it was possible to reproduce the upper state ro-vibrational levels to within the experimental accuracy, i.e. ～0.17 × 10^?3 cm^?1. Very accurate rotational and centrifugal distortion constants were derived from the fit together with the following band centres: ν₀(ν_5, ³⁵Cl₂CO) = 851.012737(20) cm^?1, ν₀(ν_5, ³⁵Cl³⁷ClCO) = 849.995451(90) cm^?1, ν₀(ν_{2 +} ν_3, ³⁵Cl³⁷ClCO) = 864.42370(50) cm^?1, ν₀(ν_1, ³⁵Cl₂CO) = 1828.202514(40) cm^?1 and ν₀(ν_1, ³⁵Cl³⁷ClCO) = 1827.246444(20) cm^?1.     

An X-ray diffraction study of anharmonic thermal vibrations in the ionic conductor,barium chloride fluoride (BaClF)

Integrated intensities of X-ray reflections from a barium chloride fluoride single crystal were measured at 24, 180, 289, 402, 467 and 610°C. The intensities were used for the determination of the anharmonic potential parameters up to the third order. Harmonic potential parameters for each ion were obtained from the temperature dependence of thermal parameters, and anharmonic potential parameters were determined by the least-squares procedures, utilizing the temperature factor formalism based on the cumulant expansion. As a result, it has been found that the Ba²⁺ and Cl^? ions show an anharmonicity, while no significant anharmonic effect was detected for the F^? ion. From the potential calculated around the Cl^? and F^? ions, it was found that both Cl^? and F^? ions diffuse more easily within the (001) plane than along the c axis.     

A Mössbauer study of octahedral site symmetries in systems Co x Mn3−x−y Fe y O4 and Ni x Mn3−x−y Fe y O4

A Mössbauer study of cation distribution in systems Co _x Mn_3?x?y Fe _y O₄ and Ni _x Mn_3?x?y Fe _y O₄ has been made. It has been found that in both systems all specimens withy<0.6 value exhibit quadrupole doublets corresponding to site symmetries Fe³⁺(I) and Fe³⁺(II) of octahedral site. As more and more cobalt or nickel is introduced into the matrix the intensity of the inner quadrupole doublet increases while on introducing iron that of the outer quadrupole doublet increases. After a certain concentration of iron the inner doublet starts becoming more intense. It is suggested that this arises possibly from the substitution of cations in the second co-ordination sphere of Fe³⁺(I) and Fe³⁺(II) sites. Fory>0.6 the Mössbauer spectra show relaxation effects.     

Pairs of F centres and CN− molecules in KCl: An ENDOR analysis

Abstract

Pair defects consisting of F centres and CN^? molecules as substitutional impurity anions (F_H(CN^?) centres) exhibit a strong coupling between the F centres and the CN^? molecules. This leads to an optical pumping of the CN^? vibrations via the F centre absorption band. We performed an Electron Nuclear Double Resonance (ENDOR) investigation in order to analyse the microscopic structure of these aggregate centres. The CN^? molecule occupies a [110] nearest anion position with respect to the F centre in two dynamic dipole orientations even at low temperature.     

The influence of nickel concentration on photoluminescence spectra of ZnSe:Ni samples

Photoluminescence (PL) spectra of ZnSe samples grown by iodine transport method and doped with Ni during the growth process and grown from the melt and doped with Ni by diffusion from a gas phase are investigated in visible and infrared (IR) ranges at 77 and 300 K. It is shown that under sub-band excitation, the PL spectra for the undoped samples of both types are similar and may be attributed to self-activated luminescence with participation of iodine- and V_Zn-based centres. The PL study for ZnSe samples doped with Ni carried out at various Ni concentrations, temperatures, and excitation intensities gives reason to ascribe the observed bands in near-IR and IR ranges to ³T₂(F)→³T₁(F) and ³T₁(P)→³T₁(F) intracentre transitions within the Ni_Zn²⁺(d⁸) ion.     

Optimal bounds for the pion form factor from analyticity and experimental data

Optimal bounds for the pion electromagnetic form factor F(t) below threshold and on the pion mean-square charge radius 〈r_π²〉 = 6F'(0) are derived. Use is made of analyticity arguments and of experimental data on F(t) from e⁺e^? → π⁺π^? as well as e^?p → e^?nπ⁺. The method accounts in an approximate way for the statistical errors of the experimental information. Numerical results for F(t) are calculated for the CEA as well as the DESY electroproduction data.     

The microwave spectrum,structure, and quadrupole coupling constants of boron chloride difluoride,BCIF2

The microwave spectrum of boron chloride difluoride, BClF₂, has been investigated in the region 26.5–40.0 GHz. R-branch transitions belonging to the isotopic species ¹¹B³⁵Cl¹⁹F₂, ¹¹B³⁷Cl¹⁹F₂, and ¹⁰B³⁵Cl¹⁹F₂ have been observed and the derived rotational constants yield the following ground-state structural parameters: $\text{r}{}^0\text{(BF) = 1.315 ± 0.006}\text{A}\text{?}$, $\text{r}{}^{\mathrm{s}}\text{(BCl) = 1.728 ± 0.009}\text{A}\text{?}$, < FBF = 118.1 ± 0.5°. The ground-state rotational constants of the most abundant species ¹¹B³⁵Cl¹⁹F₂ are: A₀ = 10 449.32 ± 0.13, B₀ = 4705.811 ± 0.020, C₀ = 3239.702 ± 0.026 MHz, Δ_JK = 8.9 ± 1.7, and Δ_J = 1.86 ± 0.48 KHz. The asymmetry parameter κ = ?0.593291 and the inertial defect δ⁰ = 0.2361 amu Ų which is consistent with that expected for this type of molecule if planar. The ³⁵Cl quadrupole coupling constants for ¹¹B³⁵Cl¹⁹F₂ are χ_aa = ?42.8 ± 1.0, χ_bb = 30.2 ± 1.5, χ_cc = 12.6 ± 1.5 MHz with the asymmetry parameter η = 0.41.     

Optical absorption and ESR study of F centres in BaClF and SrClF crystals

Magnetic and optical properties of two types of F centres, calledF(F^?) and F (Cl^?), created in BaClF and SrClF tetragonal crystals are described. The experimerttal position of the absorption bands and the [g] principal values of each centre are the following at 78K. In BaClF, $\text{F(}\text{Cl}{}^{\mathrm{?}}\text{): λ}{}_{\mathrm{}}\text{=438}\text{nm}\text{, λ}{}_{\mathrm{\perp }}\text{=550}\text{nm}\text{, g}{}_{\mathrm{\parallel }}\text{=1.9690 ± 0.0003, g}{}_{\mathrm{\perp }}\text{=1.9798±0.0003; F(}\text{F}{}^{\mathrm{?}}\text{): λ}{}_{\mathrm{\parallel }}\text{=532}\text{nm}\text{, λ}{}_{\mathrm{\perp }}\text{=}\text{430}\text{nm}\text{446}\text{nm}\text{, g}{}_{\mathrm{\parallel }}\text{=1.9836 ± 0.0003, g}{}_{\mathrm{\perp }}\text{=1.9695±0.0003.}\text{In SrCIF}\text{, F(}\text{Cl}{}^{\mathrm{?}}\text{): γ}{}_{\mathrm{\parallel }}\text{=380}\text{nm}\text{, λ}{}_{\mathrm{hu}}\text{=465}\text{nm}\text{, g}{}_{\mathrm{\parallel }}\text{=1.996±0.002, g}{}_{\mathrm{\perp }}\text{=1.993±0.002; F(}\text{F}{}^{\mathrm{?}}\text{): λ}{}_{\mathrm{\parallel }}\text{=410}\text{nm}\text{, λ}{}_{\mathrm{\perp }}\text{=}\text{345}\text{nm}\text{363}\text{nm}\text{, g}{}_{\mathrm{\parallel }}\text{=1.997±0.001, g}{}_{\mathrm{\perp }}\text{=1.993+0.001. (∥}\text{and}\text{⊥}$ refer to the light polarization or the magnetic field direction with respect to the fourfold axis of the crystal).This attribution disagrees with that proposed by Nicklaus and Fischer, but accounts for the values of the energy levels of F(F^?) and F(C1^?) in BaClF and SrClF calculated by S. Lefrant and A.H. Harker.     

The hydrogen compensated cation vacancy VOH− in magnesium oxide

H-doped MgO single crystals show a number of infrared absorption bands in the OH stretching region. H-doped, high purity, well-annealed MgO crystals (4N grade = 99.99%), grown from the melt, show a prominent group of four equally spaced bands at 3296, 3310, 3325 and 3341 cm^?1, while lower grade 3N MgO crystals exhibit only the first two bands and the third after X-irradiation. Until now these bands were assigned to different types of OH^? ions. The present spectra indicate that the four bands form a quadruplet which is assigned to the OH stretching fundamental of one proton substituting a divalent cation [OH^?V_Mg^″O^2?]^?. In this defect the proton is expected to behave as an off-center impurity, residing probably in an XY₈ multiple well potential in the [111] directions. The 8-fold degenerate ground level will split due to tunneling into A_2u, T_2g, T_1u, A_1g states, giving rise to the observed quadruplet. The quadruplet is expected, if the proton occupies the nearly spherical well of the tetrahedral sites above each face of the octahedron forming the XY₈ system. If the proton moves towards the trigonal sites in the (111) faces, the well becomes elliptical and the quadruplet will be reduced to a doublet.     

E1-M2-E3 mixing of the 1241.7 keV transition in147Yb

The half-life of theI,K ^π=2, 2^? state at 1318 keV in¹⁷⁴Yb has been measured in the¹⁷³Yb(n, γ) reaction to be 0.486±0.015 ns. This half-life determines the absolute transition probabilities of the gamma-ray transitions to the ground state rotational band yielding the following hindrance factors relative to the Weisskopf estimate:F _W(M 2; 2, 2^?→0, 0⁺)=350;F _W(M2; 2, 2^?→2, 0⁺)≧77F _W(M 2;2, 2^?→4, 0⁺)>740;F _W(E 1; 2, 2^?→2, 0⁺)=4.5×10⁶;F _W(E 3; 2, 2^?→2, 0⁺)≈0.1;F _W(E 3; 2, 2^?→4, 0⁺)≈0.4. These data are compared to analogous transitions in neighboring nuclei.