Berichte der Bunsengesellschaft für physikalische Chemie最新文献

Two series of modified carriers (m.c.) have been prepared by doping silica with various amounts of Be²⁺ and Mg²⁺. The prepared m.c. have been used as supports for the preparation of supported Mo^(VI) oxide catalysts. The magnitude of interactions between SiO₂ and Be²⁺ or Mg²⁺ nitrates depends on the kind and content of the cation. After calcination at 600°C a greater fraction of cations remains on the support surface as well dispersed M(NO₂)₂ in the case of Mg²⁺ m.c. Concerning the Mo containing samples it was found that doping by Be²⁺ and Mg²⁺ causes a solid state transformation of octahedral Mo^(VI) to tetrahedral Mo^(VI). As before, the extent of the effect differs between Be²⁺ and Mg²⁺ and it varies with the content of cation. This effect has been attributed to the inhibition of the polymerization of monomeric Mo^(VI) species and/or to the formation of molybdate salts.

Excitation of acoustic waves in electrolytes by means of a.c. electric fields has been used to examine the structural and dynamical properties of the solutions. The acoustical signal efficiency depends on the electrolyte concentration and on the frequency of the exciting electric field. Experimental results, obtained in the aqueous solutions of LiCl, NaCl and KCl, are discussed. The influence of the electroacoustic-cell design on the obtained results is studied as well.

First principles periodic Hartree-Fock calculations are reported of the electronic and magnetic structures and hole states in the T (La₂CuO₄) phases of Sr₂CuO₂F₂, Sr₂CuO₂F_2.5 and NaSrCuO₂F₂. Sr₂CuO₂F₂ is predicted to be a highly ionic antiferromagnetic charge transfer insulator with Cu in a d⁹ ((d_x²_–y²)¹) configuration. Holes are predicted to be highly localised spin polarons which destroy the AF ordering at concentrations of 0.5 per formula unit.

Small angle neutron scattering (SANS) experiments have been carried out on a semiconductor-doped glass in order to determine the average size and shape of CdS_xSe_1−x precipitates (x ≈ 0.7). The crystallites are of spherical shape with a mean radius of R_p = 3.5 ± 0.1 nm and are rather monodisperse. The polydispersity is lower than ΔR/R_p ∼0.1. Approximately 69% of CdS_xSe_1−x are bound in the precipitates, the rest is dissolved in the glass matrix.

The band structure and solid state electronic properties of three polymerized C₆₀ phases are investigated by a crystal orbital (CO) approach based on an intermediate neglect of differential overlap (INDO) Hamiltonian. We have considered a one-dimensional (1D) body-centered orthorhombic phase as well as two 2D phases crystallizing in a body-centered tetragonal and a rhombohedral lattice. The CO results derived for the polymerized C₆₀ systems are correlated with electronic structure data of the isotropic body-centered cubic van der Waals crystal. We analyze the energy bands ϵ_i(k), the associated electronic density of states (DOS) profiles as well as the atomic net charges and so-called Wiberg bond indices which measure the strength of covalent bonds. The formation of intermolecular CC σ bonds leads to an enhanced alternation between formal double and single bonds on the soccerball. The dimensionality of the four C₆₀ fullendes considered is discussed on the basis of the different quantities evaluated by the CO formalism. The theoretical results are supplemented by C 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of polymerized and non-polymerized C₆₀ films before and after oxygen contamination.

The excess molar Gibbs energy and partial pressures at a temperature of 750 K for the solid phase of the NaBr-NaI system were determined by Knudsen effusion mass spectrometry. The parameters of the Redlich-Kister equation for G^E_m resulted in kJ mol⁻¹ as B₁ = 6.46 and B₂ = −1.12. The thermodynamic data obtained from the molecular ion intensities of NaBr⁺ and NaI⁺ and those obtained from the fragment ion intensities of Na₂Br⁺ (from Na₂Br₂) and Na₂I⁺ (from Na₂I₂) agree well. The results of this work are discussed with respect to those reported by other authors.

We present a theoretical investigation on diffusion of atomic and molecular hydrogen in crystalline as well as amorphous silicon dioxide by means of molecular dynamics simulations. We report a characterization of the migration process of atomic hydrogen in quartz and tridymite and we provide an atomistic description of the diffusion of both atomic and molecular hydrogen in silica.

In multi-component silicate glasses, under the UV-excitation, time-resolved luminescence spectra were observed. These spectra occupied the region of 350–700 nm. The dynamics of changes in radiation induced absorption and spectral-kinetic characteristics of luminescence of γ-irradiation glasses at the expiry of prolonged time were studied. It is assumed that the luminescence in these glasses is caused by quasi-molecular compelxe centers which include the elements of base substance and impurity atom. These centers can appear in the glass both in the process of its melting and under the action of ionizing radiation. It is shown that, the centers of different origin are characterized by different spectral-kinetic properties of their photoluminescence.

High resolution (0.04 cm^–1) absorption spectroscopy is applied at 9 K to study the role played on the vibrational spectra by impurities (Im), as Si⁴⁺, Ge⁴⁺, P⁵⁺, V⁵⁺, Mn⁵⁺, and S⁶⁺, in Bi₁₂SiO₂₀ (BSO), Bi₁₂GeO₂₀ (BGO), and Bi₁₂TiO₂₀ (BTO) sillenite single crystals. Up to three-phonon transitions (overtones of the F mode and combination of F and A modes) are detected for the impurities in ImO₄ tetrahedra. Weak anharmonicity effects are monitored. The presence of additional Im impurities modify the lines due to a) the stretching of OH, typical of the undoped material, and b) the multi-phonon transitions either of the intrinsic MeO₄ (Me = Si, Ge, and Ti) and of the ImO₄ tetrahedra. New bands are monitored due to the Im-OH interaction.