On excited states of the Au<Subscript>3</Subscript> cluster: an <Emphasis Type="Italic">ab initio</Emphasis> study

Excited electronic states of the Au₃ cluster are studied within the shape-consistent small-core relativistic pseudopotential model using many-body multipartitioning perturbation theory. Vertical transition energies and dipole moments are evaluated. For highly symmetric isomer, these theoretical results are in reasonable agreement with spectroscopic data from experiments.      

Mössbauer effect study of Co,Ni, Mn,and Al bearing goethites

The presence of substituting elements in magnetically ordered structure of crystals may change the shape of Mössbauer spectra of these materials. this fact was used to determine whether there is an ionic substitution of Ni, Co, Mn and Al for Fe in synthetic goethites. The approximate distribution function of the effective magnetic field in the Fe nucleusp′ (Hn) was obtained from the Mössbauer spectra. It was found that the mean value ofp′ (Hn) and its integral width can be taken as a measure of substitution in goethite.     

Effect of microheterogeneity on the kinetics of oxidation of methyl linoleate in micelles

The kinetic results of the radical chain oxidation of methyl linoleate (LH) in micelles were given. The oxidation rate depends on the average number of substrate molecules in the micelle and is almost independent of the micelle concentration under the given conditions. The chain propagation and termination were assumed to predominantly occur inside the micelle. Possible reasons for linear chain termination during the oxidation of polyunsaturated fatty esters in microheterogeneous systems were discussed.     

Mössbauer and magnetic studies of nanocomposites containing iron oxides and humic acids

A sample of volcanic ashes emanated from the Osorno volcano, southern Chile, was characterized with X-ray fluorescence, X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy, in an attempt to identify the iron-bearing minerals of that geologically recent magmatic deposit. X-ray patterns indicated that the sample is mainly constituted of anorthite, Fe-diopside-type and Ca-magnetite. The crystallographic structures of these dominant iron minerals are proposed on basis of their chemical composition and corresponding Mössbauer data to support models refined by fitting powder X-ray diffraction data with the Rietveld algorithm.     

Magnetic states of iron ions in perovskite Bi0.75Sr0.25Fe0.95Cr0.05O3–y

Bulletin of the Russian Academy of Sciences: Physics - 57Fe hyperfine interactions are measured in cubic perovskite Bi0.75Sr0.25Fe0.95Cr0.05O3–y by means of Mössbauer spectroscopy in the...     

Trivinylphosphine and trivinylphosphine chalcogenides: stereochemical trends of ³¹P-¹H spin-spin coupling constants

A combined theoretical and experimental study of the stereochemical behavior of (31)P-(1)H spin-spin coupling constants has been performed in the series of trivinylphosphine and related trivinylphosphine oxide, sulfide and selenide. Theoretical energy-based conformational analysis of the title compounds performed at the MP2/6-311G** level reveals that each of the four compounds of this series exists in the equilibrium mixture of five true-minimum conformers, namely s-cis-s-cis-s-cis, s-cis-s-cis-gauche, syn-s-cis-gauche-gauche, anti-s-cis-gauche-gauche and gauche-gauche-gauche, which were taken into account in the conformational averaging of (31)P-(1)H spin-spin couplings calculated at the second-order polarization propagator approach/aug-cc-pVTZ-J level of theory. All (31)P-(1)H spin-spin coupling constants involving phosphorus and either of the vinyl protons are found to demonstrate a marked stereochemical dependences with respect to the geometry of the coupling pathway and internal rotation of the vinyl group around the P-C bond which is of major importance in the stereochemical studies of the unsaturated phosphines and phosphine chalcogenides.     

Plasticity of soft magnetic elastomers

A simple rheological model is introduced to describe the plasticity in soft magnetic elastomers induced by an external field. In addition to the elasticity of the polymer matrix, the effect of dry friction (plasticity), which is provided by the rearrangement of the spatial structure of a dispersed magnetic subsystem in the course of the deformation of the material by a sufficiently strong field, is taken into account in the model. Model parameters are estimated from the reported experimental data on the deformation of cylindrical samples based on a soft silicon elastomer filled with quasispherical microparticles of carbonyl iron.     

Synthesis and phase formation in M 0.5(1+x) 2+ FexTi2−x (PO4)3 phosphate series

New complex phosphates of titanium, iron, and alkaline-earth metals have been synthesized. X-ray powder diffraction, differential thermal analysis (DTA), and IR spectroscopy are used to study phase formation in the series of M_0.5(1+x)Fe_xTi_2?x (PO₄)₃ (M = Mg, Ca, Sr, Ba) phosphates. Individual compounds and solid solutions are found to crystallize in the NaZr₂(PO₄)₃ and K₂Mg₂(SO₄)₃ structure types. Their crystal parameters are calculated. CaFeTi(PO₄)₃ is studied using Mössbauer spectroscopy. Its structure is refined by the Rietveld method: space group $R\bar 3$ c, Z = 6, a = 8.5172(1), Å, c = 21.7739(4) Å, V = 1367.91(4) ų.     

On the significant relativistic heavy atom effect on 13C NMR chemical shifts of β- and γ-carbons in seleno- and telluroketones

Unexpectedly large ‘Heavy Atom on Light Atom’ (HALA) effects have been found in ¹³C NMR (Nuclear Magnetic Resonance) chemical shifts of β- and γ-carbons of seleno- and telluroketones established by means of the high-accuracy calculations of ¹³C NMR chemical shifts in three representative real-life compounds, 2,2,5,5-tetramethyl-3-cyclopentene-1-selone, selenofenchone and 1,1,3,3-tetramethyl-1,3-dihydro-2H-indene-2-tellurone. The proposed computational scheme consists of the combination of accurately correlated coupled-cluster singles and doubles model approach for the non-relativistic calculations of shielding constants taking into account the solvent, vibrational and relativistic corrections, the latter obtained within the 4-component fully relativistic gauge-including atomic orbitals KT2 approach resulting in a very good agreement of the performed calculations with the experiment. The stereochemical dependence of the ‘long-range’ γ-HALA effect on the dihedral angle has been established in the model seleno- and telluroketones providing the largest shielding effect in the orthogonal orientation of the X=C_α–C_β–C_γ (X=Se, Te) moiety.     

Fokker-Planck operator for free-molecular,nonspherical, thermally nonequilibrium Brownian particles

The Fokker-Planck collision operator entering into the kinetic equation for the velocity distribution function of convex nonspherical rigid homogeneous Brownian particles in a traveling inhomogeneous monatomic gas is derived. The regime of flow past the particles is free-molecular, i.e., the characteristic particle dimensions are much smaller than the average free path of the gas molecules, the interaction between the particles and their effect on the gas phase can be neglected, and a specular-diffuse law of interaction between the molecules and the particle surface holds. The particle temperatures T _p are the same and differ from the local gas temperature T. Thermal nonequilibrium (T _p ≠ T) leads to violation of the well-known relations between the diffusion coefficients in the spaces of the translational and angular velocities and the coefficients of forces and moments exerted on a particle. The coefficients in the unknown operator are calculated for the particles in the form of bodies of revolution with longitudinal symmetry. Data characterizing the effect of the nonsphericity of the particles, i.e., spheroids and sphere-cylinders, on the degree of violation are given.