Mössbauer study of tektites

Room temperature ⁵⁷Fe Mössbauer spectroscopy has been used to investigate the structural and oxidation state of Fe in tektites from different strewn fields. Spectra have been analyzed in terms of two quadrupole splitting distributions corresponding to Fe^3?+? and Fe^2?+?. All tektites show similar distribution of quadrupole splitting. Each distribution has one peak. The Fe^2?+? sites show a narrow region of Mössbauer line shift (δ) and quadrupole splitting (ε), δ?= 1.02–1.10 mm/s and ε?= 0.85–1.00 mm/s relative to α-Fe. These values have been assigned to intermediate coordination between tetrahedral and octahedral. The Fe^3?+? sites show wider regions of hyperfine parameters: δ?= 0.25–0.45 mm/s and ε?= 0.65–0.90 mm/s. The Fe^3?+?/Fe^2?+? ratio was found to be 0.05–0.15.     

Growth and Study of Scintillation Properties of BaBrI Crystals Activated by Samarium Ions

Physics of the Solid State - BaBrI crystals activated by Sm2+ ions were synthesized by the Bridgman method. The Sm content in the samples was analyzed by the method of mass spectrometry with...     

Protonation of 1,3- and 1,4-dinitrobenzene dianions

The protonation of the electrochemically generated (0.1 M solution of tetrabutylammonium perchlorate in DMF) 1,3-dinitrobenzene (1) dianions with phenol, ethanol, tert-butanol, and 1-butyl-3-methylimidazolium cation was studied by cyclic voltammetry and chronoamperometry at the carbositall working electrode. The rate constants for the protonation (k) of the dianion of compound 1 by phenol, 1-butyl-3-methylimidazolium cation, ethanol, and tert-butanol were estimated by the comparison of the data of cyclic voltammetry and chronoamperometry with the digital simulation results, being 100, 50, 1.5, and 0.01 L mol⁻¹ s⁻¹, respectively. The similarly obtained k value for the protonation of the dianion of 1,4-dinitrobenzene (2) with phenol is 13 L mol⁻¹ s⁻¹. According to the quantum chemical calculation results, the protonation of the dianions of compounds 1 and 2 with phenol and 1-butyl-3-methylimidazolium cation can be classified as orbital-controlled reactions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1463–1466, July, 2008.     

<Superscript>13</Superscript>C-<Superscript>13</Superscript>C spin-spin coupling constants in structural studies: XL. Conformational analysis of <Emphasis Type="Italic">N</Emphasis>-vinylpyrroles

Conformational analysis of ten N-vinylpyrroles was performed on the basis of experimental ¹³C-¹H and ¹³C-¹³C coupling constants and those calculated by high-level quantum-chemical methods, and principal relations between J _CC and J _CH values and stereochemical structure of these compounds were revealed.     

Importance of spin-orbit effects on the isomerism profile of Au3: an ab initio study

Two-component relativistic density functional theory combined with high-level ab initio correlation techniques was applied to the study of the electronic structure and isomerism of Au(3). All calculations were performed with accurate small-core shape-consistent relativistic pseudopotentials. Density functional theory was used to determine the equilibrium structures of the Au(3) isomers and isomerization path and to estimate the contributions of spin-orbit effects to the ground state electronic energy along the path. The reliability of these estimates was verified through independent many-body multipartitioning perturbation theory calculations. Spin-orbit corrections were used to refine the isomerization energy profile computed by spin-orbit-free coupled cluster methods.     

Emission processes accompanying deformation and fracture of metals

Present-day physical methods of investigation reveal that the fracture and plastic deformation of metals is accompanied by emission processes, in particular, by luminescence and emission of electrons. All the metals studied thus far exhibit a capability of luminescence. The intensity, duration, and spectrum of mechanoluminescence are different for different metals. The intensity is determined by the mechanical and thermal characteristics. For a given metal, the intensity depends on dislocation density in the structure and the sample loading rate. The spectrum of noble metals is governed by the electronic structure of surface states. The dynamics of mechanoluminescence and electron emission (exoemission) depends on the rate of stress variation in the sample under study. This permits one to consider the mechanoluminescence and exoemission not only as physical characteristics but also as a potential tool for probing surface states in metals and the kinetics of emergence of mobile dislocations on the surface with a high time resolution. Fiz. Tverd. Tela (St. Petersburg) 41, 841–843 (May 1999)     

Status of the Navier–Stokes Equations in Gas Dynamics. A Review

The existing ideas on the status of the Navier–Stokes equations are changed in taking into account the following facts: generally speaking, the terms of these equations neglected in the boundary layer equations are of the order of certain Burnett terms in the conservation equations; the Navier–Stokes equations cannot be used to describe slow nonisothermal gas flows since in this case it is necessary to take the Burnett temperature stresses into account; and in the transport relations the Burnett terms determine certain effects (for example, the mechanocaloric effect).     

Magnetic hyperfine interactions of 119Sn probe atoms in the binary perovskite CaCu3Mn4O12

The manganite CaCu₃Mn₄O₁₂ doped by ¹¹⁹Sn atoms (about 1 at % with respect to Mn atoms) is studied by Mössbauer spectroscopy. The introduction of diamagnetic tin atoms is found not to affect the structure of the manganite. Tetravalent tin atoms are shown to substitute for the isovalent manganese atoms that are located in an octahedral oxygen surrounding. The cluster method of molecular orbitals is used to calculate the contributions of Mn⁴⁺ and Cu²⁺ cations that belong to different structural sublattices to the hyperfine magnetic field at ¹¹⁹Sn nuclei (H _Sn = 105 kOe at T = 77 K). These partial contributions are analyzed, and the intrasublattice Mn⁴⁺-O-Mn⁴⁺ exchange interactions are found to play a significant role in the formation of the magnetic structure of the manganite.     

Theoretical conformational analysis of unsaturated phospines and phosphinechalcogenides

A theoretical conformational analysis was performed for vinylphosphine CH₂=CHPH₂ and three vinylphosphinechalcogenides CH₂=CHPXH₂ (X = O, S, Se). According to the quantum-chemical calculations on the level of the second order perturbation theory MP2/6-311G** the prevailing conformations, their molar ratios, and relative energies were established for each compound. The analysis of the angular distribution of the probability density for the population of the rotational conformations calculated proceeding from the potential curves of the internal rotation made it possible to establish that each compound from this series existed as a mixture of two conformers, planar s-cis and twice degenerate orthogonal. The conformers transform into each other through the corresponding transition states whose nature was established as a result of the harmonic vibration analysis carried out in every case.