Effect of the type of linkage between phenyl groups on the structure and photochemical properties of 2,2-diaryl-substituted pyridoannelated [2H]-chromenes

Three 2,2-diaryl-substituted pyridoannelated [2H]-chromenes have been studied by X-ray diffraction analysis. Bonding of the benzene rings through bridges of different nature and with different length affects substantially the orientation of the benzene rings, steric interactions at the C center, the conformation of the molecule, and the C−O bond length. A correlation between the photocolorability of chromenes under study and the orientation of the benzene rings with respect to the C−O bond, which provides different prerequisites to stabilization of the C(1)-centered, cation formed upon cleavage of the C−O bond, was established. The effect of the orientation of the benzene rings on the dark reaction of ring closure was found. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1129–1135, June, 1998.     

Wavelet treatment of structure and thermodynamics of simple liquids

A new algorithm is developed to solve integral equations for simple liquids. The algorithm is based on the discrete wavelet transform of radial distribution functions. The Coifman 2 basis set is employed for the wavelet treatment. To solve integral equations we have applied the combined scheme in which the coarse part of the solution is calculated by wavelets, while the fine part by the direct iterations. Tests on the PY and HNC approximations have indicated that the proposed procedure is more effective than the conventional method based on the hybrid algorithm. Possibilities for application of the method to molecular liquids and mixed quantum-classical systems are discussed.     

Structural characterization of Si1 − x Gex ultrathin quantum wells in a Si matrix by high-resolution X-ray diffraction

The structural characteristics of silicon samples containing one and two Si_{1 ? x} Ge_x/Si quantum wells 1.8 to 15 nm thick were determined by high-resolution X-ray diffraction. A detailed analysis of X-ray rocking curves made it possible to reproduce the Ge-concentration profiles in the quantum wells. The diffusion of germanium (up to 20%) into interface layers was observed, with a consequent broadening of the quantum well interfaces.     

Mössbauer experiments in radio frequency magnetic fields: A method for investigations of nanostructured soft magnetic materials

We apply radio frequency (rf) effects, the sideband and the collapse effect, in the investigation of magnetic properties of nanostructured ferromagnetic alloys. We use the relative intensity of the sidebands in comparison to the central part of the spectrum to determine the relative samples' magnetostriction following successive preparation steps. Recent investigations of nanostructured soft ferromagnetic alloys in rf fields led to the discovery that the collapse in the Mössbauer spectra can become selective and partial. It means that the magnetisation reversal is not fast enough and varies differently in the various phases of the alloy. The application of rf magnetic fields then causes new kinds of rf forced relaxation‐type Mössbauer spectra. Experimental results and basic steps in the theoretical understanding are also presented.     

Magnetic “doublets” in Mössbauer spectra of superparamagnetic particles

It is shown that the Mössbauer magnetic hfs spectra of a superparamagnetic particle are cardinally affected by the rotation of its magnetic moment about the magnetic anisotropy field. This rotation renormalizes the nuclear g factors and qualitatively transforms the spectra. In particular, apart from the well-known magnetic sextet, five, four, three, and even two (magnetic “doublet”) lines can arise in the ⁵⁷Fe absorption spectra.     

Multistability in a BEDT-TTF based molecular conductor

The low dimensional organic conductor (BEDT-TTF)(2)Br(1.3)I(1.1)Cl(0.6) [BEDT-TTF = bis(ethylenedithio)tertathiafulvalene] is shown to be a unique molecular solid that exists in three crystalline polymorphic forms (alpha'-, alpha' "-, beta' '-phase) and, surprisingly, is able to adopt the same metal-like beta' '-phase at both low (T < 185 K) and high (T > 395 K) temperatures. Several crystals of the alpha'- and alpha' "-phases have been studied using three different techniques: dc-conductivity measurements, ESR spectroscopy, and X-ray diffraction analysis. All these techniques show the existence of the reversible semiconductor <--> metal (alpha' " <--> beta' ') phase transition at both high and low temperatures as well as the alpha' <--> alpha' " phase transition at high temperatures. The phase transitions of these polymorphs are characterized by huge hysteresis and dramatic changes in the transport and magnetic properties. Based on ab initio calculations, it is suggested that dipole-dipole interactions can play a key role in the rich polymorphism of this molecular solid.     

Size effect of Mössbauer parameters in iron oxide nanoparticles

The size dependence of Mössbauer parameters for iron oxide nanoparticles in the 10–25 nm range was investigated. It was shown that the isomer shift and hyperfine field parameters decrease with the nanoparticle size. Only at 25 nm the presence of magnetite was detected.