Kinetic model of olefin hydroalumination by HAlBui2 and AlBui3 in the presence of Cp2ZrCl2 catalyst

The mechanism of α‐olefin hydroalumination by HAlBuⁱ₂, ClAlBuⁱ₂, and AlBuⁱ₃ in the presence of Cp₂ZrCl₂ catalyst has been studied. It was established that the key intermediate of the reaction is a bimetallic complex [Cp₂ZrH₂ · ClAlBuⁱ₂]₂, which reacts with olefins and yields higher diisobutylalkylalanes. In parallel with this stage, the key complex can readily react with XAlBuⁱ₂ (X = H, Cl, Buⁱ) and form a stable trihydride complex Cp₂ZrH₂ · ClAlBuⁱ₂ · HAlBuⁱ₂, which does not exhibit reactivity in olefin hydroalumination. A kinetic model of α‐olefin hydroalumination with HAlBuⁱ₂ and AlBuⁱ₃ has been developed. The model explains the causes of the low stability of the key intermediate [Cp₂ZrH₂ · ClAlBuⁱ₂]₂ and of the different activities of organoaluminum compounds (OACs) in the olefin hydroalumination reaction. Moreover, the model gives information about the limit stages of the reaction and explains the influence of the length of the initial olefins on the rate of the whole catalytic process. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 333–339, 2007     

Frank–Condon principle and adjustment of optical waveguides with nonhomogeneous refractive indices

The adjustment of two different selfocs is considered using both exact formulas for the mode-connection coefficients expressed in terms of Hermite polynomials of several variables and a qualitative approach based on the Frank–Condon principle. Several examples of the refractive-index dependence are studied and illustrative plots for these examples are presented. The connection with the tomographic approach to quantum states of a two-dimensional oscillator and the Frank–Condon factors is established.     

In situ muSR and NMR investigation of methanol dissociation on carbon-supported nanoscaled Pt-Ru catalyst

In situ muSR and nuclear magnetic resonance (NMR) experiments on the investigation of methanol decomposition on Pt-Ru nanoscaled catalyst supported on Vulcan XC-72 carbon black (Pt-Ru/Vulcan XC-72) are presented. Avoided-level-crossing muon spin resonance measurements reveal the resonance line at magnetic field 2.018 T, we assign to transient CH₂?OMu? formaldehyde muonated radical. Results obtained allow us to estimate the contribution of chemical decomposition reaction process for the formaldehyde—carbon oxide—hydrogen conversion on Pt-Ru/Vulcan XC-72 catalytic material. NMR spectrum of the methanol covered Pt-Ru/Vulcan XC-72 consists of three broad resonance lines. Two of them are assigned to OH and CH₃ groups of methanol bound to the carbon black surface. Following the existing literature, which indicates that polymerization of formaldehyde readily takes place when the monomer is adsorbed on some active surface, the third one is assigned to the resonance signal of oligomeric species of formaldehyde. Taking into account the results of our experiments on electrochemical hydrogenation of carbon nanotubes, we do not exclude that the hydrogen arising as a result of methanol decomposition would also contribute to this signal. The high surface area of amorphous carbon nanoparticles of Vulcan XC-72 is favourable to adsorb the hydrogen on their surface.     

Influence of Plasma-Enhanced Chemical Vapor Deposition Parameters on Characteristics of As–Te Chalcogenide Films

First time the method of plasma-enhanced chemical vapor deposition was used for preparation of As–Te chalcogenide films of different chemical and phase composition. The samples were synthesized via direct interaction of arsenic and tellurium vapors into low-temperature non-equilibrium RF (40 MHz) plasma discharge at reduced pressure (0.1 Torr). The plasma parameters such as temperature and concentration of electrons were measured by moving double probe diagnostic system. The dependence of solid phase radial distribution on plasma characteristics was established. Besides, the phase and structural evolution of As–Te films based on equilibrium coexistence of two phases (AsTe and As₂Te₃) and implemented by changing of the ratio of the initial substances in gas phase has been studied and discussed.     

Re-examined principles of thrust generation by a track on soft ground

Dr. Bekker’s first book Theory of land locomotion offers in fact two different concepts of thrust generation on soft ground with respect to the slip: (a) as the push of grousers causing horizontal soil “distortion” and (b) as the shear force in the failure plane linked with the shear deformation. Bekker preferred the second concept and backed it up by the unique shear-ring measuring technique. To clear up the matter, the author decided to re-examine the thrust generation by a track plate experimentally in field conditions. The tests have shown that the initial stage of thrust generation in compressible ground is always horizontal soil compression by grousers, which divides the soil under a track into separate blocks initially at rest. This compression increases at least to the transition point, when a block is sheared off simultaneously at the bottom and in both lateral planes and starts sliding along the channel formed by the preceding grouser. The analysis of these measurements enabled to define the compressive displacement of the face of the soil block (travel of the grouser) appurtenant to the mentioned transition point, useful to define the thrust–slip curve. The case may also be described by the conventional shear stress–shear displacement relationship, imagined to take place in the bottom failure plane, however, namely the “shear displacement” is rather an unusual quantity.     

Random Copolymers of Styrene with Pendant Fluorophore Moieties: Synthesis and Applications as Fluorescence Sensors for Nitroaromatics

Five random copolymers comprising styrene and styrene with pendant fluorophore moieties, namely pyrene, naphthalene, phenanthrene, and triphenylamine, in molar ratios of 10:1, were synthesized and employed as fluorescent sensors. Their photophysical properties were investigated using absorption and emission spectral analyses in dichloromethane solution and in solid state. All copolymers possessed relative quantum yields up to 0.3 in solution and absolute quantum yields up to 0.93 in solid state, depending on their fluorophore components. Fluorescence studies showed that the emission of these copolymers is highly sensitive towards various nitroaromatic compounds, both in solution and in the vapor phase. The detection limits of these fluorophores for nitroaromatic compounds in dichloromethane solution proved to be in the range of 10⁻⁶ to 10⁻⁷ mol/L. The sensor materials for new hand-made sniffers based on these fluorophores were prepared by electrospinning and applied for the reliable detection of nitrobenzene vapors at 1 ppm in less than 5 min.