Stereo- and regioselectivity of the catalytic system MoCl5/SiO2-SnMe4 in the reaction of metathesis and cometathesis of olefins and their functional derivatives

It was shown that the catalytic system MoCl₅/SiO₂-SnMe₄ has almost 100% regioselectivity with respect to olefins. The stereoselectivity of the system is not a function of the length of the -olefin chain, temperature, or addition of functional groups (COOEt, Cl). Addition of pentachlorophenoxy and 8-hydroxyquinolyl ligands significantly reduces the activity of the catalytic system with a slight increase in the stereoselectivity with respect to the cis-isomer.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 168–171, January, 1990.     

The simplest catalytic mechanism permitting several steady states of the surface

The conditions for the existence of several steady states of the surface have been found for the simplest mechanism without the assumption of autocatalysis and without the effect of the medium on the catalyst. A possibility has been shown for the explanation of the multiplicity of steady states, found experimentally in the kinetic region, in terms of mechanisms including interactions between various intermediates.

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Near-infrared laser operation of Cr3+ centers in chromium-doped LiInGeO4 and LiScGeO4 crystals

Laser action has been demonstrated in two new tunable Cr3+-doped crystals. Absorption, emission, and excitation measurements for various crystal orientations have been performed for chromium-doped LiInGeO4 and LiScGeO4 single crystals. From the spectroscopic measurements, two optical active centers were identified: tetrahedrally coordinated Cr4+ and octahedrally coordinated Cr3+. Gain-switched, tunable laser operation of Cr3+ centers has been demonstrated in both crystals. An ultrawide tuning range from 1150 to 1480 nm for LiInGeO4 and 1220-1380 nm for LiScGeO4 has been achieved. To our knowledge this is the widest bandwidth and the most near-infrared shifted wavelength range for lasing ever demonstrated for Cr3+ ions.     

Amplitude of Aharonov-Bohm oscillations in a small semiconductor ring interferometer in the tunneling regime

The amplitude g_AB of Aharonov-Bohm oscillations in a small semiconductor ring interferometer is studied as a function of the average conductance G_AV. Experimentally, it is found that, in the tunneling regime, the relative amplitude g_AB/G_AV of h/e oscillations is constant in the rings under investigation and smaller than unity. The small value of g_AB/G_AV in ring interferometers in the tunneling regime at low temperatures is explained by the difference in the amplitudes of the interfering electron waves.     

An expert system for identification of lines in vibrational-rotational spectra

An expert system for automatic identification of the complex vibrational-rotational spectra of molecules has been developed. An iteration approach is implemented in this system, in which employment of the exact combination rule is combined with determination of the spectroscopic constants by solving of the inverse problems and comparison of the calculated parameters of spectral lines with the corresponding measured values. In order to calculate the energy levels and the frequencies and intensities of lines, the Watson Hamiltonian, the Padé-Borel approximants, and generating functions are used. The system is based on the application of pattern-recognition algorithms. Recognition training makes it possible to obtain the required flexibility of the system and to use different methods of identification based on the application of combination rules both for the analysis of strong bands and for the assignment of weak single lines. The system developed can be used to analyze the spectra of the C _s and C _2V molecules, as well as employ the calculated spectrum of a molecule of any type prepared in advance. This system was successfully used to identify the H ₂ ¹⁶ O, H ₂ ¹⁷ O, H ₂ ¹⁸ O, D₂O, HDO, H ₂ ³² S, H ₂ ³⁴ S, and H ₂ ³³ S and molecules.     

High-Order Resonances in the Water Molecule

The water-vapor spectra in the near-infrared and visible region were reanalyzed with the purpose of finding experimental evidences of unusual high-order resonance between "dark" high-bending and "bright" stretch vibration states. About 70 transitions to the (050), (060), (070), (080), (160), (061), (170), (071), and, even (0 10 0) bending states, and their resonating partners were assigned in the spectra that gives the experimental energy levels lying near or above the potential energy barrier to linearity. The assignments were confirmed by combination differences and simultaneous observation of both perturbed and perturbing levels. It was found that the high-order resonances with large changing of vibration quantum numbers are typical for the water molecule and they are caused by the strong centrifugal distortion near the linear configuration. These resonances destroy the usual polyad scheme originating from well-known Coriolis, Darling-Dennison, and Fermi resonances in H(2)O molecule. Copyright 2001 Academic Press.     

Coexistence of collective and single-particle effects in the photoresponse of a 2D electron gas to microwave radiation

The photoresponse of magnetoresistance of a high-density two-dimensional electron system to microwave electromagnetic radiation is studied. The damping of the Shubnikov-de Haas oscillation by radiation with a non-monotonic dependence of this effect on the magnetic field and the radiation-induced oscillations of magnetoresistance are observed. The damping is most pronounced within isolated narrow magnetic field intervals that closely correspond to the expected positions of magnetoplasma resonances in the sample under study and also near the cyclotron resonance position. A “window” is observed in the photoresponse near the field value predicted on the basis of a single-particle electron spectrum consisting of broadened Landau levels. The radiation-induced oscillations, the window in the photoresponse, and the damping of the Shubnikov-de Haas oscillations near the cyclotron resonance are described in terms of the theory based on the concept of the nonequilibrium filling of single-electron states. Thus, it is demonstrated that the photoresponse pattern observed in the experiment is formed by both single-particle and collective (magnetoplasma) effects.