Deformation and thermodynamic instability of a C84 fullerene cage

Quantum chemical calculations of electronic and geometric structures were performed for molecules of 24 isomers of C₈₄ fullerenes obeying the isolated pentagons rule. The reasons for the instability of isomers not obtained experimentally were established, and the possibility of obtaining some of them was proven. It was shown that the deformation of hexagons and pentagons is the most important geometric parameter directly connected with the thermodynamic instability of fullerenes having closed shells, reflecting the local strain of the molecules.     

IR and NMR spectra,intramolecular hydrogen bonding and conformations of para-tert-butyl-aminothiacalix[4]arene in solid state and chloroform solution

It is demonstrated that dissolution of aminothiacalix[4]arene in chloroform results in transformation of 1,3-alternate conformation, adopted in single-crystal and bulk polycrystalline solids, to the pinched-cone form. This conformer is stabilised by the intramolecular hydrogen bonds of two distal amino-groups acting as H-donors with another two amino moieties that appear as H-acceptors. The H-bonds cause quite small (ca. 10–20 cm^?1) red shift of the IR bands of the NH₂ stretching vibrations, which suggests rather weak NH?N hydrogen bonding. This latter is sufficient to stabilize the pinched-cone conformation in the chloroform solution, but the energy gap between the pinched-cone and other conformations is small, and solid-state intermolecular forces easily overcome it, leading to realisation of the 1,3-alternate conformer. The comparison of the DFT computed and experimental vibrational and NMR spectra demonstrates good quality of present quantum-chemical computations, allows complete interpretation of the spectra and reveals simple IR and NMR spectroscopic markers of the conformers of aminothiacalix[4]arenes.     

Isomer ratios for products of photonuclear reactions with middle-weight nuclei

The isomer ratios for nuclei ^104m,g Ag, ^110m,g In, ^108m,g In as products of the photonuclear reactions ¹⁰⁷Ag(γ, 3n)^104m,g Ag, ¹¹³In(γ, 3n)^110m,g In, ¹⁰⁹Ag(γ, 5n)^104m,g Ag, ¹¹⁵In)(γ, 5n)^110m,g In, ¹¹⁵In(γ, 7n)^108m,g In are obtained. The Bremsstrahlung of electrons with energies within 32–84 MeV from the LU-40 linear accelerator was used for the irradiation of targets. The energy resolution and mean current of the electron beam were ～1% and 5 μA, respectively. The induced activity was used to obtain experimental isomer ratios. An HPGe spectrometer with an energy resolution of 1.9 keV for ⁶⁰Co γ-line 1332 keV was used to acquire the instrumental γ-ray spectra of the activation products. A set of serial measurements with various acquisition times was performed. The cooling times varied from 5 seconds to several hours for Ag and up to tens of hours for In specimens. The obtained experimental isomer ratios are compared with the results from theoretical calculations.     

Simple numerical model of radio wave multiple scattering effects in the ionospheric plasma layer

Numerical simulation of radio energy transfer in the ionospheric layer with random small-scale irregularities for the case of a point ground-based source and total reflection has been carried out using a specially designed algorithm based on Monte Carlo method ideas. The model demonstrates a redistribution of the reflected radiation power at the Earth's surface caused by multiple scattering. The data obtained can serve as confirmation of the effect of the anomalous attenuation of the signal power in the vicinity of the sounder. This result is in agreement with a more rigorous theory of the anomalous attenuation effect based on the solution of the radiative transfer equation.     

Experimental study of discontinuities in a cylindrical slot line

Radiophysics and Quantum Electronics -     

Mechanochemical Activation of Solid Salts K2PtX6 (X = Cl,Br)

Mechanochemical treatment of solid-phase K₂PtX₆ salts in a vibrating mill in an argon or air atmosphere produced paramagnetic Pt(III) complexes via the homolytic cleavage of the Pt–X bond. Lewis acid sites were found on the surface of the mechanically activated K₂PtCl₆ salt using the paramagnetic probe method. The sites can be attributed to coordinatively unsaturated Pt(IV) complexes formed via Pt–Cl bond heterolysis.     

Amplification of holographic gratings in photorefractive crystals

In this work, we have theoretically and experimentally investigated the process of image amplification in photorefractive crystals as a result of the self-diffraction phenomenon. We have found that the amplification process is of the threshold type and is observed only for an angle of convergence of the light rays greater than a threshold value. The gain coefficient is rather high. For the LiNbO₃ crystal, at a wavelength of 0.63 µm the gain coefficient reached 15 dB; at a wavelength of 0.44 µm, the gain was greater than 50 dB.Tomsk State Academy for Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 22–26, June, 1994.