Vol 53, No 3 (2019)

Segregation of di- and trivalent impurities to the (00.1), (01.2) and (11.3) surfaces of α-Al₂O₃ has been investigated using molecular mechanics simulation. In this work, the focus has been on segregation energy calculations depending on impurity size, distance to the surface, and surface coverage. It has been shown the anisotropic segregation of dopants. The segregation energy to the most stable (00.1) surface has the lowest absolute value for all investigated impurities. For trivalent impurities at the (01.2) surface the dependence of the segregation energy on surface coverage has the minimum, which corresponds to the ordered arrangement of dopants. At the (11.3) surface the multilayer segregation has been observed, whereas at the (00.1) and (01.2) surfaces the model of monolayer segregation is acceptable in most studied cases.

When irradiation generates two radicals capable of initiating chain growth with different rate constants for chain transfer, two polymerization routes with different average chain length emerge. These pathways are not mixed in the initial part of the ballistic growth. Their mixing in chain transfer events is accompanied by transition from ballistic to diffusion growth. In the sol–gel transition region, the routes are spatially separated if the chain transfer depends on the rotational mobility of the reactants and decreases with increasing viscosity as the resulting oligomers accumulate. As an example, the polymerization of tetrafluoroethylene in solutions of silanes and oxysilanes is considered.

The applicability of a uranyl oxalate actinometer as a means of measuring fluence from a source of high-intensity continuous-spectrum pulsed radiation is substantiated. A calculation procedure in a stationary photochemical system has been proposed and tested to demonstrate good agreement with computational methods.

[2+2] Photocycloaddition of a series of styryl dyes (a, b, and c, see text) in the cavity of cucurbit[8]uril (CB8) in aqueous solutions has been studied by optical spectroscopy. The complex formation constants were calculated for the 1 : 1 and 2 : 1 complexes of the styryl dyes with CB8. The optimal CB8 to dye molar ratios that correspond to the highest concentrations of the 2 : 1 complexes in the solution have been determined as 0.5, 0.3, and 1 for dyes a, b, and c, respectively. The quantum yields of photocycloaddition have been calculated from the results of dye photolysis in the presence of CB8: 0.06, 0.02, and 0.04 for a, b, and c, respectively. The fluorescence decay kinetics has been studied on the picosecond timescale. The lifetimes found are 1–2 ps, which correspond to the characteristic time of the solvation shell effect on the redistribution of the dye charge in the excited state. The long component of the fluorescence decay on the order of tens of picosecond is also observed. This component decreases in the presence of CB8, indicating the formation of dimeric state.

The photovoltaic composite formed by narrow-gap copolymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(bithiophene)] and methanofullerene [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) has been studied in a wide energy range of generating photons, 1.32–3.14 eV at T = 77 K, by the light-induced electron paramagnetic resonance. It has been shown that some polarons are captured by spin traps formed in the copolymer matrix, and the concentration and depth of such traps are determined by the photon energy. The recombination kinetics of polarons and fullerene radical anions after turning off the light can be described in the framework of a second-order bimolecular process. The formation of spin traps in the copolymer matrix and the exchange interaction between different spin packets cause the extreme sensitivity of magnetic resonance and electronic parameters of charge carriers to the number and energy of generating photons.

The main results of successful 30-year’s working on the Gammatok-100 radiation research facility at the Institute of Problems of Chemical Physics to study various radiation-induced chemical transformations are summarized. The advantages of the unique radiation facility, the design features of which allowed its continuous operation during the entire time of its existence, are noted. Reloading gamma-radiation sources in the facility has made it possible to increase the efficiency of its use by increasing the radiation dose rate (more than 50 times) and intensifying scientific research. The prospects for the development of new basic and applied areas of radiation chemistry are presented.

The main operating modes of a radiofrequency induction plasma torch with a vortex stabilization of the atmospheric-pressure gas discharge at have been studied in an argon-hydrogen mixture in the range of Ar/H₂ = 12–4. The dependences of the electron temperature T_e and number density n_e on the Ar/H₂ ratio have been experimentally studied. It has been found that the electron temperature and concentration in pure argon plasma are 0.88 eV and 7.6 × 10¹⁴ cm⁻³, respectively. When the Ar/H₂ ratio decreases, the electron temperature decreases to 0.42 eV, and the electron number density is 8 × 10¹² cm⁻³. The calorimetric method used to estimate the gas temperature T_g, has given a value of 2500 K. The process of BCl₃ reduction with hydrogen has been studied at the implemented operating modes of the induction plasma torch. The main products of the reduction of boron trichloride are a polycrystalline boron powder and dichloroborane. The morphology of boron and its phase composition and impurities have been studied. The average particle size of the boron powder is 200 nm.