Modification of the intersubband excitation spectrum in a two-dimensional electron system under a perpendicular magnetic field

Under an external magnetic field, new branches of spin- and charge-density waves have been studied in a quasi-two-dimensional electron system whose ground state has more than one Landau level occupied by electrons. These collective excitations can be treated as manifestations of the multicomponent nature of the electron system in magnetic field, whereas the occupied Landau levels should be associated with degrees of freedom.     

Cyclotron spin-flip mode in the extreme quantum limit

In a two-dimensional electron system, the combined excitation (the cyclotron spin-flip mode) associated with changes in both orbital and spin quantum numbers is investigated. The energy of the cyclotron spin-flip mode is studied as a function of the electron filling factor. Comparative dependences of the decay times of the cyclotron spin-flip mode and the magnetoplasmon are measured. It is shown that, as the filling factor increases from v = 0 or decreases from v = 1, the damping of the cyclotron spin-flip mode increases significantly, while the magnetoplasma mode remains undamped.     

Influence of γ-irradiation on the kinetics of heat release during the interaction of an aqueous solution of HNO3 with aliphatic hydrocarbons

The influence of preliminary γ-irradiation and γ-irradiation during hte oxidation process on the kinetics of heat release in the systemsn-decane—aqueous solution of HNO₃ and a solution of tributyl phosphate in a kerosene—aqueous solution of HNO₃ was studied. The preliminary γ-irradiation of the system at 43°C increases the initial rate of the process (k ₁). The increase is proportional to the irradiation dose at doses up to 150kGy, then the increase ink ₁ is retarded, and the further course of the process becomes practically independent of the irradiation dose. The effect of γ-irradiation during the oxidation depends on the temperature of the system: at temperatures lower than 80 °C, γ-irradiation increases the rate of heat release, whereas at higher temperatures, γ-irradiation decreases the rate of heat release. The effects observed were explained by the competition of NO₂ accumulation due to the radiolysis of nitric acid and processes of the addition of NO₂ to unsaturated hydrocarbons produced by the radiolysis of the organic phase. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1116–1120, June, 1998.     

Preparation and properties of secondary amides of 1,1-dinitroalkanecarboxylic acids

The previously unknown secondary amides of 1,1-dinitroalkanecarboxylic acids were prepared by the reaction of polynitroimidoyl fluorides with water in the presence of mineral acids. They are inert with respect to electrophiles, but react with nucleophiles with the cleavage of the C-C bond between the carbonyl C atom and the C atom of the dinitromethylene group. An X-ray structural study of the amides was carried out and their thermochemical characteristics were determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 877–881, May, 1994.     

Magnetooptic measurements of the cyclotron mass and g-factor of light holes in GaAs

An emission line appearing in the hot-luminescence spectrum of GaAs at a frequency shifted from the laser line by the cyclotron energy of light holes is observed and investigated. Analysis of the magnetooscillations of the intensity of this line shows that the line is due to the recombination of a photoexcited electron and a light hole after the hole undergoes energy relaxation between Landau levels. The dependence of the cyclotron mass and g factor of light holes on the hole energy was measured directly and a very strong nonparabolicity of the valence band of GaAs, several times greater than the theoretical estimates, was observed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 11, 766–771 (10 December 1996)     

Synthesis of titanium nitride and carbonitride nanopowders in confined-jet flow plasma reactor

The synthesis of titanium nitride and carbonitride nanopowders from titanium tetrachloride vapor in a stream of hydrogen–nitrogen plasma, generated by an arc torch, in confined-jet flow reactor has been experimentally studied. Single-phase nanopowders with a NaCl-type cubic crystal lattice as assemblies of preferably cube-shaped nanoparticles of a 20–150 nm size and aggregates based on them have been obtained in the experiments. By varying the synthesis parameters, it has been possible to prepare titanium nitride nanopowders with a specific surface area in the range of 11–39 m²/g containing 18.8–22.5 wt % nitrogen, which corresponds to the empirical formula TiN_0.79–TiN_0.99. The titanium carbonitride nanopowders had a specific surface area of 13–23 m²/g and carbon and nitrogen contents of 7.5–13.6 and 13.5–5.1 wt %, respectively.     

Intersubband collective excitations in a quasi-two-dimensional electron system in external magnetic field

The spectrum of collective excitations in a quasi-two-dimensional electron system was studied by the method of Raman scattering spectroscopy. In an applied magnetic field, such systems exhibit collective excitations related to the electron transitions between dimensionally quantized subbands with a change in the Landau level index (intersubband Bernstein modes). It is shown that these modes interact with the fundamental intersubband excitations of the charge and spin densities, the interaction energy being determined by the excitation quasimomentum. Interaction of the intersubband Bernstein modes and the fundamental intersubband excitations with quasi-two-dimensional LO phonons was studied. Behavior of the new branches of collective excitations in a quasi-two-dimensional electron system possessing more than one occupied Landau level was studied and the nature of these branches was determined.     

Preparation and properties of N-fluoro- and N-nitrobis(2,2,2-trinitroethyl)ureas

Fluorination and nitration of bis(2,2,2-trinitroethyl)urea has given the novel N-fluoro-bis(2,2,2-trinitroethyl)urea and N-nitro-bis(2,2,2-trinitroethyl)urea. The thermal decomposition rates and parameters for bis(2,2,2-trinitroethyl)urea and its derivatives have been found, and the standard enthalpies of combustion, and the standard enthalpies of formation of these compounds calculated therefrom, have been determined.Institute of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1857–1863, August, 1992.     

Heat release kinetics in the reaction of decane with nitric acid

The kinetics of the reaction of decane with nitric acid (25.07–75.53 %) at 57.8 to 119 °C in an acid-decane-gas triphasic system was studied. The main contribution to the rate of heat release is made by the oxidation of decane with nitrogen dioxide in the organic phase proceedingvia the mechanism of a degenerate branched-chain reaction. Nitration plays the role of a chain termination reaction. The acid phase is the source of NO₂, whose content increases with oxidation. The equilibrium of the nitrogen dioxide distribution in the triphasic system was analyzed. The kinetic law of the reaction, the dependences of the reaction constants of the initial and catalytic stages on temperature and the acid phase composition were determined. The results allow one to calculate the rate of heat release in the decane-HNO₃ system under any conditions of the process.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1986–1991, August, 1996.