Vol 44, No 5 (2025)

To estimate the rate constants of monomolecular reactions using quasi-equilibrium statistical theory, information on the density of discrete states of molecules is required. In the present work, a new approach to calculating the density of discrete states of stable molecules and transition complexes is proposed, which is based on the numerical inversion of the Laplace transform. To test the method, the calculations of model systems including H₂O, NH₃, CD₄ and с-C₃H₆ molecules were carried out. It is shown that at energies less than 200 kcal/mol, the relative error in calculating the density of discrete states does not exceed 0.5%. The results obtained by this method can be used, for instance, to estimate the rate constants of reactions involving organic radicals formed in the troposphere and tropopause.

Broad ion beam etching by Ar⁺ with low energy up to 1000 eV has been utilized to modify physicochemical properties of the monocrystalline Silicon (100) surface. The silicon surface modification results in etching delay time during its vacuum-plasma etching in a SF₆/O₂/Ar mixture. The etching delay time of the modified Silicon has been found to be significantly affected by conditions of preliminary silicon treatment with the ion beam such as the ion energy and the ion incidence angle. The enhancement in the etching delay time has been detected while lower ion energy and higher ion incidence angle are applied. The combination of the ion beam etching and the vacuum plasma etching could be concerned as the suitable way to form silicon structures.

The possibility of obtaining porous two-dimensional cobalt structures (films) with submicron thickness using cobalt oxalate as a precursor during heat treatment in a hydrogen flow has been established. It is shown that the formation of two-dimensional structures on liquid low-melting metals (In, Ga) allows avoiding the formation of cracks and increases the integrity of Co films. It is shown that the thickness of Co films on Si reaches 100 nm, but the linear size of such cobalt sheets does not exceed 20 microns. The use of low-melting indium as a substrate makes it possible to increase the average size of Co films compared to Co films on silicon without an intermediate indium layer. The material is a thin two-dimensional layered structure of porous cobalt formed by interlacing metal chains. The film thickness is ~ 500 nm, and the linear size reaches 200 microns. The possibility of obtaining a durable metal film of Co-10% Ga on a massive drop of gallium measuring 20x15 mm has been established.

Quantum chemical calculations are performed to determine the heats of hydrogenation for the simplest nanosized Au₃^–/Ni₂⁺ bimetallic system via three possible reaction pathways. It is shown that the reaction pathway releasing maximum energy is Au₃^–/Ni₂⁺ + H₂ → (Au₃H₂)^–/Ni₂⁺ with a heat of reaction of 43.7 kcal/mol. Quantum chemical methods are also used to calculate the heats of reaction for several reaction pathways between Au₃^–/Ni₂⁺ and oxygen. It is found that the pathway that releases maximum energy adds one O atom to Au₃H₂ while the other one combines with nickel, (Au₃H₂)^–/Ni₂⁺ + O₂ → (Au₃H₂–O)^–/(Ni₂O)⁺, with a heat of reaction of 39.0 kcal/mol. The reaction mechanism and energy budget are determined for the elementary steps involved in the production of gold Au₃^– and water from the oxide (Au₃H₂–O)^–. Based on the calculated results, an explanation is proposed for experimental results on successive exposure of a gold–nickel bimetallic nanocoating to hydrogen and oxygen. Since contact between gold and nickel results in negatively charged gold and positively charged nickel particles, the calculations are performed for negatively and positively charged gold- and nickel-containing particles, respectively.

In this study, the rate constant of the reaction between hydroiodic acid and a chlorine atom was measured using the resonance fluorescence (RF) method in a flow reactor within the temperature range of 298–366 K. Measurements were performed by detecting the RF of both chlorine atoms and iodine atoms, the latter being a product of this reaction. In both cases, similar expressions describing the temperature dependence of the rate constant were obtained. A possible explanation for the observed decrease in the reaction rate constant with increasing temperature in the reactor is proposed.

The patterns of occurrence and propagation of low–velocity detonation (LVD) in ammonium perchlorate and its mixtures with polymethylmethacrylate and aluminum ASD-4 with a relative density of up to 0.98 in durable non-destructive shells when initiated from the blind end are determined. It is shown that the addition of polymethylmethacrylate to ammonium perchlorate facilitates the transition of burning to LVD. The influence of the size of the oxidizer particles, the diameter, and the structure of mixtures on the spread of LVD is revealed. It is established that the ignition and burning of aluminum in a mixture with 15% polymethylmethacrylate 75% ammonium perchlorate 10% ASD-4 with a porosity of 2% occurs ~ 6 microseconds after the passage of a shock wave through it.

In this paper, a comparative experimental and theoretical study of two etioporphyrin complexes (Cu-EtioP-III and VO-EtioP-III) with transition metals is carried out. The sublimation enthalpies of Cu-EtioP-III and VO-EtioP-III were determined to be 145(3) kJ/mol and 195(5) kJ/mol, respectively using the Knudsen effusion method with mass spectrometric control of the vapor composition. The electronic absorption spectra of vacuum-sublimated Cu-EtioP-III layers were simulated using TD-DFT calculations for mono-, di-, tetra- and hexameric forms with the geometric structure corresponding to the crystal unit cell. Comparison of the results with similar data for VO-EtioP-III allows us to draw conclusions about the ability of the simplest natural porphyrinoids to form intermolecular bonds during aggregation (in thin layers, crystals).

Variations of nanoporosity obtained on casting of membranes from the original highly dispersed polyphenylene oxides (PPO) of various crystallinity (from 0 to 69.2%) on the bases of the data, obtained by the methods of positron annihilation and low temperature gas (N₂, CO₂) sorption, are discussed. The notion of nanoporosity includes microporosity and mesoporosity of the materials with pore sizes from some Å up to several tens of nanometers. A combination of the results of positron annihilation and sorption measurements with oxygen permeation data for the created membranes allow to conclude that, on transition from powder to solid membrane, microporosity is mostly stays unhanged while mesoporosity essentially transforms.

Gravity waves (GWs) are one of the triggers of ionospheric disturbances that can influence ionospheric propagation of radio waves and the work of radio-technical systems. The paper considers the actual problem of estimating the response of the F2-layer of the ionosphere to the propagation of GWs from the meteorological storm region in the troposphere. The study is carried out by the numerical modeling method based on the solution of the ionospheric plasma diffusion equation taking into account the perturbation of the nEᵤtral wind under the GWs action. The amplitude of the perturbation was set based on numerical calculations of the physical model of the GSM TIP with inclusion of a realistic GWs source. The numerical estimates showed that the nEᵤtral wind perturbations in the thermosphere with a period of several hours lead to a significant decrease of the electron density and an increase of the maximum height of the F2-layer under geomagnetically quiet conditions.