Vol 12, No 6 (2018)

Recently it has been theoretically predicted and experimentally confirmed that at altitudes of 80–110 km from the Earth’s surface the signals of the global navigation satellite systems (GNSS) are delayed as a result of a multiple resonance scattering by the Rydberg complexes. The attenuation of GNSS signals occurs mainly in the lower atmosphere layers, where the greatest effect is achieved through interaction with charged aerosol layers. A thunderstorm conditions are of particular interest whereby the presence of strong electric fields and hydration of aerosols can lead to the detachment of OH radicals from water clusters. Since the spectrum of radiation and absorption of these radicals for rotational transitions is part of the microwave range, they are expected to make an additional resonance contribution to the delay of radio signals thus necessitating a detailed study of the electronic structure of the OH radical. This paper offers the ab initio calculations of the dipole moment function for the ground X²Π state of the OH molecule using the dipole length approach and the finite-field method. The comparison with the experiment shows that in extended model spaces the approximation of the dipole length leads to more accurate values of the dipole moment than the finite-field method.

The paper considers the relativistic multimode Jahn–Teller effect ²E_u × (b_1g + b_2g + e_u) for square molecular complexes with a heavy central atom and an odd number of electrons. All the 32 elements of the double symmetry group D′_4h, are determined that which are space-matrix operators. A vibronic 4 × 4 matrix is obtained in the quadratic approximation with respect to the normal modes for the contributions of the electrostatic Hamiltonian and in the linear approximation for the contributions of the spin–orbit coupling. Fourmode potential energy surfaces are presented in the form of analytical expressions.

We compare the dynamics of two elementary reactions of recombination of atomic ions, namely, of the termolecular process of two ions and the third body (1) and of the bimolecular interaction of an ion with the diatomic cluster (2) consisting of the second ion and the neutral atom. It is shown that, despite the fact that both processes yield the same products, the main dynamical characteristics of these processes differ. First of all this concerns the excitation function which confines recombination for (2) by a collision energy up to 2 eV. The opacity functions of both processes have different structures. The distributions of the product vibrational energy in both the processes exhibit a non-equilibrium character, while the rotational energy distributions are equilibrium.

The dynamics of polaron on a one-dimensional harmonic lattice in a constant electric field is considered in detail. Calculations were performed with parameters approximately corresponding to the parameters of polyacetylene and DNA. The polaron in a constant field comes out to a steady state characterized by a constant profile and velocity. The energy imparted to the polaron by the electric field is converted to longitudinal coherent lattice vibrations. For several thousand lattice points, these vibrations are constant in their frequency and wavenumbers, which weakly depend on the strength of electric field.

In the oxidation of linoleic acid esters in micelles the high kinetic isotope effect has been found to be equal to 23.6. The low value of the oxidation rate of linoleic acid ester deuterated in bis-allylic position (LD₂) is explained by the absence of its interaction with HO₂^. radicals formed in the course of oxidation. The influence of superoxide dismutase on kinetics of (LD₂) oxidation inhibited and non-inhibited by nitroxyl radical, as well the absence of LD₂ oxidation when the process is initiated by HO₂^. radicals, confirms this conclusion.

The kinetics and products of the thermal decomposition of 2,4,6-triazido-3,5-difluoropyridine in melt at temperatures of 120–160°C have been studied using pressure measurements, differential thermal analysis, and IR spectroscopy. The reaction occurs in two macroscopic steps, each described by a first-order kinetic equation. In the first, the activation energy and the common logarithm of the pre-exponential factor are 35.6 ± 1.2 kcal/mol and 15.1 ± 0.6 s^–1, respectively. For the studied compound (and certain other heterocyclic azides, such as 2,4,6-triazido-1,3,5-triazine and 2,4,6-triazidopyrimidine), the pre-exponential factor is anomalously high. This is due to the fact that the 2,4,6-triazido-3,5-difluoropyridine molecule contains no hydrogen atoms. For such azides, the usual decomposition mechanism (cleavage of the azide group with subsequent attack of nitrene on a hydrogen atom of a neighboring molecule) is impossible, which favors the stability of the formed nitrene. In this case, the reaction occurs through a complex chain polymerization mechanism, which leads to the formation of specific condensed products: packs of planar polyconjugate carbon–nitrogen networks with a porphyrin-like structure.

A mechanism for the thermal reduction of graphite oxide is proposed. The process begins with the homolysis of the C–C bond in the basal plane of graphite oxide with subsequent reactions of isomerization of the formed radicals. The formation of both CO and a significant amount of CO₂ was explained to occur via the cleavage of 1,3-dioxetane, which forms by the disproportionation and recombination of free radicals.

In this paper, the flame penetration of a dilute methane–oxygen mixture through obstacles containing fine-meshed iron grids with Pd-wire turns is studied, using high-speed recording. It is shown that the Pd catalyst can, under certain conditions, suppress the development of flame propagation in a dilute methane–oxygen mixture since the Pd surface is highly efficient in the termination of active reaction centers. Therefore, kinetic factors can be important even under conditions of high turbulence. Numerical simulation using the Navier–Stokes equations for a compressible reaction medium in the low Mach-number approximation shows a qualitative agreement with a number of experimental regularities. The results obtained are of interest for the model development of turbulent flows in reactive media and in matters relating to explosion safety.

Measurements of the complex magnetic susceptibility as a function of the temperature, alternating field amplitude, and the parallel applied constant field values for a series of YBa₂Cu₃O_y high-temperature superconductor samples synthesized by two different methods using of the sol–gel technology have been carried out. Regularities in the change of crystalline sizes and critical superconducting parameters are determined depending on the synthesis conditions. For all the samples, both the average temperatures of the transition to the superconducting state and their ranges, which characterize the homogeneity of the sample, remain at the level of the maximum values achievable for this compound. It is concluded that different types of the nanoscale inhomogeneity of the crystalline structure manifest themselves in the differences of the temperature dependences of the transport critical current. Means of further improving the sol–gel method for producing fine-grained ceramics with desired properties are outlined.

The effect of organic cosolvents (ethanol and isopropanol) on the viscosity characteristics of acetic acid aqueous solutions of chitosan is studied. Sorption and deformation–strength properties, as well as resistance to the process of enzymatic degradation of materials obtained from solutions, are determined. It is shown that the introduction of cosolvents into the chitosan–1% acetic acid system is accompanied by a consistent decrease in the intrinsic viscosity of polymers. It is found that, in the presence of cosolvents, at concentrations below the crossover concentration, chitosan molecules exist as systems of interacting (aggregated) macromolecules rather than isolated macromolecular coils. A change in the conformation of chitosan and the type of macromolecular aggregates in acetic acid solutions in the presence of cosolvents leads to a number of consequences: polymer units become less accessible to an enzyme preparation, the rate of enzymatic degradation decreases, and mechanical characteristics of film materials change.

An abrupt change in the electrophysical properties of aqueous colloidal nanodiamond solutions, which is associated with a change in the spatial structure of nanodiamond-based aqueous nanoassociates, is shown. The freezing point depression and the hysteresis of conductivity and dielectric permeability are determined. The zone crystallization of a detonation nanodiamond in aqueous solutions is studied.

A method of searching for a basis of nonlinear parametric functions that affords expressions reflecting the process kinetics was used for complex multistage polymerizations. The basis of functions found for the given polymerization, which differs only in the termination of the kinetic chain, characterizes the degree of relationship and independence of the kinetic rate constants of each stage from one another.

Crumb rubber–starch composites of various compositions were produced by shear deformation in a closed-type mixer (Brabender). It was found that the introduction of starch increases the elastic modulus, decreases the elongation at break, and hardly influences the ultimate tensile strength. The observed increase in the mechanical parameters after exposure to soil is likely to be due to crosslinking under environmental action, which was confirmed by IR spectroscopy. Using X-ray microtomography, the porosity in the matrix was calculated, and exposure to soil was shown to increase the porosity.

An impulsive model of dissociation of diatomic molecules with an ionic bond (for instance, alkali halide molecules) at a graphite surface is proposed. Within the framework of this model, a single encounter of an ion with the surface can consist of several elastic hits of the ion against graphite pseudoparticles of various masses. These hits instantly follow each other and are described in general in the same way as in Logan’s and Stickney’s well-known “hard-cube model” of scattering of atoms from a solid surface. The calculation results for dissociation of KI molecules with a translational energy from 4 to 14 eV are presented.

The chemical composition of the middle atmosphere (composed of the troposphere, stratosphere, and mesosphere) and its changes in the 21st century are considered. The initial data were obtained from the interactive two-dimensional radiation–chemical model SOCRATES, which calculates the height profiles of components with a resolution of 1 km in the latitudinal zone from 85° S to 85° N, with a step of 5°. The initial conditions were taken to be the Intergovernmental Panel on Climate Change (IPCC) RCP 4.5 scenario for June and January of 2000 and 2100 at a latitude of 50° N. For these conditions, the height profiles and the total content of the long-lived components N₂O, CH₄, and CO₂; chlorofluorocarbons (CFCs) CFC-10 (CCl₄), CFC-11 (CCl₃F), CFC-12 (CCl₂F₂), CFC-113 (CCl₂FCClF₂), CFC-114 (CClF₂CClF₂), CFC-115 (CClF₂CF₃), halon-2011 (CBrClF₂), and halon-1301 (CBrF₃), hydrochlorofluorocarbon (HCFC) HCFC-22 (CHClF₂); acids HF, HCl, HBr, and HNO₃; atmospheric trace gases O(³P), O(1D), H, OH, HO₂, H₂O₂, Cl, Cl₂, ClO, OClO, HOCl, ClONO₂, ClNO₂, Cl₂O₂, N, NO, NO₂, NO₃, N₂O₅, HO₂NO₂, Br, BrO, HOBr, BrONO₂, and BrCl, as well as the chemical families O_x (O₂ + O(³P)), HO_x (OH + HO₂), NO_x (NO + NO₂ + NO₃), ClO_x (Cl + ClO), and BrO_x (Br + BrO). Among other conclusions, it has been shown that for June 2100, the relative change (in %) in the total content of components in the ClO_x, O_x, BrO_x, NO_x, and HO_x families in the stratosphere, in comparison with June 2000, would be–57.5%, +4.0%,–25.7%,–13.9%, and–4.1%, respectively. For January, the corresponding values for ClO_x, O_x, BrO_x, NO_x, and HO_x are–59.1%, +7.3%,–26.2%,–7.1%, and–3.6%, respectively. Similar comparisons have been made for the other components mentioned above. Almost all chemically active components are highly sensitive to the season change.

The author’s name should read H. Schmidt instead of Kh. Shmidt