Том 124, № 5 (2018)

A procedure for diabatization of quantum-chemical data is proposed that allows one to surmount the problem of -shaped peaks of nonadiabatic matrix elements \( < j|\frac{\partial }{{\partial R}}|k > \) by passing to a hybrid diabatic representation of a system of coupled channel equations of nuclear dynamics with the use of model nonadiabatic matrix elements that approach initially specified matrix elements. Results of the application of this method within the framework of the Landau–Zener model are presented for the example of the CaH collision system.

The possibility of using the available spectroscopic databases for high-precision measurements of spectral parameters of gases has been studied. A new approach to measuring concentrations of gaseous components (НCl, CO, NO, SO₂) in gas mixtures employing the HITRAN or GEISA spectroscopic databases has been proposed. A certification method of control gas mixtures using Fourier-transform IR spectroscopy has been developed to transfer the mole-fraction units to working standards in order to reduce the required number of reference standards and improve the accuracy of measurements.

We discuss the fluorescence spectra from a set of points in histological sections of colon tissue with different levels of pathology that were stained with hydrophilic semiconductor CdSe/ZnS nanoparticles that were modified by a unique method at the phase interface. The shifts in the fluorescence spectra that were recorded for stained cells at different pathologies are described using the electrochromism of the nanoparticles. Aqueous solutions of the CdSe/ZnS nanoparticles with different pH values are used as systems that model the acidity of a biological medium. It has been shown that the shifts of the fluorescence bands of the CdSe/ZnS nanoparticles are caused by a change in the local electrical field that is induced by solvated ions near their surface at different pH values of the solutions. The application of the CdSe/ZnS nanoparticles as nanoprobes for the local pH in biological tissue is discussed in the context of this model.

The possibility of using a new composite material based on porous silicon containing silver nanoparticles and synthesized by means of a unique implantation nanotechnology as an optically sensitive material in biological and chemical sensors is tested experimentally. It is demonstrated that detection of small amounts of the studied organic substance (methyl orange dye) is possible due to the effect of surface-enhanced Raman scattering (SERS) from the molecules affected by the local electromagnetic field of the silver nanoparticles.

We have examined low-frequency Raman spectra of intermolecular vibrations of weak aqueous solutions of hydrogen peroxide and water. The differences between the observed Raman frequencies and the data from the literature on the IR-absorption frequencies of the same vibrations, as well as the interrelations between the frequencies and the widths of Lorentzian contours that approximate the vibrational spectra of the dynamic susceptibility, have been discussed. Based on a model of free damped vibrations of a classical oscillator with an inhomogeneous broadening, we have explained these effects for the first time. The homogeneous line widths and the damping times of the observed intermolecular vibrations have been determined. The eigenfrequencies of these vibrations have been calculated, and they have been shown to agree well with the data from the literature on the frequencies of IR absorption of water. We have shown that these parameters of intermolecular vibrations for water and for aqueous solutions of hydrogen peroxide differ from each other.

Spectral, kinetic, and nonlinear optical regularities that demonstrate the exchange of electronic excitations between the components of hybrid associates of Ag₂S colloid quantum dots (1.7–1.8 nm) in gelatin with molecules of thiazine dyes (Ds) are found. When the IR luminescence of Ag₂S quantum dots (QDs) is excited by radiation from the thionine absorption region, its enhancement due to nonradiative resonant energy transfer is observed. The association with methylene-blue molecules blocked the IR luminescence of Ag₂S QDs upon its excitation by radiation from the absorption region of the dye due to the transfer of charge carriers. It is demonstrated that the hybrid association of thionine molecules and Ag₂S QDs adversely affects the nonlinear optical properties of the latter, which manifests itself in inverse saturated absorption by the action of 10-ns second-harmonic pulses (532 nm) of a Nd³⁺:YAG laser. For the associates of Ag₂S QDs with methylene-blue molecules, the radiation focusing caused by the transfer of charge carriers from the dye and the change in the population of small traps in nanocrystals is found. It is concluded that the direction of the transfer of electronic excitations and the photophysical processes in these objects are determined by the mutual arrangement of the HOMO–LUMO levels of the dye with respect to the levels of dimensional quantization of the Ag₂S QDs.

We present the results of our experimental investigation of the transmission of plates of zinc-selenide crystal doped with iron at a level of 0.23 mass % in the terahertz-frequency range and compare them with the transmission of undoped samples. We show that the presence of iron impurities in a zinc-selenide sample makes the medium more transparent in the frequency range from 0.35 to 0.5 THz. The transmission of a doped sample in this range increases to 20% compared to pure ZnSe. This result can be used in the future to create efficient devices for controlling terahertz radiation.

The optical and physicochemical properties associated with the change (oxidation, thermolysis and photolysis), during the operation, of the spatial and electronic structures of the polyfunctional hydrocarbon compounds, oils, oil products, and N-, O-, and S-containing heteroaromatic compounds and additives, which comprise a variety of fuel and lubricant compositions involved in the structural and phase rearrangements, as well as in the formation of colloidal and micelle aggregates altering the structure with respect to their hydrocarbon, chemical, and fractional compositions, are investigated. The spectroscopic-luminescent properties of the compounds and their ion-radical forms were studied using optical and spectroscopic methods and quantum-chemical calculations when the excitation energy in the full spectra of singlet and triplet (for the ion, quartet and doublet) electronic excited states was deactivated. Intramolecular mechanisms of the hyperfine electron–nucleus interaction between the active groups of quasi-oscillators in the structure of polyfunctional compounds in the paramagnetic states of hydrocarbons, which form the electronic structure of the triplet–triplet transitions induced by pumping in the optical absorption spectra, are studied. It is shown that the mechanism of multistep ionization, fragmentation, and appearance of radicals and the electronic-vibrational mechanism of an increase in the vibration temperature up to T = 6000–7000 K are developed during the action of the ultraviolet (UV) pumping pulse of a nanosecond duration until the light emission, which gives rise to thermolysis and recombination that create the conditions for the combustion and explosion when the excitation energy is localized on a limited number of groups of quasi-oscillators in the structure.

The transformation of light by a nonlinear beamsplitter is considered. The beamsplitter is formed by a plane interface between two transparent dielectrics, at least one of which has a Kerr nonlinearity; i.e., its refractive index depends on the intensity of the penetrating radiation. It is shown that the interpretation of the result of calculation of quantum fields at the outputs from such a beamsplitter indicates a violation of the principle of causality in the sense that a subsequent event affects the previous one.

A multiqubit channel (quantum gate) is considered. A procedure of calculating the distance from the quantum-gate matrix to the subspace of matrices, which are tensor products of the transformation matrices of qubit subsystems, is proposed. The value of this distance indicates the degree of independence of transformation of these qubit subsystems. The proposed approach is considered as applied to waveguide implementation of quantum bits.

The optical-reflection spectra of microarrays of silicon nanopillars are studied in the visible and near-IR regions. The microarrays of silicon nanopillars are formed by electron-beam lithography and reactive ion etching. The reflection spectra of nanopillar arrays with pitches of 400, 600, 800, and 1000 nm are measured. The height of nanopillars in the array is 0.5 μm, and the diameter varies from 150 to 240 nm. It is noted that the spectral features of the reflection are caused by increased absorption of individual nanopillars and interference effects inside the array. A relation between the geometric parameters of nanopillars and the resonance reflection characteristics is determined taking into account the influence of the substrate.

A thin film of As₅₀S₅₀ chalcogenide glass modified by femtosecond laser radiation at a wavelength of 800 nm has been studied. The character of the modification has been analyzed by interferometry, atomic-force microscopy, and Raman spectroscopy. The relationship between a change in the refractive index upon the sample modification and structural changes in the glass network is determined.

The efficiency of interval methods for selecting variables and the divisive method of interval optimization by a genetic algorithm is considered with the purpose to increase the accuracy of temperature calibration by projection onto latent structures. The fluorescence spectra of Yb³⁺:CaF₂ recorded in the 880–1120 nm band with a resolution of approximately 0.2 nm in the temperature range from 66 to 150°C in 2°C increments are used as an example. The best result for the root-mean-square error of temperature prediction in the test sample (0.45°C) was obtained by interval projection onto latent structures by a combination of moving windows. The use of methods for selecting spectral variables improved more than two times the accuracy of temperature calibration.