Vol 124, No 1 (2018)

The spectrum of excitation of Rydberg states of thallium atoms has been investigated using a collimated atomic beam in a two-step isotope selective laser scheme 6²P_1/2 → 6²D_3/2 → Tl** in the presence of an electric field with a strength of up to 1.5 kV/cm near the level 16F_5/2. The optical transitions 6D_3/2 → 18D_3/2 and 6D_3/2 → 16G_7/2, which were induced by an external electric field and dipole-forbidden, have been studied experimentally. The values for the scalar polarizabilities (in units сm^–1/(kV/сm)²) α₀(16F_5/2) = 3.71 ± 0.3, α₀(18D_3/2) = 11.70 ± 0.25, and α₀(16G_7/2) = 44.1 ± 0.9, which are compared with the calculated one, have been obtained. The new values of energy parameters for the states 18D_3/2 and 16G_7/2 have been determined.

The spectrum of transitions to high-lying odd states of the neodymium atom in the UV range from 317 to 323 nm is studied by resonance laser excitation and ionization. Fifty-five of the 72 transitions detected are observed for the first time. For the brightest lines (18), the lower levels of transitions are identified, the energies of the upper levels are determined (31023.813–33437.403 cm^–1), and the isotope shifts between ¹⁴²Nd and ¹⁴⁴Nd are measured. The shifts for all stable even neodymium isotopes are measured for five transitions (142–150).

General formulas are derived that describe the changes in equilibrium distances, valence angles, and vibrational frequencies of a polyatomic molecule in a strong laser field. It is shown that the coordinates of normal vibrations do not change in the second order in the field strength. For a nonlinear triatomic molecule of the type of A₂B, the changes of geometrical characteristics and vibrational frequencies are obtained in an explicit form.

A molecular simulation of the solvent effect on radiative rate constant k_r of singlet oxygen is carried out. This study included a search for the most probable conformations of the complexes of molecules of singlet oxygen and ten solvents and calculation of dipole moments M of transitions a¹Δ_g–b¹Σ_g⁺ (M_a–b) and a¹Δ_g–X³Σ_g^-(M_a–X) of the oxygen molecule for them. Averaging of M_a–b by conformations, taking into account the probability of their formation for complexes without atoms with a large atomic number (Cl, S), yields values that, as a rule, correlate well with the behavior of k_r in the experiment. Taking into account the possibility of decreasing the distance (compared to equilibrium) between molecules in a collision complex at room temperature made it possible to achieve satisfactory agreement of the calculated and experimental data also for complexes with CCl₄, C₂Cl₄, and CS₂. The obtained data indicate that a number of factors affect k_r. The correlation of k_r with molecular polarizability in a number of cases is due, on the one hand, to its effect on the strength of dispersion interactions in the complex and, on the other hand, to the fact that it to some extent reflects the position of the upper filled orbitals of the solvent molecule. Both factors affect the degree of mixing of the π orbitals of the singlet oxygen molecule with the orbitals of the solvent molecule, which, as was found earlier, facilitates the activation of the a¹Δ_g–b¹Σ_g⁺ transition and the borrowing of its intensity by the a¹Δ_g–X³Σ_g^- transition.

Entire luminescence spectrum of a commercial photosensitizer Radachlorin in aqueous solution has been recorded under laser excitation at 660 nm and analyzed. The peak of singlet oxygen phosphorescence at 1274 nm has been observed. The results obtained were compared with those recorded with laser excitation at 405 nm and reported earlier. The comparison showed the similarity of relaxation and luminescence processes occurring in both cases. Effective absorption cross sections were determined at each excitation wavelength, it was also shown that the singlet oxygen quantum yield is independent of photosensitizer concentration. The lifetime of the first excited triplet state in Radachlorin was determined. The results obtained can be used for optimization of the conditions of singlet oxygen generation and detection in solutions and biological samples.

We study the features of the electronic structure and the IR, UV, and visible spectra of a series of triphenylamines substituted with phenylethynyl groups. The analysis is performed at the level of the density functional theory (DFT) and its nonstationary version in comparison with the experimental data of IR and electron spectroscopy. It is shown that, in the excited state, there is a change in the alternation of single, double, and triple bonds in accordance with the character of bonding and antibonding in the lowest vacant molecular orbital. The gradual introduction of additional phenylethynyl groups does not cause frequency shifts in the IR spectra of the molecules under study, but significantly affects the intensity of the corresponding IR bands. A similar effect is also observed in the electronic-absorption spectra of these compounds. This can be used for optical tuning of triphenylamines as promising materials for organic light-emitting diodes and solar cells.

It has been revealed that a sensitized luminescence of AntAcBF₂ is observed in the boron difluoride dibenzoylmethanate (DBMBF₂)–boron difluoride anthracenoylacetonate (AntAcBF₂) system in the polystyrene matrix. The emission mechanism of energy transfer from DBMBF₂ to AntAcBF₂ has been established. The luminescence properties of bilayer films with one layer containing DBMBF₂ and another one containing AntAcBF₂ have been investigated. At luminophore contents in equimolar quantities, one observes a white luminescence of the bilayer polymer composite.

A simple description of the action of an extremely intense and short radiation pulse on a quantum object is proposed. The general approximate solution of the transient Schrödinger equation is concretized for the case of electric-dipole transitions in a hydrogen atom.

The interaction of two one-dimensional spatial vector structures of a Bose–Einstein atomic condensate in a trap with significant transverse dimensions and oscillating walls has been simulated numerically. Different types of coupled structures and different scenarios of their collisions are revealed. A comparison is made with the properties of scalar solitons, which are described by the traditional nonlinear Schrödinger equation.

An algorithm for wavefront calculation of ordinary and extraordinary waves after propagation through hemispherical components made of a uniaxial crystal is developed. The influence of frequency dispersion of n_о and n_e, as well as change in the direction of the optic axis of the crystal, on extraordinary wavefront in hemispheres made of from leuco-sapphire and a plastically deformed analog thereof is determined.

In the Rayleigh–Gans–Debye approximation, we have solved the problem of the sum-frequency generation by two plane elliptically polarized electromagnetic waves from the surface of a dielectric particle of a cylindrical shape that is coated by a thin layer possessing nonlinear optical properties. The formulas that describe the sum-frequency field have been presented in the tensor and vector forms for the second-order nonlinear dielectric susceptibility tensor, which was chosen in the general form, containing chiral components. Expressions describing the sum-frequency field from the cylindrical particle ends have been obtained for the case of a nonlinear layer possessing chiral properties. Three-dimensional directivity patterns of the sum-frequency radiation have been analyzed for different combinations of parameters (angles of incidence, degrees of ellipticity, orientations of polarization ellipses, cylindrical particle dimensions). The mathematical properties of the spatial distribution functions of the sum-frequency field, which characterize the symmetry of directivity patterns, have been revealed.

A method for rapid calculation of a flux of stimulated fluorescence of a multilayer optically dense medium with inhomogeneous distribution of the fluorophore has been developed. The light field in the medium at the excitation wavelength of fluorescence is represented by a superposition of incident collimated, incident diffuse, and reflected diffuse fluxes. A two-stream approximation is used to describe the light field in the medium at the wavelength of emission of the fluorescence. Fluxes in adjacent elementary layers of the medium and on its surface are connected by simple matrix operators that are obtained using a combination of engineering approaches of radiation-transfer theory and single-scattering approximation. The calculations of fluorescence fluxes of a four-layer biotissue that are excited and recorded at 400–800 nm are compared with their Monte Carlo simulation with a discrepancy of 1%. The effect of the propagation medium on the fluorescence spectra of 5-ALA-induced protoporphyrin IX that are recorded from human skin was studied, and a technique for their correction that is based on measurements and quantitative analysis of the diffuse reflectance spectrum of skin was proposed.

The serum of patients with multiple myeloma was examined by refractometric methods before and after the course of antitumor therapy. It was found that the amount of protein in the serum of patients with multiple myeloma, determined by the value of the serum refractive index, tended to decrease after the course of treatment. The value of the refractive index of blood serum can be used as an additional criterion for assessing the dynamics of changes in blood-serum properties during antitumor therapy.