Optics and Spectroscopy (v.109, #6)

Compton scattering of photon by atomic ion by A. N. Khopersky; A. S. Kasprzhitsky; A. M. Nadolinsky; O. A. Khoroshavina (819-822).
The angular and energy dependences of the differential cross sections for the nonresonance Compton scattering of a linearly polarized X-ray photon by the Be atom and beryllium-like ions O4+ and Mg8+ are studied theoretically. The many-particle effects of radial relaxation of the electron shells in the field of vacancies and stabilization of the core shells were taken into account. The calculated results are predictive in character.

Finite nuclear size correction to vacuum polarization in hydrogen-like ions by A. I. Bondarev; Yu. S. Kozhedub; N. S. Oreshkina (823-828).
The finite nuclear size corrections to the Dirac binding energy of an electron and to the vacuum polarization in hydrogen-like ions are considered. These corrections were calculated for the 1s 1/2, 2s 1/2, 2p 1/2, and 2p 3/2 states in a wide range of the nuclear charge Z = 1–100. The results obtained are compared with the available analytical data.

The possibility of cancelling the signal of linear polarization upon coherent excitation of 4s 3 S 1 atoms via a Λ scheme from 3p 3 P 1 and 3p 3 P 2 levels is demonstrated using an ensemble of sulphur atoms as an example.

The electronic structure, the equilibrium geometric configuration, and the charge distribution are calculated for the positive endofullerene ion [Ce@C60]+. It is shown that the equilibrium distance from the Ce atom to each of the six nearest C atoms almost coincides with the sum of the cerium ionic radius and the carbon atomic radius. The spectrum of electronic transitions in the visible and UV regions is presented.

A method is developed for the semiempirical calculation of fine structure parameters from the experimental energy intervals between magnetic sublevels. The calculations are performed using the configuration of neutral carbon as an example. The calculated parameters are used to calculate the 2p 2 configuration energy spectrum and the gyromagnetic ratios of the 3 P 2 and 1 D 2 levels, as well as the magnetic splitting of triplet levels. The results are compared with available experimental and theoretical data. It is confirmed that the dependence of the energy of magnetic sublevels of np 2 configurations on the magnetic induction is parabolic for sublevels with the projections M = 0, ±1 and is linear for sublevels with M = ±2.

The tautomeric composition of isolated adenine has been analyzed using computational IR spectroscopy. A comparison with experimental data has demonstrated that, in addition to adenine-N9H, which dominates in the quantitative content, two more tautomers that have the N9H imino and N7H amino forms exist in the isolated state and in the gas phase.

The resonance Raman spectra of adenine in the gas phase under excitation with laser radiation at wavelengths of 266, 218, and 200 nm have been investigated experimentally. The quantum-mechanical calculations of the intensity distribution in the resonance Raman spectra of three adenine tautomers are performed in the Herzberg-Teller approximation with the inclusion of the Duschinsky and frequency effects. Conclusions regarding the tautomeric composition of adenine in the gas phase are drawn from comparison of the results of quantum-mechanical calculations with experimental data.

Construction of the stationary state classification is considered for nonrigid molecular systems whose geometrical symmetry of internal dynamics is determined by continuous axial groups. The construction is based on the methods of symmetry group chains.

Precision measurements of optical excitation functions for zinc atom by N. M. Erdevdy; O. B. Shpenik; V. V. Zvenigorodsky; J. E. Kontros (868-875).
The excitation of zinc atoms by ultramonoenergetic electrons is experimentally studied. The optical excitation functions for 19 atomic spectral lines that originate from the n 1 S 0, 41 P 1, n 1 D 2, n 3 S 1, 43 P 1, 63 P 2, and n 3 D j levels are studied in detail. In the excitation functions measured from the excitation threshold to 19 eV for the spectral lines originating from the n 1 S 0, n 3 S 1, n 1 D 2, and n 3 D j levels, specific features caused by postcollision interactions of emitted and scattered electrons are observed for the first time in the energy region of 10.9–17.0 eV near the thresholds of autoionization states.

We measured the IR absorption spectra of self-associates and complexes with carboxylic acids of 3,5-dimethylpyrazole (DMP), diphenylformamidine (DPFA), diphenyltriazene (DPT), and diphenylguanidine (DPG) in solutions in a wide range of concentrations and temperatures and calculated spectroscopic, geometric, and energy characteristics of complexes in the quantum-mechanical harmonic and anharmonic 1D and 2D approximations. Spectroscopic data show that, in the case of DMP, cyclic trimers are predominantly formed; DPFA and DPG form cyclic dimers with two NH...N bonds in inert solvents, whereas, upon the complexation of DPT, cyclic structures do not occur, and only open dimers are formed. Upon the interaction of DMP, DPFA, and DPT with weak carboxylic acids (HCOOH, CH3COOH, CH2ClCOOH) in CCl4 or in CH2Cl2, molecular cyclic structures with NH...O=C and OH...N H-bonds are formed, whereas cyclic dimer complexes with stronger acids (CHCl2COOH, CCl3COOH, CF3COOH) predominantly have the structure of hydrogen-bonded ion pairs with proton transfer from the hydroxyl group to the proton-acceptor nitrogen atom. The calculations of the structure and vibrational frequencies using various basis sets of atomic functions confirm the formation of cyclic complexes in accordance with experimental results and, in the case of interaction with strong carboxylic acids, the proton transfer along the OH...N hydrogen bridge.

Luminescence properties of transparent ceramics Y3Al5O12:Yb by M. M. Chugunova; I. A. Kamenskikh; V. V. Mikhailin; S. A. Usenko (887-892).
We present the results of studying the luminescence properties of transparent ceramics Y3Al5O12:Yb obtained by the vacuum sintering and nanocrystalline technology. In the course of research, we measured the luminescence and luminescence excitation spectra, as well as the temperature and kinetic behavior of luminescence. Our results are analyzed in comparison with the characteristics of corresponding single crystals. We revealed that processes of generation and relaxation of electronic excitations that occur in ceramics, in particular, in the charge transfer state, are similar to processes occurring in crystals. The behavior of two charge-transfer luminescence bands at 340 and 490 nm is studied. In the range 300–600 nm, we revealed a broad emission band of radiation of other type, which is also observed in spectra of undoped ceramics. This broad band is attributed to F+ centers. Emission and excitation spectra of charge transfer luminescence at a maximum of the temperature dependence of 100 K are measured for the first time. We found that, upon excitation in the charge transfer band, luminescence in ceramics is more intense than in single crystals with similar concentrations of Yb and has a higher quenching temperature.

The spectra of the optical functions of Bi2Te3-Sb2Te3 solid solutions recorded in the range of 350–4000 cm−1 exhibited features caused by the response of free-carrier plasma and interband transitions forming the fundamental absorption edge in these materials. An increase in the Sb2Te3 percentage in the solid solution to 80% is accompanied by discontinuities of the functional dependences of the parameters characterizing plasma oscillations and a sharp increase in the optical band gap E g opt. The set of optical functions has been simulated in the adiabatic approximation taking into account the effect of plasmons and interband transitions and the general polarization background of the crystal. The results obtained make it possible to detail the pattern of change in the physical properties of Bi2Te3-Sb2Te3 solid solutions, which are of great practical importance for thermoelectric materials science.

Exciton absorption spectra of Cs2CdI4 and Rb2CdI4 ferroelastic solid solutions by V. K. Miloslavskii; O. N. Yunakova; E. N. Kovalenko (899-904).
The exciton absorption spectra of thin films of (Cs1 − x Rb x )2CdI4 solid solutions have been investigated and the refractive index n(λ) in their transparency window in the concentration range of 0 ≤ x ≤ 1 has been measured. The exciton-band parameters and optical permittivity ɛ(x) have been found to linearly depend on the concentration. It is established that excitons are incorporated into the CdI2 sublattice of the solid solutions and belong to intermediate-coupling ones. The characteristics of excitons in ferroelastics are compared with the corresponding parameters for CdI2, RbI, and CsI, which are used as components to synthesize ternary compounds.

We performed comparative studies of the temperature quenching of dual fluorescence of acetonitrile solutions of several molecular probes with proton transfer reaction in an excited singlet state of 4′-(dieth-ylamino)-3-hydroxyflavone (FET), 1-methyl-2-(4-methoxy)phenyl-3-hydroxy-4(1H)-quinolone (QMOM), and 3-hydroxyflavone (3HF) parent molecule at different energies of excitation quanta. In accordance with expressions obtained from balance equations for photoreactions of the kinetic and thermodynamic character, the intensity ratios of fluorescence bands as functions of the degree of quenching behave differently. Namely, the quenching increases the relative intensity of bands normal form/tautomer for reactions of the kinetic type, retaining this ratio unchanged for reactions of the thermodynamic character. Our experimental studies showed that, for fluorescent probes with the kinetic reaction (3HF and QMOM), the intensity ratio fluorescence bands increases almost linearly with the degree of quenching, whereas, in the thermodynamic case (FET), this ratio is independent of this parameter. Conclusions about the character of reactions that we obtained in this work agree well with data of independent investigations of these molecules by laser spectroscopy with high time resolution, and the obtained relations allow us also to judge the mechanism of temperature quenching in the case of the reaction of the kinetic type. The method can be used for comparatively simple express selection of molecular probes, candidate for new applications.

Nature of the influence of a solvent on the fluorescence quantum yield of solutions of the fluorescent probe 4-dimethylaminochalcone by N. G. Bakhshiev; S. K. Gularyan; G. E. Dobretsov; A. Yu. Kirillova; O. M. Sarkisov; V. Yu. Svetlichnyĭ (913-916).
The fluorescence quantum yields of solutions of 4-dimethylaminochalcone (DMC) in a series of individual solvents of different chemical nature have been measured using a technique based on studying the kinetics of fluorescence decay. A new quantitative regularity, namely, the dependence of the fluorescence quantum yield on the absolute solvation shift in the fluorescence spectrum due to the gas-solution phase transition, has been revealed. The opinion has been advanced and justified that the revealed regularity has a fundamental character, which is determined by the dominant contribution from the universal intermolecular interactions to the formation of the properties of the solvated DMC molecule in the excited electronic state.

Luminescence and magnetic properties of europium(III) carboxylatodibenzoylmethanates by N. V. Petrochenkova; I. A. Tkachenko; A. G. Mirochnik; V. E. Karasev; V. Ya. Kavun (917-920).
This paper reports on the results of an investigation of the luminescence and magnetic properties of europium(III) carboxylates, which are determined by the structure of the Stark and Zeeman sublevels. It has been established that the energy splittings λlum between the 7 F 0 ground level and the 7 F 1 term in the luminescence spectra of these compounds well correlate with the energy splittings λmagn obtained from magnetochemical measurements.

The generation of lower (third) and higher harmonics of femtosecond laser radiation in plasmas produced by laser ablation of different targets with a small atomic number Z (B, Be, Li) has been investigated. The high (10−3) efficiency of third-harmonic generation was observed in plasma produced on the boron surface. Efficient third-harmonic generation was also observed in beryllium plasma using femtosecond pulses of Ti:sapphire laser radiation (λ = 790 nm) and its second harmonic (395 nm). We could tune the higher harmonics generation spectrum by tuning the crystal converter when using 395-nm radiation to be converted. It is shown that, in plasmas formed on targets with small Z, the conversion efficiency and limiting generated harmonic order depend on the delay between the ablation pulse and the pulse to be converted.

Intermolecular interaction in plant oils from refractive and density measurements by B. Andriyevsky; L. Andriyevska; T. Piecuch (932-937).
Refractive indices n and density ρ of three plant oils (Anise, Nigelle, and Juniper berries) have been measured in the temperature range of 10–60°C. The model of the effective electric field E′ acting on a molecule in the material, E′ = E + xP, with the unlimited value of the coefficient of polarization input x has been applied to the analysis of the results obtained. The value x of the oils studied have been found to be in the range of 0.193–0.269, which is smaller than a similar value for water (x water > 0.3), known as a strong polar liquid.

The strong spatial dispersion effects in a layered metal-dielectric metamaterial are demonstrated by analyzing its dispersion properties and calculating its transmission and reflection coefficients. The descriptions of this metamaterial by a model of effective medium and by an exact method of transmission matrices are compared in detail. It is shown that the electromagnetic properties of the considered metamaterial cannot be completely described in terms of the local effective model, because of the occurrence of additional eigenmodes, which are caused by the spatial dispersion. This circumstance is a critically important feature near the resonant absorption line of surface plasmon-polaritons.

It is shown that the Ritz ballistic hypothesis, which is based on the vector summation of the speed of light with the velocity of the radiation source, contradicts the fact of existence of the Sagnac effect. Based on a particular example of a three-mirror ring interferometer, it is shown that the application of the Ritz ballistic hypothesis leads to an obvious calculation error, namely, to the appearance of a difference in the propagation times of counterpropagating waves in the absence of rotation. A review is given of experiments and of results of processing of astronomical observations and discussions devoted to testing the Ritz ballistic hypothesis. A number of other physical phenomena that refute the Ritz ballistic hypothesis are considered.

Self-asymmetrization of phase grating profile in a nematic S layer: Partially continuous model by V. A. Berenberg; V. Yu. Venediktov; V. A. Laskin (966-970).
The self-asymmetrization of dynamic phase grating profile in a model medium with properties of nematic liquid crystal, caused by the internal electric field induced in this medium, has been numerically simulated.

The generation of spontaneous (noise) gratings during the simultaneous formation of a holographic grating in thin (on the order of the cutoff thickness of the TE0 waveguide mode) AgCl-Ag films by two laser beams with λ = 532 nm and polarization vectors that make an angle of 45° with the plane of incidence have been studied. The electron microscopy images and diffraction patterns have revealed a significant difference of the spontaneous-grating structure from the structure obtained under irradiation by one laser beam. The spontaneous gratings have a significant spread in the directions of their wave vector, and the diffraction pattern (recorded using a probe beam with λ = 337 nm) has the form of a bundle of diverging arcs that intersect at one point. This difference is caused by self-diffraction from the holographic grating, which is responsible for the main diffraction peaks with odd orders, the growth of spontaneous gratings because of the interference of the beams diffracted by the holographic grating with the waveguide TE0 modes scattered in the film, and silver transport to the interference minima. The diffraction patterns are quantitatively analyzed and the period of the new (formed under two-beam irradiation) spontaneous gratings is calculated. The calculation results are in good agreement with the experimental data.

Analog asymmetrization of profile of thin dynamic holographic grating in liquid-crystal matrix transparency by V. Yu. Venediktov; V. A. Laskin; I. M. Pasechnik; V. A. Savinov (978-980).
The recording of dynamic holographic grating in an electrically addressed matrix liquid-crystal spatial light modulator, which asymmetrizes the grating profile due to the application of optical feedback (nonlinear or adaptive interferometer) with television closing of feedback loop, has been studied.

The problem on the propagation of meridional rays in conical optical fibers (focons) has been considered in terms of the geometric optics model. A sine condition for the ray parameters at reflection points has been obtained. A general equation that relates the geometric size of a focon with the ray parameters at the entrance and exit of the focon has been deduced. The equation is valid for all physically possible taper angles of a focon. The aperture properties of two types of focons (hollow and dielectric) have been analyzed. The entrance and exit aperture angles appear to be piecewise continuous or piecewise smooth functions of the parameters, which is related to the discreteness of the number of ray reflections. The main properties of the considered types of focons with typical values of the parameters have been illustrated by numerical calculations of the aperture angles.