Light scattering by nanosized systems with different spatial organizations

The integrodifferential equation method is used to study the spectrum of a nanoparticle colloid for the example of interaction of three arbitrarily arranged dielectric particles made up of nonresonant atoms (the eigenfrequency of the transition is far from the emission frequency) with incorporated barium atoms in an external optical radiation field. The effect on the light-scattering properties of a nanosphere in the ensemble of its distant “neighbors” is studied; an additional peak associated with them is observed as a frequency close to the resonance for an isolated nanosphere, which under certain conditions has higher intensity than the main peak corresponding to optical near-field resonance in a two-particle system. The dependence of the spectrum of the nanosized system on the geometric structure is studied, and it is shown that very precise tuning of the resonance frequency is possible by varying the angular distribution of the particles. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 641–646, September–October, 2006.     

Radiation-stimulated diffusion in solids

Irradiation of solids produces a microscopic nonequilibrium state in which the vibrational energy distribution function of the atoms deviates from the thermodynamically equilibrium function. Expressions are obtained for the nonequilibrium distribution function and for the frequencies of activational transitions of atoms out of a potential well. It is shown that the radiation stimulation of diffusion processes involves a deviation of the temperature dependences of the frequencies of transitions of the atoms out of positions of equilibrium from the Arrhenius law. Under subthreshold irradiation conditions the rate of diffusion processes is higher for atoms whose vibrations thermalize over long times and depends linearly on the irradiation intensity. Under above-threshold irradiation conditions the characteristics of cascade regions in solids — their sizes and the vibrational excitation energy of the atoms — can be determined by comparing the computed and experimental temperature dependences of the diffusion coefficient. Zh. Tekh. Fiz. 68, 67–72 (August 1998)     

Incipient crystallization of transition-metal tungstates under microwaves probed by Raman scattering and transmission electron microscopy

Microwave synthesis was used to produce nanosized transition-metal tungstates in environmentally friendly conditions not yet reported by the literature: 110 and 150 °C, for times of 10 and 20 min. X-ray diffraction evidenced incipient crystallized materials, while transmission electron microscopy indicates nanostructured regions of about 2–5 nm inside an amorphous matrix. Raman spectroscopy was used to probe short-range ordering in the achieved samples and also to obtain a reliable set of spectra containing all the Raman-active bands predicted by group-theory calculations. The vibrational spectra showed no extra feature, indicating that the microwave processing was able to produce short-range ordered materials without tetrahedral distortions. These distortions are frequently reported when commercially modified kitchen microwave units are employed. In this work, the syntheses were conducted in a commercial apparatus especially designed for fully controlled temperature–time–pressure conditions.     

The high frequency magnetic properties of self assembled Fe–Co–Si–N nanogranular thin films

The effect of a variation in Si and N concentration on the microstructure, crystal structure and high-frequency magnetic properties of Fe–Co–Si–N nanogranular thin films was investigated. The films, prepared by rf magnetron sputtering, consisted of nanosized grains of FeCo as well as a Si and N rich intergranular amorphous phase. The Si concentration had a significant effect on the crystal structure of the FeCo phase. The resistivities of the Fe–Co–Si–N films were significantly enhanced by an increase in Si concentration. The resonant frequency of the Fe–Co–Si–N films could be tuned from 0.45 GHz to 2.1 GHz by controlling Si concentration. The N concentration greatly influenced magnetic properties and the variation in resonant frequency is in agreement with Kittel’s equation.     

Role of coherence in interaction of opticalradiation with macromolecules

Based on analysis of the properties of macromolecules in a coherent optical radiation field and taking into account experimentally established data on the specificity of the interaction between laser radiation and biomolecules (the dependence of the efficacy of the interaction on the coherence length, the presence of an effect in a region of the spectrum far away from the absorption band), we propose a mechanism for wave interaction of coherent optical radiation with macromolecules, and we construct a very simple mathematical model for such interaction. Using the mathematical model, we calculate the dependence of the vibrational energy of the macromolecule in a coherent radiation field on the coherence time and the intramolecular relaxation rate. We show that the increase in the vibrational energy of the macromolecules strongly depends on the radiation coherence length. When exposed to incoherent radiation, the vibrational energy of the biomolecules remains practically constant, while when exposed to laser radiation (coherence length ≈3 cm), the vibrational energy of the atoms increases by 2–4 orders of magnitude, leading to a change in the conformation of the biomolecules and the activity of enzymes. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 225–231, March–April, 2006.     

Vibrational studies of lithium-intercalated SnSySe2−y (0≤y≤2) layered compounds

We report the vibrational properties of lithium-intercalated SnS_ySe_2−y (0≤y≤2) layered compounds. Infrared absorption spectra have been recorded as a function of temperature in the frequency range 50–600 cm⁻¹. The new bands are interpreted as vibrational modes of lithium atoms against the nearest-neighbouring-chalcogen atoms located in the van der Waals gap. Results are analyzed in terms of stretching vibrations of Li-S₄ and Li-S₆ entities. From a comparison of the spectra, it is concluded that lithium ions are more likely to occupy tetrahedral sites in the lithium-rich phases. Using a simple model of lattice dynamics, the coupling force constants are determined and compared with those of the pristine materials. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Dynamics of cold atoms in a quadrupole magnetic trap with an orbiting potential

We study the dynamics of atoms confined to a quadrupole magnetic trap with an orbiting potential. For typical values of the experimental parameters of the trap, the rotating magnetic field is shown to produce high-frequency modulation of atomic momenta with an amplitude comparable to the widths of the momentum distributions for the lowest oscillation states of atoms in the time-averaged potential. We find the quantum-statistical momentum and position distributions of atoms and show that at temperatures much higher than the effective vibrational temperature of the atoms in the trap the quantum-statistical momentum and position distributions are Gaussian. We also establish that at temperatures comparable to the effective vibrational temperature of the atoms the quantum-statistical momentum distribution has an annular structure in the trap’s symmetry plane, which is due to the deep modulation of the atomic momenta caused by the rotating magnetic field. Zh. éksp. Teor. Fiz. 114, 23–36 (July 1998)     

Influence of size effects on <Emphasis Type="Italic">para</Emphasis>-dichlorobenzene lattice dynamics

We have obtained experimental low-frequency Raman spectra for light scattering by nanoparticles of para-dichlorobenzene of size ∼300–70 nm. As their sizes decrease, the line frequencies decrease. The size of the nanoparticles was determined using an electron microscope. We found that in the lattice vibrational spectrum of nanoparticles of size 300–70 nm, a summed spectrum appears from α-para-dichlorobenzene and β-para-ichlorobenzene. This is consistent with molecular dynamics calculations of the structure of the nanoparticle and calculations of the histograms for the lattice vibrational spectra by the Dean method.     

Sintering properties of nanosized 90W–7Ni–3Fe composite powder

In order to study the sintering properties of nanosized 90W–7Ni–3Fe composite powder synthesized by spray drying-hydrogen reduction process, melting point and phase changes of nanometer 90W–7Ni–3Fe composite powder whose average particle sizes were in the range from 60 to 91 nm were measured by DTA, and sintering characteristic of specimens was studied at different sintering temperatures and times. Fracture morphology and W grain sizes of sintered specimens were measured by SEM and optical micrograph, respectively. Relative density, tensile strength and elongation of sintered specimens were also measured and analysed. The sintering temperature is lower than 80 °C in comparison traditional 90W–Ni–Fe powder. Mechanical properties are low because of appearance of cavities and vapour due to high oxygen content of nanosized 90W–7Ni–3Fe composite powder during liquid sintering.     

Lattice vibrational spectra of nanocrystalline films of <Emphasis Type="Italic">para</Emphasis>-substituted benzene

We have obtained experimental low-frequency Raman spectra for para-dibromobenzene nanofilms of thickness ∼10 μm and ∼400 nm. With a decrease in the film thickness, the line frequencies are lowered, the linewidths increase, additional lines become more intense. We modeled the film structure by the molecular dynamics method and calculated the histograms of the lattice vibrational spectra by the Dean method. We found that as the film thickness decreases, the lattice parameters increase, the orientational disorder increases at its boundary. The structure of the studied film is similar to the structure of the para-dibromobenzene single crystal. In order to correctly interpret the lattice vibrational spectra, we need to take into account surface vibrations and the presence of vacancies in the structure. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 838–842, November–December, 2008.     

Structure-sensitive changes in the terahertz absorption spectra of merocyanine dye derivatives

The low-frequency vibrational modes of the series of merocyanines (malononitrile derivative) have been investigated by pulsed terahertz spectroscopy. The terahertz absorption spectra are shown to contain both intermolecular and intramolecular vibrational modes in the range of 0.15–3.45 THz (5–115 cm⁻¹). An unambiguous correlation is established between the purposeful modification of the molecular structure of merocyanine dyes and the change in their terahertz absorption spectra.     

Spectroscopic manifestations of isotope substitution in ultrasound jet-cooled complex molecules and their van der waals complexes

It is shown that, upon formation of ultrasound jet-cooled var der Waals complexes of polar molecules of 9-cyanoanthracene, 3-aminophthalimide, and 3-amino-N-methylphthalimide with water molecules, pronounced manifestations of isotope substitution in the ligand molecules take place, which manifest themselves in shifting 0–0-transitions by 5–7 cm⁻¹ and changes in frequencies of intramolecular vibrations. Spectroscopic effects of isotope substitution of atoms of the amino group are established for substituted phthalimides. We propose a new mechanism of the effect of isotope substitution on frequencies of electronic transitions which cannot be reduced to the known one (realized by means of changes in values of the zero vibrational energy) and is based instead on the change in the charge density distribution in the molecule. Belarusian State University, 4, F. Skorina Ave., Minsk 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 148–154, March–April, 1997.     

Inelastic neutron scattering in Zr<Subscript>2</Subscript>NiH<Subscript>1.9</Subscript> and Zr<Subscript>2</Subscript>NiH<Subscript>4.6</Subscript>

In this paper we report the results obtained from inelastic neutron scattering measurements on Zr₂NiH_1.9 and Zr₂NiH_4.6 using triple-axis spectrometer at Dhruva reactor, Trombay. The spectrum up to 35 meV represents largely the lattice modes of Zr and Ni atoms. The vibrational frequencies of hydrogen atoms are expected predominantly at higher energies. The phonon spectra from 35–180 meV were recorded using a Be filter as analyser. In order to analyse the observed neutron spectra, we assume a set of Ein-stein modes due to the hydrogen atoms which are delta functions in energy. These delta functions are broadened by the resolution of the instrument. The vibrational frequencies obtained from the fitting of the observed phonon spectra have been assigned to various tetrahedral sites in both the compounds.     

Effect of molecular nitrogen on the electron mobility in a mixture of argon and optically excited sodium vapor

A parametric study of the electron energy distribution function (EEDF) and the electron mobility in the mixture Na + Ar + N₂ is carried out. An analysis is made of the conditions that obtain in a photoplasma when the detachment of the mean electron energy from the neutral gas temperature is due to superelastic collisions (collisions of the second kind) with excited sodium atoms. The case of low ionization of the medium at low vibrational temperatures of the ground state of the nitrogen molecules is considered. To find the EEDF a numerical solution of the Boltzmann transport equation is carried out. It is found that in the indicated mixture the presence of nitrogen leads to a depletion of the EEDF in the region of efficient vibrational excitation of the molecules and promotes the formation of inversion in the EEDF ∂f(ɛ)/∂ɛ>0 in the energy range corresponding to the Ramsauer minimum in the cross section of elastic collisions of electrons with the argon atoms. It is shown that the nonequilibrium character of the EEDF leads to a complicated dependence of the electron mobility on the partial ratios of the components of the mixture, the degree of ionization of the medium, and the population of the resonantly excited sodium atoms. Zh. Tekh. Fiz. 69, 14–19 (April 1999)     

Anharmonic analysis of vibrational states for five-membered heterocyclic compounds

We have used the DFT/B3LYP method with 6-31G*(**) basis sets for analysis of the vibrational spectra and geometric structure of pyrrole, furan, thiophene, and selenophene in the anharmonic approximation. We have determined the influence of resonance effects on the nature of the vibrational states. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 153–156, March–April, 2007.     

Optimization of pulse lamps for dye lasers

We carry out investigations of the generation efficiency of a dye laser in which, as a source of pumping, tubular lamps are used that are enclosed in shells to withstand the pressure of the xenon filling them. It is found that the optimum pressure is 60–80 torr, which ensures the greatest luminous efficiency of the lamps in the short-wave region of the spectrum at standard electrical parameters of the power supply system. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 134–137, January–February, 1998.     

Filtration of IR radiation by three-component polymer-crystalline systems

We have investigated the regularities in forming the spectral characteristic of three-component polymeric-crystalline polytetrafluorethylene-Ge-LiF interference systems in the wide IR spectral region 0.8–160 μm. The efficiency of suppressing short-wave radiation by structurally asymmetric imerference systems consisting of polytetrafluorethylene and quasihomogeneous layers with a high refractive index is shown. Two of this kind of three-layer systems are sufficient for suppressing background radiation within the wavelength interval from the visible range to ∼35 μm owing to multiple reflection at the boundaries of elementary Ge and LiF layers that form quasihomogeneous layers (λ ∼ 1.7–17.0 μm) and also due to absorption in the Ge (λ<1.7 μm) and Lif (λ ∼ 17–35 μm) layers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No_ 3, pp. 379–381, May–June, 2000.     

Interfaces between nanostructures and stepwise creep in highly oriented polymers

A comparative laser-interferometric study of steady creep in oriented ultrahigh-molecular-weight polyethylene films differing in the structure of interfaces between nanosized structural units has been carried out to gain a better understanding of the creep mechanism in oriented polymer materials. In contrast to conventional methods, laser interferometry permits measurement of creep rates from very small strain increments (0.3 μm) to within 1%. This technique made it possible to detect the stepwise nature of plastic deformation in creep. The data obtained suggest that the creep rate and its periodic changes are controlled by the structure of the interfaces, and that the plastic deformation itself occurs to a considerable extent through shear of nanosized structural units relative to one another by an “acceleration-deceleration” type. It is proposed that the “deceleration” phase is due to a glide resistance created by some “stoppers” having either physical or chemical nature, which become destroyed and reappear again in the course of creep. Fiz. Tverd. Tela (St. Petersburg) 41, 1788–1791 (October 1999)     

Calculation and analysis of vibrational spectra of adenine–thymine,guanine–cytosine,and adenine–uracil complementary pairs in the condensed state

We have calculated the frequencies of the normal vibrations of the complementary nucleic acid base pairs adenine–thymine, guanine–cytosine, adenine–uracil, corresponding to the Watson–Crick structure, and the adenine–uracil pair, corresponding to the Hoogsteen structure, in condensed states and we interpret the spectra. We determine the contributions of hydrogen bonds to the vibrational modes of the complementary pairs. We have analyzed the nature of the relative displacements of the nucleic acid bases as integral molecular units along the hydrogen bonds. We show the role of hydrogen bonds in tautomeric interconversions of complementary nucleic acid base pairs. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 84–92, January–February, 2009.