A Semiconductor Laser of the Visible Range as an Exciting Source of Raman Scattering

A possibility of application of semiconductor lasers of the visible range as exciting sources for Raman spectroscopy is studied. An experimental set-up for measuring Raman spectra of polycrystalline dielectrics and broad-gap semiconductors excited by a semiconductor laser with a wavelength of 640 nm was created. The conditions under which the spectral width of the lasing line of a semiconductor laser was within 10^-3 cm^-1 in the continuous mode with a power of 10 mW are realized. The characteristics of various types of exciting sources used in Raman spectroscopy are compared. The results of studies of the characteristic Raman spectra excited with a semiconductor laser in polycrystalline sulfur are presented.     

Structure of fullerene-containing soot at different formation stages of arc discharge vaporization of graphite

Electron microscopy is used in a study of nanoclusters of the carbon soot deposited on a probe in different areas of arc discharge during graphite vaporization under conditions favorable for fullerene synthesis. It is found that the spatial network of soot nanoclusters consists of alternating regions of higher density or associates of carbon particles. Two types of nanoclusters have been identified with the correlation radii of the associates equal to 0.6–0.8 and 1.6–2.2 nm, respectively. Type I nanoclusters are dominant in the soot microparticles, and their structure shows practically no variations with increasing separation r of the soot collector from the discharge axis over the range of distances studied, r=1–9 cm. The effective radius R ₀ of the “elementary” particles making up the associates in the soot nanoclusters of Type I calculated with the use of scaling relationships is 0.15–0.17 nm and is close to the gas-kinetic radius of carbon atoms. Type II nanoclusters have been identified in soot collected at r>3 cm. Values of R ₀ calculated in this case are 0.6–0.9 nm and decrease with increasing r, which indicates the presence of fullerene molecules in these nanocluster associates.     

Renormalization Effects in the Spectrum of a Coherently Driven Exciton–Biexciton System

Starting from the total Hamiltonian of an excited exciton–biexciton system, nonresonant renormalizations in the electronic spectrum of a coherently driven direct semiconductor are considered. Stringent group-theoretical inclusion of the particle spin in the Hamiltonian allows one to account for the dependence of different renormalization effects on polarizations of the incident laser fields. On the example of circularly polarized driving and probing pulses it is shown that the kind of observed renormalization is defined by the pump-and-probe polarization geometry. Thus, the exciton optical Stark effect must appear in the case of co-circular pump-and-probe, whereas a mixing of the polariton and biexciton spectra is possible only in the case of counter-circular pump-and-probe. The polariton--biexciton dispersion renormalization may manifest itself as synchronous splittings of the exciton--polariton and biexciton spectra under resonant pumping at a frequency of the polariton--biexciton transition, or in their shifts in opposite directions under near-resonant pumping. The mechanisms of both kinds of renormalization effects are analyzed, and the dependence of their characteristics on the pump parameters and microscopic parameters of the exciton–biexciton–photon system is established. An evaluation of the characteristics shows that the effect of polariton–biexciton dispersion renormalization dominates in the spectra of semiconductors with stable biexciton formation. Results of the theoretical study provide an adequate explanation of available experimental data.     

Secondary anti-stokes emission from the bulk of gallium phosphide at 4.2 K

Secondary radiation (photoluminescence and Raman scattering) emitted by gallium phosphide single crystals at helium temperatures is investigated. It is established for the first time that, in the case when the secondary emission spectra are excited by a cw low-power He-Ne laser, whose linewidth lies in the transparency region of GaP, anti-Stokes photoluminescence from the bulk of the sample occurs due to interband and impurity recombination. The results obtained make it possible to carry out a qualitative and quantitative analysis of impurities which are present in the bulk of a semiconductor by recording the bulk anti-Stokes photoluminescence spectra at low temperatures.     

On the properties of charge-exchange dipole excitations and the T > component of a giant dipole resonance in spherical nuclei

Within the semimicroscopic approach based on the random-phase approximation that takes exactly into account a single-particle continuum and on a phenomenological inclusion of the fragmentation effect, it is proposed to describe the strength functions for charge-exchange giant dipole resonances and cross sections for photoabsorption and for partial “direct + semidirect” (γ, p) reactions in the vicinity of a giant E1 resonance with allowance for the isospin-splitting effect. The results of the calculations performed for some magic and semimagic nuclei without resort to free parameters are compared with available experimental data.     

Reaction of haloadamantanes with salts of nitro compounds

Silver and mercury salts of nitro compounds react with bromo- or chloroadamantanes with the formation of products of C- and/or O-alkylation, the ratio of which depends on the structure of the initial reactants. The direct experimental evidence of nitronic esters to be isomerized into nitro derivatives and of their role as intermediates in the formation of the nitro derivatives in the alkylation of nitro compounds has been presented for the first time.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiva Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1798–1803, August, 1992.     

Molecular structure of N-mesityl-6H-anthra[9,1-bc]pyrrol-6-one

The molecular and crystalline structure of 1-(2,4,6-trimethylphenyl)-6H-anthra-[9,1-bc]pyrrol-6-one was determined by the x-ray structural method. There is a larger uniformity of the bonds in the benzene ring of the isoindole fragment than in the N-substituted isoindoles; this derives from the electronic influence of the keto group. The structure of the whole molecule does not have marked 1,10-anthraquinoid character.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 485–490, April, 1988.     

Nitration of salts of sulfamides with nitric anhydride

Conclusions The nitration of the sodium salts of sulfamides with nitrogen pentoxide leads to the formation of the corresponding N-nitrosulfamides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1804–1806, August, 1971.     

Nanotubes fabricated from Ni-naphthalocyanine by a template method

Novel naphthalocyanine (Nc) nanotubes with special wall structures were fabricated by a template method using Nc molecules as building blocks. Thermal stabilization of the ordered columnar structures of the tetrakis(tert-butyl)naphthalocyanine (Ni-BNc) molecules, induced from the pi-pi interactions in the nanoscale channels of an alumina template, resulted in Nc nanotubes with walls consisting of well-ordered Nc molecular disks. Further thermal treatment of Ni-BNc at 600 degrees C produced carbonized Nc nanotubes containing ordered columnar, graphitic wall structures with the graphene disks arranged perpendicular to the tube axis. These nanotubes may be useful for extending the application of Nc molecules for nanodevice fabrication.     

The structure ofO-arylmercury derivatives of dihydroxy-9,10-anthraquinones and their reactions with anions

The structure of mono- and di-O-arylmercury-derivatives of quinizarin (1,4-dihydroxy-9, 10-anthraquinone) and anthrarufin (1,5-dihydroxy-9, 10-anthraquinone) and their reactions with Br^–, Cl^–, OH^–, and^tBuO^– anions in the solid state and in aprotic solvents were examined by vibrational and electron spectroscopy. These reactions result in cleavage of the O-Hg bond. The formation of ions or contact ion pairs depends on the size and nature of the counterion; quinizarin dianions give very strong ion pairs with K⁺ cations, which do not cleave in DMSO. The electronic structure of mono- and dianions of the compounds studied is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2933–2940, December, 1996.