Obtaining spectrally selective images of objects in attenuated total reflection regime in real time in visible and terahertz ranges

An imaging attenuated total reflection (ATR) spectrometer for the terahertz range is created for the first time. The spectrometer uses a powerful free-electron laser. Images are recorded with a microbolom-eter detector array as a source of frequency tunable monochromatic radiation. Recording spectrally selective images of dynamic objects at a rate of 20 frames per second in the visible and terahertz ranges is demonstrated. In the terahertz range, images of the interdiffusion of liquids with strongly differing optical constants are obtained. Optimal configurations for the operation of the ATR spectrometer are found. Merits and demerits of the method are considered, as well as ways of improving the quality of image.     

Crystal structure and thermal expansion of RbNaCaTh(Si8O20)

RbNaCaTh(Si₈O₂₀), which crystallizes in the turkestanite structural type, was synthesized by a solid-phase reaction for the first time. The crystal structure of this compound was refined by the Rietveld method (space group P4/mcc). The temperature dependence of the unit cell parameters was studied using high-temperature X-ray diffraction analysis, and the thermal expansion coefficients of this compound were determined.     

Kinetics of the gas-phase reaction of OH with HCl

The reaction of hydroxyl radicals with hydrogen chloride (reaction 1) has been studied experimentally using a pulsed-laser photolysis/pulsed-laser-induced fluorescence technique over a wide range of temperatures, 298-1015 K, and at pressures between 5.33 and 26.48 kPa. The bimolecular rate coefficient data set obtained for reaction 1 demonstrates no dependence on pressure and exhibits positive temperature dependence that can be represented with modified three-parameter Arrhenius expression within the experimental temperature range: k1 = 3.20 x 10(-15)T0.99 exp(-62 K/T) cm3 molecule(-1) s(-1). The potential-energy surface has been studied using quantum chemical methods, and a transition-state theory model has been developed for the reaction 1 on the basis of calculations and experimental data. The model results in modified three-parameter Arrhenius expressions: k1 = 8.81 x 10(-16)T1.16 exp(58 K/T) cm3 molecule(-1) s(-1) for the temperature range 200-1015 K and k1 = 6.84 x 10(-19)T2.12 exp(646 K/T) cm3 molecule(-1) s(-1) for the temperature dependence of the reaction 1 rate coefficient extrapolation to high temperatures (500-3000 K). A temperature dependence of the rate coefficient of the Cl + H2O --> HCl + OH reaction has been derived on the basis of the experimental data, modeling, and thermochemical information.     

Effect of humic acids on biodegradation of 2-methyl-4-chlorophenoxyacetic acid: A chromatographic study

The effect of humic acids on biodegradation of 2-methyl-4-chlorophenoxyacetic acid in the active sludge medium was studied by analyzing their solutions by chromatography-mass spectrometry. The mechanism of the transformation of the herbicide in the presence of humic acids was examined.     

A luminescence visualizer for exact convergence of laser beams in photon-echo spectroscopy, four-wave mixing, and related techniques

A convenient and efficient technique for controlling exact focusing of several noncollinear laser beams into the same point of a luminescent sample is proposed for optical photon-echo spectroscopy and four-wave mixing experiments. The technique proposed is based on a confocal luminescence microscope equipped with a sensitive multichannel detector for visualizing samples with a large magnification. The high efficiency of the scheme developed is confirmed by experimental study of photon echo in a polymer film doped with luminescent dye molecules.     

Phase transitions in mixed-layer Aurivillius phases

The Aurivillius phases Bi₇Ti₄NbO₂₁, CaBi₈Ti₇O₂₇, and SrBi₈Ti₇O₂₇ were synthesized by solid-phase reactions. The results of high-temperature X-ray diffraction and thermal analyses of certain Aurivillius phases are presented. Principal regularities of thermal expansion of the synthesized compounds are established. A correlation between the Curie temperature and the structure of the compounds was found.     

Complexation of Nitroxide Radicals with Cyclodextrins: Kinetics of Crystal Complex Formation

Using the ESR method in combination with the stop-flow technique the kinetics of crystal complex formation of hydrophobic nitroxide radicals with cyclodextrins has been studied upon mixing cyclodextrin aqueous solutions with nitroxides emulsified in aqueous milieu. The - and -cyclodextrins and the piperidine nitroxide radicals with a OC(O)C_mH_2m+i (m = 7, 10, and 17) substituent in a para-position were used. It was established that the complexation process in the system emulsion of probe–cyclodextrin solution consists of two mainstages. The first stage is the transfer of probes from drops into aqueous solution and the formation of complexes RC_n, where R is the probe, C is cyclodextrin, n = 1, 2 and 3. The second stage is crystal complex formation and growth from solution of RC_n complexes. The results obtained indicate that mainly RC₃ complexes take part in crystallization. It was observed that the characteristic time of crystallization is approximately inversely proportional to the concentration of RC₃ complexes.Equilibrium constants of the processes R + C RC, RC + C RC₂ have been determined. It was found that complexation and further crystallization lead to the formation of monodispersed microcrystals.     

Synthesis and study of the structure of o-hydroxyaryl-1,2,4-oxadiazoles

The reaction of 4-oxo-1,3-benz- and -naphthoxazinium perchlorates with hydroxylamine leads to 5-(o-hydroxyaryl)-1,2,4-oxadiazoles rather than to 3-(o-hydroxyaryl)-1,2,4-oxadiazoles, as was previously assumed. The structure of the compounds obtained was proved by alternative synthesis, as well as by mass spectrometry and comparison of the experimentally found and calculated dipole moments and Kerr constants of the possible structures of the o-hydroxyaryl-1,2,4-oxadiazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 540–549, April, 1992.     

Molecular structure of 1,3-dinitro-10-phenylphenothiazine

Conclusions An x-ray study has shown that the product of cyclization of 1(o-N-phenylaminophenylthio)-2,4,6-trinitrobenzene is 1,3-dinitro-10-phenylphenothiazine; consequently, the cyclization proceeds with a prior Smiles rearrangement.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1802–1808, August, 1980.