Theoretical Study into the Dichroism of the Absorption Bands in the IR Spectra of Oriented Polymers

The IR dichroism of the polarized absorption bands of oriented polymers has been considered. An equation has been obtained that makes it possible to calculate the dichroism of the absorption bands for a different degree of the polymer orientation. This equation has been simplified especially for structurally insensitive absorption bands. In this case it allows one to determine the type of polarization of absorption bands.     

Profile Shape of Absorption Spectra in the IR Spectra of Carbohydrates

In the IR spectra of mono-, di-, and polysaccharides, the profile shapes of eight absorption bands have been investigated. They turned out to be symmetric and very close to the dispersion one for all the bands considered. It has been found that in mono- and disaccharides the minimum halfwidth of the bands is 10 cm^–1 and in polysaccharides it is higher by a factor of two or more. The halfwidth ratios of different bands in one and the same spectrum can differ severalfold. As is shown, double differentiation of the IR spectra makes it possible to investigate the profile shape of absorption bands when there is marked background absorption or these bands significantly overlap with other bands.     

Structure of the Absorption and Fluorescence Spectra of Solutions of Silico-Organic Polymers

The spectroscopic characteristics of new -linked polymers, whose main chain contains tetracoordinated silicon, acetylene groups, and 1,4-biphenyl or 2,7-fluorene, in chloroform have been investigated. It has been established that the spectral features of the absorption, fluorescence, fluorescence excitation, and fluorescence polarization spectra of these polymers are due to the inhomogeneous broadening of the electronic states of the centers of two types formed in the disordered polymer chain.     

Accuracy in Calculating the Intensities of the Absorption Bands in IR Spectra by Direct Quantum-Chemical Methods

To obtain information on the accuracy of quantum-chemical computations of the integral intensities of the absorption bands in IR spectra, calculations were performed by the density functional and ab initio methods for a number of polyatomic molecules that include the atoms of halogens, sulfur, phosphorus, etc. The results are compared with quantitative experimental data. A sufficient scatter in the calculated and experimental values has been found, but statistical processing of the results by the bootstrap method has revealed a regular deviation that can be partially compensated for by the coordinate scaling method.     

Simulation of the influence of the polymer conformation,orientation, crystallinity,and stretching on its IR absorption spectrum

Using cis-1,4-polyisoprene as an example, the influence of the conformation and orientation of the polymer chain on its polarization absorption spectra has been simulated. It has been shown that if a change in the orientation of the polymer chain leads to a monotonic change in the intensities of the absorption bands with their maxima positions remaining unchanged, then changes in the polymer chain conformation additionally cause a shift and the appearance of new absorption bands. According to the results of the calculation of the vibrational spectra, the inversion of the IR dichroism of the absorption bands of polymers is associated with the conformation transition. We simulate the influence on the IR absorption spectrum of the degree of crystallinity of cis-1,4-polyisoprene, in which the amorphous and amorphous-crystalline states are considered as a mixture of noninteracting polymer chains, where each state is characterized by a certain ratio of conformers. Likewise, the changes in the IR absorption spectrum of cis-1,4-polyisoprene under its stretching have been investigated. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 727–733, November–December, 2005.     

Calculation and Analysis of the IR Spectra of Cytosine in Various Phase States

Plane vibrations and intensities of the IR spectra of the ketone and enol forms of cytosine and deuterocytosine in various phase states are calculated and analyzed. It is shown that in a crystalline state and an aqueous solution cytosine forms a hydrogen bond of two types: C₂=O₈...HN₁ and C₂=O₈...HN₁₀, with a stronger intermolecular interaction in both phases being implemented by the hydrogen bonds between the O₈ and N₁ atoms. A satisfactory interpretation of the spectrum of the isolated molecules of cytosine, with the simultaneously existing ketone and enol tautomeric forms, is possible in the presence of the structural isomers of the enol form that differ in the position of multiple bonds.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 149–156, March–April, 2005.     

Exciton Reflection Spectra and the Structure of the Valence Band of Arsenic Chalcogenides

The polarized reflection spectra of arsenic sulfide crystal have been measured with high accuracy. The identical character of the triplet structures of the reflection spectra of As₂S₃ and As₂Se₃ has been established. On the basis of the well-known theoretical calculations of the bands of As₂Se₃, it is suggested that the three uppermost valence bands of both compounds are caused by the p states of arsenic, rather than sulfur, and are split into 0.1 and 0.2 eV. Underneath (about 0.4 eV) there are bands attributable to spin-orbital splitting of the p states of arsenic.     

Calculation of the intensity and dichroism of the IR absorption bands of oriented polymers

An algorithm for calculating the intensity and dichroism of polarized IR absorption bands of oriented polymers is proposed. The absorption curves in the IR spectrum of amorphous cis-1,4-polyisoprene and the dichroism of its absorption bands have been calculated. The polarization IR spectra of oriented amorphous cis-1,4-polyisoprene for a stretching ratio equal to 3 have been constructed. The calculated values of the absorption-band dichroism are in fairly good agreement with the experimental data.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 129–132, January–February, 2005.     

IR spectra of tellurium germanate glasses and their structure

We have used IR spectroscopy to study the structure of tellurium germanate glasses synthesized in the system TeO₂-GeO₂-B₂O₃-PbO. The structure of the glasses consists of [BO₃], [BO₄], [GeO₄], [GeO₆], [TeO₃], and [PbO₆] groups. Changes in the coordination of boron and germanium ions occur when the PbO and GeO₂ contents in the glasses increase. The glasses are attractive for designing optical and laser devices. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 78–81, January–February, 2007.     

Method for assigning absorption bands in IR spectra of polyatomic molecules with respect to internal vibrational coordinates

A method is proposed for assigning absorption bands in IR spectra of polyatomic molecules. An algorithm is developed and a Fortran program is written based on this method. The method is illustrated for the example of the toluene molecule. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 169–173, March–April, 2007.     

Manifestation of Spatial Modulation in the Vibration Spectra of (N(CH3)4)2CuCl4 Crystals

The specific manifestations of the spatial modulation in the vibration spectra of (N(CH₃)₄)₂CuCl₄ crystals have been investigated. It has been shown that because of the narrow temperature range of existence of the incommensurate phase and the complexity of the spectra being analyzed, reliable resolution of additional modes arising under the influence of both incommensurate and commensurate modulation is only possible using a computer approximation of the spectra obtained. In accordance with the theoretical models considered, additional modes have been observed mainly in the region of low-frequency skeletal vibrations exhibiting a marked dispersion.     

Trends in the spectral distribution of the absorption coefficient of complex organic molecules

General trends in formation of the observed vibrational spectra are analyzed by calculating spectral distributions of the absorption coefficient in the IR region for 45 molecules of different classes ignoring the electrooptical paramaters of particular bonds and structural groups. It is shown that for many molecules, only vibrations of peripheral X-H bonds make a prevailing contribution to the total integral absorption in a wide spectral range. The effect of increasing intensities of some bands is clearly observed for skeleton vibrations, when optical parameters of external X-H bonds are zero. V. I. Vernadski Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences, 19, Kosygin St., Moscow, 117975, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 491–496, July–August, 1998.     

Calculation of polarized IR absorption spectra for trans-1,4-polyisoprenes of various conformations

Polarized IR spectra for two conformations of trans-1,4-polyisoprene (α-and β-gutta-percha) were calculated. The IR dichroism of the absorption bands was calculated for both conformations. The computed results for polarized IR spectra and IR dichroism agree reasonably well with the respective experiment data. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 470–475, July–August, 2008.     

Modeling of IR Spectra of Selectively Substituted Glucopyranoside Nitrates

The frequencies of the normal vibrations of the molecules of 2,6- and 3,6-di-O-nitro-methyl--D-glucopyranosides and 2,3,6-tri-O-nitro-methyl--D-glucopyranoside have been calculated within the valence-force-field approximation in combination with calculation of the absolute intensities of the IR absorption bands of these molecules by the CNDO/2 method. The regularities in the structure of the complex IR absorption bands characteristic for nitro groups formed as a result of selective nitrosubstitution have been explained.     

Modeling of IR Spectra of Compounds on the Basis of Analogy between Fragmental Compositions of Structures

The possibility of using representations of the structures of compounds in the form of nonisomorphic k-vertex connective fragments for modeling IR spectra of compounds with a given structure on the basis of the spectra of their close structural analogs selected from a database is shown. Statistical justification of the approach and examples of modeled spectra are given.     

分子偶极聚合物驻极体的红外和可见光谱研究

本文利用红外和可见吸收光谱研究了具有二阶非线性光学活性的分子偶极聚合物驻极体材料中偶极子的取向稳定性与分子结构之间的关系，讨论了制备时所用的溶剂对材料微结构的影响。结果表明该材料在玻璃态温度下极化时，引起生色团分子偶极矩沿电场方向取抽，是建立在生色团分子共轭л体系被破坏的基础上，这是一种亚稳态。偶氮类分子的顺-反结构在光、热的作用下极易发生转变，是引起常温下生色团分子有序取向结构松驰的主要原因。制备时所用的溶剂将影响生色团分子在聚合物基底中的存在形式，进而影响分子偶极聚合物驻极体的稳定性。     

Detection of the vapor of asymmetric dimethyl hydrazine in the atmosphere by the method of spectrophotometry in the near IR range

We proposed and tested a method of detecting and determining the content of asymmetric dimethylhydrazine (ADMH) in the atmosphere based on measuring the absorption spectra in the near IR spectral region. The method is shown to permit confident diagnostics of the presence of an ADMH cloud in the atmosphere with a concentration of several maximum permissible concentrations (MPC). A. N. Sevchenko Scientific-Research Institute of Physical Problems, 7 Kurchatov Str., Minsk, 220064, Belarus; e-mail: valakh@pfp.bsu.unibel.by. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 796–799, November–December, 1999.     

Change in the IR spectra of polar liquids in an electric field

The IR absorption spectra of thin nitrobenzene, ethylene glycol, and glycerin layers in an electric field are investigated. It was established that the spectrum change and electro-optical effects depend on the molecular structure of these liquids. Grodno State University, 22, Ozheshko St., Grodno, 230023, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 441–444, May–June, 1998.     

IR Spectrum of C8H2: Integrated Band Intensities and Some Observational Implications

Polyynes are of astrophysical interest since they appear to be involved in organic chemistry in very different mediums. In Titan's atmosphere, the lightest polyyne, C₄H₂, was detected by Voyager. Recently C₄H₂ and C₆H₂ have been discovered in a protoplanetary nebula, suggesting polyynes as a possible chemical pathway to PAH (polycyclic aromatic hydrocarbons). Moreover, several experimental simulations and modeling imply their production from the photochemistry of methane and their involvement in the formation of organic aerosols. After the study of C₄H₂ and C₆H₂ spectra in the UV and IR wavelength range, we report here the first spectrum of gaseous C₈H₂ in the range 400–4000 cm⁻¹ at room temperature and low resolution. The task was hardly achieved because of the high instability of this molecule with temperature and pressure. To avoid exothermic polymerization, the compound as mixed with a solvent. We have performed a separate spectroscopic study of the solvent to determine C₈H₂ partial pressure within the mixture. This allowed us to calculate C₈H₂ integrated band intensities. In the studied wavelength range, C₈H₂ presents three main bands similar to those of C₆H₂ in terms of vibrational type, position, and relative intensity. To study the possible identification of these polyynes by spatial observatories (Cassini–Huygens, ISO), we have also measured the C₆H₂ and C₈H₂ infrared spectra in the range 400–1500 cm⁻¹ at 0.35 cm⁻¹ resolution.