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.     

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.     

Application of polarization methods to the detection of “latent” absorption bands of a food color

A spectral-optical investigation of the color of the red plum peel found in different aggregate states has been performed with the aim of its standardization in accordance with the demands of the food industry. The absorption spectra as well as the rotary dispersion and linear dichroism spectra of this food color have been obtained. The latter made it possible to reveal bands of individual pigments of the above-indicated color, “latent” in its absorption spectrum, and determine the positions of their maxima. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 563–565, July–August, 1999.     

Anisotropy of the faraday rotation in orthoferrites

Faraday rotation in plates of orthoferrites, cut normally to the optical axis, depends strongly on the polarization of the incident light in the vicinity of the absorption bands, where linear dichroism is large     

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.     

Spectral features of polarized light absorption and anisotropy of a local field in the D ho discotic

The polarized IR absorption spectra of monodomain planar-oriented films of a discotic liquid crystal D _ho are obtained for the first time. The spectral effects induced by the resonance dipole-dipole interaction of molecules, which have been predicted earlier, were observed. It was found that molecular excitations in isotropic and liquid-crystal phases are mixed due to local-filed effects and this mixing affects the relative intensity and dichroism of the absorption bands. New methods were suggested for measuring the local-field parameters in the D _ho phase from intensities and positions of the polarized absorption bands taking into account the mixing of molecular excitations. The two-dimensional crystal lattice of molecular columns was shown to reduce the local-field anisotropy of this phase.     

IR dichroism and orientation in segmented polyurethane-urea elastomers

Reconsidered and discussed in the present work is the limited possibility of the application of the orientation parameter for characterization of the orientation behavior of segments of polymer chains during deformation when this parameter is calculated from IR dichroism with inversion of dichroism for several absorption bands. Studies on orientation effects in uniaxial deformation of a polyether-urethane-urea elastomer obtained on the basis of polytetra-methylene glycol with a molecular mass of about 1000, 2,4-tolylendiisocyanate, and 4,4′- diphenylmethanediamine have been made using the x-ray diffraction technique. The results of the investigations agree with the assumption that in the polymer investigated conformation transitions in hard segments may be responsible for the IR dichroism inversion.     

Applications of linear Dichroism Spectroscopy

Abstract

Linear dichroism is the phenomenon of anisotropic absorption of light. It is shown by materials containing oriented molecules for which the absorption varies with the direction. The absorption intensity is proportional to the square of the scalar product between the electric field vector of the light and a molecule-characteristic transition moment vector, the absorption being maximum when the light vector is polarized parallel to the transition moment and zero when perpendicular to it. Linear dichroism can therefore provide (1) directions of transition moments when the molecule orientation is known (spectroscopic applications), or (2) information on molecular orientation when the transition moments are known (structural applications). Both applications are useful in several chemical systems, but so far the use of linear dichroism has been confined to a relatively small number of specialized laboratories, not least because of a lack of appropriate commercial instruments. Plane-polarized spectra have long been measured on crystals and other well-oriented materials, but systems with less complete orientation have usually been studied by birefringence which has allowed greater sensitivity. Birefringence and linear dichroism are related by the dispersion equations and therefore in principle contain the same basic information. However, linear dichroism is better suited for practical use since it is related in a very simple way to more-or-less well-separated quantal transitions, while birefringence is a complicated average over all transitions in the molecule.     

Magnetic Circular Dichroism Spectra of p-Disubstituted Benzenes Possessing Both Electron-Donating and Accepting Groups

Abstract

The magnetic circular dichroism (MCD) and absorption spectra of some p-disubstituted benzenes possessing both electron-donating and accepting groups were measured. The electronic spectra of the above compounds are characterized by the appearance of two absorption bands, one of which appears at 25000–40000 cm^?1 region with large intensity, and another at 40000–50000 cm^?1 region with rather small intensity. These absorption bands, especially the latter one, have been investigated by means of the MCD spectra and molecular orbital calculations based on the Pariser-Parr-Pople method.     

Piezospectroscopic study (78°K) of radiation- produced absorption bands in Si†

Abstract

A detailed study has been made on two sharp sub-bands, 3.45 μ (2900 cm^?1) and 3.61 μ (2765 cm^?1) of the 3.3 μ broad defect absorption band in irradiated Si. Our results indicate that the 3.45 μ and 3.61 μ bands are observed in all types of Si (n-, p-type, and intrinsic) subjected to fast neutron reactor irradiation. Spectra were measured at 78 °K under the effect of a variable uniaxial compressive stress with polarized light. A relatively large dichroism is observed for all three stress directions ?100?, ?110?, and ?111?. We also confirm that both sharp bands exhibit splitting and energy shifts under the action of stress. The model of the divacancy defect given by Watkins and Corbett⁽⁵⁾ has been utilized to explain the data. The dichroism can be accounted for by the effects of Jahn-Teller alignment which arises from the strong bonding of nearest neighbor atoms of the divacancy. The splittings of the bands are small indicating that the Jahn-Teller distortion is little altered in the ground and excited states. The splittings appear to be most sensitive to stress along the vacancy-vacancy axis and a tentative model for the transitions is given.     

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.     

Influence of terahertz laser radiation on the spectral characteristics and functional properties of albumin

The exposure of albumin (transport protein of blood serum) to laser radiation with a frequency of 3.6 THz resulted in a change in the intensity of characteristic bands in UV absorption spectra and in circular dichroism spectra. These changes depend on the exposure duration and the laser radiation power and indicate conformational changes in protein molecules.     

Spectral features of a nematic liquid crystal consisting of biaxial molecules with internal rotation

Expressions for the components of the optical permittivity tensor of a nematic liquid crystal consisting of biaxial π-conjugated molecules with a conformational degree of freedom (internal rotation) are obtained. A relationship between the intensity and dichroism of absorption bands in isotropic and nematic phases and the parameters of conformational, orientational, and mixed conformational and orientational orders of the molecules is established. A distribution function for the molecules is obtained that takes into account the mutual correlation of their conformational and orientational degrees of freedom. The effect of this correlation on the above-noted order parameters, the dichroism of the absorption bands, and the dependence of the measured oscillator strengths of molecular transitions on the character and degree of orientational order of biaxial molecules is studied. On the basis of comparison with experimental data, the relative role of different terms in the distribution function that are responsible for the correlation between the conformational and orientational degrees of freedom of the molecules is ascertained.     

基于光子晶体异质结构的磁可调石墨烯多带吸收

石墨烯在光电子学领域具有广泛应用,但石墨烯的吸收率较低限制了其在某些方面的应用。为了改善单层石墨烯的吸收特性,在前人研究的基础上,设计了石墨烯和光子晶体异质结构构成的复合结构。利用4×4传输矩阵法研究了外磁场、费米能量和设计波长等参数对石墨烯吸收特性的影响。结果表明,所设计的光学结构使石墨烯既保持了原有的宽吸收带,还增加了数目可调的窄吸收带。由于考虑到磁光效应,石墨烯的吸收特性表现出一定的磁圆二色性。对于各吸收带,通常情况下左旋圆偏振光的吸收率要大于右旋圆偏振光的吸收率。但调节外磁场和费米能量,可使各吸收带具有99%以上的吸收,在一定的条件下,还可实现近完美的100%吸收。研究结果为光电子学领域中基于石墨烯的相关器件的设计提供了参考。     

Study of the precipitation behavior of NaCl:Pb and KCl:Pb by optical spectroscopy2

The aggregation and precipitation behavior of lead in NaCl and KCl crystals has been systematically investigated by absorption and luminescence spectroscopy. For NaCl, absorption bands at 265 and 285 nm have been identified which correspond to intermediate stages in the formation of a double band (262–266 nm) associated with PbCl₂ precipitates. The kinetics of growth during ageing as well as the thermal annihilation behavior have been obtained for all bands. The emission spectra for excitation at those absorption bands have also been determined. For KCl, absorption bands at 265 and 280 nm develop during ageing at 160 and 200°C and their growth-rate is markedly enhanced by plastic straining. Their emission spectra involve a main band at $\text{\$}\text{?}$550 nm. In contrast to NaCl, no stage has been found where those absorption bands feed into a final band, which could be associated with PbCl₂ precipitates.     

Absorption- and uniaxial stress experiments in the a band of Pb2+ centres in KBr,RbBr, KI and RbI

The absorption lineshape and the stress induced dichroism of the A band of Pb²⁺ centres in KBr, RbBr, KI and RbI have been measured as a function of temperature from 4 K to room temperature. The moments of the absorption bands and of the dichroic spectra have been determined, and the effective coupling constants of the linear electron-lattice interactions of the ¦A〉 state as well as the frequencies of the interaction modes have been evaluated. Above 200 K the temperature dependence of the moments gives strong evidence that nonlinear electron-lattice interactions are important, particularly in the case of KBr:Pb²⁺.     

含铅空位PbWO4晶体光学性质的模拟计算

为了研究钨酸铅晶体中铅空位对光学性质的影响,利用完全势缀加平面波局域密度泛函近似,按照能量最低原理采用共轭梯度方法,对含铅空位的PbWO4(PWO)晶体进行结构优化处理。计算了含铅空位的PWO晶体的电子结构、复数折射率、介电函数及吸收光谱,并与完整的PWO晶体进行了比较。结果表明：完整的PWO晶体在可见和近紫外区域内无吸收,而含铅空位的PWO晶体在可见和近紫外区域出现2个明显的吸收峰,这2个吸收峰可分解成4个高斯线型的吸收带,它们的峰值分别为350nm、405nm、550nm和670nm。可以得出这样的推论：PWO晶体中350nm、420nm、550nm和670nm吸收带的出现都与铅空位的存在有关。     

Linearly and circular dichroism in a semiconductor with a complex valence band with allowance for four-photon absorption of light

This paper presents a theoretical study of the linear and circular dichroism of multiphoton absorption of light in semiconductors with a complex valence band. Matrix elements of optical transitions between subbands of the valence bands of a p-GaAs semiconductor are calculated. Transitions connected with both nonsimultaneous absorption of single photons and simultaneous absorption of two photons are taken into account. An expression for the temperature dependence of the coefficient of multiphoton absorption of polarized radiation with allowance for transitions between subbands of heavy and light holes is obtained.     

Sensitized UV luminescence from single crystals of zinc oxide

The reflection, absorption, excitation, photoluminescence, and cathodoluminescence spectra have been studied for indium-doped single crystals of ZnO. The temperature quenching of the UV-radiation bands has also been studied. These studies have made it possible to establish that the UV-radiation bands are excited during quantum absorption corresponding to “band-band” transitions and also by exciton absorption. The studies have also made it possible to calculate the activation energy of the temperature quenching. In the photoluminescence spectrum of ZnO crystals there is a wide radiation band in the 3950–4050-Å region which could be described by transitions in donor-acceptor pairs. It is shown that the band of the equidistant series at 3834 Å is complex in character.