Polarized Infrared and Raman Spectra and Ab-initio Calculations of Benzotriazole

Abstract

The i. r. spectra of benzotriazole have been measured from 4000 to 60 cm^?1: polarized spectra of single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been investigated. The structural parameters and vibrational frequencies have been determined from ab-initio Hartree-Fock gradient calculations using the 6–31G* basis set. A detailed arsignment of most of the observed bands has been proposed on the basis of the i. r. dichroism, Raman polarization data and frequency calculations.

     

Solid solutions of paradichlorobenzene in paradibromobenzene with vacancies present in their structure

The results of polarization studies of the low-frequency optical Raman spectra of solid solutions of paradibromobenzene with p-dichlorobenzene (10% paradichlorobenzene) are reported. The spectra of lattice vibrations of the mixed crystals are calculated, and it is shown that vacancies can be present in their structure, in agreement with the experimental spectra. The existence of vacancies is manifested by the appearance of secondary lines in the low-frequency spectrum, in the vicinity of 70 cm⁻¹. The intensities of the lines are related to the number of vacancies. The diffusion activation energies in mixed crystals of paradibromobenzene with paradichlorobenzene with vacancies present in their structure are calculated at different temperatures on the basis of the method of atom-atom potentials. It is shown that the activation energy in these mixed crystals is not as dependent on the temperature variation and the crystallographic direction as in crystals of the constituent components. Fiz. Tverd. Tela (St. Petersburg) 39, 1564–1566 (September 1997)     

Infrared and Raman Spectra of bis-Thiourea Lead(II) Chloride

Abstract

PbCl₂.2[(SC(NH₂)₂] is an important complex for environmental chemistry. Single crystals were studied using infrared absorption, and Raman spectroscopy in low temperature conditions (10 K). Assignments of the lead complex bands were made by searching correlations and group frequencies with separate PbCl₂ and thiourea spectra in the solid state. Lattice modes separation was achieved down to 20 cm^?1 in Raman and down to 50 cm^?1 with far infrared spectroscopy. Spectral signatures of the unusual seven-coordinated lead in the complex were tentatively determined and are in accordance with structural data.

     

Photoluminescence and multiphonon resonant Raman scattering in Ni-and Co-doped Zn1−x MnxTe crystals

Low-temperature photoluminescence, exciton reflection, and multiphonon resonant Raman scattering spectra of Ni-and Co-doped Zn_1−x Mn_xTe crystals were investigated. Intense emission occurs in a broad spectral region (1100–17 000 cm⁻¹) in the crystals containing Ni atoms. It is caused by intracenter transitions involving Mn²⁺ ions and transitions between the conduction band and a level of the doubly charged acceptor. The features of the exciton photoluminescence and multiphonon resonant Raman scattering involving longitudinal-optical (LO) phonons at various temperatures are investigated. The insignificant efficiency of the localization of excitons on potential fluctuations in the Zn_1−x Mn_xTe:Co crystals is established. A temperature-induced increase in the intensity of the 5LO multiphonon resonant Raman scattering line due to the approach of the conditions for resonance between this line and the ground exciton state is observed in these crystals. Fiz. Tverd. Tela (St. Petersburg) 40, 616–621 (April 1998)     

The composition dependence and new assignment of the Raman spectrum in lithium tantalate

The Raman scattering spectra of lithium tantalate crystals with different compositions were investigated. The comparison of the Raman data obtained for the congruent and the near-stoichiometric crystals reveals some differences in the shape and the number of Raman peaks, which lead to a new assignment of the long-wavelength optical phonons. And quantitative relationships between the linewidth of Raman peaks (142 cm⁻¹ for E-phonon and 861 cm⁻¹ for A₁-phonon) and the crystal composition were firstly presented. Two local Raman lines, 278 and 750 cm⁻¹, were found for the congruent crystals and attributed to the intrinsic defects, Li vacancy and anti-site Ta ion, respectively.     

Polarized Infrared and Raman Spectra of 2(3H)-Benzoxazolone

Abstract

The infrared spectra of 2(3H)-benzoxazolone have been measured from 4000 to 180 cm^?1. The polarized spectra of single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been recorded and the polarization of many lines has been determined. On the basis of the i.r. dichroism, Raman spectra and correlative arguments most of the fundamental vibrations have been assigned.     

Influence of Diffusion Parameters on the Spectral Characteristics of Raman Modes of Titanium-Diffused Lithium Niobate Planar Waveguides

ABSTRACT

A systematic investigation on the influence of the diffusion parameters (time and temperature) and initial titanium film thickness on the spectral characteristics of the LiNbO₃ Raman modes is reported. Raman spectra are measured in the range 50–1000 cm^?1 ～2 µm below the surface of the crystals. Broadening of the Raman lines and, therefore, crystal lattice disorder induced by the titanium ions are found to depend on the fabrication parameters. The disorder associated with the titanium ions near the surface of LiNbO₃ is encoded in the broadening of the A₁(TO₁) Raman line. A linear relation between the A₁(TO₁) mode broadening and the Ti concentration is presented. The diffusion theory is used to explain the experimental data. Raman spectroscopy combined with diffusion theory can be used to estimate the evolution of the titanium surface concentration.     

Radiolysis of mixed KI + RbI and KI + CsI powders

Abstract

Pure and mixed powders of KI + RbI and KI + CsI are irradiated by X-rays at room temperature. V-type defects are identified by means of Raman scattering experiments. Raman spectra show that similar defects are obtained in pure powders or crystals. Iodine molecules are stabilized in KI in the form of large clusters (I₂)_n while I³ _- ions are obtained in RbI and CsI.     

Identification of I3 − and I5 − clusters in irradiated ki by X-ray photoelectron,Raman and optical absorption spectroscopies

Abstract

Raman and XPS measurements have been performed on KI crystals irradiated near 200 K. The Raman studies show I₃ ^? and I_n ^? (n = 5, 7,—) clusters which anneal together with F- and V- centres at 338 K. A small development of (I₂)_n aggregates occurs during the anneal; these decay near 378 K and are responsible for a broad and weak residual V-band. The I 3d _5/2 XPS peak has been fitted to reveal the presence of 3 components after low energy argon- ion bombardment. These are identified as due to normal lattice iodine, I₃ ^? and 1₅ ^? whose behaviour is consistent with the Raman work.     

Raman scattering in crystalline fluorosilicate hexahydrates of iron and manganese at a phase transition

The work reports a Raman scattering study of FeSiF₆·6H₂O and MnSiF₆·6H₂O crystals within the 2–340 K temperature range. The crystals are ordered at low temperatures. Phase transition-induced changes in the spectra have been observed. An analysis of the number and polarization of the Raman lines has permitted determination of the symmetry of the high-and low-symmetry phases. A possible mechanism of the phase transition is proposed. Fiz. Tverd. Tela (St. Petersburg) 39, 929–939 (May 1997)     

Raman and Infrared Spectra of Crystals with the Cadmium Iodide Structure

Abstract

Raman and far infrared spectra (in the frequency range 20–360 cm^?1) have been recorded for polycrystalline samples of six crystals having the cadmium iodide layered structure. The four fundamental zone-center vibrational frequencies are assigned for CoBr₂, FeBr₂, MgBr₂, MnBr₂, CdI₂ and MgI₂. Values of the principal interlayer force constants are deduced from a simple linear chain dynamical model, and comparisons are made with recent results from spectroscopic studies of crystals with the related cadmium chloride structure.     

Vibrational Spectroscopy of the Borate Mineral Priceite—Implications for the Molecular Structure

ABSTRACT

Priceite is a calcium borate mineral and occurs as white crystals in the monoclinic pyramidal crystal system. We have used a combination of Raman spectroscopy with complimentary infrared spectroscopy and scanning electron microscopy with Energy-dispersive X-ray Spectroscopy (EDS) to study the mineral priceite. Chemical analysis shows a pure phase consisting of B and Ca only. Raman bands at 956, 974, 991, and 1019 cm^?1 are assigned to the BO stretching vibration of the B₁₀O₁₉ units. Raman bands at 1071, 1100, 1127, 1169, and 1211 cm^?1 are attributed to the BOH in-plane bending modes. The intense infrared band at 805 cm^?1 is assigned to the trigonal borate stretching modes. The Raman band at 674 cm^?1 together with bands at 689, 697, 736, and 602 cm^?1 are assigned to the trigonal and tetrahedral borate bending modes. Raman spectroscopy in the hydroxyl stretching region shows a series of bands with intense Raman band at 3555 cm^?1 with a distinct shoulder at 3568 cm^?1. Other bands in this spectral region are found at 3221, 3385, 3404, 3496, and 3510 cm^?1. All of these bands are assigned to water stretching vibrations. The observation of multiple bands supports the concept of water being in different molecular environments in the structure of priceite. The molecular structure of a natural priceite has been assessed using vibrational spectroscopy.     

Raman spectroscopy of isotopically pure (<Superscript>12</Superscript>C, <Superscript>13</Superscript>C) and isotopically mixed (<Superscript>12.5</Superscript>C) diamond single crystals at ultrahigh pressures

The Raman scattering by isotopically pure ¹²C and ¹³C diamond single crystals and by isotopically mixed ^12.5C diamond single crystals is studied at a high accuracy. The studies are performed over a wide pressure range up to 73 GPa using helium as a hydrostatic pressure-transferring medium. It is found that the quantum effects, which determine the difference between the ratio of the Raman scattering frequencies in the ¹²C and ¹³C diamonds and the classical ratio (1.0408), increase to 30 GPa and then decrease. Thus, inversion in the sign of the quantum contribution to the physical properties of diamond during compression is detected. Our data suggest that the maximum possible difference between the bulk moduli of the ¹²C and ¹³C diamonds is 0.15%. The investigation of the isotopically mixed ^12.5C diamond shows that the effective mass, which determines the Raman frequency, decreases during compression from 12.38 au at normal pressure to 12.33 au at 73 GPa.     

A study of molecular motion and Raman processes in K3H(SO4)2 and KHSO4 single crystals by observation of H and K spin-lattice relaxation

The spin-lattice relaxation rates for ¹H and ³⁹K nuclei in K₃H(SO₄)₂ and KHSO₄ single crystals, which are potential candidate materials for use in fuel cells, were determined as a function of temperature. The spin-lattice relaxation recovery of ¹H can be represented for both crystals with a single exponential function, but cannot be represented by the Bloembergen-Purcell-Pound (BPP) function, so is not related to HSO₄ motion. The recovery traces of ³⁹K, which predominantly undergoes quadrupole relaxation, can be represented by a linear combination of two exponential functions. The temperature dependences of the relaxation rates for ³⁹K can be described with a simple power law T₁⁻¹=αT². The spin-lattice relaxation rates for the ³⁹K nucleus in K₃H(SO₄)₂ and KHSO₄ crystals are in accordance with a Raman process dominated by a phonon mechanism.     

Bromine metallization studied by X-ray absorption spectroscopy

The experimental data carried out by M?ssbauer and magnetic resonances investigations of the structural phase transitions in K₂ZnCl₄ crystals are discussed by a simple electrostatic model, calculating, the lattice contributions to the local electric potential V(r), electric field intensity E(r) and electric field gradient tensor, (r) and taking into account both the fractional electric point charges and rigid lattice approximations. The validity of the model is proved by a good fit of the computing results and experimental data of quadrupole splitting parameters at K sites obtained by ³⁹K-NMR methods in high temperature incommensurate phase ( Pnam symmetry). The experimental results obtained by M?ssbauer and EPR methods in commensurate phase (Pna2₁ symmetry) of iron and copper doped K₂ZnCl₄ crystals are explained by relaxing the rigid lattice approximation. The insertion of probe ions appear to be done on not-exactly-Zn²⁺ site. Received 3 February 1999 and Received in final form 4 May 1999     

Broadening of IR Absorption Bands of p-Methoxybenzylidene p,n-Butylaniline (MBBA) Under the Influence of an A.C. Electric Field

Abstract

Infrared and Raman spectroscopy has been widely used at last decade to elucidate the properties of liquid crystals, the structure of the liquid crystal molecules and the molecular motion in various types of mesophase¹. Among more than 50 papers dealing with liquid crystals only a few consider the influence of electric field on mesophase vibrational spectrum. First Nelf² has used the electric field to orient nematic sam ples of p-methoxybenzylidene p′-cyanoaniline for the investigations of IR dichroism. Assuming that a large liquid crystal line domain acts like a rigid dipole and taking into account the effects of the walls an expression for the dichroism ratio was derived to evaluate the degree of orientational order. Later, Ohnishi³ has applied a d.c. electric field to a cell filled with MBBA and studied the changes in the relative transmittance of some bands in the region 4000–1000 cm^?1 of the dynamic scattering mode. Pan and Wang⁴ found that in the presence of turbulence due to the application of electric field, the intensity of all Raman bands decreases drastically but without any shift in the peak positions.     

Phase transitions in PbZr0.72Sn0.28O3 single crystals studied by Raman spectroscopy

ABSTRACT

Raman light scattering measurements in the temperature range from 80 to 830 K were performed on a PbZr_0.72Sn_0.28O₃ single crystal. The frequencies of the Raman lines were analyzed and discussed in terms of the sequence of structural phase transitions. It was found that Raman spectrum displays important changes near 440, 480 and 493 K. The incorporation of more than 25 mol% of Sn⁴⁺ ions into the structure of PbZrO₃ enhances polar fluctuations above T_C as compared to the less Sn-doped crystals. These fluctuations lead to appearance of a ferroelastic intermediate phase below T_C. It is demonstrated that the structural phase transformation in PbZr_0.72Sn_0.28O₃ can be considered as the result of softening of a number of modes.     

The influence of hydrostatic pressure on Raman spectra of TIS and TlInSe2

First order Raman spectra of TIS and TlInSe₂ single crystals excited with 1.064μm line of the continuously operated YAG: Nd³⁺ laser have been investigated in equilibrium conditions under various hydrostatic pressures up to 1.08 × 10⁹ and 7.06 × 10⁸ Pa, respectively. Mode parameters γ_j = (1/ν_j)(dν_j/dP) were determined for all the Raman bands observed. Comparison of a set of these parameters in both crystals showed that the character of binding interatomic forces in these crystals appeared to be similar. For both crystals the intensity of Raman bands decreased with increasing the pressure.     

Control of radiation spatial coherence under synchronous amplification in crystalline LiF:F 2 − amplifier

A technique of spatial coherence control, based on the synchronous amplification of a radiation in LiF crystals with F ₂ ^? color centers, is demonstrated. Spatial radiation distributions of stimulated Raman scattering (SRS) in oxide crystals were investigated under picosecond laser excitation. Low spatial radiation coherence was revealed for both the transient and quasi-stationary SRS. Spatially incoherent SRS was transformed to spatially coherent radiation as a result of phase—locked picosecond synchronous laser pumping of nonlinear Raman and LiF: F ₂ ^? crystals and the Stokes radiation amplification in the color center crystal.     

Raman scattering study of ion bombardment induced amorphization of SiC

Abstract

Lattice disorder induced by ion bombardment of SiC surfaces has been studied using Raman spectroscopy. After bombardment with 15 keV H⁺, D⁺ or He⁺ to fluences of 10¹⁹ cm^?2 the SiC surface was found to amorphize as indicated by changes in the Raman spectra. Raman studies of the annealing behavior of the damaged surface showed that no recrystallization of the amorphous layer occurred after 12 hours at 1000°C. By using different wavelengths of the exciting radiation the spatial distribution of the ion induced damage was investigated. Evidence for the preferential sputtering of Si resulting in a carbon rich surface layer is discussed.

Based on work performed under the auspices of the US Energy Research and Development Administration.

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