Laser-induced Raman scattering in calcium titanate

The Raman spectrum of polycrystalline calcium titanate prepared by a liquid mix technique and heated to 800°C has been recorded at room temperature using an argon-ion laser as exciter. The observed spectrum was interpreted on the basis of factor-group C_2V. Not all of the Raman active modes predicted by factor group analysis were observed and this could be due to: over-lapping of bands, or very low polarizabilities of some of the modes or masking of the weak bands by intense bands. The band at 639 cm^?1 is tentatively assigned to the TiO symmetric stretching vibration (γ₁) and the bands at 495 and 471 cm^?1 to torsional modes. The bands in the region 180–340 cm^?1 are assigned to the OTiO bending modes and the 155 cm^?1 band to the Ca(TiO₃) lattice mode. The observed Raman bands are compared with the available infrared absorption data and, as expected, some coincidences in frequencies are seen for this compound with a noncentrosymmetric structure.     

Vibrational spectrum of Li2B4O7 crystals

The polarized infrared reflection spectra of Li₂B₄O₇ were studied in the spectral range 80–1600 cm^?1 and compared with Raman spectra. From the spectrum dispersion analysis, the frequencies, damping, and dielectric oscillator strengths were determined for all vibrational modes observed. A calculation of the effective charges and an analysis of the chemical-bond types of the Li₂B₄O₇ crystal structural units were carried out on the basis of the obtained data.     

Vibrational spectrum of Li2B4O7 crystals

Polarized IR reflection spectra of Li₂B₄O₇ crystals are studied in a spectral range of 80–1600 cm^?1 and compared with their Raman spectra. Based on the results of the dispersion analysis of the spectra, the frequencies, damping constants, and oscillator strengths of all vibrations are determined. The inversion of frequencies of the longitudinal and transverse vibrations of the A ₁ and E symmetry in a range of 900–1150 cm^?1 is found. Based on the data thus obtained, the effective charges are calculated and the types of chemical bonds are analyzed for structural groups of the Li₂B₄O₇ crystal.     

Far infrared absorption of amorphous GaAs and Ge

Far infrared reflection spectra of amorphous GaAs and Ge have been obtained in the frequency region from 30–600 cm^?1. For each material, curves of ω?₂ vs frequency have been obtained whose corresponding reflectivity curves give a best fit to the data. The peak value of the abdorption coefficient is about 4000 cm^?1 for GaAs and 160 cm^?1 for Ge. The results are compared with Raman spectra and with theoretical calculations.     

The Vibrational Spectra of 9-Fluorenone and Some of Its Isotopic Isomers

Abstract

Vibrational spectra of 9-Fluorenone, 9-Fluorenone-¹⁸O and 9-Fluorenone-d₈ have been recorded in the solid state and solutions in the infrared and (4000–100 cm^?1) and in the Raman (4000–50 cm^?1). Differential infrared linear dichroic spectra have also been measured. The assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes.     

The effects of incommensurability on the phonon modes in the one-dimensional superionic conductor K-hollandite

Polarized Raman and infrared spectra of the one dimensional (1-D) superionic conductor (K_2xMg_xTi(_8?x)O₁₆; x = 0.77) have been measured over the phonon frequency region 10–1000 cm^?1 as a function of temperature and pressure. The majority of the IR and Raman active modes predicted by group theory for the (Ti, Mg)O₆ framework were observed. The frequencies and their IR and Raman scattering cross-sections for the incommensurate lattice of K⁺ ions were calculated using a one dimensional linear chain model. This model assumes Coulomb interaction between nearest neighbors that are located in a sinusoidal potential due to the framework lattice. Several broad Raman bands were attributed to amplitudon type modes from the one dimensional incommensurate K⁺ ion sublattice. The IR active phason modes could not be identified unambiguously due to the underlying TiO framework vibrations which are known to possess large anharmonicity and oscillator strenghts.     

Far infrared optical properties of proustite (Ag3AsS3)

The infrared reflection and transmission spectra of Ag₃AsS₃ single crystals have been between 20 and 650 cm^-1 at room temperature. Fourteen phonon modes were observable in reflectivity with the dominant restrahlen bands occuring at 360 cm^-1 and 35 cm^-1 for E? c and at 335 cm^-1 and 35 cm^-1 for E⊥ c. These measurements indicate that generation of far infrared radiation by mixing of two laser frequencies using proustite as the down-conversion crystal is not possible.     

Raman spectrum of strontium titanate

The Raman spectrum of strontium titanate has been recorded using λ 4358 of mercury as exciter. The observed spectrum consists of 7 Raman lines, one of which is of low frequency, as expected from the recent theory of Cochran. 6 of these Raman lines have been interpreted as the first order spectrum arising from a small deviation of the cubic strontium titanate from its idealized symmetry. It has been shown that one normal mode of SrTiO₃ neglected by J.T.Last, will be really active in infrared absorption in the region of 440 cm^?1 and that it has to be taken into account in the interpretation of the infrared spectra of titanates. The four vibrational modes of the unit cell of SrTiO₃ correspond to frequencies of 90, 335, 441 and 620 cm^?1 observed in Raman effect. The large width of the Raman lines and the additional lines at 256 cm^?1 and 726 cm^?1 have been attributed to a splitting of the longitudinal and transverse optical modes. With the observed frequencies it has been found possible to account for in a satisfactory manner the specific heat of SrTiO₃ in the range 54·84° K to 1800° K.     

Studies on the complex behavior of optical phonon modes in wurtzite (ZnO)1−x (Cr2O3) x

This paper reports on the use of phonon spectra obtained with laser Raman spectroscopy for the uncertainty concerned to the optical phonon modes in pure and composite ZnO_1?x (Cr₂O₃) _x . Particularly, in previous literature, the two modes at 514 and 640 cm^?1 have been assigned to ZnO are not found for pure ZnO in our present study. The systems investigated for the typical behavior of phonon modes with 442 nm as excitation wavelength are the representative semiconductor (ZnO)_1?x (Cr₂O₃) _x (x = 0, 5, 10 and 15 %). Room temperature Raman spectroscopy has been demonstrated polycrystalline wurtzite structure of ZnO with no structural transition from wurtzite to cubic with Cr₂O₃. The incorporation of Cr³⁺ at most likely on the Zn sub-lattice sites is confirmed. The uncertainty of complex phonon bands is explained by disorder-activated Raman scattering due to the relaxation of Raman selection rules produced by the breakdown of translational symmetry of the crystal lattice and dopant material. The energy of the E ₂ (high) peak located at energy 53.90 meV (435 cm^?1) due to phonon–phonon anharmonic interaction increases to 54.55 meV (441 cm^?1). A clear picture of the dopant-induced phonon modes along with the B ₁ silent mode of ZnO is presented and has been explained explicitly. Moreover, anharmonic line width and effect of dislocation density on these phonon modes have also been illustrated for the system. The study will have a significant impact on the application where thermal conductivity and electrical properties of the materials are more pronounced.     

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.

     

Vibrational spectra of nitromethanes and the effects of internal rotation

Infrared spectra have been obtained in gas and crystalline phases for CH₃NO₂, CD₃NO₂, and CHD₂NO₂. A few Raman liquid measurements have also been made. The crystal spectra show the methyl group to be locked in conformation I,

with isolated CH stretching frequencies 3065 (ν_∥CH) and 3000 (ν_⊥CH), respectively. In the gas phase, the bands due to ν_aCH₃ and ν_aCD₃ are split, the splitting being compatible with isolated frequencies of 3065 (ν_∥CH) and 3006 (ν_⊥CH) cm^?1, respectively. These indicate a variation of 0.006 Å in bond length during internal rotation. The gas phase infrared band at 3028.7 cm^?1 and the Raman liquid band at 3024 cm^?1 in the spectra of CHD₂NO₂ represent averages of the frequencies during internal rotation. All calculations are performed with a potential function involving variations both in diagonal bond stretching, and in off-diagonal stretching interaction constants, proportional to cos2π, where π is the internal rotation angle.In the Appendix, vibrational assignments below 1600 cm^?1 are examined. Product rule considerations and intensity changes upon deuteration lead to a conflict with the infrared gas phase band contour over the assignment of the rCD₃ mode at 884 cm^?1. This and other features in the gas phase spectra may arise from the internal rotation.     

Vibrational Assignment of 2-Benzoyl Pyridine and its 18O Labelled Isomer

Abstract

Vibrational spectra of 2-benzoyl pyridine and 2-benzoyl pyridine-¹⁸O have been recorded in the solid and molten state in the infrared (4000–100 cm^?1) and in the Raman (4000–50 cm^?1). Polarized Raman spectra in the molten state have also been measured. The assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes.     

白云鄂博变生褐钇铌矿的Raman光谱和光致发光谱

测定了白云鄂博变生及退火结晶的褐钇铌矿和褐铈铌矿的Raman光谱，并讨论了结构、成分对Raman光谱的影响.它们的Raman光谱出现在840—600，340—280及200—50cm^-1的三个区，前两者为NbO^3-₄四面体的伸缩振动和弯曲振动频率，后者为稀土离子和NbO^3-₄四面体的外振动模式，通过对褐钇铌矿族矿物Raman光谱的比较分析，表明aman光谱可以有效地反映出该类矿物的结构畸变.还发现 关键词：     

Polarized Raman spectra of brushite (CaHPO4.2H2O) crystal. Investigation of the phosphate stretching modes,study of the LOTO splitting

Polarized Raman measurements were recorded on a monoclinic brushite (CaHPO₄.2H₂O) crystal in the 800–1200 cm⁻¹ spectral range, corresponding to the P O stretching modes. This study is a continuation of the investigation of the phosphate stretching modes observed in polarized infrared reflectance spectra of brushite crystal. In such ionic non‐centrosymmetric crystals, the splitting between the transverse and longitudinal components of the optic vibrations was observed in the polarized Raman spectra recorded at several scattering geometries. A″ symmetry modes of the brushite crystal were measured. Using a simple model based on the symmetry of the PO₄ group, the Raman intensities of the stretching modes are calculated and compared with experimental bands. Copyright © 2016 John Wiley & Sons, Ltd.     

Raman scattering in TlInS2xSe2(1−x) layered mixed crystals (0.25≤x≤1): Compositional dependence of the mode frequencies and line widths

The Raman spectra of TlInS_2xSe_2(1−x) layered mixed crystals were studied for a wide composition range (0.25≤x≤1) in the frequency region 10-360 cm⁻¹ at room temperature. The shift of Raman-active phonon frequencies versus mixed crystals composition x were established. The effect of crystal disorder on the line width broadening of three high-frequency Raman-active modes is reported.     

Infrared lattice vibration spectra of tetragonal ZnP2

Infrared reflectivity spectra of tetragonal ZnP₂ are measured in the frequency range from 40 to 600 cm^-1 for both polarization directions E ⊥ c and E 6 c. The parameters of 9 E modes and 4 A₂ modes are determined by a dispersion analysis of the spectra. Three additional A₂ modes are detected by infrared transmission measurements. The results obtained are compared with previous Raman scattering and two-phonon combination mode spectra.     

The Raman and infrared spectra of vitreous BeF2

We report the polarized Raman spectra, the infrared reflectivity and the infrared dielectric constant of vitreous BeF₂, for vibrational frequencies up to 1500 cm^-1. The high frequency modes of the Raman spectrum are assigned to combination overtones as well as to transverse and longitudinal fundamental vibrations.     

A Raman scattering study of long-wavelength optical phonons in hexagonal ammonium fluoride single crystals

All the predicted Raman active translatory vibrations of wurtzite ammonium fluoride (space group C⁴_6v are observed and assigned on the basis of their polarization selections obtained with single crystals. The fundamental ammonium ion librations could not be detected, but a frequency of about 545 cm^?1 is deduced from the analysis of the observed second order Raman spectrum.The TO-LO splitting for the A₁ and E₁ polar phonons is a lot more important than the A₁ — E₁ splitting (125 cm^?1 compared to 1–3 cm^?1); thus, the effect of long-range electric forces strongly dominates over that of the anisotropy of the shortrange interatomic forces. Only very weak directional dispersion could be detected on the quasi-mode spectra. From the observed TO and LO frequencies, one evaluates ?₀ ? 3.95 in good agreement with dielectric experimental data.     

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 spectra of single-crystal C60

We have analysed the Raman spectra of C₆₀ single crystals between room temperature and 10K and studied the temperature-induced phase transition in this material. The spectra show crystal field splitting of the internal Raman modes but no evidence for a line shift near the phase transition. The photo-induced transformation of the crystals and its implication on the interpretation of the Raman spectra is discussed. In the low temperature phase we observed two lines at 30 cm^–1 and 41 cm^–1 which we assign to the librational modes of the crystal.