Vibrational Spectra of Thiazole-2-Carboxylic Acid and Thiazole-2-Carboxylate Ion

The i-r. spectra of thiazole-2-carboxylic acid and thiazole-2-carboxylate ion as CsI pellets and Nujol mull as well as Raman spectrum of an aqueous solution of the salt have been investigated. Most vibrations have been assigned on the basis of group frequencies and by correlation between the spectra of both molecules. The -COOH characteristic vibrations have been assigned as vibrations of the intermolecularly associated species.     

Raman spectra of alkyl-substituted azaoxa[8]circulenes: DFT calculation and experiment

Raman lines in spectra of recently synthesized azaoxa[8]circulenes have been assigned in detail on the basis of obtained experimental data and B3LYP/6-31G(d) calculations. Particular features of the structure of three azaoxa[8]circulenes have been considered based on data of X-ray structural analysis and DFT calculations. Regularities in changes of the geometric parameters have been found for benzene, furan, pyrrole, and naphthalene rings that occur upon formation of the macroring in comparison with free molecules. Raman spectra of macrorings have been shown to contain a characteristic set of lines the frequencies of which differ from those of analogous lines in Raman spectra of benzene, pyrrole, furan, and naphthalene. Results of quantum-chemical calculations agree well with experimental data with respect to line frequencies and intensities due to recalculation of Raman activities of normal vibrations into intensities of Raman lines.     

三种二元水溶液体系中氢键对拉曼线宽的影响

采用显微共聚焦拉曼光谱对三种二元水溶液(乙腈/水、二甲基亚砜(DMSO)/水和丙酮/水)进行测量,得到含有氢键作用的水溶液体系拉曼频移和线宽随浓度的变化规律。应用混合模型和相互作用体系的线宽经验公式对实验结果进行了分析。结果表明,含有氢键作用的水溶液体系中,氢键作用越强线宽越大,并且线宽随单位浓度变化率大;同种氢键体系中,线宽不仅受浓度浮动的影响,氢键作用也是一个重要的影响因素,定量分析证明线宽与浓度、氢键作用关系很好地符合Ojha等提出的线宽公式。     

Multiscaling wavelet analysis of infrared and Raman data on polyethylene glycol 1000 aqueous solutions

Infrared and Raman scattering spectra of aqueous solutions of poly(ethylene glycol) with nominal weight 1000 Da have been collected and analyzed as a function of the water content both in terms of a two-state physical model and in terms of an innovative multiscale wavelet cross-correlation approach. Both the analysis procedures allow to highlight the spectral shape changes occurring when water is added to pure polymer, showing the effectiveness of the wavelet analysis. It is shown that, provided that the pure polymer spectral contribution is subtracted from the aqueous solutions spectra, the shape of the intramolecular O–H stretching band can be reproduced by a superposition of the spectrum of bulk water and of the spectrum of hydration water, i.e., the spectrum relative to the water molecules bonded to the polymer chain. The weight of the bonded-water spectrum changes with concentration furnishing a polymer hydration number value which well agrees with hydration number data, reported in literature, obtained with other techniques. On the other hand, the intramolecular infrared O–H stretching band and the low-frequency Raman spectra, for all the investigated polymeric aqueous solutions, when analyzed through a multiscale wavelet cross-correlation approach reveal that significant spectral changes are registered in the 0.00–0.46 water weight fraction range. Such complementary experimental and analytic findings suggest the picture that when the water content increases, the water molecules saturate the two lone pairs of each oxygen atom of the polymer furnishing a hydration number which agrees with previous determinations and hence supporting the validity of the wavelet approach.     

Neutron Scattering and Vibrational Spectra of Molecular Crystals

Infrared and Raman spectra of a number of molecular crystals have been measured for studying molecular vibrations and the intermolecular and intramolecular force fields. The infrared absorption bands arise from interaction of the electric wave with the oscillating dipole moment of the crystal. Raman scattering covers inelastic photon scattering processes and accordingly Raman lines arise from the oscillating polarizability of the crystal. Thus, the vibrational modes observed in infrared absorption or Raman scattering spectra are k = 0 modes, for which translationally equivalent molecules vibrate in phase.     

Phonon spectrum of a naphthalene crystal at a high pressure: Influence of shortened distances on the lattice and intramolecular vibrations

The Raman spectra of a naphthalene crystal have been measured at room temperature in the pressure range up to 20 GPa. The pressure shift and Grüneisen parameters for intermolecular and intramolecular phonons have been determined. The maximum rate of the pressure shift for intermolecular phonons is 44 cm^?1/GPa, and the rate of the pressure shift for intramolecular phonons lies in the range from 1 to 11 cm^?1/GPa for different modes. The pressure dependence of the phonon frequencies for direct and inverse pressure variations has a hysteresis in the pressure range from 2.5 to 16.5 GPa. It has been shown that the linear dependence of the intermolecular phonon frequency on the crystal density has a peculiarity, which indicates a possible phase transition at a pressure of 3.5 GPa. The pressure dependence of intramolecular phonons related to the stretching vibrations of hydrogen atoms exhibits features that are characteristic of intermolecular phonons, which is associated with the influence of shortened distances between the hydrogen atoms of the neighboring molecules on the intermolecular interaction potential.     

Vibrational Assignment of N-Phenylphthalimide and 15N-Phenylphthalimide

Abstract

The i.r. spectra of N-phenylphthalimide and ¹⁵N-phenylphthalimide have been measured in 4000–100 cm^?1 frequency range as KBr and polyethylene pellets and as chloroform solutions. The Raman spectra (4000–50) cm^?1 of microcrystalline powder of the of the same compounds have also been investigated.

A detailed assignment of most of the observed frequencies has been proposed on the basis of the group vibrational concept, isotopic shift data and analogies with the spectra of related molecules. Some literature data have been discussed and some frequencies are reassigned.     

The fluctuation hypothesis of hydrogen bonding

To describe the distortion perturbations of the water molecules in solutions the quantum-mechanical method of partial oscillators has been developed. This method allows one to separate in a simple manner two types of influences on vibrations of OH oscillators, viz. the intermolecular perturbations resulting in the different strengths of hydrogen bonds and intramolecular coupling between stretching vibrations. Here the coupling is treated quite strictly, whereas the intermolecular perturbations are introduced phenomenologically. The calculation of the distribution of distortions among molecules in liquid H₂O and D₂O induced by non-equivalency of the two hydrogen bonds of the water molecule has been made on the basis of the method developed, and the parameters of the mean statistical molecule have been found from the experimental spectrum of HOD. The depolarization ratios of vibrations in Raman spectra of the mean statistical molecules H₂O and D₂O have been computed as an illustration of the possibilities of the proposed calculation method. All the estimates show that the stretching oscillators of H₂O and D₂O molecules are significantly coupled in spite of the great distortion of the symmetry of water molecules in the liquid state.     

Lattice dynamics and Raman scattering spectrum of elpasolite Rb<Subscript>2</Subscript>KScF<Subscript>6</Subscript>: Comparative analysis

Raman scattering spectra of elpasolite Rb₂KScF₆ are studied in a wide temperature range including two phase transitions: from the cubic to the tetragonal phase and then to the monoclinic phase. The experimental Raman scattering spectrum is compared with the lattice vibration spectra of these phases calculated using an ab initio approach. A number of anomalies (caused by structural rearrangement during the phase transitions) are revealed and quantitatively analyzed in the ranges of both the intramolecular vibrations of the octahedron molecular ScF₆ ions and low-frequency intermolecular lattice vibrations. The interaction between low-frequency intramolecular vibrations and the intermolecular modes is found to be significant, and strong resonance interaction of the rotational soft modes (which are recovered below the phase transition points) with hard low-frequency vibrations of the rubidium ion sublattice is detected. These interactions are shown to substantially complicate the spectra.     

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.

     

Effects of polymorphic transitions on the vibrational spectra of cyclopentane and cyclohexane crystals

The Raman spectra of these compounds in their various crystalline modifications have been examined and compared with those for the amorphous state. Temperature and phase state have marked effects on the frequencies and intensity distribution for some lines. The symmetry of the intermolecular forces can affect the vibrational spectra of naphthenes.     

Raman spectra of solutions of uranyl compounds

The frequencies of the spectra of aqueous and nonaqueous solutions of a number of uranyl salts were analyzed. The previous assignment of the frequency of 200 cm^–1 to the deformational vibrations of the uranyl ion [1] was confirmed. The activity of this frequency in the Raman spectrum is determined by the structure of the complex compounds.     

UV-Raman study and theoretical analogue of picolinic acid in aqueous solution

High quality Raman spectrum of picolinic acid aqueous solution with ultraviolet (UV) excitation of 325 nm was obtained in this article. The state of picolinic acid in aqueous solution has been investigated over a wide range of solution pH values. The distinct changes of UV-Raman spectra accompanied with the pH variations indicate the changes of molecule structure. The calculations based on density functional theory were used to analyze the states of picolinic acid in aqueous solution. By comparing the experimental frequencies with the calculated ones, it can be concluded that when pH value varies from high to low, the picolinic acid tends to change from the anion form to the zwitterion that have the intermolecular hydrogen COOH?N bond.     

蒽分子晶体的喇曼散射

在室温和液氮温度下,用氩离子激光器的5145Å激光激发,测量了蒽单品的喇曼散射谱,其喇曼活性主模振动的实验值和理论值符合的较好。计算了旋转振动的均方振幅,并对低波数振动喇曼谱的温度效应进行了讨论。     

Raman Spectra of Porphyrins

The spectroscopy of porphyrins has been developing rapidly during the last two decades, this class of compounds being of great biological importance and possessing a number of significant properties. Different spectroscopic techniques, viz., electronic spectroscopy including fine-structure quasiline spectra (Shpolsky effect), infrared spectroscopy, luminescence, flash photolysis, ESR and NMR spectroscopy etc., have been applied to the study of these molecules (see reference ¹ for a review). However until recently there were no publications on Raman spectra of porphyrins and related compounds although it is evident that a complete analysis of molecular vibrations is impossible without knowing the Raman frequencies, especially for centrosymmetrical molecules. We have obtained Raman spectra of two porphin derivatives, viz., copper and nickel octamethylporphin ² which seems to be, together with data on hemoglobin and cytochrome^3-5 and on chlorophylls ⁶, the first observation of Raman spectra of porphyrins. In this paper Raman spectra of several metalloporphyrins are presented including metal complexes of porphin, octamethylporphin, etioporphyrin I, meso-tetraphenylporphin and tetrabenzporphin. For some of them Shpolsky spectra have been obtained and a juxtaposition is made of the two kinds of spectral data concerning the frequencies of molecular no- modss. Also some data of infrared spectra are presented.     

Raman scattering of light in silicon nanostructures: First-and second-order spectra

First-and second-order Raman scattering spectra in Si nanocrystals have been studied. The shift to lower frequencies and the substantial broadening of first-order Raman scattering lines observed to occur with decreasing nanoparticle size were established to correlate with those in second-order spectra. It is shown that the experimentally observed shifts of peaks and their broadening cannot be predicted based only on the phenomenological model of strong phonon wave function localization. The anharmonic effect originating from the heating of the nanoparticle surface by laser radiation should also be included. Proper fitting of experimental data revealed that the anharmonic constants depend strongly on nanoparticle size. The shape and spectral positions of maxima in second-order Raman scattering spectra have been theoretically described.     

Infrared and Raman spectra of Histidine: an ab initio DFT calculations of Histidine molecule and its different protonated forms

The infrared spectra of Histidine molecule have been recorded in the Nujoll mull as well as in aqueous solution in the range 400–4000 cm⁻¹. The Raman spectrum of the same molecule has also been measured. The different protonated/deprotonated forms of imidazole ring which contains different forms of Histidine1, Histidine2, Histidine3 and Histidine4 have been studied with DFT and RHF methods using several basis sets. A comparison of energies of the two neutral tautomers (Histidine1 and Histidine2) indicates that Histidine1 is more stable as compared to Histidine2 while Histidine3 (imidazolium cation) is the most stable in gas phase. The selected geometrical parameters and theoretically calculated frequencies for the above-mentioned form of Histidine were also proposed. The observed IR and Raman bands of Histidine molecule are assigned to different modes on the basis of calculated frequencies, their intensities and available literature values.     

Interpretation of resonance Raman spectra of Zn-phthalocyanine and Zn-phthalocyanine-d<Subscript>16</Subscript> based on the density functional method

We have used the density functional method (DFT) to calculate the geometric structure and the frequencies of even (gerade) vibrations of the Zn-phthalocyanine and Zn-phthalocyanine-d₁₆ molecules, and we have refined the interpretation of the resonance Raman spectra and the fine-structure fluorescence spectra. We observed a dependence of the frequencies of both stretching and bending vibrations of the aza bridges on the nature of the central metal atom. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 296–299, May–June, 2007.     

Structure of the Raman band of the OH stretching vibrations of water and its evolution in a field of second harmonic pulses of a Nd:YAG laser

A fine structure of the Raman band of the OH stretching vibrations of water at 3450 cm^-1 is found upon excitation of the spectra by short trains of second harmonic pulses from a Nd:YAG laser operating at a power of 35 MW/cm² and a pulse repetition frequency of 1 Hz. An increase in the number of pulses in a train from 2 to 128 or in their power leads to the smoothing and asymmetric narrowing of the band and to the shift of its center toward the low-frequency wing, with a subsequent relaxation to the initial state. The observed dynamics of the Raman spectra in the field of the optical pulses is interpreted as manifestation and evolution of a fluctuating network of hydrogen bonds—the destruction and formation of metastable complexes of water having the characteristic frequencies of OH vibrations. Under normal conditions, the lifetime of these complexes in the state induced by the optical field is no less than 1 s.