bluuebunny/crossref_metadata_2025_split huggingface dataset:
SERS of cytosine and its methylated derivatives on gold sols
Authors: Camafeita L. E. , Sánchez‐Cortés S. , García‐Ramos J. V. 
Published: May 2005

AbstractSERS spectra of cytosine, 1‐methylcytosine, 5‐methylcytosine and 1,5‐dimethylcytosine on a gold colloid are reported. A tentative assignment of Raman bands is made by comparison with the normal Raman spectra in aqueous solution. This analysis reveals a preferred non‐planar orientation of cytosine and 1‐methylcytosine and a more planar orientation of 5‐methylcytosine and 1,5‐dimethylcytosine with respect to the metal surface, the C=O group being determinant in the interaction. A comparative study using the result obtained previously using silver and copper colloids as supports shows important differences in the electrodynamic behaviour of these molecules which depend on the presence of the methyl substituents and the nature of the metal on which they adsorb.
Vibrational relaxation processes in isotropic molecular liquids. A critical comparison
Authors: Morresi A. , Mariani L. , Distefano M. R. , Giorgini M. G. 
Published: May 2005

AbstractDynamic processes in the liquid state can be examined from different points of view; the rapid development of highly sophisticated time‐resolved experiments and very complex computer simulation techniques have certainly improved the accuracy of some laboratory results, but they are often not followed by an adequate attempt at interpretation. In any case, the extent of the subject and the enormous spread of experimental data do not help systematic analysis.This review attempts to contribute to a critical examination of a particular aspect of the dynamics of the liquid phase. Through a study of vibrational relaxation in isotropic molecular liquids it is possible to gain information about the molecular environment and the main intermolecular forces operative in this state of matter. It is therefore possible to formulate hypotheses about the force potentials and to describe the dynamic regime of the liquid system under consideration.At present, we may single out four groups of molecues that have been investigated by these methods:(1) diatomic and/or highly symmetric molecules (e.g. HCI, O2, CH4);(2) derivatives of hydrocarbons, especially methane (e.g. CH3NO2, CHCl3, CH2Cl2);(3) aromatic and cyclic aliphatic molecules (e.g. benzene and its derivatives, cyclohexane, pyridine);(4) hydrogen bonded (with OH and/or HCO groups).This paper concerns the comparison between vibrational motions that have similar normal coordinate descriptions; for this reason, we shall limit our considerations to the second and third groups in the above list. Hydrogen‐bonded and highly symmetrical systems are excluded because they need specific considerations.The currently used basic nomenclature of this field will be illustrated, in addition to the physical meaning of the dynamic parameters usually obtained by steady‐state (continuous Raman and infrared), time‐resolved spectroscopy and computer simulation techniques; these different experimental data will be compared, when available. We shall also outline and discuss current theoretical models, and attempt to emphasize their potential and limitations.
Surface‐enhanced Raman spectroscopic studies on silver electrodes in the presence of 2‐mercaptopyrimidine
Authors: Li W. H. , Mao B. W. , Tian Z. Q. 
Published: May 2005

AbstractSurface‐enhanced Raman spectroscopy (SERS) was applied to the study of silver electrodes in the presence of 2‐mercaptopyrimidine (2MP) over a wide electrode potential range from —0.3 to —1.8 V (vs. SCE). The spectra reveal that in neutral solution 2MP was adsorbed perpendicularly on the silver electrode via its sulphur atom at potentials more positive than — 1.1 V and was electrochemically reduced at more negative potentials. The significant dependence of the SERS spectra on the solution pH and the time‐resolved SERS results suggest that hydro‐oligomerization of 2MP may take place during the electrochemical reduction process. It has been shown that SERS can be used as a unique tool to study structural changes of electrochemical interfaces through detailed molecular level analyses in the electrode potential region of hydrogen evolution.
Structure and IR and Raman polarized spectra of BaLaGa3O7 single crystals
Authors: Hanuza J. , Hermanowicz K. , Maczka M. , Ryba‐Romanowski W. , Lis T. , Berkowski M. 
Published: May 2005

AbstractX‐ray diffraction analysis was applied to a BaLaGa3O7 single crystal obtained by the Czochralski technique. It crystallizes in the tetragonal system with the space group P421m (D) and two formula units in the unit cell of dimensions a = 8.145 (2), c = 5.382 (2) Å at 300 K. Polarized IR transmission and Raman scattering spectra of oriented single crystals were measured and are discussed in terms of factor group analysis and x‐ray structure. A vibrational assignment is proposed.
Vibrational study of the structure and polarons in piperazine hexahydrate
Authors: Kanesaka Isao , Kuwano Kazuhiko , Ishioka Tsutomu 
Published: May 2005

AbstractThe Raman spectrum of piperazine hexahydrate was observed over the whole wavenumber region at various temperatures (300—29 K). The splitting between the N—H stretch and the polaron was found to be 21 cm−1 at 44 K. The bands due to the axial configuration of piperazine were above 200 K in both the H and D systems. The enthalpy difference in the equatorial—axial equilibrium was calculated to be 8.1 and 7.6 kJ mol−1 in the H and D systems, respectively. The phase transition was found at ca. 170 K, and is ascribed to the order—disorder type associated with the axial configuration. The polaron was discussed group theoretically and reinvestigated on the basis of the coupling of the N—X stretch with optical lattice modes. It is noted that the polaron is little affected by the phase transition at 170 K or disorder in hydrogen positions.
Resonance Raman spectroscopy of rhodizonates: Evidence of low‐energy transitions in the solid state
Authors: Gonçalves Norberto Sanches , Santos Paulo Sergio 
Published: May 2005

AbstractThe optical and Raman spectra of several salts of rhodizonic acid were investigated, aimed at a better understanding of the dramatic dependence of their colours on the nature of the cation. The results indicate that in addition to the maxima observed in the optical spectra, another transition in the red edge must be present in the solid state, as indicated by the large number of overtones and combination bands in the Raman spectra excited in the red. It is suggested that such a low‐energy transition observed only in the solid state is of intermolecular origin, as observed previously for other related systems.
Determination of the molecular structures of tungstates by Raman spectroscopy
Authors: Hardcastle Franklin D. , Wachs Israel E. 
Published: May 2005

AbstractAn empirical correlation is developed for relating the wavenumbers of (WO) stretching modes to WO bond lengths and bond strengths for tungsten oxide reference compounds. A least‐squares exponential fit of crystallographically determined WO bond lengths to the wavenumbers of their Raman stretching modes is presented along with a relation between WO bond strengths, in valence units, and wavenumbers of Raman stretching modes. The empirical bond length/stretching mode wavenumber/bond strength relationships lead to a unique and effective method of interpreting Raman spectra of tungstate species. This method leads to the WO bond lengths and coordination of the tungstate species. The utility of the method is illustrated by estimating the wavenumbers of the Raman stretching modes for the ideal WO4 tetrahedron and WO6 octahedron, and the bonds lengths and coordinations of the tungstate species in the reference compounds Na2WO4, PbWO4, CaWO4 and Bi2WO6. In addition, the WO bond lengths of the WO6 octahedra in crystalline Ba2MgWO6 are reported for the first time. This new approach for evaluating the Raman spectra of tungstate species is expected to be generally applicable to all tungstates, regardless of environment, physical state, or oxidation state.
Use of micro Raman spectroscopy for the quantitative determination of polyethylene density using partial least‐squares calibration
Authors: Williams K. P. J. , Everall N. J. 
Published: May 2005

AbstractA series of polyethylene samples were analysed using a micro Raman system. The data were analysed using a commercial partial least‐squares package and correlated with the polymer density. A correlation coefficient of up to 0.98 was obtained, depending on the spectral region used. A standard error of prediction of 2.15 kg m−3 was obtained and the densities of ‘blind’ samples were predicted with good accuracy.
Fourier transform Raman spectroscopy of nitrogen at high pressures
Authors: McNesby Kevin L. , Morris Jeffrey B. 
Published: May 2005

AbstractRo‐vibrational and rotational Raman spectra of nitrogen gas at 300 K over the pressure range 3‐24 MPa (500‐3500 psi) were measured using a Fourier transform spectrometer employing 1064 nm laser radiation as the scattering source. It is shown that the pressure‐induced narrowing and peak shift of the Raman spectrum of N2 observed in these experiments agrees within experimental error with data obtained by other workers using different techniques.
Temporally two‐dimensional Raman spectroscopy of liquids by six‐wave mixing with ultra‐short pulses
Authors: Tominaga Keisuke , Keogh Gary P. , Naitoh Yukito , Yoshihara Keitaro 
Published: May 2005

AbstractA temporally two‐dimensional Raman spectroscopic method was developed to observe the fifth‐order optical response of liquids. Taking advantage of temporal two‐dimensionality, this technique can unambiguously distinguish homogeneous and inhomogeneous contributions to the dephasing of low‐wavenumber vibrational modes. The measurement of the fifth‐order optical response of liquid CS2 was conducted by ultra‐fast non‐resonant six‐wave mixing using five different pulses. The experimental results are reproduced well in terms of one overdamped mode in the homogeneous limit and one underdamped mode with the width of the inhomogeneity less than 2.5 ps−1.
Ultrafast Raman echo experiments in liquids
Authors: Bout David Vanden , Berg Mark 
Published: May 2005

AbstractThe Raman echo is the first of the eight‐wave mixing spectroscopic techniques to be experimentally demonstrated in molecular systems. Practical results achievable in such high‐order experiments are described. Signal levels, competing non‐linear effects, phase‐matching requirements and other experimental design considerations are discussed. Results needed to predict the success of experiments at different power levels, Raman cross‐sections and concentrations are presented.
Femtosecond inverse Raman spectrum of molecular J‐aggregates
Authors: Misawa Kazuhiko , Minoshima Kaoru , Kobayashi Takayoshi 
Published: May 2005

AbstractThe femtosecond inverse Raman spectrum of J‐aggregates of a cyanine dye was studied theoretically and experimentally by the pump—probe experiment. The time dependence of the Raman signal intensity of the aggregates was fitted with an instantaneously responding component due to the Stark effect together with 200 fs and 1 ps lifetime components due to the excitons. The instantaneous response in the time‐resolved difference transmission spectrum including the inverse Raman, induced and saturated absorption was successfully reproduced by the calculation under sub‐resonant excitation based on the density matrix formalism.
Raman, infrared and 13C NMR studies of mixed halides of cyclopropene, C3ClnBr4—n, and cyclopropane, C3ClnBr6—n
Authors: Taylor Michael J. , Baker L.‐J. 
Published: May 2005

AbstractTetrachlorocyclopropene, C3Cl4, is converted into C3Br4 by treatment with BBr3. Use of less than the stoichiometric amount of BBr3 leads to mixed halides C3ClnBr4‐n which are identified and investigated by Raman and 13C NMR spectroscopy. The addition of Br2 to C3Cl4 yields both the isomers cis‐ and trans‐1,2‐dibromotetrachlorocyclopropane in equal quantities; the vibrational spectra are reported and partially assigned. Raman and 13C NMR of other mixed halides of cyclopropane, C3ClnBr6‐n are discussed. A 35Cl/37Cl isotope effect is detected on the carbon chemical shift of C3Cl6 I2 fails to react with C3Cl4 or C3Br4.
Resonance Raman studies of heterocyclic aromatic compounds showing ultrafast intramolecular proton transfer
Authors: Pfeiffer M. , Lenz K. , Lau A. , Elsaesser T. 
Published: May 2005

AbstractResonance Raman spectra of the three isoelectronic proton transfer systems 2‐(2′‐hydroxy‐5′‐methylphenyl)‐benzotriazole (TIN), 2‐(2′‐hydroxyphenyl)benzothiazole (HBT) and 2‐(2′‐hydroxyphenyl)benzoxazole (HBO) were measured with excitation in the range of the S0‐S1 absorption band of the enol tautomers. In each compound, about 15 modes in the wavenumber range between 120 and 1650 cm−1 show a strong coupling to the electronic transition. In TIN and HBT, combination tones of the strongest mode below 500 cm−1 and the vibrations at higher wavenumbers point to the strong anharmonicity of the low wavenumber motion. The experimental results are analysed by normal‐mode calculations, which provide insight into the microscopic elongations in the molecules. The coupling strengths derived from the spectra are used to calculate the envelope of the S0‐S1 absorption bands of TIN and HBT, reproducing the measured spectra very well. Theoretical simulations of the combination tone spectra give information on the vibrational modes involved in excited‐state proton transfer.
SERS of dicarboxylic acids on silver sols
Authors: Arenas J. F. , Castro J. L. , Otero J. C. , Marcos J. I. 
Published: May 2005

AbstractSERS spectra of succinic and oxalic acids on silver sols have been revised. For the latter molecule the vibrational spectrum has been assigned on the basis of AM1 and 3‐21G ab initio force field calculations. Also, SERS of the malonate ion is presented for the first time, showing some general characteristics similar to the aforementioned. The results have been analysed together, and a model is proposed in which the interaction with the surface is through one carboxylate group in the case of oxalic acid and through both carboxylate groups in the case of malonic and succinic acids.
High‐resolution Raman spectra of the Fermi diad in disordered crystalline CO2
Authors: Andueza J. J. , Ouillon R. , Lucarre J. P. Pinan , Ranson P. 
Published: May 2005

AbstractUsing high‐resolution Raman spectroscopy, very weak features in the biphonon spectra of disordered materials were investigated. The analysis was focused on the bound states due to the Fermi resonance in crystalline CO2. Two systems were studied: the mixed isotpic (12CO2)x—(13CO2)1−x crystals and the molecular alloys (N2O)x—(12CO2)1− x and (N2O)x—(13CO2)1− x. In the first system, it was shown that the wavenumbers and bandwidths of biphonon states at K ≈︁ O follow a concentration dependence identical with that encountered for one‐phonon states which obey the separated band limit model in mixed isotopic crystals. In the second system, the occurrence of a fine structure in the biphonon band is discussed on the basis of a strong interaction between non local matrix biphonons and quasi‐local biphonons created by the disorder.
Raman spectra, conformational stability and normal coordinate analysis of ethylmethylamine
Authors: Batista De Carvalho L. A. E. , Teixeira‐Dias J. J. C. 
Published: May 2005

AbstractRaman spectra of ethylmethylamine and ethylmethylamine‐N‐d, both in the liquid phase, at different temperatures, and in the solid phase were recorded. Additionally, Fourier transform IR (4000—400 cm−1) spectra of these compounds in the liquid phase were also obtained. Normal coordinate calculations were performed for each conformer (T, G and G′), using an optimized local symmetry force field for secondary amines. These calculations allowed the assignment of the vibrational spectra, in good agreement with the experimental evidence. Whereas in the liquid phase all the three possible conformers were detected, in the solid phase only the bands ascribed to the T conformer were observed. From the temperature dependence study of the Raman spectrum of the liquid, the enthalpy differences between conformers were determined, yielding the values 4.6 ± 0.3 kJ mol−1 for ΔHG′‐T′ 3.6 ± 0.3 kJ mol−1 for ΔHG ‐ T and 1.1 ± 0.3 kJ mol−1 for ΔHG′‐ G. These were compared with ab initio SCF‐MO results, for the isolated molecule, in order to assess the relative importance of intra‐and intermolecular effects on conformational equilibria.
Dependence on concentration and temperature of the dynamics of SO in Li2SO4, Na2SO4 and K2SO4 aqueous solutions studied by Raman spectroscopy
Authors: Rull F. , Sobrón F. , Nielsen O. F. 
Published: May 2005

AbstractThe Raman spectra of the v1(SO) band in aqueous solutions of Li2SO4, Na2SO4 and K2SO4 as a function of concentration at room temperature and for fixed concentrations in the temperature range 5—85°C were studied. It was found that the molar scattering coefficient for SO is virtually independent of the concentration and temperature in the studied range. Nevertheless, the v1(SO) band shows some asymmetry on the high‐wavenumber side for Li and Na and on the low‐wavenumber side for K, which for these last two cases has not previously been reported. Moreover, the band position seems to be correlated with the sign and amount of the asymmetry as the concentration increases. On the other hand, temperature does not have a great effect on the band profile. In the case of Na and K, there is little narrowing of the band, whereas for Li there is slight broadening and an increase in the asymmetry. Quantitative analysis of these changes was performed using the vibrational correlation function. This was modelled considering the distribution of sulphate oscillators in the aqueous media as a convolution product of an unperturbed distribution by a perturbation function. This last function assumes a feedback mechanism in which the main parameters are the coupling energy and the fraction of the distribution having interactions. The dependence of these parameters and of the Gaussian and Lorentzian contributions to the band profile with concentration and temperature are discussed.
Raman and infrared intensities in trimethylamine species, polarizability and dipole derivatives and effective charges
Authors: Murphy W. F. , McKean D. C. , Coats A. M. , Kindness A. , Wilkie N. 
Published: May 2005

AbstractRaman trace scattering intensities are reported for the d0, d3, d6, d8 and d9 deuterated species of trimethylamine. Using normal coordinates from a previous scaled ab initio force field, the data are analysed in terms of seven derivatives ∂α¯∂S in the A1 symmetry species, each of which is well defined. Similar derivatives (dα¯/dr)CH with respect to the stretching of the two kinds of CH bond are shown to be very different from each other, showing a marked effect of the lone pair. Infrared intensities were measured for the d0, d8 and d9 species. These are well reproduced by ab initio calculations at the MP2/6‐31G* level. The dipole derivative for the CHS bond trans to the lone pair is much greater than that for the Ha bond in the gauche position. The ab initio atomic polar tensors were used to obtain effective charges and other invariants, and the directions of dμ/dr for the CH bonds were determined. That for the Hs bond lies 23° off the bond direction. The ratio Xa/Xs of the abundances of the Ha and Hs conformers in the d8 isotopomer, required for the above analyses of the spectra, is calculated to be 1.80(4).
Stochastic model for correlation functions from anisotropic Raman line shapes
Authors: Ribeiro Mauro C. C. , Santos Paulo S. 
Published: May 2005

AbstractThe separation of the Raman correlation function as a product of independent vibrational and reorientational correlation functions is investigated. The present model is a unification of previous models which treat separately vibrational dephasing and reorientational relaxation within the context of the stochastic approach. It indicates that the so‐called product approximation for the Raman correlation function can fail even when the relaxation rate is distinct for vibrational and reorientational relaxations. Application to experimental data for liquid CS2 is presented.
Resonance Raman spectroscopic studies of pH indicators adsorbed on γ‐Al2O3
Authors: Bisset Alison , Dines Trevor J. 
Published: May 2005

AbstractResonance Raman spectra were recorded from methyl red, ethyl red and α‐naphthyl red adsorbed from toluene solutions on to γ‐alumina. The spectra show clear evidence for the protonation of all three indicators. Adsorption data over a wide range of equilibrium concentrations give satisfactory fits to Langmuir isotherms. Together with the spectroscopic data, the isotherms permit the determination of the densities of Brønsted acidic sites on the γ‐alumina surface. The densities of acidic sites decrease after calcination at 300°C.
Vibrational and rotational spectra, conformations and ab initio calculations of thiocyanatoethene
Authors: Beukes J. A. , Klaeboe P. , Møllendal H. , Nielsen C. J. 
Published: May 2005

AbstractInfrared spectra of thiocyanatoethene in the 4000‐400 cm−1 region in the vapour and liquid states and of the amorphous and crystalline solids at low temperatures were obtained. Additional IR spectra of the compound were recorded when isolated in argon and nitrogen matrices at 5 K using the hot nozzle technique. Raman spectra in the liquid phase at various temperatures were recorded and the amorphous and crystalline solids were investigated at liquid nitrogen temperature. Microwave spectra of thiocyanatoethene were recorded in the 10‐39 GHz region by means of Stark modulation. Areas of special interest were also investigated by use of the RFMWDR double resonance technique. Ab initio quantum chemical calculations were carried out with the 6—31G* basis set.The spectral data were interpreted in terms of an equilibrium in the vapour and liquid states between a syn and a gauche conformer, while syn was the only conformer present in the crystal. An approximate enthalpy difference of 3—6 kJ mol−1 in the vapour and 5.7 ± 1.0 kJ mol−1 in the liquid was determined, with the syn conformer being the more stable. The microwave spectrum of the syn conformer was assigned, giving rotational constants in good agreement with the results of the ab initio calculations, whereas we were not able to assign unambiguously the spectrum of the gauche conformer. The internal energy difference between the syn and gauche conformers was determined to be 4.4 ± 1.0 kJ mol−1.
KSbF6 revisited. I—A Raman and infrared study of the tetragonal phase I
Authors: Heyns Anton M. , van den Berg Magda M. 
Published: May 2005

AbstractThe polarized Raman spectra of single crystals of KSbF6‐I of P42m‐D symmetry are reported. The predicted LO‐TO splittings of the B2 and E modes were not observed and the vibrational spectra do not indicate a non‐centrosymmetric structure. The calculated relative intensities of the Raman bands in the single‐crystal spectra agree very well with the observed values. It is shown that the anions execute fourfold reorientational motions around the S4 axis of the crystals and an activation energy of 3.2 kcal mol−1 (13.4 kJ mol−1) is calculated from the variation of the linewidths of Raman bands with temperature. The barrier is penetrated by the anions and because of the jumping motions of the anions in KSbF6‐I the small distortions from a centrosymmetric structure are averaged out and the Raman and infrared spectra appear to be mutually exclusive.