bluuebunny/crossref_metadata_2025 huggingface dataset:
CARS difference spectroscopy. II—Determination of small frequency shifts and band width changes in binary mixtures
Authors: Weippert A. , Kiefer W.
Published: May 2005

The experimental verification of CARS difference spectroscopy (CARS‐DS) is presented and its application to binary mixtures is shown. The experimental set‐up allows the simultaneous measurement of CARS spectra of two different samples under identical conditions. It is shown how the method can be used for the accurate determination of small frequency shifts and band width changes in liquid mixtures. The experimental spectra obtained were analysed by their numerical simulation using a least‐squares fitting routine. As examples, experimental results for chloroform–deuterochloroform isotopic mixtures and binary mixtures of benzene and toluene of different concentrations are presented. In both cases frequency shifts and changes in the band width were observed which exhibit an almost linear dependence on the mole fraction of the probe species.
Resonance Raman investigation of the state of polyiodides in the organic conductors (PEDT‐DTDSF)2I3 and (PDM‐TTF)3I3
Authors: Zambounis J. S. , Kamitsos E. I. , Papavassiliou G. C.
Published: May 2005

The resonance Raman spectra of (PEDT‐DTDSF)2I3 and (PDM‐TTF)3I3 organic conductors were measured and analysed to investigate the state of the polyiodide counterions. It was found that both compounds are characterized by the coexistence of I3− and I5− species. The relative concentration of these polyiodides has been shown to be temperature dependent only for the first compound. This was attributed to a thermally induced disordering of the triiodide chains, which leads to a dynamic formation of pentaiodides with increasing temperature.
Multi‐channel micro‐Raman spectroscopy with near‐infrared excitation. II
Authors: Barbillat J. , Da Silva E. , Hallaert J. L.
Published: May 2005

The performances of a multiplexed near‐infrared (NIR) germanium detector and of a InGaAs photodiode‐array detector are reported. Their use with an Nd: YAG laser at 1.064 μm to obtain high‐quality fluorescence‐free Raman spectra of micro‐samples is illustrated. A comparison with Fourier transform Raman spectra of much larger samples demonstrates that NIR multi‐channel Raman spectroscopy is competitive for fluorescence‐free measurement of Raman spectra.
Spectroscopic behaviour of the two CO stretching vibrations in free and complexed theophylline
Authors: Tarulli Susana , Baran Enrique J.
Published: May 2005

The behaviour of the stretching vibration of the two CO groups in free theophylline and in some of its metallic complexes of stoichiometry [MII(tp)2(H2O)4] were investigated by means of infrared and Raman spectroscopy. It is demonstrated that after complexation an inversion of the relative band positions of these two stretching modes takes place. This behaviour could be clearly explained on the basis of the structural characteristics of the investigated complexes.
Raman and surface‐enhanced Raman spectroscopic studies of sulphanilic acid azochromotrope (SPADNS)
Authors: Siu G. G. , Chen Z. L.
Published: May 2005

The trisodium salt of 2‐(4‐sulphophenylazo)‐1,8‐dihydroxynaphthalene‐3,6‐disulphonic acid (SPADNS) was studied by Raman and surface‐enhanced Raman spectroscopy (SERS) techniques. The Raman spectra of SPADNS powder and aqueous solution were investigated and an assignment of the Raman bands was made taking into account its infrared absorpiton spectrum. SPADNS tatomers, o‐hydroxyazo and o‐quinone hydrazone, are also discussed. Although the assignment is still preliminary owing to the complex structure of the SPADNS molecule, it provides useful information for SERS investigations of SPADNS in aqueous silver sol and on silve film. The results of SERS are compared with those of visible absorption spectra and x‐ray photoelectron spectra (XPS) and the adsorption configuration of the SPADNS molecule on a silver surface is considered.
Laser power dependence of Raman scattering on YBa2Cu3O7−x thin films
Authors: Liang N. T. , Tse W. S. , Chang M. C. , Chen H. T. , Chen T. T.
Published: May 2005

Good‐quality high‐Tc YBa2Cu3O7−x thin films deposited by the laser ablation method were investigated by Raman spectrosocpy. The vibrational spectra of thin films of YBa2Cu3O7−x at various laser intensities and with different polarizations were measured. The Raman modes change on increasing the laser power and in general such changes are reversible. However, as the laser intensity is increased above a certain value, dramatic changes occur in the Raman peaks, as a result of damage to the sample.
Behaviour of the 1025 cm−1 band of SERS spectra due to pyridine on a silver electrode in aqueous halide media
Authors: Saito Hiroshi
Published: May 2005

The 1025 cm−1 band which occurs in the SERS of pyridine and halide anion was investigated in detail on a silver electrode in neutral and acidic solution. The 1025 cm−1 band was observed to increase in intensity when the silver electrode was treated with the ORC procedure in the presence of pyridine and halide and the concentration of pyridine was then diluted in neutral solution. On the other hand a band began to appear strongly at 1025 cm−1 when the solution was acidified with HCl after the ORC. It was confirmed that the 1025 cm−1 band appearing on dilution in neutral solution has by the same origin as the 1025 cm−1 band which appeared on acidification. The behaviour of the band can be understood if it is assumed that the species giving rise to the 1025 cm−1 band is a silver–pyridine–halide complex generated by the electrode reaction during the ORC.
Raman and infrared spectra, conformational stability, barriers to internal rotation and ab initio calculations of acetyl isocyanate
Authors: Durig J. R. , Guirgis G. A. , Krutules K. A. , Sullivan J. F.
Published: May 2005

The Raman (3100–10 cm−1) and infrared (3100–30 cm−1) spectra of acetyl isocyanate, CH3C(O)NCO, and the d3‐isotopomer were recorded for the gases and solids. Additionally, the Raman spectra of the liquids were recorded and qualitative depolarization values were obtained. The observed bands are assigned on the basis of the more stable cis (syn) conformer (isocyanate group cis to the carbonyl bond) and less stable trans (anti) conformer in the vapor state. ΔH of the gas is estimated to be 433 cm−1 [1.24 kcal mol−1 (1 kcal = 4.184 kJ)] from the relative intensity of the conformer pair at 800 and 763 cm−1. From the temperature dependence of the Raman spectrum of the liquid, two conformer pairs were used to determine experimentally a ΔH value of 370 ± 60 cm−1 (1.06 ± 0.17 kcal mol−1) but now with the trans conformer the more stable form. In the annealed crystalline solid, only the trans conformer remains. The fundamental asymmetric torsion of the cis conformer was observed at 79 cm−1 with two excited states falling to lower frequency. Utilizing these data and ΔH for the gas the potential function governing the conformer interchange was estimated. A complete vibrational assignment is proposed for both conformers based on infrared band contours, Raman depolarization data, group frequencies and normal coordinate calculations. The experimental confirmational stability, barriers to internal rotation and fundamental vibrational frequencies are compared with those obtained from ab initio Hartree–Fock gradient calculations employing the RHF/6–31G* basis set and to the corresponding quantities obtained for some similar molecules.
Vibrational spectra and conformation of 2,3‐diiodobuta‐1,3‐diene
Authors: Karlsson A. , Klaeboe P. , Nielsen C. J.
Published: May 2005

Raman and infrared spectra of the very unstable compound 2,3‐diiodobuta‐1,3‐diene were recorded in the crystalline state at low temperatures in the spectral ranges 3300–10 and 4000–200 cm−1, respectively. Owing to a rapid polymerization rate at room temperature, only incomplete IR data were obtained of the sample in CCl4 solution. The vibrational spectra were analysed and support a planar anti conformer present in the cyrstal. The vibrational assignments are presented, supported by force constant calculations.
Vibrational spectra and conformations of 2,2‐di(fluoromethyl)‐1,3‐difluoropropane and assignments based upon ab initio force fields
Authors: Gatial A. , Sablinskas V. , Klaeboe P. , Powell D. L. , Nielsen C. J.
Published: May 2005

The IR spectra of 2,2‐di(fluoromethyl)‐1,3‐difluoropropane were recorded in the vapour and liquid states and as a solute in solvents of different polarity. Additional IR spectra were obtained for plastic and crystalline solids at low temperature and at high pressure, and also of the compound isolated in argon and nitrogen matrices, using the hot nozzle technique. Corresponding Raman spectra of the liquid, of solutions and of the plastic phase were recorded at different temperatures in addition to the crystalline solid. There are six possible staggered conformations with symmetries D2d, S4, C1*, C1, C2 and Cs in this molecule, and all but the last two were detected in the spectra. The two most stable conformers are S4 and D2d which have no 1,3‐parallel CF interactions. Among them S4 is ca. 0.5 and 1 kJ mol−1 lower in energy than D2d in the plastic phase and in the matrices, respectively, and S4 is present in the low‐temperature and high‐pressure crystals. A plastic phase, in which more conformers were present, was observed at temperatures below Tmelt and at high pressure. The C1* and C1 conformers both have enthalpies 5–10 kJ mol−1 higher than S4 and their bands are enhanced at increased temperatures both in the plastic crystal and in the matrices. They have dipole moments around 2–3 D, and the intensities of their bands increase in polar solvents. The enthalpy differences ΔH° were calculated from variable‐temperature measurements in the plastic crystal and in the matrices, and confirmed by Gaussian 90 with basis sets 6–31G* and 6–31G and by semiempirical and molecular mechanics calculations: MNDO, AM1 and MM2. A nearly complete assignment of the fundamentals belonging to S4 is presented. Additional bands are attributed to the D2d, C1* and C1 conformers from annealing experiments at different temperatures in the N2 matrix and in the amorphous phase. The assignments are based on the spectral observations and on the results of force constant calculations, involving scaled ab initio force constants.
Vibrational spectra in the region of OX stretches in SnCl2 · 2X2O (X = H or D) at room temperature
Authors: Kanesaka Isao , Ogawa Tadashi
Published: May 2005

Polarized Raman spectra in the region of the OH stretches and the decoupled OD stretches in a crystal of SnCl2 · 2X2O (X = H or D) at room temperature are reported, together with infrared and Raman spectra in the polycrystalline state. Seven decoupled modes for four types of hydrogen bond were observed, which were assigned on the basis of six types of water configuration. A slight shift was found for some bands above 3350 cm−1 on going from the decoupled to the coupled state. The Raman band assigned to the in‐phase v1 mode was observed at 3060 (2275) cm−1 in the H (D) system, which was only lower by 89 (54) cm−1 than the decoupled mode. These spectra were analysed on the basis of a force field with intra‐ and intermolecular interaction constants using 72 water molecules with disorder in the hydrogen positions which satisfy a periodic boundary condition. The observed spectra were essentially explained in terms of the initial set of force constants, except for a medium band at ca. 3200 cm−1, which was accounted for using a shoulder in the decoupled spectra.
Raman spectroscopic study of the conformational equilibrium of liquid 3‐fluorostyrene
Authors: Ribeiro‐Claro P. J. A. , Teixeira‐Dias J. J. C.
Published: May 2005

The Raman spectra of liquid 3‐fluorostyrene show pairs of bands whose temperature‐dependent intensities clearly suggest the occurrence of a conformational equilibrium. From these bands, assigned to cis and trans conformers, a trans–cis energy difference of 0.70 ± 0.20 kJ mol−1 was obtained for the liquid phase, higher than the reported gas‐phase microwave and ab initio values. The effects of dilution with several solvents of different polarity properties are reported and the improved relative stability of the cis form in high‐polarity solvents is interpreted in terms of medium effects on intramolecular through‐space dipole–dipole interactions.
Use of the transform method in the interpretation of the Raman excitation profiles of a bichromophoric system
Authors: Ribeiro Mauro C. C. , de Oliveira Luiz F. C. , Constantino Vera R. L. , Toma Henrique E. , Santos Paulo S.
Published: May 2005

The use of the transform method was extended so as to permit the treatment of the resonance Raman effect with the participation of two interfering electronic transitions. The relevant equations were tested in the model system [Ru(bipy)2(violurate)]PF6, the Raman excitation profiles of which show clearly the presence of two chromophoric moieties. The present results strongly suggest that the two relevant excited states participate by means of Albrecht's A terms, whereas the vibronic coupling by the B term is not decisive. The independence of the two chromophoric moieties is reflected in distinct displacements of the respective potential minima.
Fourier transform Raman spectroscopic detector system for the analysis of polymers by gel permeation chromatography
Authors: Edwards H. G. M. , Johnson A. F. , Lewis I. R.
Published: May 2005

An attempt was made to use a Fourier transform (FT) Raman spectrometer as a detector with a gel permeation chromatograph which was otherwise configured in the usual way for the measurement of molar mass distribution in polymers. A low‐volume flow cell was constructed and the detector response tested both off‐line and, in a preliminary way, in‐line with the chromatograph. The particular objective was to establish whether it would be possible to measure the microstructural variation in polybutadiene with polymer molecular weight during the chromatographic process. The detector sensitivity was assessed for a range of polybutadienes with different cis‐1,4‐, trans‐1,4‐ and vinyl‐1,2‐ contents using tetrahydrofuran as solvent and eluent. Data obtained using visible Raman (488.0 nm) excitation and near‐infrared (1064 nm) excitation were compared. Although it has been established that the Raman spectrometer is one of the best instruments for the evaluation of the microstructure of polybutadiene when used in a conventional way, it lacks the necessary sensitivity to provide quantitative information on polydienes which elute from a chromatograph. However, there is no reason in principle why an FT‐Raman spectrometer should not be used as a concentration detector and for the simultaneous more detailed analysis of polymer composition or micro‐structure during the chromatographic process, provided that the scattering intensity of the solute is high relative to the eluent. The potential advantages and the observed problems of what appears to be a novel experiment with an FT‐Raman instrument are discussed.
Application of Raman spectroscopy to industrial ion‐exchange membranes. 3—poly‐4‐vinylpyridinium membranes
Authors: Bribes J.‐L. , Hasdou A. , Maillols J.
Published: May 2005

Raman spectra of poly‐4‐vinylpyridinium anion‐exchange membranes, immersed in aqueous solutions, were recorded. Assignments of some specific vibrational bands are proposed, allowing intensity measurements of appropriate signals versus pH or time. Membranes with low intrinsic pK values were analysed and the results were in agreement with those obtained by other techniques. Deprotonation kinetic data were obtained in relation to the reduced proton leakage of these materials.
Analysis of the deformation of aramid fibres and composites using Raman spectroscopy
Authors: Andrews M. C. , Young R. J.
Published: May 2005

It is demonstrated that Raman spectroscopy can be used to study both the deformation micromechanics of high‐performance aramid polymer fibres and of these fibres in model, single‐fibre epoxy resin matrix composites. It is shown that the peak position of the 1610 cm−1 aramid Raman band shifts to lower frequency under the action of tensile stress or strain due to the macroscopic deformation leading to direct stretching of the polymer molecules. These strain‐induced band shifts can be used to map the distribution of stress or strain along a discontinuous, aramid fibre inside an epoxy resin matrix from which the interfacial shear stress can be calculated. It is shown that the behaviour is consistent with that predicted by the classical shear‐lag analysis. The technique was also used to study the fragmentation process for an aramid fibre in an epoxy resin matrix in which the matrix strain exceeds the failure strain of the fibre. It is further demonstrated that the technique can be used to compare the interfacial properties of aramid fibres where the interfacial shear stress is found to be higher for sized fibres than for those which have been de‐sized.
Estimation of crystallinity in polyethylene by Raman spectroscopy
Authors: Rull F. , Prieto A. C. , Casado J. M. , Sobron F. , Edwards H. G. M.
Published: May 2005

The quantitative determination of crystallinites of polyethylene samples from the analysis of vibrational bands due to δ(CH2) twisting and v(CC) stretching in the Raman spectra between 950 and 1500 cm−1 was assessed. Several methods based on manual resolution of band envelopes and on computer‐derived information using Gaussian and Lorentzian profiles were compared. The major source of error was found to be the estimation of the amorphous and crystalline interphase content, αb. A new method for the determination of sample crystallinity is proposed based on the time‐dependent Fourier transform deconvolution of the spectral region between 950 and 1500 cm−1, which takes into account the baseline corrections and the influence of vibrational band shoulders in this region to obtain consistent values of αa, αb and αc.
Raman studies of sodium fluoroborate single crystals
Authors: Brooker Murray H.
Published: May 2005

Raman spectra of oriented single crystals of NaBF4 were measured at 77 and 298 K. The number of bands and the intensities were in excellent agreement with the unit cell group predictions for the known crystal structure, D, Z = 2. The results for the ν1, ν2 and ν4 regions were in excellent agreement with those of Bates [J. Chem. Phys. 55, 489 (1971)]. A recent study by Rajakumar et al. [J. Raman Spectrosc. 23, 75 (1992)] is erroneous. The new measurements permitted the assignment for the Raman bands in the ν3 region. Peaks in the external mode region were very weak because both the Na+ and BF4− ions have spherical symmetry, small polarizabilities and small polarizability derivatives with respect to normal coordinates. Only three weak peaks of the nine predicted external‐modes were observed (88 cm−1, Ag; 110 cm−1, B2g; and 214 cm−1, B2g). Crystals grown from aqueous solution were found to contain water and as much as 0.1% of BF3OH− as a substitutional impurity. Peaks due to the O–H (O–D) stretching vibration were detected in the crystals at 3641 (2688) cm−1 and peaks due to the B–OH (B–OD) stretching vibration were detected as 773 (748) cm−1.
Study of second‐order excitations in α‐iodic acid crystal by means of polariton k‐spectroscopy
Authors: Chekhova M. V. , Penin A. N.
Published: May 2005

Polariton spectroscopy was used for studying the dispersion of linear and non‐linear susceptibilities of an α‐iodic acid crystal in the vicinity of second‐order vibrations (wavenumber range 1000–1200 cm−1). The measurements were carried out by means of k‐spectroscopy (spectroscopy in the space of wavenumbers). Here k‐spectroscopy was applied to the resonant case when the polariton frequency lies close to one of the lattice resonances and therefore the angular line shape of scattering is not Lorentzian. To measure the crystal parameters at this frequency, the angular spectrum was analysed and a procedure was developed for angular line shape processing that allows the following values to be calculated: the real and imaginary parts of the dielectric function; the real and imaginary parts of the quadratic susceptibility; and the imaginary part of the cubic susceptibility. All these parameters were measured for an α‐HIO3 crystal in the range containing a few second‐order excitations and also a first‐order vibration of the OH group at 1160 cm−1. The results allow some conjectures to be made regarding the nature of the second‐order excitations.
Study of intact and modified erythrocyte membranes with laser Raman spectroscopy
Authors: Goheen S. C. , Lis L. J. , Kucuk O. , Westerman M. P. , Kauffman J. W.
Published: May 2005

Raman spectra of erythrocyte membranes which were intact and erythrocyte membranes which were modified by extrinsic protein extraction procedures were examined. In all cases, there was no apparent correlation between protein extraction and membrane lipid fluidity. The extraction of the band 6 protein by 0.15 M NaCl but not 0.001 M NaDH raised the erythrocyte membrane α‐helical content while the extraction of all extrinsic proteins by 0.1 M NaOH resulted in a decrease in protein α‐helical content. The study shows that either peripheral protein extraction and/or salt solutions can modify the secondary structures of the remaining intrinsic membrane proteins.
Raman study on p‐nitroaniline in channels of the molecular sieve AlPO4–5
Authors: Marlow F. , Hill W. , Caro J. , Finger G.
Published: May 2005

Zeolite‐like molecular sieves are characterized by a regularly arranged micropore system. These pores can order adsorbed molecules. The resulting guest–host composites are promising materials for spectroscopy because of the non‐random orientation of the transition matrix elements. By studying the Raman scattering of p‐nitroaniline (PNA) within a large aluminophosphate AlPO4–5 crystal, it was found that the PNA molecules are very well aligned inside the pores, forming dipole chains with intermolecular interactions as in the solid.
Raman, Pre‐resonance Raman and electronic spectra of [VO(biuret)(SO4)] · 3H2O
Authors: Jubert A. H. , Diez R. Pis , Etcheverry S. B. , Baran E. J.
Published: May 2005

Information on the vibrational and electronic properties of the [VO(biuret)(SO4)] · 3H2O complex was improved in order to gain a deeper insight into the characteristics of the metal–ligand bonds. Normal Raman and pre‐resonance Raman studies were performed, which allowed a better characterization of the metal–ligand modes and a thorough analysis of the electronic spectrum. The results were also compared with theoretical semi‐empirical molecular orbital calculations.
Study of the pyridine–methanol system using four‐channel Raman spectroscopy: Concentration dependence of frequencies, line widths and integrated intensities
Authors: Kreyenschmidt M. , Eysel H. H. , Asthana B. P.
Published: May 2005

Spectra of the pyridine–methanol system were recorded in the range 300–3820 cm−1 using the technique of four‐channel Raman spectroscopy. The relative concentrations of the two components were varied in different mixtures, such that the mole fraction of pyridine, C, was 0.1, 0.2, 0.3, 0.5, 0.7, 0.8 and 0.9. The isotropic part (Iiso) of the Raman scattered intensity was recorded for all seven mixtures and for pure pyridine (C = 1.0) and pure methanol (C = 0.0) in the region 950–3820 cm−1 only, since below 950 cm−1 the isotropic part of the intensity was too weak to provide any useful information. The most important aspect of this study was the experimental determination of integrated isotropic intensities in two regions, namely 960–1080 and 2700–3650 cm−1, and the study of their variations with changing concentration of pyridine in the different mixtures. The most striking result was the observation of excess intensity over a linear concentration dependence in the region 960–1080 cm−1. The variations in frequency shifts and line width changes measured from the isotropic part of the Raman spectra of different mixtures in the region 960–1080 cm−1, and especially in the region 2700–3650 cm−1, are discussed with a view to understanding the origin of such variations.
Surface‐enhanced resonance hyper‐Raman (SERHR) spectroscopy of photochromatic molecules
Authors: Baranov A. V. , Bobovich Ya. S. , Petrov V. I.
Published: May 2005

The surface‐enhanced resonance Raman and surfaces enhanced hyper‐Raman (SERHR) spectra of a photochromatic indigoid dye were obtained. The influence of stationary additional lighting (AL) at the absorption bands of the photoisomers on the SERHR intensities was observed. This is connected not only with the changes in the photoisomer concentration on the silver surface under AL but also with different scattering intensities of the resonance hyper‐Raman spectra of isomers due to their different symmetries.
Raman spectra of m‐nitrobenzoic acid–Diethanolamine single crystal
Authors: Zhang Delong , Lan Guoxiang , Hu Shifen , Wang Huafu , Zheng Jinmin
Published: May 2005

Raman spectra of m‐nitrobenzoic acid–diethanolamine single crystal in the wavenumber range 10–3500 cm−1 were recorded at room and liquid nitrogen temperatures. The internal vibrations were assigned. The Raman spectra provide evidence for the formation of hydrogen bonds in the crystal.
Relationship between atomic polarizability tensors and valence optical theories of Raman intensities
Authors: Dudev T. , Galabov B.
Published: May 2005

The relationships between the valence optical theory of Raman intensities and the atomic polarizability tensors model were studied. It is shown that the atomic polarizability tensors can be expressed in terms of electro‐optical parameters. The theoretical relationships derived are illustrated with a numerical example.
Raman spectra of human keratotic biopolymers: Skin, callus, hair and nail
Authors: Williams A. C. , Edwards H. G. M. , Barry B. W.
Published: May 2005

Fourier transform Raman spectra of human keratotic biopolymers were obtained. The spectra from skin stratum corneum, callus, nail and hair were fluorescence free and the samples did not degrade during analysis. Assignments consistent with the vibrational wavenumbers were made to characterize the molecular and conformational nature of the samples. The principal structural dissimilarities were in the sulphur content of tissues containing hard keratin (hair and nail) and soft keratin (stratum corneum and callus).
Analysis of processes in latex systems by Fourier transform Raman spectroscopy
Authors: Claybourn M. , Massey T. , Highcock J. , Gogna D.
Published: May 2005

Fourier transform Raman spectroscopy near‐infrared (NIR) laser excitation was used to follow an emulsion polymerization reaction involving methyl methacrylate, butyl acrylate and allyl methacrylate monomers in a water continuous phase. The effect of NIR absorption is discussed in relation to the monomers and water. For the system studied, only parts of the spectrum are shown to suffer from significant self‐absorption due to the water. Fortunately, for monitoring the polymerization reaction through the loss in the band due to the symmetric CC stretch, self‐absorption is shown not to play a significant role.
CARS studies of H2O motional narrowing in high‐pressure and high‐temperature H2ON2 mixtures
Authors: Grisch F. , Pealat M.
Published: May 2005

CARS spectra of the ν1 band of water vapour at room temperature and 2100 K over a large pressure range (200–19 × 105 Pa) were studied experimentally and theoretically. The influence of N2 and H2O on the rotational relaxation processes of H2O in H2ON2 mixtures was investigated. Modelling of the CARS spectrum was performed using the relaxation matrix inversion procedure. Two rotational relaxation models based on energy and angular momentum transfer were tested and good agreement between experiment and theory was found for all the conditions studied. At 19 × 105 Pa and 2100 K, motional narrowing was found to be weak, allowing calculation of the CARS spectrum with the simple isolated‐line model.
Spectra and structure of silicon‐containing compounds. XVIII—Raman and infrared spectra, conformational stability, vibrational assignment, barrier to internal rotation and ab initio calculations of ethyldichlorosilane
Authors: Afifi M. S. , Guirgis Gamil A. , Mohamed Tarek A. , Herrebout W. A. , Durig J. R.
Published: May 2005

The Raman (3200–10 cm−1) and infrared (3200–30 cm−1) spectra were recorded for gaseous and solid phases of ethyldichlorosilane, CH3CH2SiHCl2. Additionally, the Raman spectrum of the liquid was recorded and quantitative depolarization values were obtained. In the spectra of the gas and liquid, both the trans and gauche conformers are present with the gauche conformer being the dominant rotamer at ambient temperature, but at −126°C the trans conformer dominates the spectrum. Only the trans form is present in the vibrational spectrum of the solid. In the Raman spectrum of the liquid at ambient temperature, the amount of the gauche conformer is significantly reduced compared with that present in the gas. From the relative intensities of two pairs of Raman lines of the liquid at 192/180 and 661/709 cm−1 as a function of temperature, the enthalpy difference is found to be 143 ± 17 cm−1 (408 ± 48 cal mol−1) with the trans rotamer the more stable conformer. Similar variable‐temperature studies of the infrared spectrum with the sample dissolved in liquid krypton were carried out and the value of the enthalpy difference was determined to be 61 ± 10 cm−1 (172 ± 30 cal mol−1). This value should be near the ΔH value for the Gas. The asymmetric torsion is observed at 71 cm−1 for the gauche conformer and the potential function governing the conformational interchange is estimated. The fundamenal modes of both conformers were assigned utilizing band contours, depolarization values, group frequencies and normal coordinate calculations. The SiH bond distance was determined to have values of 1.475 and 1.476 Å for the trans and gauche conformers, respectively, from the stretching wavenumbers. All of these data are compared with the corresponding quantities obtained from ab initio gradient calculations employing the RHF/3–21G, RHF/3–21G*, RHF/6–31G*, MP2/6–31G*, and/or MP2/6–31 + G* basis sets. Complete equilibrium geometries were calculated for both conformers. The results are compared with corresponding quantities obtained for some similar molecules.
Raman and far infrared spectra, structural parameters, and ab initio calculations on acetyl chloride
Authors: Durig J. R. , Davis J. F. , Guirgis G. A.
Published: May 2005

The Raman spectra (3100–10 cm−1) of gaseous, liquid and solid acetyl chloride (CH3CClO) and acetyl‐d3 chloride (CD3CClO) were recorded and qualitative depolarization values were obtained for the liquid. Additionally, the infrared spectra (3100–50 cm−1) of the gas and solid were recorded. A complete vibrational assignment is proposed for both isotopomers. The assignments are supported by normal coordinate calculations utilizing force constants from the ab initio calculations. The methyl torsion is observed at 162.8 cm−1 from which a threefold barrier of internal rotation of 622 cm−1 (1779 cal mol−1) is calculated. Utilizing the frequencies for the isolated CH stretching frequencies from the CHD2CClO molecule, r0 parameters of 1.093 and 1.096 Å were obtained for the CHs and CHa bond distances. The heavy atom r0 structural parameters were obtained from previously reported rotational constants from ten isotopomers. Ab initio calculations were carried out employing the RHF/3–21G*, RHF/6–31G* and MP2/6–31G* basis sets to obtain the vibrational frequencies, force constants, infrared and Raman intensities, structural parameters and barriers to internal rotation. The theoretical results were compared with the experimental quantities when appropriate.
Order‐disorder phase transition in diethylenetriammonium chlorocadmate single crystals determined by Raman spectroscopy
Authors: Jebari F. , Becker P. , Carabatos‐Nédelec C.
Published: May 2005

The Raman spectra of diethylenetriammonium chlorocadmate [(denH3)CdCl5] single crystals were studied in the Raman shift range from 250 to 500 cm−1 for temperatures between 10 and 428 K. A phase transition at Tc = 168 K was observed and characterized. In particular, two Raman bands were sensitive to temperature; they correspond to the torsion motions of NH3+ at 353 cm−1 and to the skeleton deformations of the (denH3)3+ cations at 336 cm−1 to which NH3+ belongs. The analysis of the NH3+ torsion mode based on an order‐disorder model allowed the determination of the activation energy U(300 K) = 0.91 kcal mol−1 The assumption of cluster fluctuations also allowed the critical exponents to be obtained for the transition δ = 0.71 and β = 0.35, the orientation correlation time τc = 0.5 × 10−12 s at 300 K and the correlation length ζ0 ≈ 13b, b being the lattice parameter. It is concluded that the skeleton deformation mode is a localized excitation coupled to jumps of the torsion mode of NH3+.
Enhanced Raman scattering from silver metal gratings coated with p‐nitrobenzoic acid films
Authors: Fujimaki H. , Suzuki Y. , Hatta A.
Published: May 2005

The Raman scattering from echelette silver gratings coated with p‐nitrobenzoic acid (PNBA) films was measured as a function of the angle of incidence of the exciting laser beam. It was found that on excitation of surface plasmon polaritons (SPPs) on the grating, the Raman scattering intensity of the adsorbed PNBA− species is enhanced by a factor of five compared with its intensity at off‐resonance angles of incidence. However, an enhancement of about a factor of 10 in our estimation is observed with s‐polarized radiation independent of the angle of incidence, indicating the presence of some supplementary mechanism other than the high‐field intensity of SPP in the enhancement process. No Raman bands due to PNBA were observed in the thickness range up to 50 nm.
Raman study of temperature‐induced phase transitions in lead hafnate (PbHfO3)
Authors: Sharma Shiv K. , Jayaraman A. , Chowdhury C. Pal , Wang S. Y.
Published: May 2005

Results of a high‐temperature Raman spectroscopic investigation up to 522 K carried out at ambient pressure on an antiferroelectric PbHfO3 multi‐domain single crystal are reported. The changes in the Raman spectral features show that temperature‐induced phase transitions occur at 435 ± 1 and at 484 ± 1 K. The first transition is possibly to a tetragonal structure and the second is to the cubic perovskite phase. The behavior is consistent with the earlier x‐ray study of PbHfO3. No soft mode behavior associated with the transitions was detected in the Raman spectra of PbHfO3. The changes observed in the high‐temperature Raman spectra of PbHfO3 are similar to those found in the spectra of isostructural PbZrO3.
Fourier transform Raman study of the conformers in poly(ethylene terephthalate)
Authors: Rodríguez‐Cabello J. C. , Quintanilla L. , Pastor J. M.
Published: May 2005

Fourier transform (FT) Raman spectroscopy has been proved to be an adequate technique for the study of the quantitative structural changes which take place in poly(ethylene terephthalate) on annealing. The two‐phase conformational model proposed previously in the infrared domain using photoacoustic FTIR has been extended to the Raman domain. Moreover, typical Raman spectral changes with the thermal process have been directly related to conformational rather than crystallinity changes. The correlation between the percentage of the trans isomer obtained by FT‐Raman and skin layer crystallinity values obtained by differential scanning calorimetry allows the crystalline and amorphous trans isomer contents to be obtained and their evolution with the annealing process to be followed.
Conformational equilibria for 2‐ and 3‐chlorostyrene: Raman and Fourier transform infrared spectra and ab initio calculations
Authors: Ribeiro‐Claro P. J. A. , Teixeira‐Dias J. J. C.
Published: May 2005

Ab initio SCF MO calculations at the 3–21G level and the vibrational spectra [Raman and Fourier transform (FT) IR] of liquid‐phase 2‐chloro‐ and 3‐chlorostyrene are reported. For 2‐chlorostyrene, the ab initio calculations predict skew and gauche minima, with an energy difference of 11.5 kJ mol−1, and no evidence of more than one conformer was found in the liquid‐phase Raman and FTIR spectra. The Raman spectra of liquid 3‐chlorostyrene show pairs of bands whose temperature‐dependent intensities clearly suggest the occurrence of a conformational equilibrium. From these bands, assigned to non‐planar cis and trans conformers, a trans–cis energy difference of 2.3 ± 0.5 kJ mol−1 was obtained for the liquid phase.
Vibrational spectrum of liquid nitromethane revisited using polarization‐sensitive coherent anti‐stokes Raman scattering (PCARS) spectroscopy
Authors: Shkurinov Alexander , Jonusauskas Gediminas , Rullière Claude
Published: May 2005

Polarization‐sensitive coherent anti‐Stokes Raman scattering (PCARS) spectroscopy was applied for the first time for detailed analyses of vibrational resonances of neat liquid nitromethane in the spectral range 900–1500 cm−1. The polarization PCARS properties show that the main totally symmetric band ν4 at 917 cm−1 and its observed asymmetry on the lower wavenumber side (previously assigned to hot bands) are in fact two different bands. The origin of this observed asymmetry in the lower wavenumber side of the totally symmetric vibrational mode ν4 is then discussed. Spectroscopic parameters (wavenumbers, bandwidth, polarization ratio, etc.) of vibrational spectra are then determined precisely for complex spectral bands of neat liquid nitromethane taking into account unique PCARS properties.
Vibrational study of superionic phase transitions in the mixed alkali acid sulphate Cs0.5Rb0.5HSO4
Authors: Abid Y. , Mhiri T.
Published: May 2005

Raman spectra (10–1100 cm−1) of polycrystalline samples of Cs0.5Rb0.5HSO4 were studied at temperatures ranging from 300 to 500 K. An assignment of most of the observed band is proposed. The first‐order phase transitions previously detected at 350 and 405 K were characterized:

These transitions are believed to be governed by librarians of the SO ion and the SOH stretching mode. The I→II transition is characterized by the conversion of infinite (HSO4−)n chains to cyclic (HSO4−)2 dimers. The superionic II → III transition corresponds to the weakening of SO…︁H…︁OS hydrogen bonds and to the melting of the proton sublattice to a quasi‐liquid state where proton and SO ions contribute to the unusual high conductivity. The activation energy associated with the oscillation of the proton between two SO groups is E0 = 12.1 kJ mol−1. This was extracted from the plot of Δν1/2 vs. temperature for the νSOH band at 875 cm−1. It is of the same order of magnitude as that estimated from conductivity measurements.
Caesium hydrogensulphide CsS(H,D): Hydrogen bonds and disorder of the hydrogensulphide ions
Authors: Lutz H. D. , Beckenkamp K. , Jacobs H. , Kirchgässner R.
Published: May 2005

IR and Raman spectra (4000–50 cm−1) of caesium hydrogensulphide and also deuterated specimens were recorded in the temperature range 6–520 K. The spectra confirm the presence of SH−…︁SH− hydrogen bonds in CsSH in contrast to other MSH compounds (M = alkali metal). The temperature evolutions of the wavenumbers and half‐widths of the SH stretching and librational modes clearly display the partly second‐order phase transitions. These are driven by thermally activated disordering of the SH− ions from the antiferroelectrically ordered low‐temperature polymorph (LTM) via a one‐dimensionally disordered middle‐temperature polymorph (MTM) to the three‐dimensionally disordered room‐temperature form (RTM) of the CsCl type. The transition temperatures between these polymorphs differ depending on the degree of deuteration, viz. 105 and 115 K and 190 and 210 K for CsSH and CsSD, respectively, owing to the greater strengths of SD−…︁SD− bonds compared with SH−…︁SH− hydrogen bonds. In the RTM, the fraction of SH− ions which form hydrogen bonds decreases with increase in temperature. The strength (νSH = 2480–2550 cm−1, rH…︁S = 275–300 pm) and geometry (H…︁SH angle ≈90°) of SH−…︁SH− hydrogen bonds is also discussed.
First‐order spatial dispersion effects in the Raman spectrum of NaClO3
Authors: Ouillon R. , Pinan Lucarre J. P. , Ranson P.
Published: May 2005

In cubic crystals the infrared‐active triply degenerate modes split into an LO and a doubly degenerate TO mode. For crystals with T symmetry, first‐order spatial dispersion splits the polar TO modes into a set of two circularly polarized T+ and T− modes whose frequencies have only a small separation. Using incoherent high‐resolution Raman spectroscopy (a tandem Fabry–Perot Raman double monochromator of limiting resolution 0.005 cm−1), we have measured the splitting of the low‐energy TO lattice modes in the optically active material sodium chlorate.

Experiments were performed in various scattering geometries to separate the optical Raman‐active modes of different symmetries (A, E, LO and TO modes). Furthermore, the difference in the Raman response of the T+ and T− modes to left or right circularly polarized incident light was detected and analysed.

We measured for the three low‐energy TO modes (77, 98 and 125 cm−1 at T = 6 K) a splitting of 0.08, 0.08 and 0.105 cm−1 respectively in a right angle geometry and 0.11, 0.11 and 0.135 cm−1 respectively in a backscattering geometry (an increase in agreement with a shift proportional to the wave vector length).
From nucleic base to polynucleotide: A vibrational analysis of the repetitive subunits involved in poly(rl) strands
Authors: Ulicny J. , Ghomi M. , Tomkova A. , Miskovsky P. , Chinsky L. , Turpin P. Y.
Published: May 2005

Ultraviolet resonance Raman spectra of inosine and its deuterated species (C8‐d, Nl‐d and C8‐, Nl‐deuterated derivatives) in aqueous solution have been collected (λexc = 257 and 281 nm) and reported in the spectral region between 400 and 1800 cm−1. The observed vibrational modes have been assigned using the Wilson GF method with an empirical harmonic valence force field and a non‐redundant set of internal co‐ordinates. This normal mode analysis is based on previous work on the vibrational assignments of the hypoxanthine nucleic base and the furanose ring with various geometries. Here the analysis has been carried out by using three different nucleoside conformations as determined from x‐ray studies of molecular crystals. The most striking features of the present work are: (i) the assignments of inosine vibrational modes are very different from those of the hypoxanthine base; (ii) the best fit between measured and calculated vibrational wavenumbers and their isotopic shifts upon selective deuteration has been obtained from inosine structures containing an N‐type sugar (C3′‐endo) associated with a low‐anti base. In addition, we have tested the reliability of the force field in the case of inosine residues involved in a canonical A‐RNA helical structure by comparing the calculated wavenumbers of the most characteristic vibrational modes with those observed in off‐ and on‐resonance Raman spectra of poly(rI).
Enhancement of Cα hydrogen vibrations in the resonance Raman spectra of amides
Authors: Jordan Trace , Spiro Thomas G.
Published: May 2005

Ultraviolet resonance Raman (UVRR) spectra of polypeptides and proteins exhibit a band at ca. 1390 cm−1 whose intensity is sensitive to helical content. The assignment of this band, designated amide S, has been contentious. To study the vibrational origin of amide S, relevant amide model compounds and their selectively deuterated iso‐topomers were synthesized. N‐Methylacetamide, N‐methylpropionamide and N‐methylisobutyramide possess a methyl, methylene and methine group, respectively, adjacent to the amide carbonyl. The UVRR spectrum of the natural abundance species show resonantly enhanced vibrational bands in the region 1350–1380 cm−1. These bands disappear on deuteration of the (C)Cα. hydrogen atoms, while the amide III modes shift up to a common position (ca. 1335 cm−1) and increase in intensity. These results suggest that amide S can be assigned to a (C)Cα hydrogen bending vibration, which acquires resonance intensity by vibrational mixing with the CN stretch of the nearby amide III mode. Variation of this mixing with the CαH/CO dihedral angle can explain the sensitivity of amide III to protein secondary structure. Additional UVRR and Fourier transform IR data reveal that (C)Cα‐deuteration has a smaller effect on the amide I, I′, II and II′ vibrational modes. Finally, it is established that UVRR spectra for NMA in H2O and D2O show an absence of torsional fundamentals or overtones. These results are interpreted as indicating an energy barrier to cxcited‐state isomerization, which argues against an alternative assignment of amide S to the amide V overtone.
Spectra and structure of small‐ring compounds. LXII—Raman and infrared spectra, conformational stability, vibrational assignment and ab initio calculations of cyclopropylmethyltrifluorosilane
Authors: Little T. S. , Vaughn C. A. , Zhu Xiang , Dakkouri M. , Durig J. R.
Published: May 2005

The Raman (3500–20 cm−1) and infrared (3500–50 cm−1) spectra of gaseous and solid cyclo‐propylmethyltrifluorosilane, c‐C3H5CH2SiF3, were recorded. Additionally, the Raman spectrum of the liquid was obtained along with qualitative depolarization values. The spectra of the gas and liquid were interpreted on the basis of the predominance of a conformation having a gauche structure and this form exists exclusively in the solid. Spectral evidence to support the existence of a higher energy cis conformer where the SiF3 group is cis to the cyclopropyl ring is observed in the Raman spectra of the gas and liquid. From studies of the Raman spectra at various temperatures, the conformational enthalpy difference was determined to be 490 ± 122 cm−1 (1.4 ± 0.35 kcal mol−1) and 548 ± 110 cm−1 (1.57 ± 0.32 kcal mol−1) (1 kcal = 4.184 kJ) for the gas and liquid, respectively. The cyclopropyl torsion was observed as a weak infrared band centered at 77 cm−1 in the spectrum of the gas. A complete assignment of the normal vibrational modes is provided. Ab initio calculations utilizing the RHF/6‐31G* and MP2/6‐31G* basis sets are consistent with the gauche rotamer lying 554 cm−1 (1.6 kcal mol−1) and 296 cm−1 (0.85 kcal mol−1), respectively, lower in energy than the cis conformation. It is estimated that there is only 4–10% of the higher energy conformer present in the vapor at ambient temperature. Optimized structural parameters were obtained for both conformers with both basis sets and the results should provide good starting parameters for the analysis of the electron diffraction data. The force field obtained with the RHF/6–31G* basis set was used to perform a normal coordinate analysis. These results are compared with corresponding quantities for some similar molecules.
Raman and infrared spectra, conformational stability, barrier to internal rotation, and ab initio calculations for 1,1‐dichloromethyl methyl ether
Authors: Stidham Howard D. , Vlaservich A. Charla , Hsu David Y. , Guirgis Gamil A. , Durig J. R.
Published: May 2005

The Raman (3200–30 cm−1) and infrared (3200–50 cm−1) spectra of 1,1‐dichloromethyl methyl ether are reported for the gas, liquid, amorphous solid and annealed polycrystalline solid. These spectral data were interpreted on the basis that in the fluid phases there is a mixture of trans and gauche conformers but only the trans conformer remains in the annealed solid. From the temperature‐dependent relative intensity of Raman bands at 379 and 427 cm−1 in the liquid, an enthalpy difference of 656 ± 84 cm−1 (1.88 ± 0.24 kcal mol−1 or 7.85 ± 1.0 kJ mol−1) was obtained with the trans conformer the more stable form. Complete vibrational assignments are made for the much more abundant trans form, and a number of fundamentals are assigned for the gauche conformer with the aid of ab initio computations made with the 3–21G and 6–31G* basis sets. The harmonic force fields obtained using the 3–21G basis set are reported for both conformers together with scaled and unscaled wavenumbers and the accompanying potential energy distributions. The results are compared with the corresponding quantities obtained for some similar molecules.