Size‐dependent Raman and infrared studies of PbSe nanoparticles

Micro‐probe Raman and far‐infrared absorption spectroscopies were used to prove the existence of optical phonon modes of PbSe nanoparticles prepared by colloidal chemistry and preliminarily characterized by transmission electron microscopy. To the best of our knowledge, this is the first time that evidence of the surface phonon (SP) mode by Raman spectroscopy has been experimentally observed. The wavenumber of the SP mode is consistent with its prediction by a dielectric continuum model. While for different PbSe nanoparticle sizes the observed SP mode does not show any obvious change in its position, there is a clear shift by approximately 4 cm⁻¹ toward higher wavenumber in the appearance of the LO(Γ) in the Raman spectra from the 3 nm to the 7 nm PbSe nanoparticles. Far‐infrared measurements demonstrate the presence of the transverse optical TO(Γ) and of the coupled phonon modes. Copyright © 2008 John Wiley & Sons, Ltd.     

Decoherence effects in case of molecular rotations in solids

A single XH₃ group interacting with an ensemble of lattice oscillators is considered using the Feynman-Vernon formalism. It is shown that the influence functional depends explicitly on the difference between winding numbers of the paths contributing to the path-integral expression for the reduced density matrix. However, the resulting interference is suppressed due to the presence of the Debye-Waller factor in the influence functional. The meaning of this result in connection with the topology of the XH₃ rotation angle is also discussed. Finally, the emergence of a gauge-like potential term describing one aspect of the XH₃-lattice interaction is indicated.     

Raman and infrared studies of synthetic Maya pigments as a function of heating time and dye concentration

Maya Blue is a famous indigo‐based pigment produced by the ancient Mayas. The organic/inorganic complexes inspired by Maya Blue have led to a new class of surface compounds that have novel applications to pigment industries. Materials analyzed in the present work are made by a synthetic route, and demonstrate chemical stability similar to that of the ancient Maya Blue samples. However, we have learned that stable complexes can be synthesized at much higher dye concentrations than used by the Mayas. Analysis by FT‐Raman and FT‐IR spectroscopy demonstrates the partial elimination of the selection rules for the centrosymmetric indigo, indicating distortion of the molecule. This distortion accounts for the observed color changes, as the molecular orbital structure is modified, allowing the complex to stabilize. The spectroscopic data also shows the disappearance of the indigo N H bonding, as the organic molecules incorporate into palygorskite material. A structural change of indigo to dehydroindigo during heating is suggested by this result. Infrared data confirm the loss of zeolitic water and a partial removal of structural water after the heating process. Evidence of bonding between cationic aluminum and dehydroindigo through oxygen and nitrogen is revealed by FT‐Raman measurements at higher dye concentrations. Copyright © 2007 John Wiley & Sons, Ltd.     

拉曼光谱与拉曼效应的量子模型结构分析

散射光谱这种新谱线对应于散射分子中能级的跃迁,为研究分子结构提供了一种重要手段,引起学术界极大兴趣,拉曼也因此荣获1930年诺贝尔物理学奖。并称这种谱线为拉曼光谱。介绍了拉曼光谱的基本原理、拉曼光谱的应用以及其发展,由于拉曼光谱非常弱,实验要求比较高,最后介绍了实验仪器及利用拉曼光谱研究分子的结构。     

Raman and infrared intensity analysis of CHCl3 and CDCl3

Raman and infrared intensity analysis of CHCl₃ is attempted to determine the bond polarisability derivatives and bond dipole moments and their derivatives respectively, on lines expained in our earlier papers.     

银岛膜表面胸腺嘧啶吸附行为的表面增强拉曼光谱和表面增强红外光谱研究

利用激光刻蚀法制备了具有化学纯净表面的银岛膜,该岛膜有很好的表面增强特性。利用表面增强拉曼光谱和表面增强红外光谱对胸腺嘧啶分子在银岛膜表面的吸附状态进行了对比研究。表面增强拉曼光谱中CN和C—O伸缩振动模式的出现表明胸腺嘧啶分子由原来的酮式结构变成了烯醇式结构;C(4)O伸缩振动谱带明显增强和N(3)的去质子化异构体特征峰的存在证明胸腺嘧啶分子是通过O(8)和N(3)的共同作用倾斜地吸附在银岛膜表面。对10-5 mol.L-1胸腺嘧啶在银岛膜表面上的红外光谱利用欧米采样器进行了反射法测量,发现其红外吸收增强了200倍。红外信号分析的结果支持了胸腺嘧啶分子通过O(8)与银表面发生相互作用的论断,同时也可得出胸腺嘧啶倾斜地吸附在银岛膜表面的结论。     

Near‐infrared Raman spectroscopy for gastric precancer diagnosis

Raman spectroscopy is a molecular vibrational spectroscopic technique that is capable of optically probing the biomolecular changes associated with neoplastic transformation. The purpose of this study was to apply near‐infrared (NIR) Raman spectroscopy for differentiating dysplasia from normal gastric mucosa tissue. A total of 65 gastric mucosa tissues (44 normal and 21 dysplasia) were obtained from 35 patients who underwent endoscopy investigation or gastrectomy operation for this study. A rapid NIR Raman system was utilized for tissue Raman spectroscopic measurements at 785‐nm laser excitation. High‐quality Raman spectra in the range of 800–1800 cm⁻¹ can be acquired from gastric mucosa tissue within 5 s. Raman spectra showed significant differences between normal and dysplastic tissue, particularly in the spectral ranges of 850–1150, 1200–1500 and 1600–1750 cm⁻¹, which contained signals related to proteins, nucleic acids and lipids. The diagnostic decision algorithm based on the combination of Raman peak intensity ratios of I₈₇₅/I₁₄₅₀ and I₁₂₀₈/I₁₆₅₅ and the logistic regression analysis yielded a diagnostic sensitivity of 90.5% and specificity of 90.9% for identification of gastric dysplasia tissue. This work demonstrates that NIR Raman spectroscopy in conjunction with intensity ratio algorithms has the potential for the noninvasive diagnosis and detection of precancer in the stomach at the molecular level. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectroscopy for milk fat quantification: line shape analysis of the Raman and infrared spectra

This paper presents a systematic analysis of the infrared absorption spectra and Raman scattering of the triacylglycerol molecule predominant in raw bovine milk. Gas chromatography measurements were also performed and revealed the palmitic, stearic, and oleic acids as the most predominant fatty acids in the composition of milk. Based on the gas chromatography results, infrared, and Raman spectra of the triacylglycerol with this combination of fatty acids were simulated. The theoretical spectra were compared with the experimental ones of milk fat and fluid raw milk. Assignment of bands of milk fat was proposed, which can be used for a quality monitoring of the product. We also performed a multivariate model of partial least squares from samples of fluid milk with different concentrations of fat. As a result, the most important variables in the projection were selected as vibrational markers for quality monitoring and quantifying of this important constituent of milk. Copyright © 2016 John Wiley & Sons, Ltd.     

Resonance Raman studies of photochemical molecular devices for multielectron storage

Resonance Raman spectroscopy was utilized for the first time to characterize the nature of the ¹metal‐to‐ligand charge transfer (MLCT) state of a ruthenium complex containing the redoxactive tetraazatetrapyrido‐pentacene (tatpp) ligand. The presented results show that the long‐wavelength absorption is originating from transitions involving the terminal phenanthroline and the tatpp ligands. Copyright © 2008 John Wiley & Sons, Ltd.     

Determination of the spectral width of Raman gain regions for different far infrared laser gases using a metal mesh Fabry Pérot interferometer

In this paper we report on the determination of the spectral width of Raman gain regions for different far infrared laser gases using a metal mesh Fabry Pérot interferometer. By use of broadband pump radiation emitted from a high pressure CO₂ laser we generated far infrared radiation within the Raman gain regions via stimulated Raman scattering. The spectral width of the far infrared radiation was determined using a Fabry Pérot interferometer in high interference order. We applied the method to study stimulated Raman scattering in D₂O and methylfluoride at different gas pressures.     

氮化铝薄膜的红外吸收光谱和喇曼光谱的研究

本文报道用直流平面磁控溅射法在Si片上生长c轴高度择优取向AIN薄膜的光学特性.俄歇谱分析表明薄膜是高纯的.从红外吸收光谱上分析获得晶格振动纵、横模的频率分别为2.5×10~(13)HZ和1.8×10~(13)Hz.从喇曼光谱上分析获得AIN薄膜的光学声子频率为297、512、607、656、832cm~(-1).与几种已知的纤锌矿结构二元化合物的声子频率模式类比获得AIN的光学声子模式.进一步分析表明AIN是一种静电力大于原子间各向异性力的晶体,且声子的最高频率与r~(-3/2)N~(-1/2)成正比.     

Computing Raman and infrared wavenumbers of nanostructures: application to silicon nanowires

The characterization of nanostructures with spectroscopic methods is a fundamental tool in nanoscience. For novel nanostructures, the interpretation of spectral features is a challenging task. To address this issue, we present the “Symmetry‐Filtered Molecular Dynamics (SFMD)” method to calculate Raman and infrared wavenumbers from molecular dynamics (MD) simulations, employing only the symmetry of the atomic structure. Explicit and expensive calculations of the electric polarizability or the dipole moment are not required. Therefore, our method can be easily used with any standard MD software. On the basis of the density functional tight‐binding method for the MD simulations, we apply our method to bulk silicon and small‐diameter hydrogen‐passivated silicon nanowires. For bulk silicon, we study the wavenumber shift of the Raman peak with temperature and obtain results that are in good agreement with experiments. We further show that thermal lattice expansion is a minor effect (22%) and that temperature‐driven anharmonic effects (78%) are the main contributions to that wavenumber shift. By analyzing the bond lengths of different silicon nanowires, we found that surface stress manifests as a 0.37% shortening of bonds only in the outermost silicon layer. We further analyzed the diameter‐dependent wavenumber shift of a Raman peak in silicon nanowires. We found that the main contribution to the wavenumber shift comes from the phonon confinement effect and surface stress leads to an additional shift of 9–22%. Our results indicate that our method is able to produce quantitative results that can be compared with experiments. We propose our method to be used for the understanding of Raman and infrared spectra of novel bulk and nanostructures. Copyright © 2012 John Wiley & Sons, Ltd.     

Polarized Raman scattering and infrared spectroscopy of a natural manganocolumbite single crystal

A well‐ordered natural manganocolumbite single crystal of high quality was used as a prototype for the first determination of the polarized optical phonon modes of materials with the columbite structure. Electron microprobe and X‐ray diffraction characterizations determined the chemical formula as Mn_0.60Fe_0.40(Nb_0.80Ta_0.20)₂O₆, a cationic ordering of 81%, and the crystal structure as belonging to the Pbcn group. Polarized Raman and infrared‐reflectivity spectroscopies on oriented samples allowed us to discern 50 of the 54 predicted gerade (Raman) modes and 31 of the 38 predicted ungerade (infrared) modes for the columbite structure. The selection rules were verified, and polarization leaks only due to slight sample misorientation, confirming the high purity, ordering and quality of the material. From the polar phonon spectra, intrinsic dielectric merit factors < ε_r> = 29.2 and < Q_u × f> of 64 THz were determined, showing adequate values for designing applications in microwave circuitry. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman and infrared spectra of tere-phthalaldehyde

The laser Raman spectrum of tere-phthalaldehyde powder has been recorded on a Jobin Yvonhg 2S spectrophotometer with a~100 mW Argon-Ion laser. The infrared spectrum of the solid substance has been recorded on a Perkin-Elmer 621 spectrophotometer in the region 300–4000 cm^-1 using KBr and nujol mull techniques. The observed frequencies have been assigned in terms of the fundamentals, overtones and combinations assumingD _2h point-group symmetry.     

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.     

Crystal structure and phonon modes of ilmenite‐type NaBiO3 investigated by Raman and infrared spectroscopies

NaBiO₃ is an ilmenite‐type compound presenting a trigonal structure. In this work, we have performed optical spectroscopic investigations using Raman scattering and infrared reflectivity for this material. By using group‐theory calculations, it was possible to determine the number of optically active modes. Fitting procedures besides Kramers–Kronig (KK) procedures lead to a consistent collection of phonon modes. The Raman spectrum showed nine active first‐order modes, while the infrared one revealed eight polar phonons, in good agreement with the theoretical predictions. The results allowed us to confirm the R3 (#148) space group for this compound, and to establish a set of active phonons not yet reported in the literature. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectra of acetonitrile in imidazolium ionic liquids

Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids' polarity. This is accomplished by investigating the Raman bandshape of the ν (CN) band, corresponding to the CN stretching mode of CH₃CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH₃CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1‐alkyl‐3‐methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the ν (CN) band of CH₃CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the ν (CN) band were corroborated by the analysis of the symmetric ν₁ (CD₃ ) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright © 2010 John Wiley & Sons, Ltd.     

Femtosecond multipulse polarization spectroscopy of molecular vibrations and rotations in liquids

Simultaneous control over the vibrational and rotational molecular responses in ultrafast optical Kerr-effect signals in acetonitrile, toluene, and chloroform at room temperature is achieved by means of non-resonance excitation with two 30-fs orthogonal linearly polarized laser pulses. It is shown that the orientational response of the molecules can be suppressed and their vibrational response isolated by enhanced the delay between the exciting pulses and their relative intensity.     

Correlation of monomer structures of tripalmitin with the spectroscopic fingerprint of polymorphs: infrared,Raman, and DFT study

In the light of application of vibrational spectroscopy in medical diagnosis, it is necessary to have a tool to distinguish between different lipids that may be present in biochemical samples such as cells and tissues. One of the most common lipids in the human body are triglycerides. Therefore, the aim of this work was to investigate the model triglyceride, namely tripalmitin in order to find the differences between the vibrational signatures of its polymorphs and interpret them with the help of quantum‐chemical computations. Although monomeric models are not sufficient to reproduce polymorphs structure, analysis of these models is very helpful in understanding of relations between the structure and changes in vibrational spectra. Copyright © 2012 John Wiley & Sons, Ltd.