Raman Spectra of Carbohydrates

The Raman spectra of 13 different carbohydrates are investigated by a laser Raman spectrometer. It is found the C—H stretching vibrations around 3000 cm⁻¹ is the best region for qualitative analysis of these compounds. All compounds show an O—H stretching vibration around 3370 cm⁻¹ which was not mentioned by earlier works. Excessive background noise appears in many spectra, probably due to their amorphous stuctures.     

Polarized Raman Spectra VII Correlations and Assignments of Raman Lines in p-Polyphenyls

The Raman spectra of powdered biphenyl, p-terphenyl, and p-quaterphenyl are compared with each other and also with the Raman spectrum of benzene. Most Raman lines in polyphenyls can be considered as derived from normal vibrations in benzene. The intense lines are thus assigned and the correlations between them are established.     

Raman Spectra of Tungsten-Bearing Solutions

Raman spectroscopy at 25 °C was performed to analyze speciation in quenched solutions after experiments on sodium tungstates and sodium tungstate bronze dissolution at t=500 °C, p=1000 bar. The experiments were conducted under different oxidation-reduction conditions in sodium chloride solution media. The spectra of the quenched solutions were different from those of the reference solutions of 0.02 mol⋅kg⁻¹ W(VI) (H₂O) in the pH range 2.3–7.2. Thermodynamic models were established and the fields of predominance of different isopolytungstate species at 25–50 °C were determined. The experimental results of tungstate dissolution demonstrates that reduced tungstate solutions may contain a significant amount of tungsten species with valence states lower than W(VI).     

Polarized Raman Spectra V. Photoelectrically Recorded Spectra of Anthracene Single Crystal

The polarized Raman spectra of anthracene single crystal are accurately measured by photoelectrical method. All the strong lines are polarized in the cc and bb polarizations, and they should be assigned to the A_g representation in the molecular symmetry group of anthracene. The polarization data are not sufficient to decide the symmetry of a Raman line; therefore, the assignments recently reported by Suzuki, Yokoyama anb Ito^f and by Ting² based on polarizations have to be revised. The correct assignments agree very well with the fluorescance work by Lacey and Lyons,³ and offer strong evidences supporting our theory proposed recently.⁴ This theory is also tested by calculating the polarization of the most intense line at 1401 Kaisers (cm^?1). The resut is very good.     

Raman and Infrared Spectra for All-trans-astaxanthin in Dimethyl Sulfoxide Solvent

The Raman and infrared spectra of all-trans-astaxanthin (AXT) in dimethyl sulfoxide (DMSO) solvent were investigated experimentally and theoretically. Density functional cal-culations of the Raman spectra predict the splitting of the υ₁ band into υ_1-1 and υ_1-2 compo-nents. The absence of splitting in Raman experimental spectra is ascribed to the competition between the two symmetric C=C stretching vibrations of the backbone chain. The υ₁ band is very sensitive to the excitation wavelength: resonance excitation stimulates the higher-frequency υ_1-2 mode, and off-resonance excitation corresponds to the lower-frequency υ_1-1 mode. Analyses of the intramolecular hydrogen bonding between C=O and O-H in the AXT/DMSO system reveal that the C4=O1...H1-O3 and C4'=O2...H2-O4 bonds are strengthened and weakened, respectively, in the electronically excited state compared with those in the ground state. This result reveals significant variations of the AXT molecular structure in different electronic states.     

Theoretical Study on Resonance Raman Spectra of Tetraoxaporphyrin Dication by TDDFT Calculation

The B state excited resonance Raman scattering of tetraoxaporphyrin dication (TOP²⁺) was theoretically studied with DFT/TDDFT calculations and the sum-over-states approach of polarizability including both the A and B terms contributions. The resonance Raman spectra calculated with PBE1PBE, B3LYP, Cam-B3LYP, and B3LYP-D3 functionals are similar to each other in general, with PBE1PBE and B3LYP being better in reproducing resonance Raman intensities in comparison with the experiment. The calculated relative intensities of the totally symmetric modes are excellently consistent with the experiment. The TDDFT calculations manifested a considerable deformation of the B state along theυ2,υ6, υ7, and υ8 modes, which is responsible for the strong resonance Raman intensities of these modes. The resonance Raman intensities of non-totally symmetric modes were calculated to be weaker than the totally symmetric modes by one or two order of magnitude, whichqualitatively agrees with the experiment. However, the resonance Raman intensity of the υ10 mode (C_βC_β stretch, B_1g symmetry) predicted by TDDFT calculations is unexpectedly small whereas that of the υ11 mode (symmetric C_αC_m stretch, B_1g symmetry) is too large, which is assumed to be caused by the Jahn-Teller instability for the B state of TOP²⁺.     

镧铁磷酸盐玻璃结构的拉曼光谱分析

采用熔融-冷却法制备了xLa2O3-(40-x)Fe2O3-60P2O5(x=0,2,4,6,8,10mol%)系列玻璃。利用Raman光谱对玻璃结构进行表征,并测试了玻璃的密度和维氏硬度。结果表明,在玻璃形成范围内,玻璃结构以焦磷酸盐结构为主,伴有少量的正磷酸盐和偏磷酸盐结构单元。玻璃密度和硬度均随La2O3含量的增大而增加,La3+的引入有利于增强玻璃结构的稳定性。     

Metal Complexes of Aniline: Infrared and Raman Spectra

Abstract

The literature for the years 1965–1987 has been searched for all significant papers which refer to the vibrational spectra of metal complexes of aniline and substituted anilines. These papers have been reviewed with particular reference to isotopic labelling and metal ion substitution studies as assignment techniques and to the structural and bonding information which can be derived from the spectra. Compounds of the following classes are included: [M(an)₂X₂] (M = Mn, Co, Ni, Cu, Zn, Cd, Hg; an = aniline, X - Cl, Br, I, NCS); cis- and trans-[Pt(an)₂X₂] (X = Cl, Br, I, NO₂); [M(R-an)₂X₂] (M = Mn, Co, Ni, Cu, Zn; R-an = o-, m- and p-toluidine and other substituted anilines; X = Cl, Br, I); aniline adducts of metal β-ketoenolates; the complexes trans-[PtL(R-an)X₂] (L = CH₂?CH₂ or CO, R-an = aniline or a substtuted aniline, X = Cl, Br); and other miscellaneous systems comprising aniline as a ligand.     

Fourier-transform surface-enhanced Raman scattering study on thiourea and some substituted thioureas adsorbed on chemically deposited silver films

Adsorption of thiourea, N,N′-diphenylthiourea (DIPTU), N-ethyl-N′-phenylthiourea (ETPTU) and N-(p-nitrophenyl)thiourea (NPTU), from acidic and neutral solutions, on chemically deposited silver film substrates are investigated using Fourier transform surface-enhanced Raman scattering (FT-SERS) technique. A strong band in the low frequency region, around 230 cm⁻¹ in the FT-SERS spectra of all these systems, assigned to Ag–S stretch, indicates a preferential adsorption through the sulfur atom. The frequencies and bandwidths of benzene ring vibrational modes in ETPTU as well as DIPTU are almost unaffected by adsorption indicating that benzene rings do not interact directly with the silver surface. A cis-cis conformation (both imino H-atoms cis with respect to thione sulfur atom) is proposed for DIPTU and ETPTU on the silver surface. In the case of NPTU, an additional interaction through the benzene ring is also observed as shown by the frequency shifts and band broadening of some benzene ring modes and weak intensity of the C–H stretching band.     

Carbon-13 NMR Spectra of Peracetylated Derivatives of Methyl L-Arabinofuranoside and Oligosaccharides Related to Arabinoxylan

Abstract

The ¹³C NMR signals of methyl tri-O-acetyl-l-arabinofuranosides were assigned on the basis of heteronuclear shift correlated NMR spectra. From the enzymic digest of barley-hull arabinoxylan two oligosaccharides, i.e., α-l-Araf-(1→3)-β-d-xylp-(1→4)-d-xylp and α-l-Araf-(1→3)-β-d-xylp-(1→4)-β-d-xylp-(1→4)-d-xylp were obtained. The NMR spectra of their per-O-acetylated derivatives were assigned, and discussed.     

Ab initio simulation of benzene Raman intensities

C₆H₆ Raman scattering activities calculated from harmonic model ab initio Hartree–Fock 6–311 ++ G(d, p) polarizability derivatives (and harmonic force fields calculated at the same level) accurately simulate experiment (to within 1% for the a_1g modes). Accurate predictions are also made for the e_2g modes (to within 5% for ν₇ and ν₉, and more poorly for ν₆ and ν₈ [in Fermi resonance with ν₆ + ν₁]) and for the e_1g out-of-plane mode, ν₁₀. Only the ν₆ in-plane CCC bending mode scattering activity is found to be anomalous. Systematic variation of the basis set indicates that the benzene scattering activities and depolarization ratios are strongly dependent on inclusion of both carbon and hydrogen atom diffuse functions in the basis set. Predictions are also made for ¹²C₆D₆ and for unmeasured intensities in ¹³C₆H₆. Measurements of a_1g mode scattering activities in the latter molecule are predicted to be useful in testing the harmonic Hartree–Fock Raman intensity model.     

Polarized Raman Spectra II. Anthracene Crystal

The polarized Raman spectrum in crystalline anthracene is recorded using an Ar⁺ laser as the light source. With the polarization data, empirical criteria of assigning molecular vibrations to A_g and B_sg representations are derived. These criteria are discussed in the light of the theory developed in Part I of this series.¹ The lack of vibrational exciton structures in the spectrum of anthracene crystal is the strongest evidence to discredit the conventional polarizability theory and to support the theory presented in Part I. The assignments of 11 A_g and 9 B_sg vibrations in anthracene-h₁₀, and also 12 A_g and 7 B_sg vibrations in anthracene-d₁₀ are reported.     

Solid Solubility,Raman Spectra and Electrical Property of the Solid Solutions Ce1‐xNdxO2‐δ by Sol‐gel Route

Ce_1‐xNd_xO_2‐δ (x = 0.05–0.55) solid solutions prepared by sol‐gel route were crystallized in a cubic fluorite structure. The solid limit was determined to be as high as x = 0.45. Raman spectra of the solid solutions with lower composition exhibited only one band, which was assigned to F_2g mode. Increasing composition produced broad and asymmetric F_2g mode with an appearance of low frequency tail. The new broad peak observed at higher frequency side of the F_2g mode associated with the oxygen vacancy in the lattice. The impedance spectra of the solid solutions showed definitely ionic conduction, and Ce_0.80Nd_0.20O_2‐δ solid solution possessed a maximum conductivity. At 500 °C, the conductivity and activation energy were 2.65 × 10^?3S/cm and 0.82 eV, respectively.     

Conformational Stability, Raman and Infrared Spectra, Vibrational Assignment, and Ab Initio Calculations of Allyltrifluorosilane

The Raman spectra (3500 to 30 cm^–1) of allyltrifluorosilane, CH₂CHCH₂SiF₃, in the liquid with quantitative depolarization ratios and solid states, and the infrared spectra (3500 to 30 cm^–1) of the gas and solid have been recorded. Additionally, the mid-infrared spectra of the sample dissolved in liquified xenon as a function of temperature (–100° to –55°C) have been recorded. All of these data indicate there are two conformers, the more stable gauche rotamer and a very small amount of the cis conformer in the fluid states, but only the gauche form remains in the polycrystalline solid. The variable temperature studies of the infrared spectrum of the xenon solution indicate a relatively large enthalpy difference of 354±30 cm^–1 (4.23±0.36 kJ/mol) between the conformers. The fundamental frequencies for the asymmetric (54 cm^–1) and SiF₃ (48 cm^–1) torsions for the gauche conformer were observed in the far infrared spectrum, and from the SiF₃ torsional frequency the barrier to internal rotation is calculated to have a value of 525 cm^–1 (6.28 kJ/mol). A complete vibrational assignment is presented for the gauche conformer that is consistent with the predicted wavenumbers utilizing the force constants from ab initio MP2/6-31G* calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational wavenumbers have been obtained from RHF/6-31G* and/or MP2/6-31G* ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with corresponding results for some similar molecules.Taken in part from the dissertation of Y. E. Nashed, which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree     

Infrared and Raman Spectra,Conformational Stability,Ab Initio Calculations,and Vibrational Assignments for Cyclopropyldifluorosilane

The infrared (3200–30 cm^–1) spectra of gaseous and solid Cyclopropyldifluorosilane, c-C₃H₅SiF₂H, and the Raman spectra (3200–20 cm^–1) of the liquid with quantitative depolarization values and the solid have been recorded. Both the syn (cis) and skew (gauche) conformers have been identified in the fluid phases, but only the syn conformer remains in the solid. Variable temperature (–55 to –100°C) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. From these data, the enthalpy difference has been determined to be 73 ± 10 cm^–1 (209 ± 29 cal mol^–1), with the syn conformer being the more stable rotamer, which is at variance with the predictions from ab initio calculations. A complete vibrational assignment is proposed for both conformers based on infared band contours, relative intensities, depolarization values, and group frequencies. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G* calculations. Utilizing the frequencies of the silicon–hydrogen sketch, the rm Si—H bond distances of 1.474 and 1.472 Å have been obtained for the syn and skew conformers, respectively. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G* and 6-311 +G** basis sets at levels of restricted Hartree-Fock (RHF) and/or Moller–Plesset (MP) to second order. The potential energy terms for the conformer interconversion have been obtained from the MP2/6-31G* calculation. The results are discussed and compared to those obtained for some similar molecules.     

Analysis of the Electronic Spectra in Polyphenyls

Though the spectra in polyphenyls are often broad and structureless, the general pattern of these spectra is very similar to those in polyacene series. The systematic behavior of the α, p, and β bands in p-polyphenyls can be explained in terms of simple MO theory with the first order configuration interaction. The behavior of the p and β bands can also be approximately calculated by straightforward exciton theory. The usefulness of the exciton theory is best demonstrated in the case of m-polyphenyls.     

Contacted Ion Pairs in Aqueous CuCl2 by the Combination of Ratio Spectra,Difference Spectra,Second Order Difference Spectra in the UV-Visible Spectra

The microstructure of aqueous CuCl₂ has been studied through lots of technologies for many years; however, it remains a controversial subject. In this study, a new spectroscopic method has been proposed to analyze the UV-visible spectra of thin film of CuCl₂/H₂O solutions at different concentrations. This method is the combination of ratio spectra, difference spectra and second order difference spectra. By using this method, two new bands at ~230 and ~380 nm are obviously observed. The bands are assigned as the contacted ion pairs[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2-, which demonstrates that ion pairs exist in the CuCl₂/H₂O solution. Such finding agrees with the recent theoretical spectra obtained by time-dependent density functional theory. Furthermore, the populations of the contacted ion pairs are discussed. This study not only offers the direct spectroscopic evidence of[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2- in aqueous CuCl₂, but also suggests that the spectroscopic analysis method is powerful to extract the weak bands in a strong overlapping spectrum.     

亮氨酸与异亮氨酸的表面增强拉曼光谱

报道了在蛋白质氨基酸中唯一一对异构体氨基酸——亮氨酸和异亮氨酸的FT-拉曼光谱和在银胶基底上的表面增强拉曼光谱(SERS). 归属了各振动、增强峰位并分析了异构体氨基酸分子内不同振动模式引起的拉曼位移及其在不同pH值下SERS的变化. 分子内不同的振动模式主要源于异构体氨基酸中一个甲基和主链的不同连接次序, 表现在拉曼光谱; 亮氨酸的甲基摇摆ρ(CH₃)和非对称变形δ_as(CH₃)在962, 945, 924和1454, 1408 cm^－1; 异亮氨酸的ρ(CH₃), δ_as(CH₃)在922和1448, 1420, 1394 cm^－1. C—CO, C—C, H—O…H及骨架晶格振动峰位基本对应. 饱和液态的拉曼光谱和SERS中, 各基团振动峰位的差异表现得更为明显. 初步推测了这对氨基酸异构体在银表面吸附状态的模型.     

Surface-enhanced Raman scattering (SERS) on silver electrodes as a technical tool in the study of the electrochemical reduction of cyanopyridines and in quantitative analysis

The SER spectra of 4-, 3- and 2-cyanopyridines adsorbed on a silver electrode are presented. The results show that cyanopyridines may adsorb in two different orientations, end-on (with the N atom of the Py ring bound to the surface) and flat, and that for potentials more negative than −1.1 V (SCE), the cyanopyridine radical anions can also be detected. The SERS intensity vs. potential curves show more than one potential of maximum SERS intensity which are assigned to the existence of more than one species on the electrode surface. The analytical potentially of SERS on electrodes has also been investigated. It is shown that the relative SERS intensity (ν_CN of the 4-CNPy (2120 cm⁻)/breathing mode of Py (1008 cm⁻¹)), at a fixed Py bulk concentration and at a fixed potential and exciting radiation, depends linearly on the 4-CNPy bulk concentration in the range 10⁻⁷-10⁻⁵M. The selectivity of the technique has also been investigated by studying the SER spectrum and the SERS intensity vs. potential curves for a mixture of 10⁻³M 4-CNPy, pyridine (Py) and 4-methylpyridine(4-MePy) in 0.1 M KCl aqueous solution.     

The alkali metal cation effect on the surface-enhanced Raman spectra of phosphate anions adsorbed at silver electrodes

The interaction of adsorbed phosphate anions with alkali metal cations at the Ag|aqueous solution interface has been investigated by surface-enhanced Raman spectroscopy (SERS). Formation of ion pairs at the interface was evident from the cation-induced perturbations in the SER spectra of anions. The frequency of the external vibration, silver–oxygen (Ag---O′), was not sensitive to the nature of cation, while the relative intensity of this mode was cation-dependent and was explored as a sensitive probe for the monitoring of coadsorption of ions at the interface. From the internal phosphate vibrations, both asymmetric modes, δ_as(PO) and ν_as(PO), were found to be the most sensitive to the nature of the cation. At a relatively positive potential (0.00 V vs. Ag | AgCl) the spectral parameters for the Cs⁺ and K⁺ cations were very similar indicating the same bonding type with anions. A more inhomogeneous chemical environment for the phosphate oxygen atoms was detected in the case of Na⁺ and Li⁺ cations. An increase in ν_as(PO) frequency by ca. 10 cm⁻¹ was the characteristic spectral signature for the interaction of phosphates with Li⁺. The formation of water-shared ion pairs at the interface was suggested based on the absence of splitting in the ν_as(PO) mode and the previously observed frequency sensitivity of this band to solvent H₂O substitution by D₂O. At negative potential (−0.80 V), a stabilization effect of Cs⁺ on the phosphate adlayer was detected based on the twofold increase in intensity of the ν(Ag---O′) mode compared with Li⁺. Splitting of the ν_as(PO) mode suggested the contact interaction of anions with specifically adsorbed Cs⁺ cations.