ISSN:0377-0486    

DOI:10.1002/jrs.1250260802

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractTetrachlorocyclopropene, C3Cl4, is converted into C3Br4by treatment with BBr3. Use of less than the stoichiometric amount of BBr3leads to mixed halides C3ClnBr4‐nwhich are identified and investigated by Raman and13C NMR spectroscopy. The addition of Br2to C3Cl4yields both the isomerscis‐ andtrans‐1,2‐dibromotetrachlorocyclopropane in equal quantities; the vibrational spectra are reported and partially assigned. Raman and13C NMR of other mixed halides of cyclopropane, C3ClnBr6‐nare discussed. A35Cl/37Cl isotope effect is detected on the carbon chemical shift of C3Cl6I2fails to react with C3Cl

ISSN:0377-0486    

DOI:10.1002/jrs.1250260803

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractTime correlation functions from depolarized light scattering experiments at several temperatures were examined by biexponentials that simultaneously account for the unique axis molecular reorientations (on the picosecond time‐scale) and collisional processes (on the subpicosecond time‐scale). The first are found to be systematically slower than those obtained in previous studies. The important role played by dipolar interactions on the molecular organization in the liquid is confirmed. Comparison with dieletric relaxation times indicates that rotational diffusion provides only an approximate description of molecular reorientation in liquid acetonitrile. Application of the J‐diffusion model shows that the exponential decay of the observed orientational correlation functions cannot be taken as evidence of rotational diffusion in liquid acetoni

ISSN:0377-0486    

DOI:10.1002/jrs.1250260804

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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‐S1absorption band of the enol tautomers. In each compound, about 15 modes in the wavenumber range between 120 and 1650 cm−1show a strong coupling to the electronic transition. In TIN and HBT, combination tones of the strongest mode below 500 cm−1and 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‐S1absorption bands of TIN and HBT, reproducing the measured spectra very well. Theoretical simulations of the combination tone spectra give information on the vibrational modes involv

ISSN:0377-0486    

DOI:10.1002/jrs.1250260805

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe bands at 2485 and 940 cm−1observed in the Raman spectra of 2,5‐dimercapto‐1,3,4‐thiadiazole represent the hydrogen‐bonded ν(SH) stretching and δ(C‐SH) in‐plane bending modes, respectively. A quantitative study of the hydrogen bonding was carried out using intensity measurements of the bands assigned to the hydrogen‐bonded and the free δ(C‐SH) in‐plane deformations at 940 and 919 cm−1, respectively, as a function of temperature. The Fourier transform (FT) Raman spectra were recorded over the temperature range 303‐403 K using an environmental chamber fitted into the FT Raman sample compartment. The equilibrium constants between the free and the hydrogen‐bonded molecules were determined over this temperature range and the average enthalpy for hydrogen‐bond formation was obtaine

ISSN:0377-0486    

DOI:10.1002/jrs.1250260806

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe Fourier‐transform (FT) Raman spectra of genuine samples of scrimshaw are reported and compared with those of fake scrimshaw, ivory and human milk tooth. The major spectral features in all systems examined were assigned. The application of the FT‐Raman technique to the non‐destructive diagnostic identification of scrimshaw and simulated scrimshaw artefacts is demonst

ISSN:0377-0486    

DOI:10.1002/jrs.1250260807

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractFourier transform surface‐enhanced Raman (FT‐SER) spectra of 18 polyaromatic hydrocarbons (PAHs) were measured on a silver surface which had been previously roughened by an oxidation‐reduction procedure in an electrochemical cell. The sample was placed on the clean surface as a solution in an organic solvent and the solvent allowed to evaporate. All the samples had significantly different SER spectra. Detection limits were around 10−9mol for most compounds but were higher for a few compounds, particularly azulene. For most samples the SER spectrum obtained was similar to the FT‐Raman spectrum of the solid sample. For one sample, azulene, a different spectrum was obtained by the SER technique, indicating a different, or additional, SER mechanism for this sample. A brief investigation of the quantitative aspects of the technique showed that, over the range studied, the intensity of the SER spectrum was related linearly to the amount of compound present on th

ISSN:0377-0486    

DOI:10.1002/jrs.1250260808

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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 3‐21Gab initioforce 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 acid

ISSN:0377-0486    

DOI:10.1002/jrs.1250260809

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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−xcrystals and the molecular alloys (N2O)x—(12CO2)1−xand (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 cr

ISSN:0377-0486    

DOI:10.1002/jrs.1250260810

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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−1for ΔHG′‐T′3.6 ± 0.3 kJ mol−1for ΔHG ‐ Tand 1.1 ± 0.3 kJ mol−1for ΔHG′‐ G. These were compared withab initioSCF‐MO results, for the isolated molecule, in order to assess the relative importance of intra‐and intermolecular

ISSN:0377-0486    

DOI:10.1002/jrs.1250260811

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY