摘要:

AbstractLa simulation des contours expérimentaux des spectres Raman de rotation pure permet d'évaluer le rapportR= αb/αapour H2S et D2S. Les valeurs deR, des polarisabilitiés moléculaires et des polarisabilités de liaison évoluent avec la deut

ISSN:0377-0486    

DOI:10.1002/jrs.1250211102

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractInfrared and Raman spectra (5–3500 cm−1) of polycrystalline samples of (C3H7NH3)2PbCl4and of its deuterated derivative were investigated in the temperature range 90–300 K. An assignment of the observed bands at room temperature is proposed. A temperature dependence study of the frequencies, ν, and half‐widths, Δν1/2, of some low‐frequency Raman bands revealed two phase transitions at about 110 and 170 K, whereas the deuterated compound showed only one phase transition at about 150 K in the same temperature range. These transitions are believed to be governed by libration of the cation coupled with NH3group jumps between different potential wells. The value of activation energy,E0= 3.2 kJ mol−1, was calculated from the plot of Δν1/2νs.temperature; it is of the same order of magnitude as the potential barrier,V6= 3.53 kJ mol−1, calculated from the torsional frequenc

ISSN:0377-0486    

DOI:10.1002/jrs.1250211103

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe Raman spectrum of the soft mode and adjacent low‐frequencyATOmodes in pure and barium‐doped lead germanate was measured as a function of temperature,T, through the ferroelectric‐paraelectric phase transition. The barium concentrations studied varied from 2.3 to 6.6%. The Raman spectra were analysed for all the temperatures and dopings by least‐squares fitting of a model response function. In general, the phonon line widths increase with the amount of barium doping whereas the soft frequency decreases. Both the soft optic frequency and the mode strength display Curie‐Weiss behaviour close to the Curie temperature,Tc. When they are plotted as a function ofTc‐T, the various fitted soft‐mode parameters generally behave in a qualitatively similar fashion for the different specimens. However, on a quantitative basis, the agreement is less good, showing that the behaviour of the soft mode does not scale simply asTc‐T. This may indicate that the influence of the different polarizabilities of the barium defects is important in

ISSN:0377-0486    

DOI:10.1002/jrs.1250211104

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractAn easily accessible interactive method for the analysis of Raman spectra consisting of many overlapping peaks is presented. A combination of a three‐ or four‐dimensional grid and gradient searching is applied. The method can handle spectra with up to about 50 lines, based on a broad background. Analytical and user‐defined or tabulated basic functions can be included. The merits of the method are discussed with both artificial and real sp

ISSN:0377-0486    

DOI:10.1002/jrs.1250211105

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractPreresonance Raman spectra of methylpyridines (picolines) are presented for different incident laser wavelengths. A strong intensity variation of the non‐totally symmetric vibration 10α is observed, which implies a vibronic coupling of the lowest nπ* excited state with the next ππ* (B2uandB1u) states. In addition an intensity increase of some totally symmetric vibrations is observed and their possible implications for the geometry of the excited ππ* states are di

ISSN:0377-0486    

DOI:10.1002/jrs.1250211106

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractSurface‐enhanced Raman scattering ofcis‐ andtrans‐4‐methoxycinnamonitrile (4MCN) was investigated in aqueous silver sols. Both isomers adsorbed on the silver surface via the cyano group. The adsorption strength for thecisisomer appeared to be greater than that for thetransisomer. However,cis‐4MCN, adsorbed selectively on the silver surface, was readily converted to thetransisomer via a laser‐assisted surface reaction. The exact mechanism of the photoisomerization is not yet completely understood. It is thought that the reaction occurs via the absorption of a single visible photon which is in resonance with the low‐energy tail of the broadened absorption band of the adso

ISSN:0377-0486    

DOI:10.1002/jrs.1250211107

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractA zero‐order calculation was made for n‐undecamide and of itsN,N‐deuterated species by transferring the force constants from normal fatty acid amides. The observed and calculated frequencies agreed with an average error of 11 cm−1. Potential energy distributions and eigenvectors calculated in the process were utilized to make unambiguous vibrational assignments for the two molecules under invest

ISSN:0377-0486    

DOI:10.1002/jrs.1250211108

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractIndustrial membranes (made of polyacrylic acid chains grafted onto a polyethylene matrix), immersed in heavy water, were studied by Raman spectroscopy. The homogeneity of the graft density was sufficient to permit the determination of relative graft rations of different samples. Plots of measured ionization versus the pH of solutions in equilibrium with immersed membranes lad to intrinsic pKdeterminations. For this kind of membrane, it was established that the average lengths of the polyacrylic chains are of the same order of magnitude. Consequently, the different graft ratios depend only on graft density.

ISSN:0377-0486    

DOI:10.1002/jrs.1250211109

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe theory of light‐scattering intensities originally discussed by Fleury and developed recently by the present authors for LaP5O14was applied to the second‐order ferroelectric phase transition in tris(sarcosine)calcium chloride, (CH3NHCH2COOH)3CaCl2· It was found that the combination of critical exponents 2β‐γ′ = +0.05 ± 0.002; this is in good agreement with mean field theory, which predicts exactly zero, and sets strict limits on the intensity (small) of any dynamic central mode near the Curie temperatureTc.To′, the transition temperature extrapolated from soft‐mode frequency squaredvs.temperature, was found to be 131.5 ± 0.1 K, about 1 K aboveTc, demonstrating weak acoust

ISSN:0377-0486    

DOI:10.1002/jrs.1250211110

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe IR and polarized Raman spectra of the addition compound KIO3· Te(OH)6were recorded and analysed. Bands indicate that the IO3−ion is distorted in this crystal and its symmetry is less than its free ion symmetry,C3ν. The TeO6ion occupies a lower symmetry,C1, than its free ion symmetry

ISSN:0377-0486    

DOI:10.1002/jrs.1250211111

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY