摘要:

AbstractThe Raman and far‐infrared spectra of crystalline nitromethane and its fully deuterated analogue were recorded over the frequency range 20–400 cm−1and at temperatures between 20 and 150 K. In the spectra of CH3NO2, 15 of the 21 Raman‐ and 13 of the 15 infrared‐active lattice modes predicted by group theory were observed. The corresponding numbers for CD3NO2were 17 and 14, respectively. Isotopic frequency shifts together with inertia and intensity arguments were used to assign the peaks. Frequency coincidences in the two types of spectra are indicative of a non‐centrosymmetric cell. Several features are attributed to the torsional mode or interactions wit

ISSN:0377-0486    

DOI:10.1002/jrs.1250200602

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractTellurc acid ammonium phosphate (TAAP) is a new class m ferroelectric with a transition temperature of 45°C. Structural data and preliminary spectroscopic studies confirmed the presence of NH…O hydrogen bonds. Raman spectroscopic studies on this crystal were carried out in the temperature range 20–80 °C to look for possible spectral changes as a result of phase transition. A detailed analysis of the line width and frequencies was carried out across the phase transition in order to understand the nature of the phase transition. From the spectral features of the bands in different regions it is inferred that the groups TeO6, PO4and NH4do not undergo changes that could trigger the phase transition. On the other hand, the broadening of the bands in the range 2600–3400 cm−1suggests the possibility of an order–disorder type of transition phenomenon involving hydrogen bonds. This is further supported by the shift of the transition temperature from 45 to 87°C

ISSN:0377-0486    

DOI:10.1002/jrs.1250200603

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe effect of static inhomogeneous environmental broadening of Raman excitation profiles and Raman peak intensity distribution of solute molecules was investigated. Homogeneous bradening is represented by Lorentzians and inhomogeneous broadening by Gaussians, where the latter reflect distributions in the purely electronic transition. The Raman scattering cross‐section is calculated analytically, and by means of recent optical bandshape theory for Voigt profiles it can be recast into rapidly converging and easily tractable series expansions well suited for numerical data fitting. The profile expressions also apply to arbitrary values of the broadening parameters and in these respects improve on several previous approaches to inhomogeneous broadening. Notable outcomes are that the excitation profile takes the from of a series of Franck–Condon modulated Voigt profiles when the broadening parameters are small compared with the vibrational frequencies of the Raman‐active modes. In this limit only diagonal terms in the sum over vibrational quantum numbers contribute. When the broadening parameters are not small, non‐diagonal terms are important and lead to additional broadening, profile maximum shifts and bandshape dis

ISSN:0377-0486    

DOI:10.1002/jrs.1250200604

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractA detailed temperature‐dependent Raman study of oriented single crystals of CdSiF6· 6H2O down to 10 K was made in the region of internal vibrations and lattice modes. The frequency shifts, Iinewidths and intensities of some of the modes associated with the [Cd(OH2)6]2+and (SiF6)2−ions show abrupt changes at temperatures around 220 K and some doubly degenerate modes split into two components. These studies suggest that the system undergoes a structural phase transition atca.2

ISSN:0377-0486    

DOI:10.1002/jrs.1250200605

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe Raman spectrum of sulphonated copper phthalocyanine on a silver electrode surface is reported for four excitation wavelengths in theQ‐band region at voltages between +0.6 and −0.6 V (vs SCE). SERS activity is observed and the bonding and orientation of the surface species are voltage dependent and are inferred from a vibrational analysis. Maximum scattering intensity is observed at −0.2 V (vs SCE) and is attributed to molecules bonded edge‐on to the surface through SO3

ISSN:0377-0486    

DOI:10.1002/jrs.1250200606

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe Raman spectra of ferroelectric [NH(CH3)3]3Sb2Cl9single crystals were studied at temperatures ranging from 90 to 390 K. An assignment of most of the observed bands is proposed. A second‐order phase transition around 364 K leading to a high‐temperature paraelectric phase manifested itself by spliting of the antisymmetric CH3stretching band (3035 cm−1) below the transition temperature. A temperature dependence study revealed the existence of disorder in the crystal. A systematic measurement of the CH3torsional vibration Raman band (305 cm−1) was performed and the activation energy (Ea= 2.39 kcal mol−1) of an unidentified organic group HN(CH3)3+motion was extracted from the half‐width versus temper

ISSN:0377-0486    

DOI:10.1002/jrs.1250200607

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe FT‐IR and laser micro‐Raman spectra of ten silylated nucleoside derivatives of uridine and their synthetic precursors,tert‐butyldimethylsilyl chloride and monomethoxytrityl chloride, were measured at room temperature. Some spectral differences are clearly evident for the 2′‐ and 3′ ‐silylated isomers; such distinctions are difficult to observe by other spectroscopic methods (e.g.1H NMR spectroscopy). The differences in the positions of the CO stretching vibrations for the uracil base in uridine and the silylated derivatives are due chiefly to variations in the extent of hydrogen bonding in the solids. In addition, several bands attributable to SiO modes in the silylated compounds h

ISSN:0377-0486    

DOI:10.1002/jrs.1250200608

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractLattice vibrational Raman spectra of (5‐dimethylaminopenta‐2, 4‐dienylidene)dimethylammonium perchlorate were measured for two crystal modifications at various temperatures. The phonon frequencies below 200 cm−1were different for the two crystal forms. A phase transition was found by means of Raman spectra and differential scanning calorimetry (DSC). With increase in temperature of the crystal, the orange form is converted to the yellow form atca.370 K, and this transition is irreversible. Near the transition temperature, the Raman bands of both forms were observed simultaneously. This observation and an endothermic peak in the DSC curve show that two forms are correlated by a first‐order phase t

ISSN:0377-0486    

DOI:10.1002/jrs.1250200609

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

ISSN:0377-0486    

DOI:10.1002/jrs.1250200601

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY