摘要:

AbstractThe non‐linear Raman spectrum of 4‐cyano‐4′‐heptylbiphenyl is reported. Measurements of depolarization ratios of the vibrational bands at 2224 cm−1(CN stretching), 1606 cm−1(aromatic ring stretching) and 1185 cm−1(CH aromatic in‐plane deformation) are used to evaluate the order parameters (〈P2〉 and 〈P4〉) using a ‘line model’ for the molecules. The results are internally consistent and also show the same general features (including some discrepancies in 〈P4〉) reported by other workers. Nevertheless, the results demonstrate that the technique is capable of wide application to the study of the anisotropic properties of liquid crystals and provides a valuable probe into the study of t

ISSN:0377-0486    

DOI:10.1002/jrs.1250250713

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractRaman and infrared spectra of solid CH2F2(Freon 32) were recorded in both the lattice and internal mode regions for samples at temperatures between 12 and 115 K. No evidence of any solid‐state phase transition or of metastable phases was found. The spectra are consistent with a large unit cell, probably non‐centrosymmetric and containing eight molecules, with relatively loose packing compared with the other methylene halides. It is postulated that at temperatures near the melting point, the molecules undergo 180° rotational jumps which are gradually inhibited on coo

ISSN:0377-0486    

DOI:10.1002/jrs.1250250714

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractUltraviolet resonance Raman (UVRR) spectra of polypeptides and proteins exhibit a band atca.1390 cm−1whose intensity is sensitive to helical content. The assignment of this band, designated amide S, has been contentious. To study the vibrational origin of amide S, relevant amide model compounds and their selectively deuterated iso‐topomers were synthesized.N‐Methylacetamide,N‐methylpropionamide andN‐methylisobutyramide possess a methyl, methylene and methine group, respectively, adjacent to the amide carbonyl. The UVRR spectrum of the natural abundance species show resonantly enhanced vibrational bands in the region 1350–1380 cm−1. These bands disappear on deuteration of the (C)Cα. hydrogen atoms, while the amide III modes shift up to a common position (ca.1335 cm−1) and increase in intensity. These results suggest that amide S can be assigned to a (C)Cαhydrogen bending vibration, which acquires resonance intensity by vibrational mixing with the CN stretch of the nearby amide III mode. Variation of this mixing with the CαH/CO dihedral angle can explain the sensitivity of amide III to protein secondary structure. Additional UVRR and Fourier transform IR data reveal that (C)Cα‐deuteration has a smaller effect on the amide I, I′, II and II′ vibrational modes. Finally, it is established that UVRR spectra for NMA in H2O and D2O show an absence of torsional fundamentals or overtones. These results are interpreted as indicating an energy barrier to cxcited‐state isomerization, which argues against an alternative assignment of

ISSN:0377-0486    

DOI:10.1002/jrs.1250250715

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe theory of the recently discovered interferometric coherent Raman spectroscopy (ICRS) is extended to explicitly include terms resulting from non‐resonant contributions to the overall non‐linear susceptibility. The derived expression is applicable to both interferometric coherent anti‐Stokes Raman spectroscopy (ICARS) and interferometric coherent Stokes Raman spectroscopy (ICSRS) and can be applied to both neat solutions and binary mixtures. It is shown that the total description of ICRS must include a resonant term, a non‐resonant term and a resonant‐non‐resonant cross‐term, each of which exhibits analytically unique behavior in time‐domain ICRS experiments. From the complete expression one can extract relative strengths of the resonant and non‐resonant molecular hyperpolarizabilities. Resonant hyperpolarizabilities thus obtained may be used to determine absolute Raman cross‐sections, without making absolute measurements. Conversely, for a sample for which the absolute Raman cross‐section is independently known, one can determine the value of the non‐reson

ISSN:0377-0486    

DOI:10.1002/jrs.1250250716

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPolarized single‐crystal Raman spectra were collected from the borosilicate feldspar mineral danburite (CaB2Si2O8) over the region 1800–40 cm−1. The symmetry of danburite (orthorhombic) is higher than that of the other feldspars (monoclinic or triclinic) and this simplifies the vibrational analysis. A very high proportion (74/78) of the bands due to Raman‐active fundamentals are observed, making this the first such study in which most of the bands for a feldspar mineral have been observed. Assignment of bands to stretching, bending and lattice modes is problematic because of the framework structure of the feldspar. The physically unrealistic disconnection of the danburite lattice into [Si2O7]6−, [B2O]4+and Ca2+ions leads to remarkably good predictions of the numbers of bands for each symmetry species in the wavenumber ranges appropriate for the Si(B)OSi(B) stretching (1300–825 cm−1), bending (825–390 cm−1) and lattic

ISSN:0377-0486    

DOI:10.1002/jrs.1250250717

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractCARS measurements were carried out on acridine to investigate the resonance behaviour of the totally symmetric vibration in the lowest excited triplet electronic state. The lineshapes of the observed vibrational mode were analysed for different pump laser wavenumbers by means of the transform theory in the Condon approximation. Under this condition the experimentally determined CARS excitation profile was compared with that calculated from the measuredTn←T1, absorption spectru

ISSN:0377-0486    

DOI:10.1002/jrs.1250250718

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Raman and IR spectra of isopropyl thiocyanate, isopropyl‐1,1,1,3,3,3,‐d6thiocyanate and isopropyl‐d7thiocyanate were recorded as vapours, liquids and amorphous and crystalline solids. IR matrix isolation spectra were recorded in argon and in nitrogen matrices at 14 K, using the hot nozzle technique. Two conformers withCs, symmetry (anti) andC1, (gauche) were present in the vapour and liquid states whereas only one conformer (anti) existed in the crystal. The enthalpy difference was measured to be ΔH° (gauche‐anti) = 2.4 ± 0.2 kJ mol−1in the liquid from variable‐temperature Raman spectra. In argon matrices a value of 2.3 ± 0.3 kJ mol−1was obtained in the temperature range 300–600 K, similar to the value in nitrogen matrices, both assumed to be valid for the vapour phase. Annealing experiments indicated the barrier ofgauche–anticonversion to be around 9 kJ mol−1. Quantum chemical calculations with the basis sets STO–3G, 3–21G* and 6–31G* were carried out The energy difference between the conformers was calculated and scaledab initioforce constants were employed in normal coordinate calculations. Complete assignments of Raman and IR bands belonging to theanticonformer of the parent molecule and the isotopomers were carried out. Only a limited number of bands characteristic of thegauchconformer were observed since most of its Raman and IR bands overlap

ISSN:0377-0486    

DOI:10.1002/jrs.1250250719

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe high‐resolution (ca.0.008 cm−1) stimulated Raman spectrum of the strongly perturbed CH symmetric stretching region of12C2H6at room temperature and at a rotational temperature ofca.30 K, achieved in a free supersonic jet expansion chamber, is reported. The spectrum is tentatively analysed and assigned in terms of a simplified vibration‐torsion–rotation Hamiltonian. Besides the already known strong Fermi resonance, several Coriolis torsional interactions are identified as the major perturbations in this spectr

ISSN:0377-0486    

DOI:10.1002/jrs.1250250720

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractRaman spectra of styrene (S), 3‐fluorostyrene (3FS), 3‐chlorostyrene (3CS) and 3‐methylstyrene (3MS) and their complexes in α‐, β‐ and γ‐cyclodextrins (α‐, β‐, γCD) were recorded at various temperatures. The substituted styrene molecules were found to provide good group frequencies, namely,vCC andvCH, for probing the guest molecules. Generally, the CC oscillator is shown to be a good probe for studying conformational equilibria of the guest molecule perturbed by complex formation with the various CD molecules. The CH oscillators provide information concerning plausible structures for the complexes. On the whole, all the spectral observations are consistent with different types of structures for the (S, 3MS)–αCD and (3FS, 3CS)–αCD complexes. In particular, the Raman spectroscopic results suggest that, for 3MS–αCD the vinyl group keeps some rotational freedom. For 3FS–αCD and 3CS–αCD, it is suggested that the most electronegative fluorine and chlorine atoms are left outside the the CD cavity, with the vinyl group rotationally hindered. For the γCD complexes, the wider CD cavity sould be able to accommodate all the guest molecules considered keeping the conformer distributions of the pure liquids approximately. However, the inclusion process seems to hinder the internal rotation in such a way that even below 200 K the conformer distribution remains similar to

ISSN:0377-0486    

DOI:10.1002/jrs.1250250721

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractInterferometric coherent anti‐Stokes Raman scattering (ICARS) using incoherent laser light was used for time‐resolved measurements of vibrational parameters of solutions of bis(dimethylamino)heptamethine iodide in the ground and theS1, state. The vibrations at 1124, 1195, 1285 and 1304 cm−1have dephasing times in the range 0.3–1.1 ps. The shortest dephasing time is observed for the normal mode at 1195 cm−1with a large amplitude for the N atoms. The coherence peak in the ICARS signal around zero delay is broadened due to coupling to the electronic transition. The same peak width of 80 fs is found using degenerate four‐

ISSN:0377-0486    

DOI:10.1002/jrs.1250250722

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY