摘要:

AbstractA simple computer‐controlled instrument for natural and magnetic incident circular polarization Raman optical activity (ICP ROA) measurements in right‐angle scattering is described. The key spectral elements consist of a fast single‐stage monochromator equipped with a holographic notch filter, a highly efficient holographic diffraction grating and a thinned back‐illuminated, thermoelectrically cooled charge‐coupled device (CCD) detector. A temperature‐stabilized longitudinal electro‐optic modulator is employed to switch between orthogonal circular polarization states in the incident laser radiation. A polaroid film together with a mica half‐wave retardation plate are used to select particular linear polarization states in the Raman scattered radiation with the same instrumental response. High‐quality depolarized and polarized Stokes and depolarized anti‐Stokes ICP ROA spectra of (R)‐(−) and (S)‐(+)‐phenyloxirane and depolarized magnetic resonance ICP ROA spectra of copper(II) tetrabromide are presented as typical examples of the excellent

ISSN:0377-0486    

DOI:10.1002/jrs.1250250703

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe band intensities of Raman spectrum of PTZ in the solid state show a clear dependence on the laser excitation wavelength. Such a behaviour, not observed when the spectrum is obtained from PTZ in solution, indicates that in the crystal the molecular. orbital of the compound is perturbed to some extent. The PTZ · SO2complex in solution presents the same pre‐resonahce pattern as does solid PTZ, suggesting that the same PTZ orbital is involved in both cases. The most enhanced PTZ modes are those ascribed to the aromatic ring vibrations, indicating an interaction through the π molecular orbitals; it is proposed that PTZ acts as a π‐donor toward SO2on the basis of the pre‐resonance pattern of the Raman spectrum of P

ISSN:0377-0486    

DOI:10.1002/jrs.1250250704

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractResonance‐enhanced multiphoton ionization (REMPI) of16O2X3∑g−(ν = 0) through (3sσg)d1Πg, (ν = 0) by using (2 + 1) one‐colour photons is reported. This REMPI process, already observed and analysed by other authors at low pressure and low rotational temperature with mass spectrometry detection, is used to test our first detector of ionizations. Experimental difficulties have led to the design of an original arrangement of electrodes to collect electrons at room temperature and 1 Torr pressure of static molecular oxygen. A calculated spectrum is compared with the observed REMPI spectrum. The calculation uses the polarizability tensor and takes into account the competition between ionization and predissociation of the Ry

ISSN:0377-0486    

DOI:10.1002/jrs.1250250705

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe viscosity temperature dependence and the correlation radius of concentration fluctuations have been obtained in guaiacol‐glycerol solutions with various miscibility gaps up to a gap width ΔT= 0.01 °C. The correlation radius critical exponent ν changes from 0.63 when ΔT= 39°C to 0.53 when ΔT= 0.01 °C. Measurements were made using the light correlation spectroscop

ISSN:0377-0486    

DOI:10.1002/jrs.1250250706

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA theoretical analysis is presented of resonance Raman scattering in disperse absorbing media, based on consideration of non‐linear four‐photon processes. A comparison of the theory with experiments is gi

ISSN:0377-0486    

DOI:10.1002/jrs.1250250707

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe UV‐visible (300–800 nm), Raman and resonance Raman (900–1700 cm−1) spectra of two bisazo scarlet RN and brown 5R pigments have been investigated in the solid state at 300 K. A detailed analysis of the resonance Raman spectra and excitation profiles of various fundamentals in the 900–1700 cm−1range is reported through the visible absorption spectrum region: the vibrational assignments confirm that both substituted benzene‐2′‐azonaphthol derivatives are stabilized in their hydroxyazo form; the excitation profiles (EPs) established for many modes in each dye indicate interferences between two overlapping electronic manifolds. Taking account of multistate interference phenomena and inhomogeneous broadening effects, the observed EPs compare well with the calculated ones under the assumption of weakly displaced harmonic oscillators; this interpretation is supported by the observation of weak overtone and combination bands in the 1700–3000 cm−1range.Finally, conclusions are drawn about the scattering mechanisms and the nature or degree of mixing of the first electronic excited states, which appear to be quite sensitive to the substituent (Cl or NO2) on the benzene rings. Such information can be helpful for the design and synthesis of new azo dyes with

ISSN:0377-0486    

DOI:10.1002/jrs.1250250708

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractIn cubic crystals the infrared‐active triply degenerate modes split into anLOand a doubly degenerateTOmode. For crystals with T symmetry, first‐order spatial dispersion splits the polarTOmodes into a set of two circularly polarized T+and T−modes whose frequencies have only a small separation. Using incoherent high‐resolution Raman spectroscopy (a tandem Fabry–Perot Raman double monochromator of limiting resolution 0.005 cm−1), we have measured the splitting of the low‐energy TO lattice modes in the optically active material sodium chlorate.Experiments were performed in various scattering geometries to separate the optical Raman‐active modes of different symmetries (A, E, LOandTOmodes). Furthermore, the difference in the Raman response of theT+andT−modes to left or right circularly polarized incident light was detected and analysed.We measured for the three low‐energy TO modes (77, 98 and 125 cm−1atT= 6 K) a splitting of 0.08, 0.08 and 0.105 cm−1respectively in a right angle geometry and 0.11, 0.11 and 0.135 cm−1respectively in a backscattering geometry (an increase in agreement with a shift proportional t

ISSN:0377-0486    

DOI:10.1002/jrs.1250250709

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractVibronically specific subrotational period lifetimes of the predissociated 22B2state of NO2vapour (250–235 nm) have been determined by spontaneous resonance Raman scattering polarization measurements. The lifetimes of the vibronic symmetric stretching, ν1′, (100), bending, ν2′, (101), and asymmetric stretching, ν3′, (002), overtone levels are 75 ± 10 fs, 2.5 ± 05 ps and 155 ± 15 fs respectively. When one quantum of bending (ν2,′) is excited in combination with one quantum of totally symmetric stretching (ν1′), the lifetime increases from 75 ± 10 to 125 ± 15 fs (110). The 22B2state electronic origin lifetime has been previously shown to be 42 ± 5 ps independent of angular momentum quantum numbers. These results are interpreted in terms of the shape of the potential energy surface intersections in the region and the results of earlier quan

ISSN:0377-0486    

DOI:10.1002/jrs.1250250710

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractUltraviolet resonance Raman spectra of inosine and its deuterated species (C8‐d, Nl‐dand C8‐, Nl‐deuterated derivatives) in aqueous solution have been collected (λexc= 257 and 281 nm) and reported in the spectral region between 400 and 1800 cm−1. The observed vibrational modes have been assigned using the Wilson GF method with an empirical harmonic valence force field and a non‐redundant set of internal co‐ordinates. This normal mode analysis is based on previous work on the vibrational assignments of the hypoxanthine nucleic base and the furanose ring with various geometries. Here the analysis has been carried out by using three different nucleoside conformations as determined from x‐ray studies of molecular crystals. The most striking features of the present work are: (i) the assignments of inosine vibrational modes are very different from those of the hypoxanthine base; (ii) the best fit between measured and calculated vibrational wavenumbers and their isotopic shifts upon selective deuteration has been obtained from inosine structures containing an N‐type sugar (C3′‐endo) associated with a low‐antibase. In addition, we have tested the reliability of the force field in the case of inosine residues involved in a canonical A‐RNA helical structure by comparing the calculated wavenumbers of the most characteristic vibrational modes with those observed in off‐ and on‐reson

ISSN:0377-0486    

DOI:10.1002/jrs.1250250711

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractRaman spectra excited at two laser wavelengths are used to study the damage in self‐implanted silicon. Depending on the implantation conditions, a three‐layer structure can be constructed: a damaged surface crystalline layer (dsc‐Si), an amorphous layer (a‐Si) and a damaged interior crystalline layer (dic‐Si). Raman spectra can provide the structural details of these layers, together with the Rutherford backscattering–chanelling technique. Examination of the scattering intensities shows that the contribution to the Raman signals from different layers can be distinguished and separated. Further analysis of the Raman data reveals a defect‐activated low‐frequency band in the dsc‐Si layer which is sensitive to the damage and may be used for the characterization of dsc‐Si. For totally amorphlzed samples the two Raman spectra excited at 457.9 and 647.1 nm show different scattering intensity ratios for the optical‐ and acoustic‐like phonons. This novel result may indicate a depth‐dependent variation of the disordering in the amorphous layer. Quantitative comparison between the calculated and measured Raman scattering intensities provides the scattering efficiency ratios of dsc‐Si and a‐Si in samples compris

ISSN:0377-0486    

DOI:10.1002/jrs.1250250712

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY