摘要:

AbstractNew resonance Raman scattering (RRS) sequences of vibrational overtone lines of Se2−SeS−, S3−and Se3−have been observed. By a photochemical technique these centres and S2−can now be produced in alkali metal bromides and chlorides. Vibrational frequencies from RRS or Raman scattering (in the case of S2−) agree with those obtained from luminesce

ISSN:0377-0486    

DOI:10.1002/jrs.1250201002

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractCarboxylate and guanidinium groups of amino acids have been studied by ultraviolet resonance Raman (UVRR) spectroscopy. On near‐resonant excitation (192 nm) into the allowed π–π* transition of the carboxylate chromophore, the vibrational spectrum of aspartate displays only one band originating from the COO−symmetric stretching mode, consistent with anA‐term enhancement mechanism. The UVRR spectra of the guanidinium ion reveals a complex vibrational pattern, and the bands have been assigned with the aid of a normal coordinate analysis. UV enhancement is observed for both asymmetric (E′) and totally symmetric (A1′) modes, and also for the overtone of the out‐of‐plane CN3bending mode, Γ(A2″). TheE′ enhancement is suggested to reflect Jahn—Teller splitting in the first allowed electronic transitionA2″ ←E″, whereas the 2Γ(A2″) enhancement requires a lowering of the force constant for out‐of‐plane bending in the excited state, consistent with its expected tendency toward pyramidalization. Similar enhancement patterns are seen in the UVRR spectra of the guanidinium chromophore in methylguanidinium and arginine, which show, in addition, splittings and intensity redistribution due to the substituents. The excitation profiles of guanidinium and arginine reveal a complex structure that may arise from an excited‐state Jahn—Teller effect. The Raman enhancements are too low to permit detection of guanidinium or carboxylate in the UVRR spectra of prote

ISSN:0377-0486    

DOI:10.1002/jrs.1250201003

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractRaman and infrared spectra of phenolphthalein and its white and pink potassium salts together with the resonance Raman spectrum of the parent compound in alkaline solution were studied. From careful comparison of the spectra, the observed frequencies were assigned to appropriate vibrational modes and from these assignments frequencies originating from vibrations of hybridized bonds in the resonating molecular forms of phenolphthalein, believed to be present in alkaline solution were identified. It was shown that such resonating forms are present in the pink but not the white potassium salt. The spectral data also indicate that the vibrations of the carboxylate ion group do not take part in the resonance Raman phenomenon.

ISSN:0377-0486    

DOI:10.1002/jrs.1250201004

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractIR data for gaseous, liquid, solid and matrix isolated bis(fluorocarbonyl) disulphide together with the Raman spectrum of the liquid suggest the existence of two planar conformers (I and II) in equilibrium in the gaseous phase and of a planar one and other conformers of undetermined structure in the other neat phases. Wavenumbers reported for the vibration of conformer I are used to calculate an approximated force field.

ISSN:0377-0486    

DOI:10.1002/jrs.1250201005

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe complete Raman spectrum of the pyramidal triiodostannate(II) ion [SnI3]−(ν1= 162 cm−, strong, polarized; ν2= 61 cm−, medium, polarized; ν3= 148 cm−, strong, depolarized; ν4= 48 cm−, strong, depolarized) is observed in a diethyl ether extract from a solution of tin(II) iodide containing hydriodic acid. Previous reports of the frequencies of [SnCl3]−are confirmed but for [SnBr3]−ν1is revised from 211 to 205 cm−1. The complex acids H[SnX2Y] and H[SnXYZ](X, Y or Z = Cl, Br or I) are observed in solvent extracts of tin(II) mixed halide solutions and a set of ν(Sn—halogen) frequencies is compiled. Appreciable co‐extraction of [SnX2(H2O)] occurs at halogen acid conce

ISSN:0377-0486    

DOI:10.1002/jrs.1250201006

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractRaman Spectra of seven tryptophan derivatives in the crystalline state were examined to find Raman bands whose frequencies reflect the strength of hydrogen bonding at the N1H site of the indole ring or the conformation of the indole ring relative to the amino acid backbone. Two indole ring vibrations, W4 around 1490 cm−1and W6 around 1430 cm−1, showed a correlation between their Raman frequencies and the infrared frequency of the N‐1‐H stretching mode, an indicator of hydrogen bond strength. W4 and W6 increase in frequency with increase in hydrogen bond strength and the frequency variation is particularly large for W6. On the other hand, another indole ring vibration, W3, observed around 1550 cm−1, changes in frequency as a function of the torsional angle, χ2,1, of the C‐2C‐3C‐βC‐α linkage. As the absolute value of χ2,1becomes larger and the C‐α atom moves away from the C‐2 atom, the W3 frequency increases. In the Raman spectra of proteins excited with visible radiation, the W3 band is usually strong and can be used as a conformational marker, whereas the W4 band is very weak and the W6 band is overlapped by strog scattering due to C–H bending vibrations of aliphatic side‐chains. In UV resonance Raman spectra, however, all these Raman bands are enhanced and may provide key information on the hydrogen bonding and co

ISSN:0377-0486    

DOI:10.1002/jrs.1250201007

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractRaman spectra of polycrystalline NH4VO3and ND4VO3were recorded at various temperatures. Splittings were observed for most fundamentals and the external mode region contains at least eleven bands. The spectra are interpreted in terms of a group theoretical analysis based on the molecular symmetry and the known crystal structure.Wavenumber vs temperature curves for several internal and external modes show minor anomalies near 150 K, which might be due to an order–disorder phase transition. The bands assigned to ammonium ion librations are observed at room temperature, which implies that the onset of ‘free’ rotation of the NH4+ion (on the vibrational time scale) occurs at a much higher temperature in NH4VO3than it does in other ammonium

ISSN:0377-0486    

DOI:10.1002/jrs.1250201008

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractRaman frequency and intensity measurements have been performed on liquid water as H2O, D2O and H218O to study the effects of isotope substitution. Intensity data were collected digitally, normalized to account for the temperature and frequency factors and presented in isotropic and anisotropic forms. The frequency and intensity changes are consistent with the predictions of simple reduced mass calculations. In particular, there was no evidence to support the reported breakdown of the Born—Oppenheimer approximation as has been reported for H218O. The isotope invariant sum rule was checked for H216O, H218O and D2O by relative intensity studies for the OH stretching region against an internal sulfate reference peak. Identical values for the isotope invariant sum were obtained for H216O and H218O but the value for D2O was about 30% larger. The difference appears to have its origin in the more highly structured nature of D2O due to smaller anharmonic effects. Accurate frequency shifts among H216O, H218O and D2O are also presented. Surprisingly, the greatest frequency shift which accompanied18O substitution was in the low‐frequency hydrogen‐bonded region where the band at 192 cm−1for H2O shifted by 15 cm−1to 177 cm−1for H218O. This result confirms previous observations and establishes the origin of this band as a hydrogen‐bonded symmetric stretching mode which involves primarily oxygen displacement. Further support for this assignment comes from the observation that the band at 192 cm−1is slightly polarized. The effects of intermolecular coupling contribute to the band structure of the internal modes. Frequency differences in the OH stretching region of H2O and H218O suggest that only about 50% of the anisotropic intensity is due to the Raman activity of the ν3antisymmetric stretching mode while the remainder is due to the symmetric stretching modes of intermolecularly coupled water molecules. A point‐by‐point comparison of the OH stretching region for the isotropic scattered intensity of H2O and H218O revealed that the complete region from 2800 to 3800 cm−1was shifted equally by 7 cm−1, a fact that suggests that the peak maximum at about 3250 cm−1is just part of the ν1symmetric stretching mode and is not primarily due to 2ν2. The effect of intermolecular coupling in the ν2region of liquid water was confirmed by the difference in the frequency for the isotropic and anisotropic components for each of the isotopic forms of water. For H218O the peak maximum in the isotropic spectrum was at 1619 cm−1whereas the peak maximum in the anisotropic spectrum was at 1637 cm−1with the result that in the measuredI‖spectru

ISSN:0377-0486    

DOI:10.1002/jrs.1250201009

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe origin of reduction procedures used to transform (or normalize) relative Raman intensities is reviewed and discussed in detail in order to clarify the difference between an approach based on the frequency domain representation of Placzek and that based on the time domain representation of Heisenberg as developed by Gordon. These procedures are not designed to replace standard methods for the measurement of accurate absolute Raman scattered intensity. However, they do provide a practical method for a first‐order comparison of Raman spectra for samples measured under different conditions of phase, concentration and temperature and for samples measured with different excitation frequencies. Especially for the low‐wavenumber region, reduced spectra allow analyses of significant spectral features: a linear baseline may be more easily defined, which in turn permits easier measurement of peak maxima, band shapes and relative intensities. Further, certain forms of the reduced Raman spectrum may be compared directly with the corresponding infrared absorption spect

ISSN:0377-0486    

DOI:10.1002/jrs.1250201010

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe isotropic Raman spectra of monodeuterated benzene (C6H5D) in the region around 3000 cm−1were studied at temperatures of 30, 60 and 90°C and pressures up to 2 kbar. In this frequency region we observed two overlapping bands (ν1and ν12), and hence an additional broadening process, the energy relaxation to other modes, gives a contribution to the band widths. The changes in frequencies and band widths are interpreted in terms of the Schweizer and Chandler th

ISSN:0377-0486    

DOI:10.1002/jrs.1250201011

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY