Polarized Raman spectra

Galica G E, Johnson B R, Kinsey J L and Hale M O 1991 Incident frequency dependence and polarization properties of the CH I Raman spectrum J. Phys. Chem. 95 7994-8004... 

The Raman spectrum can be used to give additional information regarding the symmetry properties of vibrations. This information derives from the measurement of the depolarization ratio p for each Raman band. The quantity p is a measure of the degree to which the polarization properties of the incident radiation may be changed after scattering... 

In Chapter 8, Stavola and Pearton discuss the local vibrational modes of complexes in Si that contain hydrogen or deuterium. They also show how one can use applied stress and polarized light to determine the symmetry of the defects. In the case of the B-H complex, the bond-center location of H is confirmed by vibrational and other measurements, although there are some remaining questions on the stress dependence of the Raman spectrum. The motion of H in different acceptor-H complexes is discussed for the Be-H complex, the H can tunnel between bond-center sites, while for B-H the H must overcome a 0.2 eV barrier to move between equivalent sites about the B. In the case of the H-donor complexes, instead of bonding directly to the donor, H is in the antibonding site beyond the Si atom nearest to the donor. The main experimental evidence for this is that nearly the same vibrational frequency is obtained for the different donor atoms. There is also a discussion of the vibrational modes of H tied to crystal defects such as those introduced by implantation. The relationship of the experimental results to recent theoretical studies is discussed throughout. 

The differences in selection rules between Raman and infrared spectroscopy define the ideal situations for each. Raman spectroscopy performs well on compounds with double or triple bonds, different isomers, sulfur-containing and symmetric species. The Raman spectrum of water is extremely weak so direct measurements of aqueous systems are easy to do. Polar solvents also typically have weak Raman spectra, enabling direct measurement of samples in these solvents. Some rough rules to predict the relative strength of Raman intensity from certain vibrations are [7] ... 

Another explanation for their resonance Raman results could be a change in the zwitterionic nature of the merocyanine isomers in the different solvents which may result in changes in the Raman transition probabilities, or the spectral changes could be due to solvent shifts of the absorption spectrum, resulting in a change in the relative contribution of the different vibrational modes to each resonance Raman spectrum. We note that in the same article, the authors report the transient absorption spectra of the merocyanine forms, which clearly show that the BIPS spectrum in cyclohexane has more discrete vibrational modes than are observed in the polar solvents, which show more spectral broadening. Al-... 

For structure type Ila ligands both the v(8-8) and the totally symmetric v(M-8) vibrations are practically forbidden in the infrared spectrum, but in the Raman spectrum the corresponding bands (intense and strongly polarized) can easily be observed. 

In the Raman spectrum of f-butyllithium-7, only the strongly polarized band at 521 cm shifts significantly upon Li substitution (563 cm ) (Table 2). It was assigned to a totally symmetrical C—Li stretching mode. The peak at 525 cm in the IR spectrum was attributed to an impurity, because it exhibited widely variable intensity in various determinations and disappeared in one spectrum. ... 

The Raman spectra of 2,2 -bipyridine ° and 4,4 -bipyridine - have been studied. The experimental data agree with theoretical calculations. The resonance Raman spectrum of the radical anion of 2,2 -bipyridine has also been investigated. The Raman and IR spectra of 2,2 -bipyridine, using polarized light, have been obtained and assignments have been made. ... 

Thus each band in a Raman spectrum represents the interaction of the incident light with a certain atomic vibrations. Atomic vibrations, in turn, are controlled by the sizes, valences and masses of the atomic species of which the sample is composed, the bond forces between these atoms, and the symmetry of their arrangement in the crystal structure. These factors affect not only the frequencies of atomic vibrations and the observed Raman shifts, respectively, but also the number of observed Raman bands, their relative intensities, their widths and their polarization. Therefore, Raman spectra are highly specific for a certain type of sample and can be used for the identification and structural characterization of unknowns. 

Figure 7.11 Transformation of Raman spectra in amorphous Sbg osSeg 97, subjected to exposure of linearly polarized light curve 1, reference Raman spectrum of amorphous state curves 2-A, after exposure to = 3, 5, and 6kJ/cm, respectively. The inducing intensity was I = 1.25W/cml...

An illustrative example of the influence of symmetry on the number of vibrations is provided by the homologous series of cyclic sulfur allotropes S (n = 6-12). The IR absorptions for these ring systems are weak owing to the low polarity of S-S bonds. However, sulfur is a good Raman scatterer because S-S bonds are readily polarised. The various sulfur allotropes have different symmetries in addition to a different number of sulfur atoms and, consequently, each allotrope exhibits a characteristic Raman spectrum (Figure 3.8). ... 

See lext. XD = X-ray diffraction 1R = infrared spectrum R = Raman spectrum UV = ultraviolet spectrum H-NMR = ]HNMR spectrum C-NMR = 13CNMR spectrum F-NMR =, 9FNMR spectrum MS = mass spectrum PES — photoelectron spectrum E - electric polarization and dielectric loss measurements D = dipole moment measurements TDPAC = time differential perturbed angular correlation measurements GC = gas chromatography TA = thermal analysis M = molecular weight A = electrical conductance. c Isolated as the THF adduct M(dik)Cl3-C4HgO. 

The normal Raman spectrum obtained with 647.1 nm excitation serves as a comparison for the Raman spectra obtained with excitation frequencies of 488.0 and 514.5 nm, which lie within the 5- 5 absorption band. The tremendous enhancement of the i>,(Mo-Mo) alg mode, the high overtone progression in v, the increase in overtone bandwidth with increasing vibrational quantum number, and the increased intensity of the overtones relative to the fundamental as the excitation frequency approaches the electronic absorption maximum are all attributable to the resonance Raman effect. Polarization... 

Fig. 33. (a) Raman spectrum and (b) polarized infrared spectra of PTHF. The solid (or broken) line in (b) represents the spectrum measured with the electric vector perpendicular (or parallel) to the orientation... 

In arriving at a satisfactory analysis of the spectrum we must make use not only of the polarization data, but also of the results of deuteration studies, full [Narita, Ichinohe, and Enomoto (145)] and partial [Folt, Shipman, and Berens (55)], and studies of C—Cl frequencies in small molecules. [Mizushima, Shimanouchi, Nakamura, Hayashi, and Tsuchiya (139) Shimanouchi, Tsuchiya, and Mizushima (196)]. The lack of the Raman spectrum is a definite handicap, but is in part mitigated by the expectation that many of the Raman active fundamentals should be close to the frequencies of infrared active fundamentals. 

Fig. 6.9. A Spontaneous Raman spectrum of d62-DPPC lipids and its decomposition into Lorentzian line profiles. B Normalized multiplex CARS spectra (dots) of a planar-supported bilayer and monolayer formed by d62-DPPC on a glass-water interface for parallel-polarized input beams, together with the fit using the center frequency and line width parameters extracted from the decomposition analysis in (A) (solid line). The spectrum exposure time was 0.64 s. Error bars indicate the shot-noise standard deviation (Copyright American Chemical Society [70])...

Prior to the work of Kazanski et al. there was almost no mention of polarization effects in the bone Raman literature, although the polarized Raman spectrum of dental enamel was reported as early as 1994 [36]. The reason may well be that most Raman spectra of cortical bone have been obtained by... 

Guha and Chase reported that a Raman spectrum could be observed only in experiments that select a component of the polarizability tensor transforming as Ee or Ee [1]. The electronic matrix elements in these polarization geometries are [1]... 

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