Frequency controversial interpretations

The C—S and S—S stretch vibrations of disulfides (Edsall et al., 1950) can be observed in the Raman spectra of proteins, but their interpretation is still somewhat controversial (see, for example, Klis and Siemion, 1978 Spiro and Gaber, 1977). Using series of model compounds, Van Wart et al. (1973) have related S—S stretch frequency to the xs (C/3—S—S—Cfi ) dihedral angle, while Sugeta et al. (1972, 1973) have related the S—S frequency to the x (Car—Cj8—S—S) di-... 

Hydantoins show two bands in the carbonyl region at about 1720 and 1780 cm-1. However, their interpretation has been the subject of controversy. The low-frequency band has been attributed both to the C-4168 and the C-2 carbonyl group.169 Infrared and Raman spectra have also been interpreted in terms of carbonyl coupling similar to that found in imides.170 Other studies have confirmed this coupling.171... 

The topic of neutral soliton dynamics has been controversial for many years. The reasons have been due to a lack of definite data and a lot of different interpretations from a variety of bases for many experimental data. In this review, we tried to explain most of the important experimental results in terms of a diffuse/trap model based on observations of the ESR linewidth as functions of temperature and frequency. Anomalous broadening observed only in (CH) but not in (CD), at frequencies lower than 6 MHz was explained in a clear-cut way by this model, giving a consistent value of the maximum spin density of the neutral soliton, 0.15-0.17 in comparison with 0.17 determined by the ENDOR technique. These successes represented in the finally obtained diffusion rates which are found to be consistent between NMR and ESR seem to settle the controversy. 

Besides pcs, other light scattering techniques including Brillouin scattering and Fabry-Perot interferometry described in previous sections have been applied to probe the dynamics of polymers at higher frequencies than the more conventional techniques. Interpretations of the results from these techniques are still subjects of controversy and are not discussed here. 

A further molecular process takes place in the THz region. This represents excess contribution to the Debye vibrational density of states (VDOS) and is called Boson peak. Figure 10 gives the VDOS g(co) of PMPS normalized to the Debye density of states (g(co) co ) as measured by incoherent inelastic neutron scattering. A peak is visible at low frequencies. The inset gives the same for poly(dimethyl siloxane) (PDMS). Although the relationship of the Boson peak to fluctuations of elastic constants was discussed, its molecular interpretation is still controversial. 

EIS involves a significant body of research that has been the subject of many controversies. Impedance analysis is based on detection and interpretation of the meaning of processes that occur in response to external voltage perturbation applied at some predetermined AC frequencies. As a response to this external perturbation, the current response indicative of the physical/me-chanical structure and chemical composition of the analyzed system or sample is recorded. 

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