Depolarized Raman scattering profile

There is an indirect way to detect intermittent local collective motions. In the case of depolarized Raman scattering, the depolarization ratio is sensitive to low-frequency fluctuations in water. Depolarization is the scattering of the polarization of the electric field of light in a direction perpendicular to the original direction of polarization. Each fluctuating state has a distinct depolarization ratio. The intermittent character of the dynamics is known to appear as a so-called 1,/ frequency (f) dependence in a power spectrum. The power spectmm is obtained by Fourier transforming a time correlation function. 

in ordinary cases, the power spectrum exhibits a dependence on frequency that is stronger than f. That is, the intensity in the intermediate frequency range falls off faster than the inverse of frequency. However, the dependence can become weaker if the decay of correlation becomes slower than exponential due to repeated revisits to the same state by the system. The existence of a f spectmm is an indicator of the existence of intermittent relaxation dynamics. For example, a Fourier transform of a series of intermittent pulses, the simplest example of it, is easily shown to be a type of 1// spectmm. 

3 cm and the in-between transition region [5]. Such a baseline profile of Raman scattering of liquid water is quite different from those of unassociated liquids, which yield Lorentzian dependence in the low-frequency region. The power law part indeed corresponds to the structural rearrangement dynamics of the HB network structure. 

Detailed analysis shows that the power law part obtained from IS analysis yields a f frequency dependence with an exponent ofa = 1.3, which is in good agreement with experimental results. The signals of inter- and intramolecular vibrational motions, discussed in the previous section, are seen as two shoulders at -200 and 500 cm superimposed on this power law profile. 

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