3 " -order Raman spectroscopy polarization tensor

Fig. 1.28c). This preliminary result appears to indicate the FFMD calculated response is sensitive to the intermolecular interaction model chosen and that the node position varies with the model. The corollary to this is that the relative contributions of the anharmonic and nonlinear polarizability terms in the calculation are changing between the two models. As this change in sign along the probe axis is the one discrepancy between experiment and theory for this tensor element it remains an open question as to where the difference originates. Further calculations are in progress with a specific focus on the Dutch Cross tensor element where the experimental results have converged. The primary conclusion that should be drawn, however, is that the overall dynamics of the new simulations is in excellent agreement with previous MD calculations for the all parallel polarization response of CS2. This convergence of both the theory and the experiment is an important milestone in the advancement of fifth-order Raman spectroscopy as a probe of the liquid state.

It is important to note that the two electric fields that lead to a Raman transition can have different polarizations. Information about how the transition probability is affected by these polarizations is contained within the elements of the many-body polarizability tensor. Since all of the Raman spectroscopies considered here involve two Raman transitions, we must consider the effects of four polarizations overall. In time-domain experiments we are thus interested in the symmetry properties of the third-order response function, R (or equivalently in frequency-domain experiments... 

The second rank-order parameter S can be derived from measurements of the macroscopic tensor properties such as birefringence and diamagnetic susceptibility. It varies typically between 0.4 at the clearing temperature to 0.7 at T ni- r= 20K in nematic phase. The fourth rank-order parameter (P ) may play an important role for a subtle analysis of the orientational distribution function and can be determined using polarized Raman spectroscopy. ... 

One important use of SFG vibrational spectroscopy is the orientational analysis of ionic liquids at gas-liquid interfaces. For example, the study of the structural orientation ofionic liquids using common cation types, that is, [BMIM], combined with different anions, gives information on the effects of both cation and anion types [3, 22, 26-28]. Additional surface analytical work includes SFG studies under vacuum conditions for probing the second-order susceptibility tensor that depends on the polar orientation of the molecule and can be correlated to the measured SFG signal intensities. Supporting information is frequently obtained by complementary bulk spectroscopic techniques, such as Raman and Fourier transform infrared (FTIR) analysis, for the analysis of the pure ionic liquids. 

The information provided by the Raman spectrum of an oriented polymer differs from its infrared counterpart because of the fundamentally different processes involved in the generation of the spectra. In the infrared absorption process, as already noted, the absorption intensity is dependent on the angle between the electric vector and the direction of the dipole moment change. The Raman spectrum results from inelastic photon scattering details of which are determined by changes in the polarizability of the chemical bonds involved. Polarizability is a tensor quantity, which results in complications but, in principle, provides additional information. As we have seen, infi ared spectroscopy involves only one beam of polarized radiation, and the fraction of the nufotion absorbed by a molecule depends only on the orientation of the molecule with respect to the polarisation vector of the radiation. However, Raman scattering involves two beams of radiation, those of illumination and collection, and the scattered intensity depends on the orientation of the molecule with respect to the polarisation vectors of both beams, whidi may, of course, be different. This necessitates more detailed measurements in order to obtain the relevant information. 

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