Effects in Depolarized Light Scattering

By way of introduction let us note that the depolarized spectrum Ivh(co) calculated in Section 7.5 for independent rotors consists of a superposition of Lorentzian bands all centered at zero frequency. In the simplest case of symmetric top rotors the spectrum consists of a single band with a width [q2D + 6 9] which depends only on the translational self-diffusion coefficient D and on the rotational diffusion coefficient 0. This should be compared and contrasted with the depolarized spectrum Ivh(co) of certain pure liquids (e.g., aniline, nitrobenzene, quinoline, hexafluorobenzene) shown schematically in Fig. 12.1.1. The spectrum appears to be split. This entirely novel fea- 

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Photomultipliers are used to measure the intensity of the scattered light. The output is compared to that of a second photocell located in the light trap which measures the intensity of the incident beam. In this way the ratio [J q is measured directly with built-in compensation for any variations in the source. When filters are used for measuring depolarization, their effect on the sensitivity of the photomultiplier and its output must also be considered. Instrument calibration can be accomplished using well-characterized polymer solutions, dispersions of colloidal silica, or opalescent glass as standards. 

Flory has recently summarized the experimental evidence pertaining to local correlation and their effects on chain dimensions (49). There is experimental support for local alignment from optical properties such as stress-optical coefficients in networks (both unswelled and swelled in solvents of varying asymmetry), and from the depolarization of scattered light in the undiluted state and at infinite dilution. The results for polymers however, turn out to be not greatly different from those for asymmetric small molecule liquids. The effect of... 

The depolarization of light by dense systems of spherical atoms or molecules has been known as an experimental fact for a long time. It is, however, discordant with Smoluchowski s and Einstein s celebrated theories of light scattering which were formulated in the early years of this century. These theories consider the effects of fluctuation of density and other thermodynamic variables [371, 144]. 

FP assays are known to be susceptible to artifacts (Turek-Etienne and Small, 2003). In principle, the assays are ratiometric and should normalize for variations in total excitation energy applied as would occur with inner filter effects, and newer generations of red-shifted fluorophores should help to eliminate interference (Vedvik et al., 2004). However, introducing a test compound with fluorescent or absorbent properties at 5 or 10 pM with the typically sub-micromolar concentrations of fluorophores in an FP assay can significantly skew the measurements. For example, if the compounds are insoluble, they can scatter and depolarize light. A concentration-dependent effect on an FP assay could result from an increase in the amount of insoluble compound. 

We have performed optically heterodyne-detected optical Kerr effect measurement for transparent liquids with ultrashort light pulses. In addition, the depolarized low-frequency light scattering measurement has been performed by means of a double monochromator and a high-resolution Sandercock-type tandem Fabry-Perot interferometer. The frequency response functions obtained from the both data have been directly compared. They agree perfectly for a wide frequency range. This result is the first experimental evidence for the equivalence between the time- and frequency-domain measurements. 

This valency angle is no new idea in organic chemistry. The essential fact is that this angle is now obtained directly for the first time by means of vector combination of the moments. Hitherto, however, it has only been possible to carry out these calculations for a few substances. Hence the fact is of importance that (as I shall show by means of one or two examples) the depolarization of scattered light and the Kerr effect enable us to prove the existence of such angles and to calculate their value, even when free rotation, which gives rise to errors in the vectorial combination, is present. 

Theoretical attempts to deal with complexes of more than two atoms (molecules) are scarce. One notable exception is the intercollisional process [303, 304, 306], which models the existing correlations of subsequent collisions. Intercollisional effects are well known in collision-induced absorption, but in OILS not much experimental evidence seems to exist. Three-body spectral moment expressions have been obtained under the assumptions of pairwise interactions [198, 200, 208, 209, 212, 218, 340, 422] see also references in Part II. Multiple scattering will depolarize light and has been considered in several depolarization studies of simple fluids [273, 274, 290, 376]. 

Figure 7. Depolarized small-angle light scattering patterns (under cross-polarIzatIon condition) from perfluorinate carboxylic and sulfuric acid membranes showing the effect of swelling In water and ethanol. Reproduced from Ref. 30. Copyright 1982 American Chemical Society.

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