Raman scattering optically isotropic molecules

V. Scattering in the Raman Vibrational Bands of Optically Isotropic Molecules... 

The influence of multipolar polarizabilities has been examined subsequently in several optically isotropic molecules such as CH4, CD4, neopentane, CF4, or SF6 [4,7-14,17,18]. In this review, our attention is focused on CF4 for which both Rayleigh [8,13] and Vi Raman [17,18] depolarized and isotropic bands have been studied and published by us. In the Rayleigh studies, we measured the /j (v) and / (v) intensities that are scattered by gaseous CF4 up to 340 cm-1, in... 

V. SCATTERING IN THE RAMAN VIBRATIONAL BANDS OF OPTICALLY ISOTROPIC MOLECULES... 

T. Bancewicz and S. Kielich. Isotropic Raman scattering for non-totally symmetric vibrations of correlated molecules with intrinsic optical anisotropy. J. Chem. Phys., 75 107-109 (1981). 

I = scattered light intensity K = defined by Equation [11] N = number of events NA = numerical aperture R = distance between scattering molecule and observer S = surface area S/N - signal to noise ratio a = half angle of light cone = isotropic Raman invariant aG = isotropic ROA invariant due to the optical activity tensor = anisotropic Raman invariant =j8(G )2 = anisotropic ROA invariant due to the optical activity tensor <5 = f A) = anisotropic ROA invariant due to the quadrupole tensor fiQ = permeability of the vacuum to = angular frequency. 

In Raman spectroscopy the intensity of scattered radiation depends not only on the polarizability and concentration of the analyte molecules, but also on the optical properties of the sample and the adjustment of the instrument. Absolute Raman intensities are not, therefore, inherently a very accurate measure of concentration. These intensities are, of course, useful for quantification under well-defined experimental conditions and for well characterized samples otherwise relative intensities should be used instead. Raman bands of the major component, the solvent, or another component of known concentration can be used as internal standards. For isotropic phases, intensity ratios of Raman bands of the analyte and the reference compound depend linearly on the concentration ratio over a wide concentration range and are, therefore, very well-suited for quantification. Changes of temperature and the refractive index of the sample can, however, influence Raman intensities, and the band positions can be shifted by different solvation at higher concentrations or... 

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