Raman scattering circular differential

It is also interesting to note that circular differential Raman scattering, circular intensity differential (CID), has been reported for a series of optically active sulfoxides and a correlation found between the absolute configuration at sulfur and the differential scattering (240). Thus, all (/ )-alkyl p-tolyl sulfoxides investigated show a common (positive) CID feature in the 300 to 400 cm" region. 

As described above, there are two forms of vibrational optical activity, one derived from infrared absorption and the other from Raman scattering. Both forms involve the differential response of a molecule to the modulation of polarization of the interacting radiation between right and left circularly polarized states. In the case of infrared absorption, VCD is defined as die differential absorbance for left minus that for right circularly polarized infrared radiation. This is expressed by the relation ... 

Systems involving two centers with fixed mutual orientation have been shown to exhibit other circular differential effects with a similar linear dependence on the separation. Examples include circular differential Rayleigh and Raman scattering (Barron and Buckingham 1974 Andrews and Thirunamachandran 1978), optical rotation (Barron 1975) and two-photon circular dichroism in which only one chromophore is excited (Andrews 1976). As might be expected, on performing subsequent rotational averages for the case where A and B are randomly oriented, the odd-j terms in the rate equations vanish and consequently no circular dichroism is displayed. 

We have been discussing electronic transitions and ultraviolet or visible circular dichroism. However an optically active molecule will also have infrared CD due to its vibrational transitions. The measurement of infrared CD is very difficult, but some data exist [29]. Another related measurement is the Raman circular intensity differential [30]. It is the difference in Raman scattered intensity when right and left circularly polarized light is... 

Raman Optical Activity The Raman optical activity (ROA) effect is the differential scattering of left- or right-circularly polarized light by a chiral substrate where chirality is studied through Raman spectroscopy. 

Hug and Surbeck 35) have proposed the use of Ada. = daL — daR, the difference of the Raman differential scattering cross sections in left and right circularly polarized incident light. This is the Raman equivalent of the circular dichroism Ae = el — eR, where s is the decadic molar extinction coefficient and, unlike the measured (but not the theoretical) IR — IL which depends on both sample and instrumental factors, is solely a molecular parameter. They introduced a chirality number q defined by... 

Raman optical activity (ROA) provides a means for studying vibrational transitions via differential scattering of right- and left-circular polarized light ... 

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