Raman Optical Activity of Biological Molecules - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 151

Fig. 7.1. Two equivalent ROA experiments involving Stokes vibrational Raman
scattering at angular frequency ω − ω v in incident light of angular frequency ω far
from resonance. a The ICP ROA experiment measures I R

− I L ,where I R and I L
are the scattered intensities (shown here as unpolarized) in right- and left-circularly
polarized incident light, respectively. b The SCP ROA experiment measures I R − I L ,
where I R and I L are the intensities of the right- and left-circularly polarized com-
ponents, respectively, of the scattered light using incident light of fixed polarization
(shown here as unpolarized)

pharmaceutical compounds to chiral reagents and novel chiral materials, are
also suitable for ROA studies, for such purposes as determination of absolute
stereochemistry or enantiomeric purity, but these will not be surveyed here.
For reviews of such applications of ROA we direct the reader to a number of
excellent earlier reviews and primary references [6-11].

7.2 Theory

7.2.1 ROA Observables

In 1969, Atkins and Barron discovered the fundamental scattering mechanism
responsible for ROA in which interference between the light waves scattered
via the molecular polarizability and optical activity tensors of a molecule
yields a dependence of the scattered intensity on the degree of circular polar-
ization of the incident light and to a circular component in the scattered light
[1]. A more definitive version of the theory was presented 2 years later by Bar-
ron and Buckingham [12] which introduced as an appropriate experimental
observable the dimensionless circular intensity difference (CID), defined as
Δ= I R I L / I R + I L − (7.1)