The optical rotatory dispersion and circular dichroism of molecules containing interacting residues

We use a semiclassical formalism to derive expressions for the optical rotatory dispersion and circular dichroism associated with a dilute system of molecules represented as freely-rotating, rigid arrays of interacting residues. The relationship of the present approach to DeVoe's classical theory is discussed. Far from resonance, our results become equivalent to the equations of Moffitt, Fitts, and Kirkwood when the separation between adjacent residues is small compared to the wavelength of the light. In the resonance case, a calculation of the frequency-dependent circular dichroism per residue is carried out for a particular geometrical arrangement of the residues. These curves, for arrays both finite and infinite in extent, are compared with those obtained when a certain commonly used approximation to the orientational averaging is introduced. It is shown that this approximation is not always valid.