SPECTRUM OF LIGHT SCATTERED FROM OPTICALLY ANISOTROPIC MACROMOLECULES

Equations have been derived for the spectrum of light scattered from monodisperse, infinitely dilute macromolecular solutions. For rigid molecules it is shown that when the molecules are not very large and/or the scattering is observed at low angles the isotropic part of the scattering spectrum consists of a single Lorentzian line with full-width at half-maximum An proportional to the translational diffusion coefficient D, 1/2=(16ir/X2)D sin 2 (9/2). For asymmetric molecules whose principal axes for polarizability and diffusion coincide, the anisotropic part of the spectrum consists of a weighted sum of two Lorentzians each with half-width dependent on both the translational diffusion coefficient and combinations of components of the rotational diffusion tensor. For molecules with cylindrical symmetry, the anisotropic part of the scattering spectrum becomes proportional to a single Lorentzian with half-width dependent on both the translational diffusion coefficient and the component of the rotational diffusion tensor describing rotation of the long axis of the cylinder. When the spectrum is integrated over all scattered frequencies, the results reduce to the standard scattering expressions. It is emphasized that the rotational effects described here are due to molecular optical anisotropy and should not be confused with rotational effects in optically isotropic molecules resulting from large molecular size as described in previous papers.