Optical activity of oriented molecules

Circular dichroism and optical rotation by oriented molecules in the electric dipole approximation are studied for molecules of different symmetry groups. It is shown that these effects are not connected with each other by the Kramers-Kronig relation and are irreversible, like the Faraday effect in a magnetic field. The optical rotation by the nematic liquid crystal of p-azoxyanisole, observed earlier by Williams [J. Chem. Phys. 50, 1342 (1969)], can be explained on the basis of this theory. Finally, the optical activity of an ensemble of molecules oriented in some direction and randomly oriented around this direction, is considered.