A model for the frequency dependence of the polarizability of a polar molecule

The variation with frequency of the electric polarizability of a harmonically bound, plane rigid rotator, in the form of a flat disk carrying a permanent electric dipole, and subjected to random torques arising from collisions of the Brownian motion type, is calculated. The calculation is effected by means of the Langevin equation and linear response theory and full account is taken of inertial effects throughout. The results are used to represent the frequency dependence of the polarizability of a polar molecule possessing a permanent dipole moment only; the harmonic restoring torque is included in order to determine the effect of a mechanical potential, created by the neighbours of a polar molecule, on its polarizability.