Inertial effects in discrete sites model of rotational freedom. Autocorrelation function and dipolar absorption

Taking into account the finite character of the molecular moment of inertia, a model is presented for the angular motion of molecules submitted to thermal collisions in a multi-well potential. A correlation function is calculated, which has the following spectral consequences: an absorption due to the libration of the molecules in the wells is superimposed on a Debye-Kauzmann-type absorption. and. contrary to the Debye behavior. the transparency of the substance is recovered at higher frequencies. These properties agree with recent experimental data in the submillimeter region.