The analytic theory of dielectric relaxation is presented for an ensem
ble of dipoles, rotating in a plane under the influence of a cosine po
tential, formed by a constant intermolecular or external field E(0). T
he theory is applied to the calculation of the far IR spectrum of ice
I in the frequency-band near 200 cm(-1) and to the spectrum of a macro
molecule, performing, rotational diffusion under the influence of a co
nservative field E(0) = 10(6) V/cm.