A quantum statistical mechanics model of a three dimensional linear   rigid rotator in a bath of oscillators: IV - steady state dielectric   properties induced by a. c. and d. c. field coupling
  The long time effect of a radio frequency (rf) a.c. field superimposed on a d.c. field on the electrical susceptibility and the Kerr optical functions of polarisable fluids in inert solvent is analysed. The results obtained for the classical Brownian limit, valid for dense solvent media, well reproduce classical results published in the literature with excellent precisions in inertia, density and temperature dependences. The low density limit yields absorption-dispersion lines whose widths and shifts are density, inertia and temperature dependent. While the low density and/or large inertia susceptibility is explicitly written out as a continued fraction got by solving an infinite hierarchy of differential coupled equations, that of the Kerr effect is given in the form of successive convergents of the solutions of an infinite hierarchy of differential difference triplets. The polarisation/a.c. field phase difference is analysed. The effects of the constant field strength and the a.c. field frequency on the Kerr function are explored. In this paper, which will be named paper IV, the derivation of some quoted equations will intensionally be left out as they exist in paper III (J. Phys. A, 30:6347, 1997) of which this work is its logical continuation. 
J. T. Titantah and M. N. Hounkonnou