Itinerant oscillator models and resonance absorption in liquids

Following a suggestion by Poley¹ that the observed dispersion region of dipolar origin which lies between the Debye dispersion region and optical frequencies might be due to vibration of a molecule about a temporary equilibrium position, Hill² proposed what is now called an Itinerant Oscillator model. In such a model, it is supposed that a molecule may undergo rotational oscillations about a particular axis, where the instantaneous orientation of this axis is determined by the arrangement of the neighbors of the molecule in question. In addition to the vibrations of the molecule about this axis, the ‘cage’ of neighbors containing the molecule is assumed to undergo rotational Brownian motion.