Application of free rotational models of molecular reorientation to the explanation of high frequency effects in dielectric relaxation

Abstract

Exact solutions obtained by Gross [J. Chem. Phys. 23, 1415 (1955)] and Sack [Proc. Phys. Soc. London, Sect. B 70, 402 (1957)] for the complex polarizability of assemblies of nonelectrically interacting rotators subjected to a variety of collisions and various approximations to that quantity, specifically the Rocard equation are reappraised in view of recent attempts to use a variety of forms of that equation for the interpretation of far infrared resonance absorption spectra. It is shown that for small values of the inertial parameter (heavy damping) the Rocard equation yields a really good approximation for the complex polarizability only for the small collision model considered by Gross and Sack. In the case of large inertial parameter values it is emphasized by means of plots of the complex polarizability that such an approximation always exhibits behavior characteristic of a sharply resonant system, i.e., a pronounced absorption peak well in excess of the Debye peak and a strongly negative real part, while the exact complex polarizability spectrum for the same parameter values merely displays inertia corrected Debye relaxation. Therefore, an explanation of the resonant term other than that based on a Rocard equation with a large inertial parameter must be sought as that equation strictly applies to inertia corrected Debye (heavily damped) relaxation only. The application of the itinerant oscillator model and the three variable Mori theory to the problem is discussed in view of this conclusion.

The extended Debye model analysis of Poley absorption in glass-forming toluene

“…It can be noted that the temperature dependence of m 2 changes abruptly in the vicinity of T = 130 K. This temperature is close to the value of the glass transition temperature of toluene T g = 117 K. It turns out that the position of second resonance mode changes only slightly with decreasing temperature in range of 130-7 K. As it was previously suggested in Ref. [5] the fast dynamics are indeed sensitive to the structural arrest occurring at T g . The appearance of the new resonance process suggests that two different molecular structure on microscopic scale might be present both in supercooled and glassy states of toluene.…”

“…Recent work by Johari identify the Poley absorption with Boson peak which has been revealed by neutron and Raman inelastic scattering studies [4]. Despite enormous experimental and theoretical efforts the nature of this high frequency phenomenon is still hotly debated [4][5][6].…”