Configuration and interstitial relaxation processes

Abstract

A theory of orientational and interstitial relaxation processes is presented in which the phenomena are characterized as transitions between nonstationary zeroth order configurations. A number of different mechanisms are separated according to the relative timescales of the libron (interstitial) motion and relaxation and the phonon motions. These mechanisms lead to differing temperature dependences that should be amenable to experimental verification. The full (many) phonon participation is included and gives a polaronlike character to the relaxing libron (interstitial). The present theory of activated rate processes departs from the conventional transition state theory. The concept of the activation energy barrier to relaxation is seen to originate from an ensemble average of nuclear tunneling rates from the individual librational levels.