The One-Dimensional Quantum Rotator H 2 S¯ in Several Alkali Halides

Reorientation motions of molecules in solids can vary from classical thermally activated jumping motions between equivalent orientations to quantum mechanical free rotation. In between stand the tunneling- and phonon activated tunneling-motions1. In the classical regime the reorientation rates are strongly temperature dependent and the motion of the molecule can vary from standing still to average reorientation rates approaching the quantum rotation frequency of the free molecule. A glance at the literature reveals that thermally activated motion is a common occurence.