Dynamical disorder in glasses studied by H-2 and H-1 NMR

We review H-2 and also some H-1 nuclear magnetic resonance (NMR) results on mobile guest molecules dissolved in organic high and low molecular weight glasses. The guest molecules such as benzene exhibit high symmetry and perform a rotational jump process between equivalent orientations in the solid state. Characteristic two-phase NMR spectra and a pronounced non-exponential H-2 spin-lattice relaxation are observed. The H-1 spin-lattice relaxation is exponential, and shows a non-Arrhenius temperature dependence. All these features can be well described over a large temperature range (10-200 K) by assuming a broad distribution of activation energies and entropies. The distribution of activation energies displays significant differences for the various guest/host systems. We think the approach chosen here can also be applied to describe beta-processes or internal processes in neat glasses.