Energy landscapes in disordered systems via studying the dynamics of mobile probes

Abstract

The 2H NMR spin-lattice relaxation and lineshape of the deuterated probe molecules benzene, hexamethyl benzene and adamantane in organic high and low molecular weight organic glasses have been analyzed. The probes are characterized by rotational motion. A temperature range of 13–125 K is covered. Pronounced non-exponential relaxation is observed and described in terms of a convolution of exponential decays with a distribution of correlation times originating from a distribution of activation enthalpies, g( ΔH a, and entropies. A lineshape analysis is presented which also allows for the determination of the distribution of enthalpies. g( ΔH a) is asymmetric with a comparatively sharp cutoff at low enthalpies. Significant differences are found for different guest/host systems which may be looked upon as a fingerprint of a disordered system.