The use of differential transverse relaxation to detect mobile species in solids.

Delayed acquisition of the proton NMR in selected organic molecular solids (L-alanine, durene, ethyl fumarate, and p-hydroxybenzoic acid) is shown to allow the observation of mobile species in the presence of relatively rigid bulk molecules. The mobility is found to be thermally activated. The combination of the thermally activated motion and magic-angle spinning leads to a fraction of these species moving nearly isotropically on the time scale of the inverse of the homonuclear dipolar splitting.