THE USE OF DIFFERENTIAL TRANSVERSE RELAXATION TO DETECT MOBILE SPECIES IN SOLIDS

Delayed acquisition of the proton NMR in selected organic molecular so lids (L-alanine, durene, ethyl fumarate, and p-hydroxybenzoic acid) is shown to allow the observation of mobile species in the presence of r elatively 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 iso tropically on the time scale of the inverse of the homonuclear dipolar splitting. In the case of ethyl fumarate and alanine, there exist pop ulations with differing values of T-1 and T-1p. This indicates the co- existence of relatively rigid and relatively mobile molecules in the s ame sample. The intensities under delayed acquisition cannot always be trusted to yield quantitative information. Comparison of spectra take n under delayed acquisition and under the CRAMPS (B.C. Gerstein, R.G. Pembleton, R.C. Wilson and L.M. Ryan, J. Chem. Phys., 66 (1977) 361) t echnique is made.