SINGLE-FILE DIFFUSION OBSERVATION

Molecular diffusion in zeolites of unidimensional channel structure is studied by pulsed field gradient NMR. In contrast to ordinary diffusi on, the mean square displacement increases in proportion with the squa re root of the observation time. This behavior is explained by assumin g that the molecules are unable to pass each other (''single-file'' di ffusion). The diffusivity of an isolated molecule estimated from the m obility in the single-file system is 2 orders of magnitude larger than the largest intracrystalline diffusivities in zeolites so far observe d. The finding is supported by both the observed concentration depende nce and molecular dynamics simulations.