EVIDENCE FOR SINGLE FILE DIFFUSION OF ETHANE IN THE MOLECULAR-SIEVE ALPO4-5

We measure the diffusion of ethane in very large crystals of the molec ular sieve AIPO(4)-5 (provided by M. Davis) using pulsed field gradien t (PFG) NMR. Thanks to the large crystal size and the long longitudina l relaxation time, the mean square displacement could be monitored ove r times that arranged over an order of magnitude. The mean square disp lacement was proportional to the square root of time, providing strong evidence that the ethane molecules are moving in a single file, i.e. they are unable to pass each other. This is the first direct experimen tal evidence for single-file diffusive motion - a phenomenon that is p robably widely prevalent in both industrial catalytic and biological s ystems.