CONCERTED DIFFUSION OF MOLECULAR CLUSTERS IN A MOLECULAR-SIEVE

We show that attractive interactions between molecules adsorbed in mol ecular sieves play a vital role in the mechanisms and rates of intracr ystalline diffusion. Over a wide temperature range, the single-file di ffusion of CF4, SF6, and CCl4 in AlPO4-5 is dominated by the diffusion of molecular clusters. SF6 and CCl4 clusters diffuse by concerted mec hanisms involving all of the cluster's molecules simultaneously. The a ctivation energies, E-a, for these mechanisms are strongly size depend ent and are lower than E-a for monomer diffusion. [S0031-9007(97)04486 -4].