Superconducting magnet fringe field NMR diffusometry is applied to an adsorbate–molecular sieve system in order to obtain intracrystalline self-diffusion of adsorbed molecules. Effects of self-diffusion, exchange, relaxation, and dipolar correlation are discussed. The proper equations for one- and two-dimensional anomalous self-diffusion with and without macroscopic order are derived. The method is applied to investigate methane self-diffusion in the molecular sieve silicoaluminophosphate, type 11 (SAPO-11). It is concluded that the nature of the methane displacements in the sieve channels is single-file self-diffusion.

• Received 18 December 1997

DOI:https://doi.org/10.1103/PhysRevE.57.6844