CAGE-TO-CAGE MIGRATION RATES OF XE ATOMS IN ZEOLITE NAA FROM MAGNETIZATION-TRANSFER EXPERIMENTS AND SIMULATIONS

Xenon trapped in the alpha cages of zeolite NaA exhibits distinct NMR signals for clusters Xe-1, Xe-2, Xe-3,..., up to Xe-8. Using multisite magnetization transfer experiments, we have measured the rate constants k(mn) for the elementary processes that are involved in the cage-to-cage transfer of Xe atoms in the zeolite NaA, that is, for a single Xe atom leaving a cage containing Xe, to appear in a neighboring cage containing Xe-m-1, thereby forming Xe-m. In a random walk simulation, these rate constants reproduce over a hundred magnetization decay/recovery curves that we have measured in four samples of Xe in zeolite NaA at room temperature, in selective inversion, and complementary experiments for all the significantly populated clusters. The simulations also lead to the correct experimental equilibrium distributions, that is, the fractions of the alpha cages containing Xe-1,Xe-2,...,Xe-8.