The motions, diffusion coefficients and activation energies of C6D6 in NaEMT (E-a = 18.0 kJ/mol) and KL (E-a = 7.3 kJ/mol) zeolites have been examined by H-2 NMR technique. Two types of movement Of C6D6 exist. Below 183 K for KL and 263 K for NaEMT, benzene molecule adsorbed on cation rapidly rotates around its sixfold symmetry axis. Above these temperatures, aromatics are in isotropic motion and jump from one adsorption site to another. (C) 2004 Elsevier B.V. All rights reserved.