Probing cooperative jump-diffusion in zeolites: Neutron spin-echo measurements and molecular dynamics simulations of benzene in NaX

We report neutron spin-echo measurements of transport diffusivities for perdeuterated benzene in NaX zeolite. Corrected diffusivities from these neutron measurements were obtained for comparison with recently reported molecular dynamics simulations. Experimental diffusivities were measured with benzene loadings of 1, 2, 3 and 4.5 molecules per NaX cage, and at 300, 350 and 400 K. Both corrected and transport diffusivities increase from 1 to 3 molecules per cage, then decrease sharply to 4.5 molecules per cage. The comparison between experiment and simulation shows remarkably good agreement ill both the loading dependence and in the overall magnitudes of the corrected diffusivities, with values mostly in the range 10(-12)-10(-11) m(2) s(-1). (c) 2005 Elsevier Inc. All rights reserved.