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One-and two-dimensional 2 Hand 13 C-NMR ͑nuclear magnetic resonance͒ echo spectroscopy and 1 H static field gradient NMR self-diffusion experiments have been used to study the reorientational and translational dynamics of benzene molecules adsorbed on zeolite NaY as a function of loading. Comparison of the data with model calculations establish that the elementary motional process of the guest molecules is consistently identified as a jump process among well defined adsorption sites inside a supercage and/or a jump between nearby supercages. In cases where the zeolite cavities contain high loadings of guest molecules, each molecular jump is accompanied by concomitant relaxation of the local environment. Molecular jump events between adsorption sites correspond to the elementary processes from which long range translational diffusion evolves.

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Self-diffusion coefficients of lithium ions and water protons ͑D Li and D H ͒ in the glass-forming electrolyte LiCl:7H 2 O have been measured by nuclear magnetic resonance spin-echo experiments using ultrahigh static magnetic field gradients up to 184 T m Ϫ1 . The measurements were complemented by measurements of 7 Li and 1 H spin-lattice relaxation times. The data cover the temperature range from 313 K down to 173 K, i.e., 34 K above the glass transition temperature T g ϭ139 K. In this range D Li and D H change over five orders of magnitude. The self-diffusion data exhibit a strong non-Arrhenius temperature dependence which is typical for fragile glass formers. In the supercooled regime the ratio of the self-diffusion coefficients D H /D Li increases gradually with decreasing temperature, reflecting a decoupling of these diffusive modes. These results are discussed in relation to the behavior of the viscosity, electrical conductance and reorientational correlation time of water in this temperature range. It is found that lithium ion diffusion is closely coupled to these other transport processes, while proton diffusion begins to decouple at TϽ1.5 T g . Additionally, an analysis of 1 H and 7 Li magnetic relaxation rates 1/T 1 is given. It is found that the intermolecular modes causing 1 H-1 H dipolar relaxation and 7 Li quadrupolar relaxation also decouple from the viscosity. The results are discussed in the framework of similar phenomena observed with other fragile glasses and, more specifically, of structural changes known to occur in supercooled LiCl:H 2 O systems.

In a recent paper, we have demonstrated a dynamical spatial resolution of field-gradient nuclear magnetic resonance better than 7 nm. With an improved experimental setup we are now able to see motional amplitudes below 3 nm, thus further reducing the smallest observed amplitudes by a factor of two. In addition, we present experiments which show in detail how vibrations and oscillations affect the experiment and lead, in most unfavorable cases, to wrong interpretation of diffusion data. A simple method is applied to detect oscillations and to account for them to a certain degree.