MOLECULAR-DYNAMICS OF BENZENE IN ZEOLITE NAY STUDIED BY 2D DEUTERON NMR

H-2 NMR exchange experiments were performed to study the reorientation al dynamics of benzene molecules at full occupancy of the large voids (supercages) of the synthetic faujasite-type zeolite NaY. The 2D spect ra obtained, as well as the results of the 2D echo time-domain measure ments, are compared with model calculations utilizing an appropriate p arametrization of the data. Evidence is obtained for tetrahedral-like jumps of the benzene molecules between adjacent adsorption sites and c oncomitant small-angle reorientations. These small-angle reorientation s of amplitude 5-7 degrees are interpreted to be due to instantaneous relaxations after the hopping of neighbouring molecules in the superca ges. Over the temperature range investigated, the small-angle jumps ar e about two times faster than the inter-site jumps which exhibit an ac tivation energy of 40 +/- 2 kJ/mol. (C) 1998 Elsevier Science B.V. All rights reserved.