Molecular Motion of Hydrogen-Bonded CH3CN in
H-MFI: A 1H, 2H, and 13C
Multinuclear NMR Study.
B. H. Suits, J. Sepa, R. J. Gorte, and David White
The dynamics associated with the adsorption complex formed by
CH3CN at Bronsted sites in H-MFI have been
explored using 1H, 2H, and 13C
NMR spectra measured as a function of temperature between
78 and 400 K. A simple NMR line shape theory, based on
rapid, small angle reorientations of the CH3CN
molecular axis with a temperature-dependent amplitude,
has been used to account for the data. An anisotropic
angular motion is observed with a small amplitude at
low temperatures increasing to approximately +/- 35o
from its average position at room temperature. This motion
is primarily constrained to a plane in the zeolite, but a
distribution in amplitudes for different types of sites
is required to fully account for the data. At higher
temperatures, the powder line shapes are completely
motionally narrowed, presumably due to exchange between
physisorbed molecules and those bound to the sites.
J. Phys. Chem B104, 5124-5131 (2000).
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