Understanding intermolecular NMR chemical shifts. Application to competitive adsorption in zeolites
- Univ. of Illinois, Chicago, IL (United States)
The NMR chemical shift is extremely sensitive to intermolecular effects. We show that the results of {sup 129}Xe NMR studies of Xe in zeolite A provide information about the zeolite environment, the nature of the averaging for n Xe atoms within the same cavity, as well as the distribution among the cavities. The {sup 129}Xe nucleus reports on the changes in the structure of the zeolite cage, cation-induced differences between cages, average number of coadsorbed molecules in a cage with n Xe atoms, and even the distribution and chemical shifts of mixed clusters such as Xe{sub n}Kr. The shielding function describing the intermolecular effects on the rare gas atom by fragments of the zeolite frame work with various cations (Na{sup +}, K{sup +}, Ca{sup 2+}) has been obtained by ab initio calculations. The assumption of pairwise-additive shielding contributions permits computation of average chemical shifts in a Grand Canonical Monte Carlo simulation which can be compared directly with experiment, for Xe{sub n} as a function of temperature, for Xe{sub n}Kr clusters, and for Xe{sub n} observed in Xe-Ar mixtures in competitive adsorption, n =1-8.
- OSTI ID:
- 370828
- Report Number(s):
- CONF-960376--
- Country of Publication:
- United States
- Language:
- English
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