NMR Studies of Quantum Rotors Confined in Zeolite
We report the results of NMR studies of methane trapped in zeolite at low temperatures. Samples were prepared to contain 1.0±0.2 molecules per α-sodalite cage of zeolite-13X. The NMR spin-spin and spin-lattice relaxation times were measured for 4<T<95 K to determine the rotational dynamics of the molecules and the dependence on the concentration of the A, T and E-molecular species. The results are discussed relative to recent Monte Carlo calculations that show that the molecules are localized but free to tumble in the large α-cages at low temperatures. At higher temperatures there is an effective melting of the translational degrees of freedom for the lattice formed by the centers of the supercages. A sharp definitive jump in the NMR spin-spin relaxation is seen at this “melting” transition.
KeywordsQuantum rotors Magnetic resonance Methane Zeolite
PACS31.70.Ks 66.30.Ma 76.60.-k
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