NMR-STUDY OF XENON DYNAMICS AND ENERGETICS IN NA-A ZEOLITE

For xenon atoms adsorbed in Na-A zeolite, electronic interactions cause shifts in NMR frequencies, resulting in a spectrum with discrete peaks from xenon atoms in cages with different xenon occupancies. Using two-dimensional exchange NMR, it is possible to determine the microscopic rates of intercage motion and to relate them to the adsorption and activation energies of the xenon atoms. The dependence of the adsorption energies on xenon cage occupancy reflects the importance of the intercage interactions and is directly related to the cage occupancy distribution. Variable temperature measurements yield an activation energy of about 60 kJ/mol for the transfer of a xenon from one cage to another

Determination of molecular orientational order in cold- stretched poly (p-phenylene vinylene) thin films by DECODER C- 13 NMR

The properties of polyp-phenylene vinylene) (PPV) films depend on the degree of orientational order present in the films. Recently, Dermaut et al. reported a novel cold-stretching technique (Macromolecules 33, 5634-5637 (2000)) in which chain alignment can be introduced into PPV precursor films by uniaxially stretching them prior to the thermal elimination reaction that forms PPV. The two-dimensional direction exchange with correlation for orientation-distribution evaluation and reconstruction (DECODER) C-13 NMR technique was applied to both unstretched PPV films and PPV films that were uniaxially cold stretched to a draw ratio lambda = l/l(0) = 5. The unstretched films were found to be moderately ordered, comprised of a component present at 80% with a Gaussian distribution of 60degrees fwhm, while the remaining 20% is isotropically distributed. A distribution of 9 3 fwhm was measured by NMR in good agreement with IR dichroism measurements for the uniaxially cold-stretched films, establishing that a high degree of orientational order can be introduced by cold stretching PPV films. (C) 2002 Elsevier Science (USA)

Nanoscale insight into intermolecular interactions in organic photovoltaic blends using solid state NMR spectroscopy

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Two-Dimensional 29Xe Exchange NMR Measurements of Xenon Dynamics in Na-A Zeolite

Two-dimensional (2D) exchange NMR is a powerful tool for measuring the dynamics and energetics of adsorbed xenon atoms undergoing slow exchange between the alpha-cages of Na-A zeolite. In this proceedings, we present recently published results, as well as additional discussion and data obtained, using 2D Xe-129 NMR to determine rate coefficients for intercage xenon hopping and to correlate them with adsorption and activation energies. Variable-temperature experiments establish the activation energy for hopping between alpha-cages to be 60+/-10 kJ/mol. The dependence of these kinetic and thermodynamic quantities on xenon occupancy of the alpha-cages reflects the importance of intracage interactions on the behavior of the adsorbed guest molecules

NMR Study of Xenon Dynamics and Energetics in Na-A Zeolite

For xenon atoms adsorbed in Na—A zeolite, electronic interactions cause shifts in NMR frequencies, resulting in a spectrum with discrete peaks from xenon atoms in cages with different xenon occupancies. Using two-dimensional exchange NMR, it is possible to determine the microscopic rates of intercage motion and to relate them to the adsorption and activation energies of the xenon atoms. The dependence of the adsorption energies on xenon cage occupancy reflects the importance of the intracage interactions and is directly related to the cage occupancy distribution. Variable temperature measurements yield an activation energy of about 60 kJ/mol for the transfer of a xenon from one cage to another

Two-Dimensional Xenon-129 Exchange NMR Measurements of Xenon Dynamics in Na-A Zeolite

Two-dimensional(2D) exchange NMR is a powerful tool for measuring the dynamics and energetics of adsorbed xenon atoms undergoing slow exchange between the α-cages of Na-A zeolite. In this proceedings, we resent recently published results, as well as additional discussion and data obtained, using 2D129Xe NMR to determine rate coefficients for intercage xenon hopping and to correlate them with adsorption and activation energies. Variabletemperature experiments establish the activation energy for hopping between α-cages to be 60±10 kJ/mol. The dependence of these kinetic and thermodynamic quantities on xenon occupancy of the α-cages reflects the importance of intracage interactions on the behavior of the adsorbed guest molecules