H. Long

Cross polarization from laser-polarized solid xenon to 13CO2 by low-field thermal mixing

Abstract The first observation of nuclear spin polarization enhancement in a molecular species by coupling to laser-polarized xenon is reported. The spins of 13 CO 2 were cooled by inclusion into the xenon solid followed by thermal mixing in magnetic fields comparable to the heteronuclear dipolar interactions. High-field NMR detection yielded enhancement factors of up to 200. Moreover, a change in the sense of the helicity of the optical pumping light results in a sign reversal of the spin temperature and hence an inversion of the 13 C NMR signal.

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

Abstract 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.

NMR of optically pumped xenon thin films

NMR of 129Xe has been observed in thin films of xenon frozen onto the surfaces of glass sample cells with various geometries. The 129Xe polarization was enhanced by optical pumping, and the xenon was then transferred to a high-field pulsed NMR spectrometer allowing the observation of strong signals from xenon films of approximately 1 μm thickness. The line shape depends on the film geometry because of the bulk diamagnetic susceptibility χD of solid xenon. The spectral line shape and resonance frequency also depend on temperature.

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.