@article {421, title = {Cross-polarization from quadrupolar nuclei to silicon using low-radio-frequency amplitudes during magic-angle spinning}, journal = {Journal of Physical Chemistry B}, volume = {101}, year = {1997}, note = {J Phys Chem BWu630Times Cited:51Cited References Count:50}, month = {Apr 17}, pages = {3240-3249}, abstract = {

The dynamics of cross-polarization from the central transition of a quadrupolar nucleus (Al-27 or Na-23) to a spin-1/2 nucleus (Si-29) during magic-angle spinning and using low-radio-frequency Geld strengths are analyzed for the mineral low albite. Under these conditions additional complications in the spin-lock behavior of the quadrupolar nucleus and in the cross-polarization process were found experimentally and are examined in detail. A step-by-step procedure for optimizing cross-polarization from the central transition of a quadrupolar nucleus to a spin-1/2 nucleus is described. Significant enhancement of Si-29 NMR sensitivity and several applications are demonstrated.

}, keywords = {locking}, isbn = {1089-5647}, doi = {Doi 10.1021/Jp9623711}, url = {://WOS:A1997WU63000031}, author = {DePaul, S. M. and Ernst, M. and Shore, J. S. and Stebbins, J. F. and Pines, A.} } @article {422, title = {Determination of quadrupolar and chemical shielding tensors using solid-state two-dimensional NMR spectroscopy}, journal = {Journal of Chemical Physics}, volume = {105}, year = {1996}, note = {J Chem PhysVv625Times Cited:18Cited References Count:40}, month = {Dec 1}, pages = {9412-9420}, abstract = {

The quadrupolar and chemical shift tensors, as well as the relative orientation of the two principle axis systems, are accurately determined using a two-dimensional nuclear magnetic resonance technique. Good agreement between experimental and simulated two-dimensional spectra is obtained for a series of rubidium and sodium compounds at multiple magnetic field strengths. Extension of this technique to correlate the quadrupolar and dipolar interactions, as well as the incorporation of a purely isotropic dimension resulting in a three-dimensional experiment is also discussed. (C) 1996 American Institute of Physics.

}, keywords = {line-shapes}, isbn = {0021-9606}, doi = {Doi 10.1063/1.472776}, url = {://WOS:A1996VV62500003}, author = {Shore, J. S. and Wang, S. H. and Taylor, R. E. and Bell, A. T. and Pines, A.} } @article {462, title = {Xe-129 Nmr-Study of Tio2 (Anatase)-Supported V2o5 Catalysts}, journal = {Journal of Physical Chemistry}, volume = {98}, year = {1994}, note = {J Phys Chem-UsPk740Times Cited:19Cited References Count:61}, month = {Oct 6}, pages = {10173-10179}, abstract = {

TiO2 (anatase), V2O5, and V2O5/TiO2 (anatase) catalysts with 1.3\%, 3.0\%, and 9.8\% weight loadings of V2O5 have been studied using temperature-dependent xenon-129 NMR spectroscopy. The intrinsic chemical shift values due to the interaction of xenon with the surface are 109 +/- 3 ppm for TiO2 (anatase) and 93 +/- 5 ppm for V2O5. The V2O5/TiO2 catalysts provide strong adsorption sites for xenon which cause an initial decrease of the chemical shift values at low xenon loadings. Additionally, the spectra of pure V2O5 reveal two distinct environments for the xenon atoms, consistent with the hysteresis of the isotherm and the existence of pores. Two-dimensional exchange spectroscopy was used to measure the rates and activation energy of xenon moving between these two environments.

}, keywords = {nay zeolite}, isbn = {0022-3654}, doi = {Doi 10.1021/J100091a037}, url = {://WOS:A1994PK74000037}, author = {Kritzenberger, J. and Gaede, H. C. and Shore, J. S. and Pines, A. and Bell, A. T.} }