@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 {406, title = {Multiple-quantum magic-angle spinning and dynamic-angle spinning NMR spectroscopy of quadrupolar nuclei}, journal = {Solid State Nuclear Magnetic Resonance}, volume = {8}, year = {1997}, note = {Solid State Nucl MagWy629Times Cited:60Cited References Count:40}, month = {Mar}, pages = {1-16}, abstract = {

Several aspects of the Multiple-Quantum Magic-Angle Spinning (MQMAS) technique (L, Frydman and J,S, Harwood, J, Am, Chem, Sec., 117 (1995) 5367) are compared with Dynamic-Angle Spinning (DAS), Examples of MQMAS spectra are shown for I = 3/2 nuclei with C-Q up to 3.6 MHz, and for: Al-27 (I = 5/2) with C-Q up to 10 MHz. The MQMAS linewidth is largely independent of the magnitude of the homonuclear dipolar interaction, while the spinning sideband manifold is similar to that observed in DAS experiments, MQMAS is technically simple and routinely useful for studying nuclei with short spin-lattice relaxation times, but care must be taken in its use for quantitative studies as the excitation of the triple-quantum coherence is not uniform, In this regard, MQMAS is most useful for samples with small quadrupolar coupling constants, In the specific case of O-17, DAS would give spectra with excellent resolution in comparison to MQMAS, The different advantages of DAS and MQMAS make them useful complementary techniques in many cases,Two additional methods are also presented for extracting the chemical shift anisotropy (CSA) directly for quadrupolar nuclei using the multiple-quantum scheme, (C) 1997 Elsevier Science B,V.

}, keywords = {rb-87}, isbn = {0926-2040}, doi = {Doi 10.1016/S0926-2040(96)01277-5}, url = {://WOS:A1997WY62900001}, author = {Wang, S. H. and Xu, Z. and Baltisberger, J. H. and Bull, L. M. and Stebbins, J. F. and Pines, A.} } @article {435, title = {Triple-quantum two-dimensional Al-27 magic-angle spinning nuclear magnetic resonance spectroscopic study of aluminosilicate and aluminate crystals and glasses}, journal = {Journal of the American Chemical Society}, volume = {118}, year = {1996}, note = {J Am Chem SocVa026Times Cited:139Cited References Count:31}, month = {Jul 31}, pages = {7209-7214}, abstract = {

A new two-dimensional magic-angle spinning NMR experiment(1,2) using multiple-quantum coherences of half-integer quadrupolar nuclei was used to study Al-27 sites in crystalline samples of leucite (KAlSi2O6), anorthite (CaAl2Si2O8), and kyanite (Al2SiO5), as well as CaAl2Si2O8 glass and a magnesium aluminoborate glass. In the crystals, multiple sites are partially resolved and new results for isotropic chemical shifts and quadrupolar parameters are derived, using data collected at a single magnetic field. Data for both leucite and anorthite are consistent with previous results that correlate chemical shifts with mean intertetrahedral bond angle. Signal can be obtained from sites with quadrupolar coupling constants as large as 9 MHz, but intensities are reduced. In the aluminoborate glass, peaks for sites with different Al coordination numbers are well separated. The lack of such features in CaAl2Si2O8 glass rules out the presence of significant quantities of AlO5 and AlO6 groups.

}, keywords = {anorthite}, isbn = {0002-7863}, doi = {Doi 10.1021/Ja9606586}, url = {://WOS:A1996VA02600027}, author = {Baltisberger, J. H. and Xu, Z. and Stebbins, J. F. and Wang, S. H. and Pines, A.} } @article {452, title = {Solid-State O-17 Magic-Angle and Dynamic-Angle Spinning Nmr-Study of the Sio2 Polymorph Coesite}, journal = {Journal of Physical Chemistry}, volume = {99}, year = {1995}, note = {J Phys Chem-UsRn706Times Cited:95Cited References Count:41}, month = {Aug 10}, pages = {12341-12348}, abstract = {

Five distinctly resolved O-17 solid-state NMR resonances in room temperature coesite, an SiO2 polymorph, have been observed and assigned using dynamic-angle spinning (DAS) at 11.7 T along with magic-angle spinning (MAS) spectra at 9.4 and 11.7 T. The O-17 quadrupolar parameters for each of the five oxygen environments in coesite are correlated with the Si-O-Si bridging bond angles determined by diffraction experiments. The sign of e(2)qQ/h along with the orientation of the electric field gradient for oxygen in the Si-O-Si linkage were determined from a Townes-Dailey analysis of the data.

}, keywords = {oxygen}, isbn = {0022-3654}, doi = {Doi 10.1021/J100032a045}, url = {://WOS:A1995RN70600045}, author = {Grandinetti, P. J. and Baltisberger, J. H. and Farnan, I. and Stebbins, J. F. and Werner, U. and Pines, A.} } @article {498, title = {Quantification of the Disorder in Network-Modified Silicate-Glasses}, journal = {Nature}, volume = {358}, year = {1992}, note = {NatureJb341Times Cited:169Cited References Count:32}, month = {Jul 2}, pages = {31-35}, abstract = {

Local order in silicate glasses has been observed by many experimental techniques to be similar to that in crystalline materials. Details of the intermediate-range order are more elusive, but essential for understanding the lack of long-range symmetry in glasses and the effect of composition on glass structure. Two-dimensional O-17 dynamic-angle-spinning nuclear magnetic resonance experiments reveal intermediate-range order in the distribution of inter-tetrahedral (Si-O-Si) bond angles and a high degree of order in the disposition of oxygen atoms around the network-modifying cations.

}, keywords = {time}, isbn = {0028-0836}, doi = {Doi 10.1038/358031a0}, url = {://WOS:A1992JB34100043}, author = {Farnan, I. and Grandinetti, P. J. and Baltisberger, J. H. and Stebbins, J. F. and Werner, U. and Eastman, M. A. and Pines, A.} } @article {568, title = {Diffusive Motion in Alkali Silicate Melts - an Nmr-Study at High-Temperature}, journal = {Geochimica Et Cosmochimica Acta}, volume = {52}, year = {1988}, note = {Geochim Cosmochim AcM3100Times Cited:79Cited References Count:67}, month = {Feb}, pages = {527-538}, isbn = {0016-7037}, doi = {Doi 10.1016/0016-7037(88)90108-1}, url = {://WOS:A1988M310000028}, author = {Liu, S. B. and Stebbins, J. F. and Schneider, E. and Pines, A.} } @article {567, title = {A Si-29 Nuclear Magnetic-Resonance Study of Silicon-Aluminum Ordering in Leucite and Analcite}, journal = {Physics and Chemistry of Minerals}, volume = {15}, year = {1988}, note = {Phys Chem MinerM6832Times Cited:44Cited References Count:39}, pages = {370-382}, isbn = {0342-1791}, doi = {Doi 10.1007/Bf00311042}, url = {://WOS:A1988M683200009}, author = {Murdoch, J. B. and Stebbins, J. F. and Carmichael, I. S. E. and Pines, A.} } @article {589, title = {Relaxation Mechanisms and Effects of Motion in Albite (Naalsi3o8) Liquid and Glass - a High-Temperature Nmr-Study}, journal = {Physics and Chemistry of Minerals}, volume = {15}, year = {1987}, note = {Phys Chem MinerL0167Times Cited:40Cited References Count:57}, pages = {155-162}, isbn = {0342-1791}, doi = {Doi 10.1007/Bf00308778}, url = {://WOS:A1987L016700007}, author = {Liu, S. B. and Pines, A. and Brandriss, M. and Stebbins, J. F.} } @article {581, title = {Speciation and Local-Structure in Alkali and Alkaline-Earth Silicate-Glasses - Constraints from Si-29 Nmr-Spectroscopy}, journal = {Journal of Non-Crystalline Solids}, volume = {89}, year = {1987}, note = {J Non-Cryst SolidsG5155Times Cited:74Cited References Count:46}, month = {Mar}, pages = {371-383}, isbn = {0022-3093}, doi = {Doi 10.1016/S0022-3093(87)80279-X}, url = {://WOS:A1987G515500011}, author = {Schneider, E. and Stebbins, J. F. and Pines, A.} } @article {603, title = {Defects and Short-Range Order in Nepheline Group Minerals - a Si-29 Nuclear-Magnetic-Resonance Study}, journal = {Physics and Chemistry of Minerals}, volume = {13}, year = {1986}, note = {Phys Chem MinerE6311Times Cited:40Cited References Count:61}, pages = {371-381}, isbn = {0342-1791}, url = {://WOS:A1986E631100003}, author = {Stebbins, J. F. and Murdoch, J. B. and Carmichael, I. S. E. and Pines, A.} } @article {602, title = {New Probe for High-Temperature Nmr-Spectroscopy with Ppm Resolution}, journal = {Review of Scientific Instruments}, volume = {57}, year = {1986}, note = {Rev Sci InstrumAxa20Times Cited:15Cited References Count:19}, month = {Jan}, pages = {39-42}, isbn = {0034-6748}, doi = {Doi 10.1063/1.1139115}, url = {://WOS:A1986AXA2000010}, author = {Stebbins, J. F. and Schneider, E. and Murdoch, J. B. and Pines, A. and Carmichael, I. S. E.} } @article {620, title = {A High-Temperature High-Resolution Nmr-Study of Na-23, Al-27 and Si-29 in Molten Silicates}, journal = {Nature}, volume = {314}, year = {1985}, note = {NatureAdt99Times Cited:58Cited References Count:13}, pages = {250-252}, isbn = {0028-0836}, doi = {Doi 10.1038/314250a0}, url = {://WOS:A1985ADT9900039}, author = {Stebbins, J. F. and Murdoch, J. B. and Schneider, E. and Carmichael, I. S. E. and Pines, A.} }