@article {316, title = {Isotropic proton-detected local-field nuclear magnetic resonance in solids}, journal = {Journal of Chemical Physics}, volume = {122}, year = {2005}, note = {J Chem Phys899JFTimes Cited:1Cited References Count:31}, month = {Feb 15}, abstract = {

A nuclear magnetic resonance method is presented which produces linear, isotropic proton-detected local-field spectra for INS spin systems in powdered samples. The method, heteronuclear isotropic evolution (HETIE), refocuses the anisotropic portion of the heteronuclear dipolar coupling frequencies by evolving the system under a series of specially designed Hamiltonians and evolution pathways. The theory behind HETIE is presented along with experimental studies conducted on a powdered sample of ferrocene, demonstrating the methodology outlined in this paper. Applications of HETIE for use in structure determination in the solid state are discussed. (C) 2005 American Institute of Physics.

}, keywords = {spectra}, isbn = {0021-9606}, doi = {Doi 10.1063/1.1844296}, url = {://WOS:000227140000043}, author = {Havlin, R. H. and Walls, J. D. and Pines, A.} } @article {352, title = {Creating isotropic dipolar spectra for a pair of dipole coupled spins in high-field}, journal = {Chemical Physics Letters}, volume = {363}, year = {2002}, note = {Chem Phys Lett595CVTimes Cited:3Cited References Count:20}, month = {Sep 9}, pages = {372-380}, abstract = {

In the absence of a strong magnetic field, the dipolar interaction between two nuclear spins is independent of orientation leading to sharp lines. However, in high magnetic fields the Zeeman interaction breaks the symmetry of space and spin producing an anisotropic dipolar spectra. In the following Letter, a method that yields isotropic dipolar spectra for a pair of dipole-coupled spins is presented. This is accomplished through a suitable choice of coherence pathways and average Hamiltonians. We present a theoretical explanation as well as an experimental verification for this novel methodology. (C) 2002 Elsevier Science B.V. All rights reserved.

}, keywords = {angle}, isbn = {0009-2614}, doi = {Doi 10.1016/S0009-2614(02)01188-0}, url = {://WOS:000178090000027}, author = {Walls, J. D. and Blanton, W. B. and Havlin, R. H. and Pines, A.} } @article {359, title = {Investigations of low-amplitude radio frequency pulses at and away from rotary resonance conditions for I=5/2 Nuclei}, journal = {Solid State Nuclear Magnetic Resonance}, volume = {22}, year = {2002}, note = {Solid State Nucl Mag613WLTimes Cited:8Cited References Count:40}, month = {Sep-Nov}, pages = {97-109}, abstract = {

Additional experimental evidence of rotary resonance effects for multiple-quantum coherence conversion in a spin-5/2 system is presented. Two-dimensional plots of the relative efficiency of MQ excitation and conversion are given as a function of radio frequency (rf) amplitude and pulse width. Data are presented for the excitation of five-quantum coherence (5QC), as well as for 5QC to three-quantum coherence (3QC) conversion, 5QC to 1QC (the central transition coherence) conversion, and 3QC to 1 QC conversion. A two-fold increase in the signal-to-noise ratio is achieved by substituting low amplitude rf pulses in place of hard rf pulses for 5QC excitation and 5QC to 3QC conversion in a mixed multiple-quantum magic angle spinning (MAS) (MMQMAS) experiment. The anisotropic line shape for the low-amplitude rf pulse version of the MMQMAS experiment was observed to be distorted from the MAS line shape. The cause and implications of the distortion are discussed. (C) 2002 Elsevier Science (USA).

}, keywords = {solid-state}, isbn = {0926-2040}, doi = {Doi 10.1006/Snmr.2002.0084}, url = {://WOS:000179154400003}, author = {Logan, J. W. and Urban, J. T. and Walls, J. D. and Lim, K. H. and Jerschow, A. and Pines, A.} } @article {358, title = {Measurement of dipolar couplings in partially oriented molecules by local field NMR spectroscopy with low-power decoupling}, journal = {Journal of Magnetic Resonance}, volume = {158}, year = {2002}, note = {J Magn Reson619VETimes Cited:8Cited References Count:23}, month = {Sep-Oct}, pages = {52-59}, abstract = {

Low-power phase-modulated Lee-Goldburg homonuclear decoupling was used to record PDLF spectra of fluorine-substituted benzene derivatives dissolved in nematic thermotropic liquid crystalline solvents. The low-power decoupling minimizes sample heating during RE irradiation while still achieving highly resolved PDLF spectra. The method is illustrated by recording spectra for 1,3-dichloro-4-fluoro-5-nitrobenzene, 1,3-dichloro-4-fluorobenzene, and 1, 2-difluoro benzene dissolved in different nematic solvents. (C) 2002 Elsevier Science (USA). All rights reserved.

}, keywords = {resolution}, isbn = {1090-7807}, doi = {Doi 10.1016/S1090-7807(02)00059-9}, url = {://WOS:000179497500006}, author = {Marjanska, M. and Castiglione, F. and Walls, J. D. and Pines, A.} } @article {347, title = {Rotary resonance recoupling for half-integer quadrupolar nuclei in solid-state nuclear magnetic resonance spectroscopy}, journal = {Journal of Chemical Physics}, volume = {117}, year = {2002}, note = {J Chem Phys599CVTimes Cited:22Cited References Count:53}, month = {Oct 15}, pages = {7024-7033}, abstract = {

Investigations were made of rotary resonance recouplings (R-3) of chemical shift anisotropy (CSA), heteronuclear dipolar (HTD), and homonuclear dipolar (HMD) couplings involving half-integer quadrupolar nuclei under magic-angle sample spinning condition. Under rotary resonance conditions provided by a low amplitude rf field and a high spinning speed, the spectrum of the central transition coherence of half-integer quadrupolar nuclei shows recouplings of CSA, HTD, and HMD interactions that depend on the ratio of the rf field to the spinning speed. These new properties can be used to extract electronic and structural information about the sample that are otherwise difficult to extract in the presence of a dominant quadrupolar interaction. An average Hamiltonian theory is used to explain the recoupling properties of various interactions. Experimental implementations of the R-3 are demonstrated on model compounds with spin-3/2 systems. (C) 2002 American Institute of Physics.

}, keywords = {polarization}, isbn = {0021-9606}, doi = {Doi 10.1063/1.1506907}, url = {://WOS:000178317300016}, author = {Wi, S. and Logan, J. W. and Sakellariou, D. and Walls, J. D. and Pines, A.} } @article {349, title = {Selective excitation in dipole coupled systems}, journal = {Chemical Physics Letters}, volume = {357}, year = {2002}, note = {Chem Phys Lett558GVTimes Cited:5Cited References Count:22}, month = {May 10}, pages = {241-248}, abstract = {

In this Letter the possibility of selective excitation in coupled multispin systems is studied theoretically. A general method of transforming any selective pulse developed for uncoupled systems into a form that is selective in coupled systems is presented. This is accomplished by adding a small perturbation to a decoupling radiofrequency (RF) field. When viewed in an interaction frame given by the decoupling RF field, this method generates, in an averaged sense, a propagator similar to the propagator of uncoupled spins under a shaped RF pulse. Preliminary experimental results are presented for the case of selective excitation in proton nuclear magnetic resonance in liquid crystals. (C) 2002 Elsevier Science B.V. All rights reserved.

}, keywords = {spin-diffusion}, isbn = {0009-2614}, doi = {Doi 10.1016/S0009-2614(02)00493-1}, url = {://WOS:000175958700012}, author = {Walls, J. D. and Marjanska, M. and Sakellariou, D. and Castiglione, F. and Pines, A.} } @article {351, title = {Theoretical investigations of I=5/2 quadrupolar spin dynamics in the sudden-passage regime}, journal = {Journal of Chemical Physics}, volume = {117}, year = {2002}, note = {J Chem Phys566JRTimes Cited:3Cited References Count:44}, month = {Jul 8}, pages = {518-532}, abstract = {

The theoretical approach utilizing bimodal Floquet theory in the quadrupolar/central-transition interaction frame, presented in an earlier article [J. D. Walls, K. H. Lim, and A. Pines, J. Chem. Phys. 116, 79 (2002)], is extended to describe the more complicated spin dynamics of I=5/2 spin systems. Rotary resonance effects occur when the strength of the radio-frequency irradiation, omega(1), matches the sample spinning speed, omega(r), at the conditions omega(1) = 2/3nomega(r) (n integral). At these conditions, conversions of both triple-quantum and five-quantum coherences to central-quantum coherence are observed. Between rotary resonance conditions [ 2n/3omega(r)\<ω(1)\<[2(n+1)]/3ω(r)], five-quantum as well as triple-quantum coherences can be created from equilibrium z-magnetization via a nutation mechanism. In addition, effective transfer between five-quantum and triple-quantum coherences also is observed in between rotary resonance conditions. These effects have been investigated theoretically and verified by both numerical calculations and experimental results. (C) 2002 American Institute of Physics.

}, keywords = {SPECTROSCOPY}, isbn = {0021-9606}, doi = {Doi 10.1063/1.1483256}, url = {://WOS:000176424800003}, author = {Walls, J. D. and Lim, K. H. and Logan, J. W. and Urban, J. T. and Jerschow, A. and Pines, A.} } @article {350, title = {Theoretical studies of the spin dynamics of quadrupolar nuclei at rotational resonance conditions}, journal = {Journal of Chemical Physics}, volume = {116}, year = {2002}, note = {J Chem Phys503ECTimes Cited:12Cited References Count:20}, month = {Jan 1}, pages = {79-90}, abstract = {

A theory of the spin dynamics of I=3/2 quadrupolar nuclei in the sudden-passage limit is discussed in relation to the recently observed rotational resonance (RR) effects on the excitation and conversion of triple-quantum coherence in the FASTER multiple-quantum magic-angle spinning (MQMAS) experiments [T. Vosegaard, P. Florian, D. Massiot, and P. J. Grandinetti, J. Chem. Phys. 114, 4618 (2001)]. A novel interaction frame, which combines the quadrupolar interaction with the central transition radio frequency irradiation, is shown to be useful in understanding the complex spin dynamics at and away from RR conditions. Analytical expressions for the Hamiltonian obtained from bimodal Floquet theory are included in order to provide insight into the spin dynamics observed in the FASTER MQMAS experiments. Numerical simulations have been performed and were found to support the theoretical formalism. (C) 2002 American Institute of Physics.

}, keywords = {solids}, isbn = {0021-9606}, doi = {Doi 10.1063/1.1421613}, url = {://WOS:000172784700010}, author = {Walls, J. D. and Lim, K. H. and Pines, A.} }