The Experts below are selected from a list of 144 Experts worldwide ranked by ideXlab platform
E. Szcześniak - One of the best experts on this subject based on the ideXlab platform.
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A historical account of NMR in the solid state
Progress in Nuclear Magnetic Resonance Spectroscopy, 1995Co-Authors: E.r. Andrew, E. SzcześniakAbstract:This article attempts to chronicle major milestones in the application of NMR in the solid state over the first 50 years since the discovery of NMR in 1945. After recording the earliest experiments with solids, we discuss in approximate chronological order the following topics: structure of solids, dynamics of solids including molecular reorientation, selfdiffusion and conformational motion, quadrupole effects, NQR, metals, negative temperatures, rotating frame temperatures, magnets and experimental methods, Fourier transform methods, magic angle spinning, multiple pulse NMR, CP/MAS, CRAMPS, double resonance, Overhauser effect, magnetic materials, ordered nuclear spin systems, phase transitions in solids, surfaces of solids, zero field NMR, 2D NMR, multiple quantum and overtone NMR in solids, NMR in high temperature superconductors, NMR in fullerenes, NMR imaging of solids, NMR force spectroscopy. © 1995.
Ulrich Haeberlen - One of the best experts on this subject based on the ideXlab platform.
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eMagRes - The early days of multiple pulse NMR
Encyclopedia of Magnetic Resonance, 2007Co-Authors: Ulrich HaeberlenAbstract:The sections in this article are: 1 Biographical Sketc
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Proton Chemical-Shift Tensors of Methyl Groups; a Multiple-Pulse NMR and LORG/IGLOab InitioStudy
Journal of Magnetic Resonance Series A, 1995Co-Authors: Bernd Tesche, Ulrich HaeberlenAbstract:Abstract High-resolution proton spectra of single crystals of dimethyl terephthalate (DMT) and rotation patterns of line shifts are reported. The suppression of the proton–proton dipole–dipole interactions by Multiple-Pulse cycles works sufficiently well to achieve linewidths of less than 0.5 ppm and to follow the angular dependence of the chemical shifts of all 12 inequivalent protons in DMT in the rotation patterns. In this paper, the data from the methyl groups are analyzed. The anisotropy of the methyl proton chemical-shift (CS) tensor is +(2.9 ± 0.1) ppm. The asymmetry η is 0.25. LORG and IGLO ab initio CS calculations for the methyl ester fragment of DMT, supplemented by a hydrogen, i.e., for methyl formate, are also presented. Calculated and measured methyl proton CS tensors agree on the ±0.5 ppm accuracy level. The calculated CS tensor of the C–H proton in methyl formate is compared with the intramolecular part of the previously measured CS tensors in calcium and lead formate. Again, remarkable agreement is found between calculated and measured proton CS tensors.
Jukka Jokisaari - One of the best experts on this subject based on the ideXlab platform.
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Effects of Thermal Convection on NMR and Their Elimination by Sample Rotation
Journal of Magnetic Resonance Series A, 1996Co-Authors: Juhani Lounila, Kari Oikarinen, Petri Ingman, Jukka JokisaariAbstract:Abstract It is shown that the presence of thermal convection in a sample tube may lead to a variety of anomalous phenomena in prolonged Multiple-Pulse NMR experiments. They are investigated by applying inversion-recovery pulse sequences to 129 Xe of xenon gas dissolved in deuterated cyclohexane and acetonitrile, and to 19 F in xenon difluoride (XeF 2 ) dissolved in deuterated acetonitrile. If convection is present, the recovery of the magnetization after the π pulse may be very different from the recovery due to the spin–lattice relaxation alone. It may be much faster, very sensitive to temperature, and nonexponential, exhibiting even oscillatory behavior. In addition, the shape of the spectral lines may be seriously distorted. The results show that convection and the resulting anomalies can be effectively eliminated by rotating the sample tube at a spinning speed on the order of 10 Hz. These phenomena may provide novel methods for investigating thermal convection.
Anne Kari Nyhus - One of the best experts on this subject based on the ideXlab platform.
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Solid‐state nuclear magnetic resonance relaxation times in crosslinked macroporous polymer particles of divinylbenzene homopolymers
Journal of Polymer Science Part B: Polymer Physics, 1999Co-Authors: David E. Axelson, Anne Kari NyhusAbstract:Monodisperse porous particles of poly(divinylbenzene) prepared by the activated swelling method have been investigated by solid-state 13 C crosspolarization magic-angle spinning (CPMAS) nuclear magnetic resonance (NMR) relaxation measurements. Homopolymeric combinations of two porogens (toluene and 2-ethylhexanoic acid) and two monomers (meta- and para-divinylbenzene) were studied. Residual vinyl groups were systematically reacted with increasing amounts of bromine, producing 20 different polymers samples for which we measured crosspolarization times, T CH , proton rotating frame spin-lattice relaxation, T 1ρ H , 13 C spin-lattice relaxation, T 1 C , and proton spin-lattice relaxation, T 1 H . These parameters were chosen to reflect expected changes in a wide range of frequencies of motion as a function of structure. Relative differences in the molecular mobility of the major functional groups (aromatic, vinyl and aliphatic) is related to initial reactants used, vinyl concentration, relative reactivity of vinyl groups, distribution of vinyl groups, pore structure, and degree of crosslinking. Variable temperature 1 H combined rotation and multiple pulse NMR (CRAMPS) was used to derive activation energies for selected samples via measurement of the proton spin-lattice relaxation time, T 1 H . Irreversible thermal effects were observed in ambient temperature relaxation after heating to temperatures in the range of 393-418 K. Simple univariate statistical analyses failed to reveal consistent correlations among the known variables. However, the application of more sophisticated multivariate and neural network analyses allowed excellent structure-property predictions to be made from the relaxation time data.
Philip J. Grandinetti - One of the best experts on this subject based on the ideXlab platform.
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Solid-state nuclear magnetic resonance in the rotating tilted frame
The Journal of chemical physics, 2008Co-Authors: Nicole M. Trease, Philip J. GrandinettiAbstract:Recent methodological advances have made it possible to measure fine structure on the order of a few hertz in the nuclear magnetic resonance (NMR) spectra of quadrupolar nuclei in polycrystalline samples. Since quadrupolar couplings are often a significant fraction of the Zeeman coupling, a complete analysis of such experimental spectra requires a theoretical treatment beyond first-order. For multiple pulse NMR experiments, which may include sample rotation, the traditional density matrix approaches for treating higher-order effects suffer from the constraint that undesired fast oscillations (i.e., multiples of the Zeeman frequency), which arise from allowed overtone transitions, can only be eliminated in numerical simulations by employing sampling rates greater than 2I times the Zeeman frequency. Here, we present a general theoretical approach for arbitrary spin I that implements an analytical “filtering” of undesired fast oscillations in the rotating tilted frame, while still performing an exact diagona...
