Magic angle spinning

About: Magic angle spinning is a research topic. Over the lifetime, 5965 publications have been published within this topic receiving 198195 citations.

Heteronuclear decoupling in rotating solids

Abstract: A simple two pulse phase modulation (TPPM) scheme greatly reduces the residual linewidths arising from insufficient proton decoupling power in double resonance magic angle spinning (MAS) experiments. Optimization of pulse lengths and phases in the sequence produces substantial improvements in both the resolution and sensitivity of dilute spins (e.g., 13C) over a broad range of spinning speeds at high magnetic field. The theoretical complications introduced by large homo‐ and heteronuclear interactions among the spins, as well as the amplitude modulation imposed by MAS, are explored analytically and numerically. To our knowledge, this method is the first phase‐switched sequence to exhibit improvement over continuous‐wave (cw) decoupling in a strongly coupled homogeneous spin system undergoing sample spinning.

Sideband intensities in NMR spectra of samples spinning at the magic angle

Abstract: General integral and series expressions are derived for the intensities of sidebands observed in the magic angle spectra of inhomogeneously broadened I=1/2 systems The expressions are evaluated for a wide range of shift parameters and the results used to construct graphical and numerical methods for extracting the principal values of chemical shift tensors from the intensities of just a few sidebands The methods are illustrated by application to 31P spectra of barium diethyl phosphate The results agree well with previous single crystal measurements

Principles of high-resolution NMR in solids

Abstract: 1 Introduction.- 2 Nuclear Spin Interactions in Solids.- 2.1 Basic Nuclear Spin Interactions in Solids.- 2.2 Spin Interactions in High Magnetic Fields.- 2.3 Transformation Properties of Spin Interactions in Real Space.- 2.4 Powder Spectrum Line Shape.- 2.5 The NMR Spectrum. Lineshapes and Moments.- 2.6 Magic Angle Spinning (MAS).- 2.7 Rapid Anisotropic Molecular Rotation.- 2.8 Line Shapes in the Presence of Molecular Reorientation.- 3 Multiple-Pulse NMR Experiments.- 3.1 Idealized Multiple-Pulse Sequences.- 3.2 The Four-Pulse Sequence (WHH-4).- 3.3 Coherent Averaging Theory.- 3.4 Application of Coherent Averaging Theory to Multiple-Pulse Sequences.- 3.5 Arbitrary Rotations and Finite Pulse Width in Multiple-Pulse Experiments.- 3.6 Second Averaging.- 3.7 The Influence of Pulse Imperfections on Multiple-Pulse Experiments.- 3.8 Resolution of Multiple-Pulse Experiments.- 3.9 Magic Angle Rotating Frame Line Narrowing Experiments.- 3.10 Modulation Induced Line Narrowing.- 3.11 Applications of Multiple-Pulse Experiments.- 4 Double Resonance Experiments.- 4.1 Basic Principles of Double Resonance Experiments.- 4.2 Cross-Polarization of Dilute Spins.- 4.3 Cross-Polarization Dynamics.- 4.4 Spin-Decoupling Dynamics.- 4.5 Application of Cross-Polarization Experiments.- 5 Two-Dimensional NMR Spectroscopy.- 5.1 Basic Principles of 2 D-Spectroscopy.- 5.2 2D-Spectroscopy of 13C-1H Interactions in Solids.- 5.3 Applications of 2D-Spectroscopy.- 6 Multiple-Quantum NMR Spectroscopy.- 6.1 Double-Quantum Decoupling.- 6.2 The Three-Level System Double Quantum Coherence.- 6.3 Multiple-Quantum Coherence.- 6.4 Selective Multiple-Quantum Coherence.- 6.5 Double-Quantum Cross-Polarization.- 7 Magnetic Shielding Tensor.- 7.1 Ramsey's Formula.- 7.2 Approximate Calculations of the Shielding Tensor.- 7.3 Proton Shielding Tensors.- 7.4 19F Shielding Tensors.- 7.5 13C Shielding Tensors.- 7.6 Other Shielding Tensors.- 8 Spin-Lattice Relaxation.- 8.1 Spin-Lattice Relaxation in the Weak Collision Limit.- 8.2 Spin-Lattice Relaxation in Multiple-Pulse Experiments.- 8.3 Application of Multiple-Pulse Experiments to the Investigation of Spin-Lattice Relaxation.- 8.4 Spin-Lattice Relaxation in Dilute Spin Systems.- 8.5 Selective Excitation and Spectral Diffusion.- 9 Appendix.- A Irreducible Tensor Representation of Spin Interactions.- B Rotations.- C General Line Shape Theory.- D Homogeneous, Inhomogeneous and Heterogeneous Lineshapes.- E Lineshape and Relaxation due to Fluctuating Chemical Shift Tensors.- F Time Evolution and Magnus Expansion.- G Coherent Versus Secular Averaging Theory.- H Applications of Average Hamiltonian Theory.- I Relaxation Theory.- 10 References.- 11 Subject Index.

Isotropic Spectra of Half-Integer Quadrupolar Spins from Bidimensional Magic-Angle Spinning NMR

Abstract: Interest in the solid state nuclear magnetic resonance (NMR) spectroscopy of half-integer quadrupolar spins is strongly stimulated by the roles that these isotopes play in a variety of important systems such as minerals, structural ceramics, semiconductors, glasses, and catalysts.' In spite of the partly ionic nature of these materials, quadrupole interactions with surrounding electric field gradients often broaden the solid state NMR line shapes of these nuclei into the MHz range. Although most of this broadening can be circumvented by limiting excitations to the central -l/2 +l/2 transition? second-order effects can widen the resulting resonances and prevent the resolution of chemically inequivalent sites. In contrast to what happens in spin-'/2 spectroscopy, no single-axis spinning techniques are available for canceling the effects of these second-order anisotropies. Still, as is briefly discussed in the present Communication, bidimensional NMR methods involving multiple-quantum excitation in combination with fixed-angle sample spinning are capable of refocusing second-order quadrupolar effects and can thus be used to acquire highly resolved spectra devoid from quadrupolar, shielding, or dipolar anisotropies. Central-transition NMR experiments manage to avoid firstorder quadrupolar broadenings owing to the Hamiltonian's quadratic dependence on the S, angular momentum.2 The following term in the quadrupolee the last two, however, are anisotropic and can broaden the central transitions of powdered samples over several kHz. The effects of these anisotropies can be scaled by rapidly spinning the sample at an axis Ps3 This leads to time averaged NMR frequencies