Exploring the Oxygen Order in Hg-1223 and Hg-1201 by 199Hg MAS NMR

We demonstrate the use of a high-resolution solid-state fast (45 kHz) magic angle spinning (MAS) NMR for mapping the oxygen distribution in Hg-based cuprate superconductors. We identify observed three peaks in 199Hg spectrum as belonging to the different chemical environments in the HgO? layer with no oxygen neighbors, single oxygen neighbor, and two oxygen neighbors. We discuss observed differences between Hg-1201 and Hg-1223 materials.Comment: 4 pages, 2 figures included. Submitted to NATO Advanced Research Workshop Proceedings (Miami January 2004

Quantum rotation of ortho and para-water encapsulated in a fullerene cage

Inelastic neutron scattering, far-infrared spectroscopy, and cryogenic nuclear magnetic resonance are used to investigate the quantized rotation and ortho–para conversion of single water molecules trapped inside closed fullerene cages. The existence of metastable ortho-water molecules is demonstrated, and the interconversion of ortho-and para-water spin isomers is tracked in real time. Our investigation reveals that the ground state of encapsulated ortho water has a lifted degeneracy, associated with symmetry-breaking of the water environmen

Experimental Capability Of High Resolution O17 Using Double Rotation On Crystalline Sodium Enneagermanate

We have studied sodium enneagermanate crystal using both magic angle spinning (MAS) and double rotation (DOR) at two magnetic field strengths. Using equation for the total shift observed at two field strengths, the chemical shift is uniquely determined together with a product of the quadrupolar coupling constant (CQ = e2qQ/h) and the quadrupolar asymmetry parameter (ç). We demonstrate a computer simulation that uses the isotropic shifts and quadrupolar products as constraints and provides simulations of overlapped magic-angle spinning line shapes. In this way the quadrupolar parameters, CQ and ç, are determined separately for each crystallographic site of crystalline sodium enneagermanate. High resolution DOR spectra of oxygen-17 nuclei in sodium enneagermanate crystal illustrate the experimental capabilities. Crystalline studies of sodium enneagermanate is one of the structural data for confirming the correlations between the measured 17O quadrupolar coupling parameters and the oxygen environment. The result of these studies should provide insight to further investigation using 17O solid state NMR to study the structure of other oxide glasses and as well as other germanate-based glasses

Symmetry-based recoupling in double-rotation NMR spectroscopy

Contains fulltext : 72545.pdf (publisher's version ) (Open Access

Applications of Two-Dimensional Solid-State NMR

Contains fulltext : 76571.pdf (publisher's version ) (Open Access)2 p

Efficient amplitude-modulated pulses for triple- to single-quantum coherence conversion in MQMAS NMR

We thank EPSRC (EP/E041825/1 and EP/J501542/1) for support, for the award of a studentship to H.C. We also thank the ERC (EU FP7 Consolidator Grant 614290 “EXONMR”).The conversion between multiple- and single-quantum coherences is integral to many nuclear magnetic resonance (NMR) experiments of quadrupolar nuclei. This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency. To provide the maximum improvement, such schemes typically require time-consuming experimental optimization. Here, we demonstrate an approach for generating amplitude-modulated pulses to enhance the efficiency of the triple- to single-quantum conversion. The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation. Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches. In all cases, the ease of implementation of our method is advantageous, particularly for cases with low sensitivity, where the improvement is most needed (e.g., low gyromagnetic ratio or high quadrupolar coupling). Our approach offers the potential to routinely improve the sensitivity of high-resolution NMR spectra of nuclei and systems that would, perhaps, otherwise be deemed "too challenging".Publisher PDFPeer reviewe