Spin-locking of half-integer quadrupolar nuclei in NMR of solids:the far off-resonance case

Odedra, Smita and Wimperis, Stephen (2017) Spin-locking of half-integer quadrupolar nuclei in NMR of solids:the far off-resonance case. Solid State Nuclear Magnetic Resonance, 84. pp. 4-13. ISSN 0926-2040

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Spin-locking of spin I = 3/2 and I = 5/2 nuclei in the presence of large res- onance offsets has been studied using both approximate and exact theoretical approaches and, in the case of I = 3/2, experimentally. We show the variety of coherences and population states produced in a far off-resonance spin-locking NMR experiment (one consisting solely of a spin-locking pulse) and how these vary with the radiofrequency field strength and offset frequency. Under magic angle spinning (MAS) conditions and in the “adiabatic limit”, these spin-locked states acquire a time dependence. We discuss the rotor-driven interconversion of the spin-locked states, using an exact density matrix approach to confirm the results of the approximate model. Using conventional and multiple-quantum fil- tered spin-locking 23Na (I = 3/2) NMR experiments under both static and MAS conditions, we confirm the results of the theoretical calculations, demonstrating the applicability of the approximate theoretical model to the far off-resonance case. This simplified model includes only the effects of the initial rapid dephas- ing of coherences that occurs at the start of the spin-locking period and its success in reproducing both experimental and exact simulation data indicates that it is this dephasing that is the dominant phenomenon in NMR spin-locking of quadrupolar nuclei, as we have previously found for the on-resonance and near-resonance cases. Potentially, far off-resonance spin-locking of quadrupolar nuclei could be of interest in experiments such as cross polarisation as a conse- quence of the spin-locking pulse being applied to a better defined initial state (the thermal equilibrium bulk magnetisation aligned along the z-axis) than can be created in a powdered solid with a selective radiofrequency pulse, where the effect of the pulse depends on the orientation of the individual crystallites.

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Journal Article
Journal or Publication Title:
Solid State Nuclear Magnetic Resonance
Additional Information:
This is the author’s version of a work that was accepted for publication in Solid State Nuclear Magnetic Resonance . Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Solid State Nuclear Magnetic Resonance, 84, 2017 DOI: 10.1016/j.ssnmr.2016.11.001
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01 Dec 2016 11:22
Last Modified:
17 Sep 2023 01:59