Application of amplitude-modulated radiofrequency fields to the magic-angle spinning NMR of spin-7/2 nuclei

Madhu, P.K., Johannessen, Ole G., Pike, Kevin J., Dupree, Ray, Smith, Mark E. and Levitt, Malcolm H. (2003) Application of amplitude-modulated radiofrequency fields to the magic-angle spinning NMR of spin-7/2 nuclei. Journal of Magnetic Resonance, 163 (2), 310-317. (doi:10.1016/S1090-7807(03)00159-9).

Abstract

We report pulse sequences for the sensitivity enhancement of magic-angle spinning and multiple-quantum magic-angle spinning spectra of spin-(7)/(2) systems. Sensitivity enhancement is obtained with the use of fast amplitude-modulated (FAM) radiofrequency pulses. In one-dimensional magic-angle spinning experiments, signal enhancement of 3 is obtained by a FAM pulse followed by a soft 90 pulse. In two-dimensional multiple-quantum magic-angle spinning experiments, FAM pulses are used for both the excitation of multiple-quantum coherences and for their conversion into observable single-quantum coherences. The observed signal enhancements are 2.2 in 3Q experiments, 3.1 in 5Q experiments, and 4.1 in 7Q experiments, compared to the conventional two-pulse scheme. The pulse schemes are demonstrated on the Sc-45 NMR of Sc-2(SO4)(3) (.) 5H(2)O and the La-139 NMR of LaAlO3. We also demonstrate the generation of FAM pulses by double-frequency irradiation.

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Contributors

Author: Malcolm H. Levitt

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