Acquisition of Wideline Solid-State NMR Spectra of Quadrupolar Nuclei

Abstract

Solid-state NMR is increasingly used for the study of quadrupolar nuclei (spin > 1/2) across the periodic table. There are numerous instances where the magnitude of the quadrupolar interaction is so great that the NMR powder patterns span ranges of hundreds of kilohertz to tens of megahertz, well beyond the range of conventional wideline patterns. Such spectra, which we refer to as ultra-wideline (UW) NMR spectra, cannot be acquired using standard high-power, rectangular pulses, since the associated excitation bandwidths are often much smaller than the pattern breadths. However, it is possible to acquire high-quality UW NMR spectra utilizing a combination of frequency-stepped spectral acquisitions, CPMG echo trains, and chirped pulses. The use of probes with large detection bandwidths and high magnetic fields also greatly aid in improving spectral quality. In this article, techniques for the acquisition of UW NMR spectra are discussed, along with hardware considerations and examples of applications of UW NMR to a variety of materials.