Strategies for High-Resolution Proton Spectroscopy in Solid-State NMR

Abstract

We describe radiofrequency (RF) pulse schemes in solid-state NMR applied to samples rotating at the magic angle (MAS) to obtain high-resolution ¹H spectra. Without combined RF schemes and MAS, ¹H spectra are normally severely broadened by the strong homonuclear proton-proton dipolar couplings. This review gives an outline of a representative class of multiple-pulse sequences, designed to work with and without MAS, and commonly used for high-resolution proton spectroscopy in solid-state NMR. We give a theoretical treatment of these sequences based on Floquet theory, both single-mode and bimodal. Using this approach, we define first-order homonuclear decoupling efficiency parameters which provide the line-narrowing characteristics of the various pulse sequences when applied to fast rotating samples. These parameters are used to compare the line-narrowing efficiencies of the multiple-pulse schemes.