Advances in STMAS

Abstract

The satellite transition magic angle spinning (STMAS) experiment is a method of obtaining high-resolution NMR spectra of half-integer spin quadrupolar nuclei, such as 17O, 23Na, and 27Al, in solids. In this article, we review the major developments of the original experiment that have taken place since its introduction by Gan in 2000 (see Satellite Transition NMR Spectroscopy of Half-Integer Quadrupolar Nuclei under Magic-Angle Spinning). After a brief resume of how the basic experiment is performed, we discuss a method for removing the autocorrelation “diagonal” from the two-dimensional spectrum (DQF-STMAS), a version of the technique that self-compensates for deviation of the rotor axis from the magic angle (SCAM-STMAS), and an “ultrafast” STMAS experiment that allows a high-resolution spin I = 3/2 spectrum to be acquired in a single transient (STARTMAS). Next, we describe the unique sensitivity of the STMAS experiment to molecular-scale dynamics on the microsecond timescale and to third-order quadrupolar and second-order “cross-term” interactions involving the quadrupolar and dipolar or shielding interactions. Finally, we discuss the signal-to-noise advantage of STMAS (compared with the rival MQMAS method) and how this makes it particularly suitable for studying low-γ nuclei, such as 25Mg and 39K, and materials that can only be obtained in small quantities. Keywords: STMAS; quadrupolar; solid-state NMR; high-resolution; ultrafast acquisition