Sensitivity enhancement of solid-state NMR spectra of half-integer spin quadrupolar nuclei: Double- or single-frequency sweeps? Insights from the hyperbolic secant experiment

Improved sensitivity enhancements of the central NMR transition of non-integer spin quadrupolar nuclei in MAS powder samples are realized when only a single satellite transition spinning side band is irradiated using a conventional double-frequency sweep experiment compared to irradiation of the entire spinning side band manifold. For example, for 87Rb in RbClO4, enhancement factors of 2.2 versus 1.9 are observed when only one satellite transition spinning side band is targeted versus the entire spinning side band manifold. Similarly, for 27Al in Al(acac)3, the corresponding enhancement was 3.4 compared to 2.6.