π pulses and echo formation in magic-angle-spinning NMR

Several theoretical and experimental aspects of echo formation in inhomogeneously broadened rotating solids are described. The timing constraints upon a π-pulse train that allow the formation of rotational echoes are derived, and the effects of the RF phase upon the phase of the echo train are examined. Several new π-pulse trains of various timings, phases, numbers of pulses, and spacings are presented. These effects are explained, both rigorously and intuitively, using the previously developed MAS magnetization vector model of Olejniczak et al.