Multiple-Pulse Line Narrowing under Fast Magic-Angle Spinning

Combined rotation and multiple-pulse experiments (CRAMPS) are analyzed for the conditions of fast magic-angle spinning, where interference effects between both averaging techniques must be considered. Based on this analysis, basic multiple-pulse sequences are adapted to these conditions. As a new aspect compared with conventional CRAMPS experiments, high-speed MAS also plays an important role in the averaging of residual dipolar contributions, that is, high-order correction terms of the dipolar Hamiltonian. The efficiency in doing this was investigated by sequences for scaling the dipolar Hamiltonian and by proper homonuclear decoupling sequences. The resolution of these preliminary experiments approaches that of conventional CRAMPS experiments, whereas the demands with respect to spectrometer hardware and tuning are much lower.