Shaped Pulses for Selective Inversion of Magnetization in Solids Spinning at the Magic Angle

In order to achieve selective inversion of a chosen family of sidebands in NMR spectra of solids rotating at the magic angle (MAS spectra), a sequence of so-called DANTE pulses can be applied in synchronization with the sample rotation period. It is shown by simulation and experiment that the profiles of the offset dependence can be greatly improved by varying the amplitudes of the DANTE pulses, so that the envelope corresponds to that of a G(3) Gaussian cascade. Alternatively, the DANTE pulses may be replaced by sandwiches composed of four hard pulses, adjusted so that the time-dependence of the nutation angles matches the envelope of a G(3) Gaussian cascade. It is shown by simulations that in solids the profiles are affected by homogeneous decay of magnetization, in analogy to the influence of transverse relaxation in liquids. Applications to the intramolecular rearrangement (tautomerism) of polycrystalline tropolone illustrate that dynamic processes in the solid state can be monitored with great accuracy.