Figure 10.

Simulated FSLG decoupled proton spectra of a three-spin system at a resonance frequency of 600  $\mathrm{MHz}$ for a 3.2  $\mathrm{mm}$ MAS probe, assuming a MAS frequency of 12.5  $\mathrm{kHz}$ for C1–C4. The rf field strength along the magic angle was set to 125  $\mathrm{kHz}$ . (a) Spectrum for the full $rz$  plane. Significant additional line broadening is observed when amplitude modulations are taken into account (C2 and C4). The two remaining cases are indistinguishable, indicating that rf phase modulations do not contribute to the residual linewidth. (b, c ,d) Contributions from radial slices (all $z$  values for given $r$ ) at $r=\mathrm{0.65}$  (b) and 1.3  $\mathrm{mm}$  (c), as well as the spectrum of a spatially restricted sample (central third along the rotor axis; $z=-\mathrm{1.35}$ –1.35  $\mathrm{mm}$ ; all $r$ values; d). Stronger line broadening is observed towards the edges of the rotor where rf modulations are more pronounced. Significantly narrower lines are obtained for the restricted sample; however, considerable broadening is still observed when time-dependent rf amplitude modulations are taken into account (C2 and C4). The observed splitting of the line for C1 and C3 in (c) can be attributed to the distribution of the isotropic chemical shift scaling factors in this radial slice (see Fig. S8 for details).