Figure 14.

Magnitude of the scaling factors of the three-spin contribution to the dipolar–dipolar cross-terms in the second-order effective Hamiltonian during FSLG decoupling with an rf field strength of 125  $\mathrm{kHz}$ along the magic angle at a MAS frequency of 12.5  $\mathrm{kHz}$ in a 3.2  $\mathrm{mm}$ MAS probe. The resulting magnitudes are shown for $n_{\mathrm{1}}=\mathrm{1}$  (a) and $n_{\mathrm{1}}=\mathrm{2}$  (b) for all possible $n_{\mathrm{2}}$ values with a logarithmic scale. The largest scaling factors are obtained for combinations where $n_{\mathrm{1}}+n_{\mathrm{2}}=\mathrm{0}$ ; however, no difference between C1–C4 is observed. For other $n_{\mathrm{1}},n_{\mathrm{2}}$ pairs, significantly larger scaling factors result when rf modulations are present (C2, C3, and C4). Nevertheless, they remain several orders of magnitude smaller than the first-order contributions.