Figure 6.

Simulated time evolution of the expectation value of the ${\widehat{I}}_x$ (dotted lines) and ${\widehat{S}}_x$ (solid lines) operators during CP zero quantum ${\widehat{I}}_x\to {\widehat{S}}_x$ polarization transfers in $\mathrm{CN}$ (top row), $\mathrm{HN}$ (middle row), and $\mathrm{HC}$ (bottom row) spin pairs for C1–C4 (see Table ) in a 3.2  $\mathrm{mm}$ probe at a proton resonance frequency of 600  $\mathrm{MHz}$ , assuming a MAS frequency of 20  $\mathrm{kHz}$ . Shown are magnetization transfers for constant rf amplitude (left-hand column), a linear rf amplitude modulation (middle column), and a tangential rf amplitude modulation on the source spin (right-hand column). The rf amplitude on the destination spin was kept constant (65  $\mathrm{kHz}$ on $\mathrm{N}$ in $\mathrm{CN}$ , 50  $\mathrm{kHz}$ on $\mathrm{N}$ in $\mathrm{HN}$ , and 70  $\mathrm{kHz}$ on $\mathrm{C}$ in $\mathrm{HC}$ ), and modulations of the rf amplitude on the source spin are shown in Fig. S4. Overall, no significant effects of the time-dependent amplitude and phase modulations due to radial contributions to the rf inhomogeneity are observed for the destination spin in any of the simulated transfers.