Fig. 7.

Panel A and Panel B show the phase of the MOM and POEM rf irradiation as a function of time (in the units of τ_R) for the ¹³C (blue) and ¹⁵N (green) channel without (A) and with (B) phase alternating respectively. Panel C and Panel D show numerical simulations of the transfer efficiency as function of mixing time using MOM and POEM for the ¹⁵N–¹³C spin-pair, 1.52 Å apart in a powder sample subject to 8 kHz MAS, an external magnetic field corresponding to a 360 MHz (Larmor frequency for ¹H) spectrometer and nominal rf-field strength on the ¹⁵N and ¹³C channel of 24 kHz, respectively. Simulations used ${\delta }_{\mathit{iso}}^C=0,{\delta }_{an\mathit{iso}}^C=0$ and ${\delta }_{an\mathit{iso}}^N=0$. In Panel C and D, three different values of rf-inhomogeneity parameter, ε(0, .02, .05) are used. Simulations use C = 3ω_r, giving τ_c = 125/3 μs and rf-power of ${\omega }_{rf}^C/2\pi =24\text{kHz}$. The efficiency is reduced with increasing ε. In panel C at ε = .05, there is almost no transfer. Simulations were done with SPINEVOLUTION software [14]. Starting and target operator are I_z and S_z.