Figure 4.

Time dependence of nuclear spin polarization for four different biradical orientations for (a) nuclear spin polarization starting at thermal polarization and (b) nuclear spin polarization starting at thermal electron spin polarization. In these simulations, the hyperfine coupling (h_zz,max) and the nuclear spin-lattice relaxation are not included for 5T_1e (10 ms), then turned on at time 0 to initiate DNP. Level crossings for each orientation: blue circles, both electron-microwave and three-spin crossings (shown in Fig. 2); light blue squares, no three-spin crossing; red crosses, no electron-microwave crossing, but has three-spin crossing; green diamonds, electron-microwave crossing for higher frequency electron. 100 sets of random T_2e fields were averaged. For clarity, only some of the data points are shown.