Figure 1. Energy level diagram for an unpaired electron in the absence of hyperfine structure (a), with two unequal hyperfine coupling constants (b), and with two equal coupling constants (c). The corresponding ESR spectra are shown on

Figure 2. Figure 2. ESR absorption spectra for (a) a singlet, (b) a quartet due to hyperfine structure with two protons where A₂ > A_l an (c) a 1:2:1 intensity ratio triplet when A₁= A₂. The intensity ratios are given below the lines, the power absorbed is plotted as the ordinate, and the applied magnetic field increases from left to right.