The biggest difference between the liquid solution cwESR and frozen solution FID spectra comes from the fact that the anisotropy of the dipolar coupling of the triplet component is resolved in the latter. This interaction is responsible for the 𝑍 ± and 𝑋 𝑌 ± turning points depicted in panel (b) of figure . As shown in the SI, the spacing between the 𝑍 -and 𝑍 + turning points of the triplet component is equivalent to 2|𝐷|, where 𝐷 is the dipolar coupling (related to the maximum, 𝐷 𝑧 , eigenvalue of the dipolar coupling tensor by 𝐷 = (3/2)𝐷 𝑧 ). The sign of 𝐷 was chosen to be negative in these simulations, in keeping with the prolate spin density of FAAF.