interaction is provided by calculating the 𝐷-value using the DFT spin density. Such a calculation predicts that 𝐷 = -67.5 MHz which is comparable to the experimental value of -72 MHz with a strain of ±5 MHz. While the analysis of the FID spectra is more convincing than cwESR regarding the presence of a doublet/triplet admixture in solutions of FAAF, there is still a need for an experiment which proves conclusively and without relying on multi-parameter simulations that this admixture is truly present. Given that the admixture is already 'suspected', the experimental test is trivial: the nutation frequencies of the two components should be related by a factor of √ 2 (see SI). This effect is clearly observed in the nutation data presented in the SI, thus validating the conclusions from both cwESR and FID experiments. ) corresponds to the ENDOR spectrum at 1213.6 mT. The dashed red line superimposed on the 1213.6 mT data represents the best-fitting of a sum of 5 symmetric bimodal Gaussian functions. The centres of the bimodal Gaussians are denoted by the coloured circles; the gaps between these circles correspond to the magnitudes of the hyperfine couplings. These couplings are assigned to the protons of the AAF molecules as depicted by the colours in the skeletal structure on the right. The assignment was done by comparison of the experimental values with the DFT computed hyperfine tensors.