Theoretical predictions about ENDOR of biradicals in liquid solution

Starting from the equation of motion for the density matrix, ENDOR spectra are computed for a biradical for the first time. The model biradical carries two electronic spins S = 1/2 and two nuclear spins I = 1/2. The relaxation operator is calculated ab initio for three distinct relaxation mechanisms. These mechanisms are the modulation of the isotropic exchange interaction, the hyperfine tensor and the zero-field splitting tensor. The dependence of the ENDOR effect on the amplitudes of the radiofrequency and microwave fields, on the strength of the zero-field splitting tensor, and on the correlation times of the correlation functions is investigated.