Spin-correlated radical pairs in photosynthetic reaction centers: role of anisotropic hyperfine interaction as revealed by computational modeling

A light-induced radical pair is considered, in which one of the electron spins is coupled by an anisotropic hfi with a nuclear spin of a 12. Time evolution of the density matrix is calculated numerically. The sign of nuclear spin polarization appearing after the light flash is shown to be different for different pairs in the polyoriented sample. This polarization is accumulated when the successive light flashes are applied. Influence of nuclear transitions on ESEEM was found to be rather weak, in agreement with experiment.