Time Development of Electron Spin Polarization in Magnetically Coupled, Spin Correlated Radical Pairs

A general description of the Electron Spin Polarization ( ESP) dynamics is presented for photoinduced correlated radical ion spin pairs with particular significance to the respective primary processes in photosynthetic reaction centers. It applies to different coupling situations for the pair spins. The main emphasis is given to the tole of coherence effects. It is predicted that a regular direct detection EPR experiment in the linear response regime, combined with the zero quantum coherence generated by the photoreaction in a weakly coupled spin pair, will reveal intensity oscillations with a beat frequency Omega determined by the spin coupling and the g-factor difference of the coupled radical spins. Conditions ate specified for the experimental observation of the predicted coherence phenomena.