Transient EPR of radical pairs in photosynthetic reaction centers: prediction of quantum beats

Abstract

Transient nutation EPR of light-induced radical pairs in photosynthetic reaction centers is studied theoretically using the stochastic Liouville equation. The spin Hamiltonian employed considers Zeeman, exchange and dipolar interactions of the spin-correlated radical pair. Particular emphasis is given to the slow-motional regime, where anisotropic magnetic interactions dominate. The calculated dependence of the transverse magnetization on the static magnetic field agrees well with previous simulations of the transient spectra. Quantum-beat oscillations are predicted for the time evolution of the transverse magnetization. The beat frequency is determined by the spin-spin coupling and g-factor difference of the radical pair.