Theoretical calculations of kinetics of the radical pair P F state in bacterial photosynthesis

Abstract

Calculations of the time evolution of the population in the transient radical pair P F state and the magnetic field dependence of the effective decay time are presented. A general treatment is proposed to include (1) unequal decay rates k T and kS for the triplet and the singlet, (2) the anisotropic electron — electron dipolar interaction and (3) the multiple nuclear hyperfine interaction. It is found that the dipolar interaction and the exchange interaction have a strong impact on the field dependence of the effective decay time. In addition, the time evolution of the P F population is found to be quasi-exponential for k T >k 5, and the effective decay rate is determined much more by the singlet decay rate that the triplet decay rate as long as dominant spin-spin interactions are present. The decay curve becomes non-exponential as k S becomes larger than k T.