Experimental and theoretical studies of femtosecond time-resolved three-dimensional spectra of photosynthetic reaction centers

In this Letter, we report the three-dimensional experimental and calculated fs transient spectra of initial electron transfer in the bacterial reaction center of Rhodobacter sphaeroides. The wavelength-dependent time constants are discussed. The theoretical model invokes multiple states, which are made up of lower and upper excitonic states of the dimer P. The electron transfer rates are calculated using a multi-mode system utilizing the saddle-point approximation. We find that the wavelength-dependent time constants observed experimentally can be modelled in terms of a multi-step electron transfer mechanism.