ACCUMULATED PHOTON-ECHO STUDIES ON BACTERIAL PHOTOSYNTHETIC REACTION CENTERS - CHARGE-TRANSFER RATE DISTRIBUTION AND ELECTRON-PHONON COUPLING

The dephasing kinetics of the excitation in the P-870 band of Rb. spha eroides R26 and the mutant Rb. sphaeroides (M)Y210W was measured by ac cumulated photon echo experiments. The photon echo signal shows an ext remely fast component and a nonexponential longer decay. The fast comp onent is attributed to electron-phonon coupling, and the Huang-Rhys fa ctor is determined to be about S = 1.7. The longer decay components ar e attributed to charge transfer from the primary donor. The multiple d ecay components can be explained by assuming dispersive kinetics due t o configurational and energetic disorder. The results are compared wit h those of incoherent pump-probe and hale-burning experiments.