RADICAL PAIR QUANTUM YIELD IN REACTION CENTERS OF PHOTOSYSTEM-II OF GREEN PLANTS AND OF THE BACTERIUM RHODOBACTER-SPHAEROIDES - SATURATION BEHAVIOR WITH SUBPICOSECOND PULSES

We have measured the radical pair quantum yield of reaction centers of photosystem II of green plants and of the purple bacterium Rhodobacte r sphaeroides as a function of excitation density using sub-picosecond pulses at 77 K. The saturation behavior of both RCs can be described consistently by taking into account stimulated emission and the geomet ry of the polarized (magic angle) laser experiment. Our results show t hat the quantum yield of charge separation for the PS II RC is very hi gh, about 1, and that no annihilation occurs under these conditions.