NATURE OF THE GROUND AND FIRST EXCITED-STATES OF THE RADICAL CATIONS OF PHOTOSYNTHETIC BACTERIAL REACTION CENTERS

The band shapes of the similar to 2500 cm(-1) electronic absorption (i ntervalence) transition in radical cations of the photosynthetic react ion centres of Rhodobacter sphaeroides and Rhodopseudomonas viridis ar e analysed to extract electronic couplings, asymmetries, and reorganiz ation energies. According to this standard analysis, the charge is hig hly localized on one bacteriochlorophyll of the special pair, in accor d with interpretations of older resonance Raman data but in contrast t o interpretations of recent ENDOR and TRIPLE data; however, our conclu sions are not beyond doubt and the need for further experimental work is indicated. The significance of the observed phase-phonon lines is a lso discussed, as are some possible consequences of the nature of P+ f or the overall kinetics of the reaction centre.