Activation energy of the rate constant of P+Q−A absorption decay in reaction centers fromRhodobacter sphaeroides reconstituted with different anthraquinones

The free energy differences between the first stable charge‐separated state, P+Q− A and the thermally excited state, M, via which P+Q− A recombines, were measured in the reaction centers fromRhodobacter sphaeroides reconstituted with anthraquinones. We find that the free energy level of M is independent of the in situ redox potential of QA and consequently the free energy level of P+Q− A. This suggests that M is a state independent of P+Q− A. This is in support of the identification of M with a relaxed form of P+I−.