I was reading through an article about primary charge separation in Photosystem II when I came across the following graphic:


I assumed that the axis is measured with respect to the unexcited system, which implies that the primary excited state (ChlD1*) has energy of 2 eV more than the baseline PSII-RC. However, I also know that the light absorption of PSII peaks at $\lambda=680$ nm, and light with a wavelength of $680$ nm only carries $1.8$ eV. So how is it possible that the incoming photon seems to excite the Photosystem II reaction center to a higher energy than the photon itself carries?

  • $\begingroup$ Did you consider the quantum efficiency (QE)? The absorption peaks - yes, but nevertheless it's a distribution over wavelength (energy). $\endgroup$ Jan 9 at 0:00
  • $\begingroup$ Oh please — "an article". If you reproduce a figure from the article, please do it and us the courtesy of citing it, preferably with a link. $\endgroup$
    – David
    Jan 9 at 0:09


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