Fig. 5.

(A) Fourier transforms of the Ca EXAFS spectra of the Mn₁₃Ca₂ complex 1 (red) and PS II S₁ state (black),⁴ and (B) Fourier transforms of the Sr EXAFS spectra of the Mn₁₄Sr complex 2 (red) and Sr-reconstituted PS II S₁ state (black).⁵ Note that there are two Ca per PS II, including one Ca extraneous to the OEC. Also, note that the apparent distances (R′) of the FT peaks are shorter by ∼0.5 Å compared to the actual distances due to a phase shift induced by the potentials of the absorber–backscatterer pair on the photo-electron. The distances in the inset are from the X-ray crystal structures (XRD).