Temperature-dependence of the XANES spectra of photo-reduced myoglobin Mb(II)H2O. (Left frame) ɛ//a* spectra, polarized along the Fe-water bond. The thermally activated water dissociation is probed by the spectral changes of the ɛ//a* spectrum between 200 K and 240 K. (Right frame) ɛ//c spectra, polarized on the heme plane. Here, the relaxation of the Fe-heme system, with the displacement of the iron from the heme plane, is probed between 160 K and 240 K. Between 120 K and 160 K, an evidence for a relaxation of the intermediate Mb(II)H2O is observed in both the polarizations.