Anharmonic potential derived from EXAFS of hexaaqua transition metal complexes

EXAFS (extended X-ray absorption fine structure) experiments were performed at several different temperatures for a series of 3d transition metal ions (Cr3+, Fe3+, Fe2+, Ni2+, Co2+ and Zn2+) in aqueous solutions. Anharmonic E XAFS analyses, which include up to third order cumulant, were carried out t o study the metal-oxygen bonding potential. According to the model in which the dissociation process is dominant for the ligand water exchange reactio n, the dissociation energy has been evaluated by combining experimental res ults of temperature dependence of a harmonic Debye-Waller factor and an anh armonic third order cumulant for hydrated metal complexes. The dissociation energies deduced from the EXAFS experiments were found to correlate well w ith those having been theoretically predicted, and with the experimental wa ter-exchange rate constants.