Combined XANES and EXAFS analysis ofCo2+,Ni2+

A combined x-ray-absorption near edge structure (XANES) and extended x-ray-absorption fine-structure (EXAFS) quantitative analysis of ${\mathrm{Co}}^{2+},$ ${\mathrm{Ni}}^{2+},$ and ${\mathrm{Zn}}^{2+}$ in water solutions based on fitting procedures of both low- and high-energy ranges has been carried out. The hydrogen contribution has been accounted for in both analyses and the effect of its inclusion on the structural parameters has been highlighted. The structural results obtained from the XANES and EXAFS analyses are in good agreement, confirming the validity of the application of the multiple-scattering theory in the low-energy range of the x-ray-absorption spectra. A systematic shortening of the ion-water first shell distance of about $0.03 \mathrm{\AA{}}$ is obtained from the XANES analyses, as compared to the EXAFS one. The origin of this systematic effect has been deeply investigated and it has been found to be due to the low-energy behavior of the real part of the Hedin-Lundqvist potential used in the calculations.