Theoretical analysis of x-ray absorption near-edge structure of transition-metal aqueous complexes in solution at the metal $K$ edge

We present a detailed analysis of x-ray absorption near-edge structure spectra (XANES) of transition-metal aqueous complex in solution. The metal $K$ edges of Ni${}^{2+}$ and Co${}^{2+}$ are analyzed by multiple-scattering theory using clusters of different size and different final-state potentials. On this basis, the effect of hydrogen atoms of the water molecules on the theoretical XANES spectra has been investigated. The calculations show that the intensity ratio and width of the main features of the spectrum are sensitive to the presence and the geometrical position of hydrogen atoms. A very good agreement between experimental data and theoretical calculations has been obtained using final-state potentials built on the basis of the self-consistent field procedure and clusters with a well-defined geometrical position of hydrogen atoms.