TheK-Absorption Edges of Metal Ions in Aqueous Solution

The x-ray $K$-absorption edges of ${\mathrm{Ni}}^{++}$, ${\mathrm{Cu}}^{-+}$, ${\mathrm{Zn}}^{++}$, Cu${\left(\mathrm{N}{\mathrm{H}}_3\right)}_4^{++}$ and ${\mathrm{Cu}}_2$ ${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4^{--}$ in aqueous solution have been measured with a double crystal spectrometer. ${\mathrm{Ni}}^{++}$, ${\mathrm{Cu}}^{++}$, and ${\mathrm{Zn}}^{++}$ have similar edges. Each consists of two absorption maxima which arise from the excitation of $K$ electrons into the empty $4p$ and $5p$ levels of the ion. The final levels are broadened by the fields of the coordinated water molecules. Quite different edge structures were found in the complex ions. They probably arise from the scattering of the photoelectron by the other atoms of the ion, the same process which takes place in polyatomic gases.