Determination of Effective Atomic Charges from the Chemical Shifts of X-Ray Emission Lines

The x‐ray line shifts obtainable as differences of level shifts from various quantum mechanical calculations using the free‐ion model provided values which were in good agreement with each other at least for the $\mathrm{K\alpha }$ shifts. This justifies the determination of effective atomic charges from experimental x‐ray line shifts. The formation of inner holes can be taken into account by using the values of $\text{Z\hspace{0.17em}+\hspace{0.17em}1}$ for the charge determination of compounds of the element $Z$ . With the $\text{3d}$ elements the $\mathrm{K\beta }$ shift must be considered besides the $\mathrm{K\alpha }$ one due to the opposite effects of missing $\text{3d}$ and $\text{4s}$ electrons. The charges determined for the first time only x‐ray spectroscopically—generally between 0.8 and 1.5—as well as the $\text{3d}$ and $\text{4s}$ orbital populations change in the same manner as the values obtained from MO calculations. In contrast to the situation with the main group elements where the effective charge increases with increasing formal charge, the former decreases for formal charges above 2 with the $\text{3d}$ elements.