On the thermal broadening of core levels in metals due to many‐electron effects

Ferrell's expression for the XPS lineshape is derived in a formalism which explicitly takes the electron—electron interaction into account. Also the corresponding expression for X‐ray absorption is given. In the presence of other broadenings, which are comparable or larger than kT , the electronic part of the core‐level broadening in XPS is indistinguishable from a Gaussian. This Gaussian broadening is of the same order as the expected phonon broadening for Al at room temperature and above, but it is of little importance for Li and Na. In X‐ray absorption, the effect seems in some cases to be important when extracting phonon broadenings from experimental data.