Multiplet and lifetime effects in the $4d$ photoelectron spectrum of Eu

A high-resolution $4d$ photoelectron spectrum of Eu has been measured. The spectrum reveals a rich structure reflecting multiplet splitting due to $4d-4f,$ $4f-4f,$ and spin-orbit interaction. In order to interpret the complex ${4d}^{-1}$ multiplet structure, calculations in the intermediate coupling scheme were performed taking into account the term-dependent lifetime width of each ${4d}^{-1}$ multiplet state. The strong influence of both the $4d-4f$ exchange interaction and the term-dependent lifetime broadening on the shape of the $4d$ photoelectron spectrum is demonstrated. Due to the inner-shell character of the $4d$ and $4f$ orbitals, the spectrum of atomic Eu is similar to that of Eu and Gd solid samples having the same ${4f}^7$ occupancy.