Strong configuration interaction in the 3p photoelectron spectrum of Kr

We measured the Kr photoelectron spectrum in the region close to the $3p$ ionization threshold. Our high-resolution measurements allowed a clear observation of spectral structures due to electron correlation effects. Analysis based on relativistic multiconfiguration calculations could explain these observed peaks as due to strong configuration interactions between the $3{p}^{\ensuremath{-}1}$ state and $3{d}^{\ensuremath{-}2}nl$ states. Calculated and experimental data for peak assignments and intensity distributions are in good agreement. In addition, we measured the anisotropy parameter $\ensuremath{\beta}$, which also agreed well with theory. These findings provide a detailed view of strong configuration interactions between the $3{p}^{\ensuremath{-}1}$ and $3{d}^{\ensuremath{-}2}nl$ inner-shell hole states.