Direct double photoionization involving inner and outer electrons: First experimental determination and many-body calculations of an absolute cross section.

Abstract

Using synchrotron radiation, we have determined the absolute cross section for double photoionization involving the $2p$ and $3s$ electrons in atomic sodium. We have also calculated this cross section in the many-body perturbation theory approximation. Our experimental and theoretical results are in good agreement one with each other and represents the first absolute determination of a double photoionization cross section in the case where the two electrons belong to two different shells.