We have studied photoionization in the inner valence $3s$ subshell of K and the spectroscopic properties of the two $3s^{-1}\left({}^{1}S\right)$ and $\left({}^{3}S\right)$ resulting states. Similar to the Rb and Cs cases, the lifetime widths of the $\left({}^{1}S\right)$ and $\left({}^{3}S\right)$ states are found to be markedly different, due to the electron correlation effects. The main part of the study deals with the subsequent Auger decay of the $3s^{-1}$ states, which have the particularity to involve low energy $(\sim 5\mathrm{eV})$ Auger electrons. A magnetic bottle spectrometer with a multicoincidence technique has been used to observe and filter the Auger spectra with respect to the ${\mathrm{K}}^{2+}$ final state. The evolution of these Auger spectra has been investigated near the ionization threshold. They show strong post-collision interaction (PCI) effects, which are well reproduced by semiclassical and eikonal models. They reveal the importance of the photoelectron–Auger-electron interaction associated with these low energy Auger electrons.

• Received 21 April 2015

DOI:https://doi.org/10.1103/PhysRevA.92.012510