Photoionization cross sections of iron isonuclear sequence ions:Fe2+toFe6+

Abstract

We have measured the absolute photoionization cross sections of ${\text{Fe}}^{2+}$ to ${\text{Fe}}^{6+}$ ions in the photon energy range covering the first ionization threshold up to 160 eV. Particular interest is emphasized on the region of the $3p\ensuremath{\rightarrow}3d$ excitations. The experimental data are compared to the results of calculations we have performed using a spectral opacity code, as well as to available $R$-matrix and one-electron calculations. It is shown that often the theoretical results tend to overestimate the intensity of the $3p\ensuremath{\rightarrow}3d$ photoexcitations. An anomalously low value of the integrated oscillator strength is measured for ${\text{Fe}}^{2+}$ ion.