Calculation of the $4d$ Subshell Photoabsorption Spectra of Ba, ${\mathrm{Ba}}^{+}$, and ${\mathrm{Ba}}^{++}$

Calculations of the photoabsorption spectra for Ba, ${\mathrm{Ba}}^{+}$, and ${\mathrm{Ba}}^{++}$ near the $4d$ ionization threshold have been performed with the time-dependent local density approximation. The results are in quantitative agreement with recent experimental data and indicate that the sharp resonant structure below threshold is due to transitions to hybridized $f$ states which are strongly modified by electron-electron interactions.