Electron-impact ionization of laser-excitedBa138(…5p66s6p)andBa138(…5p66s5d)atoms

Electron-impact ionization cross sections for laser-excited ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}(\dots 5p^{6}6s6p;{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{},M=-1)$ and cascade-populated ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}(\dots 5p^{6}6s5d;{}_{}{}^1{}_{}{}^{}D+{}_{}{}^3{}_{}{}^{}D)$ atoms were measured in the threshold to 10 eV energy range. The peak cross sections for the excited species are about a factor of 2 larger than that for ground-state Ba. In addition, it was demonstrated that ionization from individual magnetic substates of various hyperfine levels can be studied. The ionization cross sections in the case of ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}\left({}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}\right)$ were found to be equal for the $M=0\mathrm{}$ and for the $M=\pm 1$ sublevels within the experimental error limit.