4D PHOTOIONIZATION OF SINGLY-CHARGED XE, BA, AND EU IONS

Using a photon-ion merged-beam apparatus, the relative photoion-yield spectra for doubly- and triply-charged ions from Xe+, Ba+ and Eu+ ions were measured in the 4d ionization region. The giant resonance peak a ppears for all target ions. The peak of Xe+ is broad and that of Eu+ i s relatively narrow, similar to those observed in the neutral atoms. T he spectrum of Xe3+ shows some structures around 87 and 93 eV. The sum mit of the giant resonance peak of Eu2+ is obviously split into two. T hese structures observed in the Xe3+ and Eu2+ spectra are not observed in the photoion spectra of the neutral targets. Some small peaks are observed in the Xe+ spectrum between 70 and 76 eV. A multi-configurati on Dirac-Fock calculation reveals that these peaks are attributed to 4 d-np and 4d-nf transitions. It was also found that the broad peak cent ered at 100 eV corresponds to shake-up resonance (4d(10)5s(2)5p(5)-->4 d(9)4f5s(2)5p(4)np [n=6,7]) processes. Some prominent peaks that do no t appear in the neutral Ba spectrum are observed clearly in the Ba+ on e. These peaks are most probably due to the 4d-nf transition followed by Auger processes.