Abstract
Photoionization spectra of europium and thulium are reported from threshold to 1350 Å. The ionization efficiency in this region is found to be dominated by autoionization. Autoionization structure, believed to be due to 4fN6s2 → 4fN5dnp transitions, is interpreted and other strong resonances listed. The ionization potential of europium is determined to be 5.664 ± 0.008 eV and that of thulium to be 6.180 + 0.008 eV.

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