6533b829fe1ef96bd128a225

RESEARCH PRODUCT

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The atomic spectrum of neutral promethium has been studied extensively by laser resonance ionization spectroscopy. We report on more than 1000 atomic transitions in the blue and near infrared spectral ranges, most of them between high excited energy levels. As Rydberg convergences could not be assigned unambiguously in the dense spectrum at high excitation energies, the first ionization potential (IP) was determined via field ionization of weakly bound states within a static electric field. By applying the saddle-point model, a value of ${\mathrm{IP}}_{(\mathrm{Pm})}=45\phantom{\rule{0.16em}{0ex}}020.8(3)\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1} [5.58188(4)\phantom{\rule{0.16em}{0ex}}\mathrm{eV}]$ was derived, which confirms previous expectations of $45\phantom{\rule{0.16em}{0ex}}027(80)$ and $44\phantom{\rule{0.16em}{0ex}}985(140)\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, which were obtained indirectly from lanthanide IP systematics.