Determination of the first ionization potential of technetium

Using resonance ionization spectroscopy the first-ionization potential of actinium has been determined by analyzing different Rydberg series in two-color resonant laser excitation. Three individual Rydberg series were investigated, converging toward the ionic ground state and toward the first- and second-excited state of the actinium ion, respectively. A combined analysis of the convergence limits leads to a consistent value for the first-ionization potential of Ac of $43\phantom{\rule{0.16em}{0ex}}394.45\phantom{\rule{0.16em}{0ex}}(19)\phantom{\rule{0.28em}{0ex}}{\text{cm}}^{\ensuremath{-}1}$, equivalent to $5.380\phantom{\rule{0.16em}{0ex}}226\phantom{\rule{0.16em}{0ex}}(24)$ eV.