The NIST compilation of ionization potentials revisited (I): From He-like to Xe-like ions

The National Institute of Standards and Technology (NIST) database on ionization potentials for neutral atoms and ions is examined. For each isoelectronic sequence, we construct a regularized perturbative series based on the large-Z (heavy cations) and Z ? N - 1 (singly charged anion) behaviors. Comparison of the NIST data with this series allows the identification of problematic values in the reported data.