Ionization energies of Cu- and Ni-like ions with Z ≤ 92

A two-stage technique is developed to interpolate and extrapolate the ionization energies of Cu- and Ni-like ions along Z with accuracy to the fifth significant digit. I) The first stage consists of scaling the known ionization energies (IE) along Z , which brings the IE( Z )-function to a quasi-straight line. Function straightening detects points where the function’s smoothness breaks down. They are fitted to the IE( Z ) curve in the same way as it is usually done in some experiments. Scaling on successive overlapping segments allows a confident extrapolation to the region Z =92. II) The verification of the obtained results in stage I is performed using the parameter of the relativistic model potential of a Dirac equation. The results of techniques I and II agree well up to Z ∼92.