Discrepancies between calculated and observed energies for 4s-4p transitions in highly charged Cu-like ions

The 4s1/2-4p1/2 and 4s1/2-4p3/2 transitions in the Cu-like ions of the elements Sn, Xe, La, Nd, Eu, Gd, Dy, and Yb (atomic numbers Z=50, 54, 57, 60, 63, 64, 66, and 70) have been observed in the spectra from the Princeton Large Torus tokamak. The experimentally determined transition energies were compared to the transition energies calculated using the multiconfiguration Dirac-Fock technique. By including previously published observations, the experimental and calculated transition energies were compared for the entire Cu i isoelectronic sequence from Ru (Z=44) to U (Z=92). Contrary to the conclusion of Cheng and Wagner [Phys. Rev. A 36, 5435 (1987)], we find significant discrepancies between the experimental and calculated transition energies. The discrepancies are attributable to electron correlation corrections that are not accounted for in the calculation.