Two-electron one-photon X-ray transition energy in the Kr isoelectronic series

Two-electron one-photon X-ray transition energies are calculated, using the Slater transition-state concept within the approximate local density-functional theory given by the Xα model, for the krypton atom and isoelectronic Rb, Yt, and Zr, respectively. The new theoretical results suggest that the transition energy is a linear function of the atomic number within the isoelectronic series