Features of the emission spectra of $\mathrm{Ni}$-like ions. Application to calculating the wavelengths of self-photo-pumped X-ray lasers

The energy levels and probabilities of radiative transitions to the ground state of $\mathrm{Ni}$-like ions with $Z=36-51$ are calculated. The energies of the upper working level $3d_{3/2}4f_{5/2}$ $[J=1]$ and the lower working level $3d_{3/2}4d_{3/2}$ $[J=1]$ of self-photo-pumped X-ray lasers along the sequence of $\mathrm{Ni}$-like ions are studied. It is shown that, at the points of intersection of levels of the same parity, a strong interaction of these levels takes place, which leads to a redistribution of the oscillator strengths of the radiative transitions from these levels. Near the intersection points, the emission spectra change abruptly with variation in the nuclear charge $Z$.