Iridium ions near $4f-5s$ level crossings are the leading candidates for a new type of atomic clocks with a high projected accuracy and a very high sensitivity to the temporal variation of the fine structure constant $\alpha$. To identify spectra of these ions in experiment accurate calculations of the spectra and electromagnetic transition probabilities should be performed. Properties of the $4f\text{-core-excited}$ states in ${\mathrm{Ir}}^{16+},{\mathrm{Ir}}^{17+}$, and ${\mathrm{Ir}}^{18+}$ ions are evaluated using relativistic many-body perturbation theory and Hartree-Fock-relativistic method (COWAN code). We evaluate excitation energies, wavelengths, oscillator strengths, and transition rates. Our large-scale calculations included the following set of configurations: $4f^{14}5s,4f^{14}5p,4f^{13}5s^2,4f^{13}5p^2,4f^{13}5s5p,4f^{12}5s^{2}5p$, and $4f^{12}5s5p^2$ in Pm-like ${\mathrm{Ir}}^{16+}$; $4f^{14},4f^{13}5s,4f^{13}5p,4f^{12}5s^2,4f^{12}5s5p$, and $4f^{12}5p^2$ in Nd-like ${\mathrm{Ir}}^{17+}$; and $4f^{13},4f^{12}5s,4f^{12}5p,4f^{11}5s^2$, and $4f^{11}5s5p$ in Pr-like ${\mathrm{Ir}}^{18+}$. The $5s-5p$ transitions are illustrated by the synthetic spectra in the 180–200 Å range. Large contributions of magnetic-dipole transitions to lifetimes of low-lying states in the region below 2.5 Ry are demonstrated.

• Received 5 May 2015

DOI:https://doi.org/10.1103/PhysRevA.92.022501