Transitions between the $4f$-core-excited states in Ir$^{16+}$, Ir$^{17+}$, and Ir$^{18+}$ ions for clock applications

TL;DR

This paper performs detailed relativistic calculations of the spectra and transition probabilities of $4f$-core-excited states in Iridium ions, aiming to support the development of highly accurate atomic clocks sensitive to variations in the fine structure constant.

Contribution

The study provides the first comprehensive relativistic many-body calculations of excitation energies, wavelengths, and transition rates for specific iridium ions relevant to atomic clock applications.

Findings

Calculated excitation energies and transition probabilities for Ir$^{16+}$, Ir$^{17+}$, and Ir$^{18+}$.

Identified significant magnetic-dipole contributions to state lifetimes.

Synthesized spectra for $5s-5p$ transitions in the 180-200 Å range.

Abstract

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 $4f$-core-excited states in Ir$^{16+}$, Ir$^{17+}$, and 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 includes the following set of configurations: $4f^{14-k}5s^{m}5p^{n}$ with $(k+m+n)$ equal to 3, 2, and 1 for the Ir$^{16+}$, Ir$^{17+}$, and Ir$^{18+}$ ions, respectively. The $5s-5p$ transitions are illustrated by the synthetic spectra in the 180 - 200 \AA range. Large contributions of magnetic-dipole transitions to lifetimes of low-lying states in the region below 2.5 Ry are demonstrated.