Experimental and theoretical studies of excited states in Ir

The properties of atomic negative ions are to a large extent determined by electron-electron correlation which makes them an ideal testing ground for atomic many-body physics. In this paper, we present a detailed experimental and theoretical study of excited states in the negative ion of iridium. The ions were stored at cryogenic temperatures using the double electrostatic ion ring experiment facility at Stockholm University. Laser photodetachment was used to monitor the relaxation of three bound excited states belonging to the [Xe] $4{f}^{14}5{d}^{8}6{s}^{2}$ ionic ground configuration. Our measurements show that the first excited state has a lifetime much longer than the ion-beam storage time of $1230\ifmmode\pm\else\textpm\fi{}100\phantom{\rule{0.28em}{0ex}}\mathrm{s}$. The binding energy of this state was measured to be $1.045\ifmmode\pm\else\textpm\fi{}0.002\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$. The lifetimes of the second and third excited states were experimentally determined to be $133\ifmmode\pm\else\textpm\fi{}10$ and $172\ifmmode\pm\else\textpm\fi{}35\phantom{\rule{0.28em}{0ex}}\mathrm{ms}$, respectively. Multiconfiguration Dirac-Hartree-Fock calculations were performed in order to extract binding energies and lifetimes. These calculations predict the existence of the third excited bound state that was detected experimentally. The computed lifetimes for the three excited bound states agree well with the experimental results and allow for a clear identification of the detected levels.