Measurement of electron affinity of iridium atom and photoelectron angular distributions of iridium anion

Abstract

The latest electron affinity value of an iridium atom is 1.564 36(15) eV, determined via a method based on the Wigner threshold law by Bilodeau and co-workers. However, they observed a significant deviation from the Wigner threshold law in the threshold photodetachment experiment. To address this dilemma, we conducted high-resolution photoelectron spectroscopy of Ir⁻ via the slow-electron velocity-map imaging method in combination with an ion trap. The electron affinity of Ir was measured to be 12 614.97(9) cm⁻¹ or 1.564 057(11) eV. We find that the Wigner threshold law is still valid for the threshold photodetachment of Ir⁻ through a p-wave fitting of the photodetachment channel $\text{I}{\text{r}}^{-}5d^{8}6s^{23}{F}_4\to \text{Ir}5d^{8}6s{b}^4{F}_{9/2}$ . The photoelectron angular distributions of photodetachment channels $\text{I}{\text{r}}^{-}5d^{8}6s^{23}{F}_4\to \text{Ir}5d^{7}6s^2{a}^4{F}_{9/2}$ and $\text{I}{\text{r}}^{-}5d^{8}6s^{23}{F}_4\to \text{Ir}5d^{8}6\text{s}{\text{b}}^4{F}_{9/2}$ were also investigated. The behavior of anisotropy parameter β indicates a strong interaction between the two channels. Moreover, the energy level ³P₂ of Ir⁻, which was not observed in the previous works, was experimentally determined to be 4163.24(16) cm⁻¹ above the ground state.