Published under license by AIP Publishing. 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 Ir-5d86s23F4 -> Ir5d86sb4F9/2. The photoelectron angular distributions of photodetachment channels Ir-5d86s23F4 -> Ir5d76s2a4F9/2 and Ir-5d86s23F4 -> Ir5d86sb4F9/2 were also investigated. The behavior of anisotropy parameter beta indicates a strong interaction between the two channels. Moreover, the energy level P-3(2) of Ir-, which was not observed in the previous works, was experimentally determined to be 4163.24(16) cm(-1) above the ground state.
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