Near-threshold laser spectroscopy of iridium and platinum negative ions: Electron affinities and the threshold law - art. no. 012505

The electron affinity of Ir is measured to be 12617.4(12) cm(-1) [1.56436(1 5) eV], from photodetachment studies on Ir-. Previous measurements of the e lectron affinity of platinum reported results which were inconsistent withi n quoted error bars. A photodetachment study with a very improved energy re solution, signal-to-noise ratio, and signal-to-background ratio, was conduc ted on Pt-, and yields a much more accurate electron affinity for Pt of 171 40.1(4) cm(-1) [2.12510(5) eV], in good agreement with the most recent meas urement. Possible explanations for the poor agreement between the earlier r esults are discussed. In both the Ir- and Pt- spectra. the data indicate th at the detachment cross section deviates from the expected Wigner threshold law, even near the detachment threshold. This behavior cannot be explained by the correction terms to the Wigner law proposed by the currently availa ble threshold detachment models.