Near-threshold laser spectroscopy of iridium and platinum negative ions: Electron affinities and the threshold law

The electron affinity of Ir is measured to be 12617.4(12) cm^-1 [1.56436(15) eV], from photodetachment studies on Ir^-. Previous measurements of the electron affinity of platinum reported results which were inconsistent within quoted error bars. A photodetachment study with a very improved energy resolution, signal-to-noise ratio, and signal-to-background ratio, was conducted on Pt^-, and yields a much more accurate electron affinity for Pt of …