High-Resolution Photoelectron Imaging and Photodetachment Spectroscopy of Cryogenically Cooled IO.

We report a high-resolution photoelectron imaging and photodetachment spectroscopy study of cryogenically cooled IO-. The high-resolution photoelectron spectra yield a more accurate electron affinity (EA) of 2.3805(5) eV for IO as well as a more accurate spin-orbit splitting energy between the 2Π3/2 and 2Π1/2 states of IO as 2093(5) cm-1. Photodetachment spectroscopy confirmed several excited states for the IO- anion predicted by theoretical calculations, including two valence-type excited states, the repulsive 3Π state, and a shallow bound 1Π state. More interestingly, we have observed two vibrational resonances which are proposed to be due to a dipole-induced resonant state, about 230 cm-1 above the detachment threshold of IO-.