Actinic Wavelength Action Spectroscopy of the IO^– Reaction Intermediate

Iodinate anions are important in the chemistry of the atmosphere where they are implicated in ozone depletion and particle formation. The atmospheric chemistry of iodine is a complex overlay of neutral–neutral, ion–neutral, and photochemical processes, where many of the reactions and intermediates remain poorly characterized. This study targets the visible spectroscopy and photostability of the gas-phase hypoiodite anion (IO–), the initial product of the I– + O3 reaction, by mass spectrometry equipped with resonance-enhanced photodissociation and total ion-loss action spectroscopies. It is shown that IO– undergoes photodissociation to I– + O (3P) over 637–459 nm (15700–21800 cm–1) because of excitation to the bound first singlet excited state. Electron photodetachment competes with photodissociation above the electron detachment threshold of IO– at 521 nm (19200 cm–1) with peaks corresponding to resonant autodetachment involving the singlet excited state and the ground state of neutral IO possibly mediated by a dipole-bound state.