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- + O-3 reaction, by mass spectrometry equipped with resonance-enhanced photo-dissociation 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.