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 characterised. 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) due to 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.