Actinic Wavelength Action Spectroscopy of the IO^– Reaction Intermediate

Abstract

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.

The combination of laser photodissociation, action spectroscopy, and mass spectrometry to identify and separate isomers

“…2). 55 In this example, IO − is m / z selected and isolated using a room temperature linear ion-trap mass spectrometer and then irradiated. Any loss of IO − parent ions can be recorded with a laser-on vs. laser-off procedure—this is a photodepletion spectrum.…”

Photochemical Mechanisms in Atmospherically-Relevant Iodine Oxide Clusters

“…IO, 22,43,[50][51][52][53][54][55] OIO, 43,51,52,[56][57][58][59][60] and I 2 O 2−3 , 61 along with kinetics/rates of these photolysis reactions. [62][63][64] Larger iodine oxides (I 2−5 O 2−12 ) have also been studied, probing photolysis reaction rates and their absorption cross sections, and photolysis reactions for iodate have been proposed.…”

Photochemical Mechanisms in Atmospherically Relevant Iodine Oxide Clusters

“…Several studies have examined photodissociation of iodine oxide molecules, including IO, ,,− OIO, ,,,− and I 2 O 2–3 , along with the kinetics and rates of these photolysis reactions. − Larger iodine oxides (I 2–5 O 2–12 ) have also been studied, probing photolysis reaction rates and their absorption cross sections, and photolysis reactions for iodate have been proposed. , Some of these iodine oxide molecules, such as I 2 O 3 , have sufficiently small absorption cross sections in the actinic region that they likely live long enough to play a role in NPF and clustering . IOP formation appears to be driven by temperature and humidity.…”