Femtosecond Photolysis of ClO2 in Aqueous Solution

Abstract

The photolysis of aqueous ClO2 has been studied with a new femtosecond transient absorption spectrometer, allowing absorbance changes as small as ΔA ≈ 1 × 10-4 to be recorded with a time resolution of 150 fs. ClO2 was photolyzed at 390 nm and the ultrafast formation and decay of photoproducts were monitored at 260, 390, and 780 nm. As expected from earlier studies, Cl atoms are formed with a quantum yield of Φ(Cl) = 0.1. However, the rate of formation is nearly 2 orders of magnitude higher than that reported. Moreover, Cl is the only photoproduct that survives 25 ps after the photolysis pulse. The main photolytic products, ClO + O, formed with a quantum yield of 0.9, disappear through fast geminate recombination, producing vibrational excited ClO2 in the electronic ground state. The vibrational relaxation of this species occurs with a time constant of 10 ps. The vanishing yield of cage escape for ClO + O, which contrasts with the reported result of the photolysis at 355 nm, indicates that the amount of ex...