Kinetic Studies of the Reactions of IO Radicals Determined by Cavity Ring-Down Spectroscopy

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We demonstrate the application of cavity ring-down spectroscopy (CRDS) to the measurement of concentrations of IO radical and of reaction rate coefficients for the reaction systems, IO + IO and IO + NO, using the source reaction, O(3P) + CF3I. By monitoring IO radicals, we obtain the 295 K rate coefficients, k(O + CF3I → IO + CF3) = (5.8 ± 1.5) × 10-12 cm3 molec-1 s-1; k(IO + IO) = (1.0 ± 0.3) × 10-10 cm3 molec-1 s-1, and k(IO + NO) = (1.9 ± 0.5) × 10-11 cm3 molec-1 s-1 at the pressures of 1250 Pa (9.4 Torr) and 4000 Pa (30.1 Torr). For the IO A 2Π3/2 − X 2Π3/2 (2, 0) bandhead at 445.04 nm we have determined an absorption cross-section, σ = (7.3 ± 0.7) × 10-17 cm2. Error limits indicate the confidence of two standard deviations and propagate the uncertainty in the absorption cross-section.