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

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 ²P_3/2 - X ²P_3/2 (2, 0) bandhead at 445.04 nm we have determined an absorption cross-section, s = (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.

*National Research Council postdoctoral associate/NIST.