Absorption cross sections and kinetic considerations of the IO radical as determined by laser flash photolysis/laser absorption spectroscopy

Independent measurements of the absorption cross section of the IO radical for the A²Π-X²Π band system are reported. A value of (3.1 ± 0.6) × 10^-17 cm² was observed for the (4,0) bandhead in good agreement with an earlier investigation. Results are also reported for the (5,0), (3,0), (2,0), and (1,0) bands over the wavelength range of 410-470 nm. However, no measurable (<2 × 10^-18 cm²) absorption was found for the (0,0) band. The atmospheric photodissociation rate constant, J_IO, for solar zenith angles of 0°-40° was calculated to have a value of 0.06 ± 0.01 s^-1. This value is a factor of 5 lower than previous estimates. Finally, the rate coefficient for the reaction IO + IO → products (3) has been measured at 760 Torr of N₂ and 300 K. The measured effective bimolecular rate constant was found to be (6.6 ± 2) × 10^-11 cm³·molecule^-1·s^-1, in good agreement with recent results by Sander (1986).