LIF study of the reactions of the IO radical with NO and NO2 over an extended range of temperature and pressure

Abstract

A pulsed laser-photolysis / pulsed laser induced fluorescence technique was used to investigate the kinetics of the reactions of the IO radical with NO and NO₂. For the reaction (1) IO + NO → I + NO₂ the rate constants between 233 and 346 K were found to be k_IO+NO(T) = (4.3 ± 1.0) × 10⁻¹²exp[(397 ± 65) K/T] cm³ s⁻¹, independent of pressure between 13 and 130 mbar as measured at 286 K. Reaction (2) IO + NO₂ + M → IONO₂ + M has been studied between 48 and 402 mbar in the temperature range 238–298 K. The rate constants were found to be in the fall-off region between second- and third-order kinetics for this pressure range. Assuming a broadening factor of F_C = 0.6, independent of temperature, a set of fall-off parameters with k₀(T) = 4.1 × 10⁻³¹ (T/298 K)^−6.3 cm⁶ s⁻¹ and k_∞ = 1.0 × 10⁻¹¹ cm³ s⁻¹ was found to adequately describe the data.