KINETICS OF THE REACTIONS OF IO RADICALS WITH NO AND NO2

A laser flash photolysis-long path absorption technique has been employed to study the kinetics of the reactions of IO radicals with NO and NO2 as a function of temperature and pressure. The IO + NO rate coefficient is independent of pressure over the range 40-200 Torr of N2, and its temperature dependence over the range 242-359 K is adequately described by the Arrhenius expression k1 = (6.9 ± 1.7) × 10-12 exp[(328 ± 71)/T] cm3 molecule-1 s-1 (errors are 2σ, precision only). These Arrhenius parameters are similar to those determined previously for the ClO + NO and BrO + NO reactions. The IO + NO2 association reaction is found to be in the falloff regime over the temperature and pressure ranges investigated (254-354 K and 40-750 Torr of N2). Assuming Fc = 0.4 independent of temperature, a physically reasonable set of falloff parameters which adequately describe the data are k0 = 7.7 × 10-31(T/300)-5.0 cm6 molecule-2 s-1 and K∞ = 1.55 × 10-11 cm3 molecule-1 s-1 independent of temperature. The IO + NO2 rate coefficients determined in this study are about a factor of 2 faster than those reported in the only previous study of this reaction. © 1990 American Chemical Society.