Pressure dependence of the reactions of HO2 with Cl and ClO

Abstract

The kinetic behaviour of HO₂ and ClO radicals in the photolysis of Cl₂–H₂–O₂–N₂ mixtures, in the total pressure range 50–760 Torr, has been investigated by molecular modulation–u.v. absorption. Rate coefficients for the reactions Cl + HO₂→ HCl + O₂(3a), Cl + HO₂→ OH + ClO (3b) and ClO + HO₂→ HOCl + O₂(6) were obtained. At 308 K the preferred values were k_3a= 4.4 × 10^–11 cm³ molecule^–1 s^–1, k_3b= 9.4 × 10^–12 cm³ molecule^–1 s^–1 independent of pressure, but owing to uncertainties in the calculated [Cl] these values may be, respectively, low and high by a factor of two. A corresponding uncertainty exists in the pressure dependence. The value of k₆=(6.2 ± 1.5)× 10^–12 cm³ molecule^–1 s^–1 at 308 K was well determined and was independent of pressure in the range 50–760 Torr.