MUTUAL COMBINATION OF CLO RADICALS

The mutual combination reaction (Formula Presented.) is proposed as the rate‐limiting step in the removal of ClO radicals at moderate pressures. The third‐‐order rate constants measured at room temperature were k1(Ar) = 3.51 ± 0.14 × 109 l2/mol2·ec; k1(He) ≈ 2.8 × 109 l2/mol2·sec, and k1(O2) ≈ 7.9 × 109 l2/mol2·sec. There is also an independent second‐order reaction (Formula Presented.) for which k3 ≈ 8 × 106 l/mol·sec. A new absorption spectrum has been observed in the ultraviolet and attributed to Cl2O2. The extinction coefficient for Cl2O2 has been measured at six wavelengths, and, between 292 and 232 nm, it increases from 0.4 × 103 to 2.9 × 103 l/mol·cm. In the presence of the chlorine atom scavengers OClO or Cl2O, Cl2O2 exists in equilibrium with ClO. The equilibrium constant Ke1 = 3.1 ± 0.1 × 106 l/mol at 298 K, and, with ΔS10 estimated to be −133 ± 11 J/K·mol, ΔH10 = −69 ± 3 kJ/mol and ΔHf0(Cl2O2) = 136 ± 3 kJ/mol. Copyright © 1979 John Wiley & Sons, Inc.