The mutual combination reaction
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 × 10
9 l
2/mol
2·ec;
k1(He) ≈ 2.8 × 10
9 l
2/mol
2·sec, and
k1(O
2) ≈ 7.9 × 10
9 l
2/mol
2·sec. There is also an independent second-order reaction
for which
k3 ≈ 8 × 10
6 l/mol·sec. A new absorption spectrum has been observed in the ultraviolet and attributed to Cl
2O
2. The extinction coefficient for Cl
2O
2 has been measured at six wavelengths, and, between 292 and 232 nm, it increases from 0.4 × 10
3 to 2.9 × 10
3 l/mol·cm. In the presence of the chlorine atom scavengers OClO or Cl
2O, Cl
2O
2 exists in equilibrium with ClO. The equilibrium constant
Ke1 = 3.1 ± 0.1 × 10
6 l/mol at 298 K, and, with Δ
S10 estimated to be −133 ± 11 J/K·mol, Δ
H10 = −69 ± 3 kJ/mol and Δ
Hf0(Cl
2O
2) = 136 ± 3 kJ/mol.
