The discharge-flow technique coupled with UV-absorption spectroscopy has been used to study the production of dichlorine trioxide, Cl2O 3, from the reaction between ClO and OClO radicals. The absorption cross section of Cl2O3 was determined to be (1.44 ± 0.10) × 10-17 cm2 molecule-1 at λmax = 267 nm (all errors reported are two standard deviations of the statistical error). The equilibrium constant for the process ClO + OClO + M ⇌ Cl2O3 + M was measured in the temperature range 243-298 K. A Second-Law analysis yielded values of ΔrH⊖ = -57.9 ± 2.1 kJ mol -1 and ΔrS⊖ = -132.6 ± 7.9 J K-1 mol-1. The rate coefficient for the formation of Cl2O3 was measured with helium as the third body at a concentration of ∼7.3 ± 1016 molecule cm-3 over the temperature range 243-283 K. Analysis of these data employing the conventional form of the rate equation for the low-pressure limit, k 0(T) = k0(300)·(T/300)-n, resulted in values of k0(300) = (2.83 ± 0.04) × 10-32 cm6 molecule-2 s-1 and n = -4.32 ± 0.1. These spectroscopic, thermochemical and kinetic data are compared with previously reported values.