KINETIC, THERMOCHEMICAL, AND SPECTROSCOPIC STUDY OF CL2O3

The UV absorption spectrum of Cl2O3 between 220 and 320 nm was measured using time-resolved transient absorption. Cl2O3 was produced following 193-nm pulsed laser photolysis of N2O/Cl2/OClO/He or Cl2-Cl2/OClO/N2 gas mixtures by reaction 1: ClO + OClO + M --> Cl2O3 + M. The absorption spectrum peaks at 267 nm with a cross section of (1.60(-0.22)+0.35) X 10(-17) cm2 (2sigma error limits including estimated systematic errors). The rate coefficient for the forward reaction 1, k1, was measured at temperatures between 200 and 260 K at N2 number densities over the range (1.1-10.9) x 10(18) molecules cm-3. The data were fit using the Troe formalism, with an F(c) fixed at 0.6, to yield k0(300) = (6.2 +/- 1.0) X 10(-32) cm6 molecule-2 s-1, k(infinity) = (2.4 +/- 1.2) X 10(-11) cm3 molecule-1 s-1, and n = 4.7 +/- 0.6 (2sigma error limits). The equilibrium constant for reaction 1, K(eq), was measured at five temperatures over the range 232-258 K. A second law analysis of this data along with data reported by Hayman and Cox [Chem. Phys. Lett. 1989,155, 11 yielded DELTAS-degrees = -21.2 +/- 4.5 cal mol-1 K-1 and DELTAH-degrees = -11.1 +/- 1.2 kcal mol-1 (2sigma error limits of the fit). These photochemical and kinetic results are compared with previously reported values. The kinetic, equilibrium, and photochemical data were included in a photochemical box model of the polar stratosphere to assess the role of Cl2O3 in stratospheric chemistry. On the basis of the results of the model, it is concluded that Cl2O3 does not play a significant role in the polar stratosphere.