KINETIC, THERMOCHEMICAL, AND SPECTROSCOPIC STUDY OF CL2O3

The UV absorption spectrum of Cl2O3 between 220 and 320 nm was measure d using time-resolved transient absorption. Cl2O3 was produced followi ng 193-nm pulsed laser photolysis of N2O/Cl2/OClO/He or Cl2-Cl2/OClO/N 2 gas mixtures by reaction 1: ClO + OClO + M --> Cl2O3 + M. The absorp tion spectrum peaks at 267 nm with a cross section of (1.60(-0.22)+0.3 5) X 10(-17) cm2 (2sigma error limits including estimated systematic e rrors). The rate coefficient for the forward reaction 1, k1, was measu red 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 d ata 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 DELT AH-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 wer e included in a photochemical box model of the polar stratosphere to a ssess the role of Cl2O3 in stratospheric chemistry. On the basis of th e results of the model, it is concluded that Cl2O3 does not play a sig nificant role in the polar stratosphere.