RATE COEFFICIENT FOR THE TERMOLECULAR CHANNEL OF THE SELF-REACTION OF CLO

The rate coefficient for the reaction ClO + ClO →M Cl2O2 has been measured by using a flash photolysis/UV absorption technique at temperatures from 200 to 263 K and pressures from 25 to 600 Torr in N2, O2, He, and SF6. Conventional single-wavelength detection and diode array spectrometry have both been employed in monitoring the reactant and product species. The UV absorption cross section of ClO has been measured in the same temperature range, from 220 to 350 nm, by using the diode array, and at 282.65 nm (the maximum of the ClO (9,0) band) by using the single-wavelength detection. The reactions of chlorine atoms with O3 and Cl2O have been used to produce ClO. The title reaction is believed to play a role in the loss of ozone from the Antarctic stratosphere during the austral spring. At the temperatures and pressures relevant to the Antarctic stratosphere, our measured values agree with the recent work of Sander et al. and are considerably smaller than the values obtained by Hayman et al. Over the range of conditions relevant to the Antarctic ozone loss, our measurements differ from Hayman et al. by a factor ranging from 1.3 to 3.0, with the discrepancy being ∼1.9 at the altitude of maximum ozone loss. We have found Cl2O2 to be the major product of this reaction under these conditions, and we have established an upper limit of 1% for the production of OClO. © 1990 American Chemical Society.