Ultraviolet absorption cross sections of Cl₂O₂ between 210 and 410 nm

The ultraviolet and infrared absorption cross sections of Cl₂O₂ have been measured. The transient Cl₂O₂ molecule was produced by using the gas-phase reaction ClO + ClO + M → Cl₂O₂ + M. Three independent ClO radical source reactions were used in this study: Cl + O₃, Cl + Cl₂O, and Cl + OClO. The Cl₂O₂ UV absorption spectrum was recorded over the range 200-450 nm with a diode array spectrometer over the temperature range 205-250 K. The Cl₂O₂ infrared absorption spectrum was recorded with a high-resolution Fourier transform spectrometer over the range 500-2000 cm^-1. Both spectrometers were optically coupled to a fast flow multipass absorption cell. The UV absorption spectrum of Cl₂O₂ is a structureless continuum with a peak at 245 nm. The measurable absorption extends out to 410 nm. The UV absorption cross section at the peak of the spectrum, 245 nm, was measured to be (6.5_-0.5^+0.8) × 10^-18 cm². Infrared absorption features centered at 560, 653, and 750 cm^-1 have been assigned to the Cl₂O₂ molecule. The present results are compared with other reported UV and IR measurements and the sources of discrepancies are discussed. The role of Cl₂O₂ in atmospheric chemistry and in particular the Antarctic ozone "hole" are discussed.