The UV and visible spectra of chlorine peroxide : constraining the atmospheric photolysis rate

The photolysis of chlorine peroxide (ClOOCl) is a key chemical step in the depletion of polar stratospheric ozone. As such, precise measurements of the absorption cross sections for ClOOCl are required. In this paper we provide two critical pieces of laboratory data with which to constrain the rate of ozone depletion. First, we provide an optically pure ClOOCl spectrum in the photolytically important UV wavelength region (200–350 nm). Second, we provide the first ever measurement of the ClOOCl spectrum in the visible region (509–536 nm) conclusively demonstrating the photolysis of ClOOCl to be negligible in this spectral region. The visible measurement is important because it can be used to anchor other previously recorded UV spectra and hence reduce the uncertainty in the ClOOCl photolysis rate. The calculated photolysis rate from this study indicates that the current models of stratospheric ozone depletion are correct.