ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-2-227-2002 The UV-visible absorption cross-sections of IONO<sub>2</sub> Mössinger J. C. 1 Rowley D. M. 2 Cox R. A. 1 Centre for Atmospheric Science, Chemistry Department, University of Cambridge, UK present address: Chemistry Department, University College London, UK 10 09 2002 2 3 227 234 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/2/227/2002/acp-2-227-2002.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/2/227/2002/acp-2-227-2002.pdf

The UV-visible absorption spectrum of gaseous IONO<sub>2</sub> has been measured over the wavelength range 245--415 nm using the technique of laser photolysis with time-resolved UV-visible absorption spectroscopy. IONO<sub>2</sub> was produced in situ in the gas phase by laser flash photolysis of NO<sub>2</sub>/CF<sub>3</sub>I/N<sub>2</sub> mixtures. Post flash spectra were deconvolved to remove contributions to the observed absorption from other reactant and product species. The resulting spectrum attributed to IONO<sub>2</sub> consists of several overlapping broad absorption bands. Assuming a quantum yield of unity for IONO<sub>2</sub><sub> </sub>photolysis, model calculations show that during sunlit hours at noon, 53° N, the first order solar photolysis rate coefficient (J value) for IONO<sub>2</sub> is 4.0 x 10<sup>-2</sup> s<sup>-1</sup>.