Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 2 3 2002 10.5194/acpd-2-765-2002 http://www.atmos-chem-phys-discuss.net/2/765/2002/ http://www.atmos-chem-phys-discuss.net/2/765/2002/acpd-2-765-2002.html http://www.atmos-chem-phys-discuss.net/2/765/2002/acpd-2-765-2002.pdf 765 788 2002-06-12 The UV-visible absorption cross-sections of IONO₂ J. C. Mössinger D. M. Rowley R. A. Cox Centre for Atmospheric Science, Chemistry Department, University of Cambridge, UK Present address Chemistry Department, University College London, UK The UV-visible absorption spectrum of gaseous IONO₂ has been measured over the wavelength range 245--415 nm using the technique of laser photolysis with time-resolved UV-visible absorption spectroscopy. IONO₂ was produced in situ in the gas phase by laser flash photolysis of NO₂/CF₃I/N₂ mixtures. Post-flash spectra were deconvolved to remove contributions to the observed absorption from other reactant and product species. The resulting spectrum attributed to IONO₂ consists of several overlapping broad absorption bands. Assuming a quantum yield of unity for IONO₂ photolysis, model calculations show that during sunlit hours at noon, 53° N, the first order solar photolysis rate coefficient (J value) for IONO₂ is 4.6 x 10^-2 s^-1.