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>.