Iodine monoxide
Other names
Iodine(II) oxide, iodosyl, oxidoiodine
3D model (JSmol)
  • InChI=1S/IO/c1-2
  • [O]I
Molar mass 142.903 g·mol−1
Appearance purple gas[citation needed]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Iodine monoxide is a binary inorganic compound of iodine and oxygen with the chemical formula IO•. A free radical, this compound is the simplest of many iodine oxides.[1][2][3] It is similar to the oxygen monofluoride, chlorine monoxide and bromine monoxide radicals.


Iodine monoxide can be obtained by the reaction between iodine and oxygen:[4]

I2 + O2 → 2 IO

Chemical properties

Iodine monoxide decomposes to its prime elements:[citation needed]

2 IO → I2 + O2

Iodine monoxide reacts with nitric oxide:[5]

2 IO + 2 NO → I2 + 2 NO2


Atmospheric iodine atoms (e.g. from iodomethane) can react with ozone to produce the iodine monoxide radical:[6][5]

I2 + 2 O3 → 2 IO + 2 O2

This process can contribute to ozone depletion.[citation needed]


  1. ^ Dix, Barbara; Baidar, Sunil; Bresch, James F.; Hall, Samuel R.; Schmidt, K. Sebastian; Wang, Siyuan; Volkamer, Rainer (5 February 2013). "Detection of iodine monoxide in the tropical free troposphere". Proceedings of the National Academy of Sciences. 110 (6): 2035–2040. doi:10.1073/pnas.1212386110. ISSN 0027-8424. PMC 3568334.
  2. ^ "Iodine oxide". NIST.
  3. ^ Haynes, William M. (9 June 2015). CRC Handbook of Chemistry and Physics, 96th Edition. CRC Press. p. 2-17. ISBN 978-1-4822-6097-7. Retrieved 27 March 2023.
  4. ^ Nikitin, I. V. (13 March 2008). "HALOGEN MONOXIDES" (in Russian). Institute of Problems of Chemical Physics, Russian Academy of Sciences. Retrieved 27 March 2023.
  5. ^ a b Brasseur, Guy P.; Solomon, Susan (28 December 2005). Aeronomy of the Middle Atmosphere: Chemistry and Physics of the Stratosphere and Mesosphere. Springer Science & Business Media. p. 379. ISBN 978-1-4020-3824-2. Retrieved 27 March 2023.
  6. ^ "The Atmospheric Chemistry of Iodine Monoxide" (PDF). NIST. Retrieved 27 March 2023.