Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso

Hydroxyl Radical

  • William M. Irvine
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_1810-4




The hydroxyl radical, containing single oxygen and hydrogen atoms, is highly reactive. In the terrestrial troposphere, it interacts with and removes a number of pollutants as well as the greenhouse gases methane and ozone. It can damage typical biological macromolecules. As a free diatomic molecule, it is widespread in the interstellar medium of our Milky Way galaxy and other galaxies, where it is frequently observed in maser emission. Some external galaxies contain so-called OH megamasers, with luminosity orders of magnitude greater than masers in our Galaxy. In the solar system, OH is a major constituent of cometary comae and an indirect measure of their water content.


The OH radical was the first interstellar molecule detected by radio astronomers, in 1963 by Weinreb et al. Measurements of the Zeeman effect for OH transitions have subsequently been used to estimate the magnetic field in the interstellar medium. In 1981, the pure rotational lines of OH...


Interstellar Medium Diatomic Molecule Molecular Cloud Continuum Emission Zeeman Effect 
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References and Further Reading

  1. Bockelee-Morvan D, Crovisier J, Mumma MJ, Weaver HA (2004) The composition of cometary volatiles. In: Festou MC, Keller HU, Weaver H (eds) Comets II. The University of Arizona Press, Tucson, pp 391–423Google Scholar
  2. Hartquist TW, Williams DA (1995) The chemically controlled cosmos. Cambridge University Press, CambridgeGoogle Scholar
  3. Weinreb S, Barrett AH, Meeks L, Henry JC (1963) Radio observations of OH in the interstellar medium. Nature 200:829–831CrossRefADSGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Department of AstronomyUniversity of MassachusettsAmherstUSA