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Photodissociation Region

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Encyclopedia of Astrobiology

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Synonyms

PDR; Photon dominated region

Definition

A photodissociation region (PDR) is an interstellar gas phase in which far-ultraviolet (FUV; 6 eV < hν < 13.6 eV, where eV is the energy of the radiation in electron volts) radiation plays a role in the heating and/or chemistry (Tielens and Hollenbach 1985a). These regions include the diffuse atomic interstellar medium, and the surfaces of interstellar molecular clouds exposed to the interstellar radiation field and to intense radiation from nearby OB stars. Note that in the following article we use the standard astronomical notation of square brackets (e.g., [CII]) indicating “forbidden” transitions, that is, transitions from a metastable state. Likewise, the ionization state of an atom is indicated by a Roman numeral, so that I indicates the neutral atom, II is once ionized, and so on (e.g., HII for ionized hydrogen).

Overview

The FUV range of energies is responsible for dissociating molecules and dominates the heating process in...

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References and Further Reading

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Author information

Authors and Affiliations

  1. Astronomy Department, University of Maryland, 20742, College Park, MD, USA

    Mark G. Wolfire

  2. Department of Physics and Astronomy, San José State University, One Washington Square, 95192, San Jose, CA, USA

    Michael J. Kaufman

Authors
  1. Mark G. Wolfire
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  2. Michael J. Kaufman
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Corresponding author

Correspondence to Mark G. Wolfire .

Editor information

Editors and Affiliations

  1. Centro de Biología Molecular, Universidad Autónoma de Madrid, Madrid, Spain

    Ricardo Amils

  2. Labo. d'Astrophysique de Bordeaux (LAB), Observatoire Aquitain des Sciences de l'Univers (OASU), Floirac CX, France

    Muriel Gargaud

  3. Centro de Astrobiología (CAB), Inst. Nacional de Técnica Aeroespacial, Torrejón de Ardoz, Madrid, Spain

    José Cernicharo Quintanilla

  4. Geophysical Lab., Carnegie Institution of Washington, Washington, District of Columbia, USA

    Henderson James Cleaves

  5. Astronomy Department, University of Massachusetts, Amherst, Massachusetts, USA

    William M. Irvine

  6. Dépt. Sc. de la Terre et de l’Atmosphère, Université du Québec, Montréal, Montreal, Québec, Canada

    Daniele Pinti

  7. Centre National d'Etudes Spatiale (CNES) DPI/E2U, Paris CX, France

    Michel Viso

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© 2014 Springer-Verlag Berlin Heidelberg

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Wolfire, M.G., Kaufman, M.J. (2014). Photodissociation Region. In: Amils, R., et al. Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-27833-4_1197-8

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  • DOI: https://doi.org/10.1007/978-3-642-27833-4_1197-8

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  • Online ISBN: 978-3-642-27833-4

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