Encyclopedia of Astrobiology

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

Self-Shielding Effects on Isotope Fractionation

Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_5195-2

Synonyms

Definition

The self-shielding effect is a phenomenon expected to occur in a gas medium illuminated by a light source, when a molecule in the gas absorbs light with a particular wavelength that may result in its dissociation. The light of this wavelength is gradually attenuated as it travels through the gas medium, leading to a decreased photodissociation rate of the target molecule. The attenuation rate of the light depends on the abundance of the molecule. When molecules with different combinations of isotopes are photodissociated by different wavelengths, this effect may cause an abundance-dependent isotope fractionation, as opposed to the common mass-dependent fractionation.

Overview

The self-shielding effect may occur when the following conditions are met. (1) Line absorption: The absorption of the photodissociating light occurs only at a narrow range of particular wavelengths. (2) The light with the wavelength of interest...

Keywords

Photochemistry Photodissociation Mass-independent fractionation 
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References and Further Reading

  1. Bally J, Langer WD (1982) Isotope-selective photodestruction of carbon-monoxide. Astrophys J 255:143–148CrossRefADSGoogle Scholar
  2. Chakraborty S, Ahmed M, Jackson TL, Thiemens MH (2008) Experimental test of self-shielding in vacuum ultraviolet photodissociation of CO. Science 321:1328–1331, See also comments on this paperCrossRefADSGoogle Scholar
  3. Clayton RN (2002) Self-shielding in the solar nebula. Nature 415:860–861CrossRefADSGoogle Scholar
  4. Kitamura Y, Shimizu M (1983) Oxygen isotopic anomaly and solar nebular photochemistry. Moon Planet 29:199–202CrossRefADSGoogle Scholar
  5. Lyons JR, Young ED (2005) CO self-shielding as the origin of oxygen isotope anomalies in the early solar nebula. Nature 435:317–320CrossRefADSGoogle Scholar
  6. Navon O, Wasserburg GJ (1985) Self-shielding in O2 – a possible explanation for oxygen isotope anomalies in meteorites? Earth Planet Sci Lett 73:1–16CrossRefADSGoogle Scholar
  7. Visser R, van Dishoeck EF, Black JH (2009) The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks. Astron Astrophys 503:323–343CrossRefADSGoogle Scholar
  8. Warin S, Benayoun JJ, Viala YP (1996) Photodissociation and rotational excitation of interstellar CO. Astron Astrophys 308:535–564ADSGoogle Scholar
  9. Yurimoto H, Kuramoto K (2004) Molecular cloud origin for the oxygen isotope heterogeneity in the solar system. Science 305:1763–1766CrossRefADSGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Department of Earth and Space SciencesOsaka UniversityToyonakaJapan