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Organic molecular anions in interstellar and circumstellar environments

Published online by Cambridge University Press:  01 February 2008

M. A. Cordiner ,
T. J. Millar ,
C. Walsh ,
E. Herbst ,
D. C. Lis ,
T. A. Bell  and
E. Roueff
M. A. Cordiner
Affiliation:
Astrophysics Research Centre, School of Mathematics and Physics, Queen's University, Belfast, BT7 1NN, U.K. email: m.cordiner@qub.ac.uk
T. J. Millar
Affiliation:
Astrophysics Research Centre, School of Mathematics and Physics, Queen's University, Belfast, BT7 1NN, U.K. email: m.cordiner@qub.ac.uk
C. Walsh
Affiliation:
Astrophysics Research Centre, School of Mathematics and Physics, Queen's University, Belfast, BT7 1NN, U.K. email: m.cordiner@qub.ac.uk
E. Herbst
Affiliation:
Departments of Physics, Astronomy and Chemistry, The Ohio State University, Columbus, OH 43210, U.S.A. email: herbst@mps.ohio-state.edu
D. C. Lis
Affiliation:
California Institute of Technology, MC 320-47, Pasadena, CA 91125, U.S.A. email: dcl@caltech.edu
T. A. Bell
Affiliation:
California Institute of Technology, MC 320-47, Pasadena, CA 91125, U.S.A. email: dcl@caltech.edu
E. Roueff
Affiliation:
LUTh & UMR 8102 du CNRS, Observatoire de Paris, 5, Place J. Janssen, F-92190, Meudon, France email: Evelyne.Roueff@obspm.fr
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Abstract

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The synthesis of organic molecular anions in TMC-1 and IRC+10216 is investigated. Modelled C2H−, CN−, C3N−, C5N− and C7N− column densities are sufficiently great that these species might be observable in IRC+10216. Density-enhanced shells in the outer envelope of IRC+10216 are found to enhance the C2H− and CN− column densities by shielding these anions from destruction by UV radiation. From a newly-derived upper column density limit of 6.6 × 1010 cm−2 for C2H− in IRC+10216 we deduce the primary production mechanism for this anion to be C2H2 + H− ⇒ C2H− + H2. In TMC-1, due to the low radiative electron attachment rates calculated for C2H−, CN− and CH2CN−, these species have modelled column densities below the detection threshold. They could, however, be produced in reactions we have not yet considered.

Keywords

AstrochemistryISM: moleculesISM: abundancesISM: cloudsstars: carbon
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Symposium S251: Organic Matter in Space , February 2008 , pp. 157 - 160
Copyright
Copyright © International Astronomical Union 2008

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