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Organic molecular anions in interstellar and circumstellar environments

Published online by Cambridge University Press:  01 February 2008

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.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2008

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