EDP Sciences
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Volume 467, Number 2, May IV 2007
Page(s) L37 - L40
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20077415

A&A 467, L37-L40 (2007)
DOI: 10.1051/0004-6361:20077415


Astronomical detection of C $\mathsf{_{4}H^-}$, the second interstellar anion

J. Cernicharo1, M. Guélin2, M. Agúndez1, K. Kawaguchi3, M. McCarthy4, and P. Thaddeus4

1  Dpt. Molecular and Infrared Astrophysics, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006, Spain
    e-mail: cerni@damir.iem.csic.es
2  IRAM, Domaine Universitaire, 300 rue de la piscine, 38400 St Martin d'Hères, France
    e-mail: guelin@iram.fr
3  Department of Chemistry, Faculty of Science, Okayama University, Tsushimanaka, Okayama 700-8530, Japan
4  Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

(Received 6 March 2007 / Accepted 30 March 2007)

Aims.Following the recent detection of C6H- in the laboratory and in space we have succeeded in studying the microwave spectrum of C4H-. We report here the first detection in space of this negative ion.
Methods.We have observed in the envelope of the carbon star IRC +10216 five lines corresponding to the J = 9-8, 11-10, 12-11, 14-13 and 15-14 rotational transitions of C4H-. The C4H- lines have a cusped shape, denoting that this ion is formed in the outer part of the envelope, like its neutral counterpart C4H.
Results.The abundance of C4H- in IRC+10216 is 1/6 of the abundance of C6H- and 1/4200 of that of C4H.
Conclusions.The detection of C4H-, after that of C6H-, confirms the theoretical prediction that C-chain anions are abundant in interstellar clouds and yields a first measurement of the electron radiative attachment rates.

Key words: stars: individual: IRC+10216 -- stars: carbon -- radio lines: stars -- astrochemistry -- line: identification -- stars: AGB and post-AGB

© ESO 2007