Astronomical detection of C4H^-, the second interstellar anion
Abstract
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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- May 2007
- DOI:
- 10.1051/0004-6361:20077415
- Bibcode:
- 2007A&A...467L..37C
- Keywords:
-
- stars: individual: IRC+10216;
- stars: carbon;
- radio lines: stars;
- astrochemistry;
- line: identification;
- stars: AGB and post-AGB