期刊
ASTRONOMY & ASTROPHYSICS
卷 517, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201015186
关键词
astrochemistry; line: identification; molecular processes; stars: AGB and post-AGB; circumstellar matter; stars: individual: IRC+10216
资金
- European Community [235753]
- Spanish MICINN [2010 CSD2009-00038, AYA2009-07304, CTQ2008-02578-BQU]
- U.S. National Science Foundation [CHE-0848110]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [0848110] Funding Source: National Science Foundation
We present the first astronomical detection of a diatomic negative ion, the cyanide anion CN-, and quantum mechanical calculations of the excitation of this anion by means of collisions with para-H-2. The anion CN- is identified by observing the J = 2-1 and J = 3-2 rotational transitions in the C-star envelope IRC + 10216 with the IRAM30-m telescope. The U-shaped line profiles indicate that CN-, like the large anion C6H-, is formed in the outer regions of the envelope. Chemical and excitation model calculations suggest that this species forms from the reaction of large carbon anions with N atoms, rather than from the radiative attachment of an electron to CN, as is the case for large molecular anions. The unexpectedly high abundance derived for CN-, 0.25% relative to CN, indicates that its detection in other astronomical sources is likely. A parallel search for the small anion C2H- remains inconclusive, despite the previous tentative identification of the J = 1-0 rotational transition. The abundance of C2H- in IRC + 10216 is found to be vanishingly small, < 0.0014% relative to C2H.
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