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ON THE UBIQUITY OF MOLECULAR ANIONS IN THE DENSE INTERSTELLAR MEDIUM

M. A. Cordiner ; J. V. Buckle ; Eva Wirström (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; Henrik Olofsson (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; S. B. Charnley ; V. P. Nada
Astrophysical Journal (0004-637X). Vol. 770 (2013), 1,
[Artikel, refereegranskad vetenskaplig]

Results are presented from a survey for molecular anions in seven nearby Galactic star-forming cores and molecular clouds. The hydrocarbon anion C6H- is detected in all seven target sources, including four sources where no anions have been previously detected: L1172, L1389, L1495B, and TMC-1C. The C6H-/C6H column density ratio is greater than or similar to 1.0% in every source, with a mean value of 3.0% (and standard deviation 0.92%). Combined with previous detections, our results show that anions are ubiquitous in dense clouds wherever C6H is present. The C6H-/C6H ratio is found to show a positive correlation with molecular hydrogen number density, and with the apparent age of the cloud. We also report the first detection of C4H- in TMC-1 (at 4.8 sigma confidence), and derive an anion-to-neutral ratio C4H-/C4H = (1.2 +/- 0.4) x 10(-5)(= 0.0012% +/- 0.0004%). Such a low value compared with C6H- highlights the need for a revised radiative electron attachment rate for C4H. Chemical model calculations show that the observed C4H- could be produced as a result of reactions of oxygen atoms with C5H- and C6H-.

Nyckelord: astrochemistry, ISM: abundances, ISM: clouds, ISM: molecules, stars: formation, carbon-chain molecules, star-formation, negative-ions, line, observations, dark clouds, cores, chemistry, tmc-1, millimeter, c6h



Denna post skapades 2013-07-11. Senast ändrad 2014-09-02.
CPL Pubid: 180110

 

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