Volume 641, September 2020
|Number of page(s)||9|
|Section||Letters to the Editor|
|Published online||23 September 2020|
Letter to the Editor
Interstellar nitrile anions: Detection of C3N− and C5N− in TMC-1⋆
Grupo de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain
2 Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain
3 Observatorio Astronómico Nacional (IGN), C/ Alfonso XII, 3, 28014 Madrid, Spain
Accepted: 30 August 2020
We report on the first detection of C3N− and C5N− towards the cold dark core TMC-1 in the Taurus region, using the Yebes 40 m telescope. The observed C3N/C3N− and C5N/C5N− abundance ratios are ∼140 and ∼2, respectively; that is similar to those found in the circumstellar envelope of the carbon-rich star IRC +10216. Although the formation mechanisms for the neutrals are different in interstellar (ion-neutral reactions) and circumstellar clouds (photodissociation and radical-neutral reactions), the similarity of the C3N/C3N− and C5N/C5N− abundance ratios strongly suggests a common chemical path for the formation of these anions in interstellar and circumstellar clouds. We discuss the role of radiative electronic attachment, reactions between N atoms and carbon chain anions Cn−, and that of H− reactions with HC3N and HC5N as possible routes to form CnN−. The detection of C5N− in TMC-1 gives strong support for assigning to this anion the lines found in IRC +10216, as it excludes the possibility of a metal-bearing species, or a vibrationally excited state. New sets of rotational parameters have been derived from the observed frequencies in TMC-1 and IRC +10216 for C5N− and the neutral radical C5N.
Key words: astrochemistry / ISM: lines and bands / ISM: molecules / ISM: individual objects: TMC-1 / molecular data
Based on observations carried out with the Yebes 40 m telescope (projects 19A003, 19A010, and 20A014) and the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescope. The 40 m radiotelescope at Yebes Observatory is operated by the Spanish Geographic Institute (IGN, Ministerio de Transportes, Movilidad y Agenda Urbana). IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).
© ESO 2020
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