Discovery of the cyclic C5H radical in TMC-1
Abstract
Cyclic C5H (c-C5H), the radical formed by substituting an ethynyl group CCH for the hydrogen atom in the c-C3H radical, has been detected for the first time in the space. The c-C5H species is an isomer of the well-known linear radical l-C5H and is ∼6 kcal mol−1 less stable. A total of 17 rotational transitions were detected for the c-C5H species in TMC-1 within the 31.0-50.3 GHz range using the Yebes 40m radio telescope. We derive a column density of (9.0 ± 0.9) × 1010 cm−2 for c-C5H. Additionally, we observed 12 lines for l-C5H and derive a column density for it of (1.3 ± 0.3) × 1012 cm−2, which results in an abundance ratio c-C5H/l-C5H of 0.069. This is in sharp contrast with the value found for the analogue system c-C3H/l-C3H, whose ratio is 5.5 in TMC-1. We discuss the formation of c-C5H and conclude that this radical is probably formed in the reaction of atomic carbon with diacetylene.
Based on observations carried out with the Yebes 40m telescope (projects 19A003, 20A014, 20D023, and 21A011). The 40m radio telescope at Yebes Observatory is operated by the Spanish Geographic Institute (IGN; Ministerio de Transportes, Movilidad y Agenda Urbana).- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 2022
- DOI:
- 10.1051/0004-6361/202244063
- arXiv:
- arXiv:2206.00955
- Bibcode:
- 2022A&A...663L...2C
- Keywords:
-
- astrochemistry;
- ISM: molecules;
- ISM: individual objects: TMC-1;
- line: identification;
- molecular data;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication as a Letter in Astronomy and Astrophysics, section 1. Letters to the Editor. The official date of acceptance is 31/05/2022