Issue |
A&A
Volume 659, March 2022
|
|
---|---|---|
Article Number | L9 | |
Number of page(s) | 5 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/202243396 | |
Published online | 24 March 2022 |
Letter to the Editor
A new protonated molecule discovered in TMC-1: HCCNCH+⋆
1
Instituto de Física Fundamental, CSIC, Calle Serrano 123, 28006 Madrid, Spain
e-mail: marcelino.agundez@csic.es, jose.cernicharo@csic.es
2
Observatorio Astronómico Nacional, IGN, Calle Alfonso XII 3, 28014 Madrid, Spain
3
Observatorio de Yebes, IGN, Cerro de la Palera s/n, 19141 Yebes, Guadalajara, Spain
Received:
22
February
2022
Accepted:
11
March
2022
In recent years we have seen an important increase in the number of protonated molecules detected in cold dense clouds. Here we report the detection in TMC-1 of HCCNCH+, the protonated form of HCCNC, which is a metastable isomer of HC3N. This is the first protonated form of a metastable isomer detected in a cold dense cloud. The detection was based on observations carried out with the Yebes 40 m telescope and the 30 m telescope of the Institut de Radioastronomie Millimétrique (IRAM), which revealed four harmonically related lines. We derived a rotational constant B = 4664.431891 ± 0.000692 MHz and a centrifugal distortion constant D = 519.14 ± 4.14 Hz. From a high level ab initio screening of potential carriers, we confidently assigned the series of lines to the ion HCCNCH+. We derived a column density of (3.0 ± 0.5) × 1010 cm−2 for HCCNCH+, which results in a HCCNCH+/HCCNC abundance ratio of 0.010 ± 0.002. This value is well reproduced by a state-of-the-art chemical model which, however, is subject to important uncertainties regarding the chemistry of HCCNCH+. The observational and theoretical status of protonated molecules in cold dense clouds indicate that there exists a global trend in which protonated-to-neutral abundance ratios MH+/M increase with increasing proton affinity of the neutral M, although if one is restricted to species M with high proton affinities (> 700 kJ mol−1), MH+/M ratios fall in the range 10−3–10−1, with no apparent correlation with the proton affinity. We suggest various protonated molecules that are good candidates for detection in cold dense clouds in the near future.
Key words: astrochemistry / line: identification / molecular processes / ISM: molecules / radio lines: ISM
Based on observations carried out with the Yebes 40 m telescope (projects 19A003, 20A014, 20D023, and 21A011) and the IRAM 30 m telescope. The 40 m radio telescope 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 2022
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