| Issue |
A&A
Volume 680, December 2023
|
|
|---|---|---|
| Article Number | A25 | |
| Number of page(s) | 11 | |
| Section | Interstellar and circumstellar matter | |
| DOI | https://doi.org/10.1051/0004-6361/202347112 | |
| Published online | 04 December 2023 | |
Millimetre and submillimetre spectroscopy of isobutene and its detection in the molecular cloud G+0.693★
1
I. Physikalisches Institut, Universität zu Köln,
Zülpicher Str. 77,
50937
Köln, Germany
e-mail: fatima@ph1.uni-koeln.de; hspm@ph1.uni-koeln.de
2
Centro de Astrobiología (CAB), CSIC-INTA,
Ctra. de Ajalvir Km. 4, Torrejón de Ardoz,
28850
Madrid, Spain
Received:
5
June
2023
Accepted:
14
September
2023
Context. Isobutene ((CH3)2C=CH2) is one of the four isomers of butene (C4H8). Given the detection of propene (CH3CH=CH2) toward TMC-1, and also in the warmer environment of the solar-type protostellar system IRAS 16293–2422, one of the next alkenes, isobutene, is a promising candidate to be searched for in space.
Aims. We aim to extend the limited line lists of the main isotopologue of isobutene from the microwave to the millimetre region in order to obtain a highly precise set of rest frequencies and to facilitate its detection in the interstellar medium.
Methods. We investigated the rotational spectrum of isobutene in the 35–370 GHz range using absorption spectroscopy at room temperature. Quantum-chemical calculations were carried out to evaluate vibrational frequencies.
Results. We determined new or improved spectroscopic parameters for isobutene up to a sixth-order distortion constant. These new results enabled its detection in the G+0.693 molecular cloud for the first time, where propene was also recently found. The propene to isobutene column density ratio was determined to be about 3:1.
Conclusions. The observed spectroscopic parameters for isobutene are sufficiently accurate that calculated transition frequencies should be reliable up to 700 GHz. This will further help in observing this alkene in other, warmer regions of the ISM.
Key words: astrochemistry / techniques: spectroscopic / molecular data / ISM: molecules / radio lines: ISM / ISM: individual objects: G+0.693-0.027
Transition frequencies from this work as well as related data from earlier work are available at the CDS. We also provide quantum numbers, uncertainties, and residuals between measured frequencies and those calculated from the final sets of spectroscopic parameters. The data are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/680/A25
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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