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.

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.

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. 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. 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.

Mariyam Fatima, Holger S. P. Müller, Oliver Zingsheim, Frank Lewen, Víctor M. Rivilla, Izaskun Jiménez-Serra, Jesús Martín-Pintado, Stephan Schlemmer

Comments: 11 pages including figures, tables, references, and appendix; Accepted for publication in Astronomy and Astrophysics
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM); Atomic and Molecular Clusters (physics.atm-clus); Chemical Physics (physics.chem-ph)
Cite as: arXiv:2309.17236 [astro-ph.GA] (or arXiv:2309.17236v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2309.17236
Related DOI:
https://doi.org/10.1051/0004-6361/202347112
Submission history
From: Mariyam Fatima
[v1] Fri, 29 Sep 2023 13:38:02 UTC (1,419 KB)
https://arxiv.org/abs/2309.17236
Astrobiology, Astrochemistry,