Laboratory Spectroscopy, Theoretical Characterization, And Astronomical Search For Syn-propenethial (CH2CHCHS)

[astro-ph.GA] We report the laboratory characterization of the higher-energy isomer of propenethial, syn-CH₂CHCHS. While the lower-energy isomer, anti-CH₂CHCHS, was detected in the interstellar medium during the QUIJOTE line survey of TMC-1, we report the non-detection of the syn isomer in the same source, deriving an upper limit to its column density of 1.5 × 10¹⁰ cm⁻². (astrochemistry)

A subsequent theoretical investigation into the origin of this non-detection reveals that the most plausible formation pathway for CH₂CHCHS is highly isomer-specific, producing nearly 95% of the anti isomer. This predicted branching ratio allows us to infer an even lower effective upper limit for the abundance of the syn isomer.

In addition, calculations of tunneling-mediated unimolecular isomerization in the gas phase show that syn-CH₂CHCHS converts to the lower-energy anti isomer on timescales of the order of 10³ years. Overall, we conclude that the detection of syn-CH₂CHCHS is highly challenging in both cold and warm interstellar environments.

These results underscore the importance of electronic-structure and kinetic effects in determining isomer abundances across diverse interstellar environments.

Germán Molpeceres, Carlos Cabezas, Marcelino Agúndez, María Mallo, Yasuki Endo, Lucie Kolesniková, Gisela Esplugues, José Cernicharo

Comments: Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2607.24656 [astro-ph.GA] (or arXiv:2607.24656v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2607.24656
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Submission history
From: German Molpeceres
[v1] Mon, 27 Jul 2026 16:52:52 UTC (2,152 KB)
https://arxiv.org/abs/2607.24656

Astrobiology, Astrochemistry,