Astrochemistry

Expanding the C3H6O2 Isomeric Interstellar Inventory: Discovery of Lactaldehyde and Methoxyacetaldehyde in G+0.693-0.027

By Keith Cowing

Status Report

astro-ph.GA

January 17, 2026

Filed under astro-ph.GA, astrochemistry, astronomy, biochemistry, biosignature, G+0.693-0.027, Interstellar, molecular cloud, organic chemistry, Spectroscopy

Expanding the C3H6O2 Isomeric Interstellar Inventory: Discovery of Lactaldehyde and Methoxyacetaldehyde in G+0.693-0.027 — Relative energies (including zero-point energy, ZPE, corrections) plotted as a function of the total dipole moment for the targeted C3H6O2 isomers, computed at the B2PLYPD3/aug-cc-pVTZ level of theory (Grimme et al. 2011) using the Gaussian 16 program package (Frisch et al. 2016). Optimized 3D structures at the same level of theory are also shown (carbon atoms in gray, oxygen atoms in red and hydrogen atoms in white). The status of detections in G+0.693 is indicated using the following color code in the molecule name: new first detections in the ISM are shown in red, tentative detections in orange, non-detections in purple and previous detections toward different sources in black. Previous detections toward other sources of methyl acetate (Tercero et al. 2013), anti and gauche ethyl formate (Belloche et al. 2009; Tercero et al. 2013; Rivilla et al. 2017; Peng et al. 2019), hydroxyacetone (Zhou et al. 2020) and 3-hydroxypropanal are also included. Also, new detections based in this work are highlighted in boldface. The 3D representations of all molecules have been visualized with IQmol ( https://www.iqmol.org/). — astro-ph.GA

The tentative detection of 3-hydroxypropanal (HO(CH₂)₂C(O)H) toward the Galactic center molecular cloud G+0.693-0.027 prompts a systematic survey in this source aimed at detecting all C₃H₆O₂ isomers with available spectroscopy. We use an ultra-deep broadband spectral survey of G+0.693-0.027, carried out with the Yebes 40 m and IRAM 30 m telescopes, to conduct the astronomical search.

We report the first interstellar detection of lactaldehyde (CH₃CH(OH)C(O)H) and methoxyacetaldehyde (CH₃OCH₂C(O)H), together with the second detections (i.e., confirmation) of methyl acetate (CH₃C(O)OCH₃) and hydroxyacetone (CH₃C(O)CH₂OH), and new detections in this source of both anti- and gauche- conformers of ethyl formate (CH₃CH₂OC(O)H), the latter tentatively.

In contrast, neither propionic acid, CH₃CH₂C(O)OH, nor glycidol, c-CH₂OCHCH₂OH (i.e., the most and the least stable species within the C₃H₆O₂ family, respectively) were detected, and we provide upper limits on their fractional abundances of ≤1.5 × 10⁻¹⁰ and ≤3.7 × 10⁻¹¹. Interestingly, all C₃H₆O₂ isomers can be synthesized through radical-radical reactions on the surface of dust grains, ultimately tracing back to CO as the parent molecule. We suggest that formation of the detected isomers is mainly driven by successive hydrogenation of CO, producing CH₃OH and CH₃CH₂OH as the primary parent species.

Conversely, propionic acid is thought to originate from the oxygenation of CO via the HOCO intermediate, which help us rationalize its non-detection. Overall, our findings notably expand the known chemical inventory of the interstellar medium and provide direct observational evidence that increasingly complex chemistry involving O-bearing species occurs in space.

M. Sanz-Novo, V. M. Rivilla, I. Jiménez-Serra, L. Colzi, S. Zeng, A. Megías, D. San Andrés, Á. López-Gallifa, A. Martínez-Henares, Z. T. P. Fried, B. A. McGuire, S. Martín, M. A. Requena-Torres, B. Tercero, P. de Vicente, L. Kolesniková, E. R. Alonso, E. J. Cocinero, J. C. Guillemin, I. Kleiner

Comments: Accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2601.07365 [astro-ph.GA] (or arXiv:2601.07365v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2601.07365
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Submission history
From: Miguel Sanz-Novo
[v1] Mon, 12 Jan 2026 09:39:28 UTC (7,360 KB)
https://arxiv.org/abs/2601.07365
Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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