![Schematic illustration of the ablation scheme used at the MATRI2CES setup. The laser fires at 5 Hz while the substrate is moved downward by a motorized Y-translator, ensuring a fresh spot is probed with each shot. -- [astro-ph.GA]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/In-situ.png?fit=1200%2C676&ssl=1)
[astro-ph.GA] Acetylene (C2H2) is commonly observed in star-forming regions, young stellar objects, and the Solar System.
Laboratory and theoretical studies have linked this simplest alkyne to volatile hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) through UV- or cosmic-ray-driven chemistry, but it remains unclear whether refractory material can efficiently form through solid-state reactions of C2H2 on dust grains.
We experimentally investigate the chemical complexity induced by UV irradiation of pure C2H2 ice and characterize both volatile and nonvolatile photoproducts. Experiments were performed with MATRI2CES under ultra-high-vacuum conditions at 15 K using 7.2–10.2 eV photons.
UV-processed ices were monitored in situ by laser desorption post-ionization reflection time-of-flight mass spectrometry (LDPI ReTOF-MS) combined with pulsed ion deflection (PID). Volatile and refractory products were measured in situ at 15 and 300 K, respectively. After a fluence of 3×1017 photons cm−2, corresponding to about 106 years in dense clouds, large saturated and unsaturated hydrocarbons containing up to 13 carbon atoms are formed.
After sublimation of the volatile products, the 300 K residue shows a rich and distinct mass spectrum consistent with refractory material containing conjugated triple (-C≡C-) and double (-C=C-) bonds.
These results demonstrate that UV processing of pure C2H2 ice can produce substantial molecular complexity and refractory hydrocarbons under astronomically relevant conditions, with possible implications for unidentified infrared emission bands.
P. Samarth, G. Fedoseev, M. Bulak, S. Ioppolo, L. Hornekær, E. F. van Dishoeck, H. Linnartz, K. -J. Chuang
Comments: 25 pages, 9 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2609.17867 [astro-ph.GA] (or arXiv:2609.17867v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2609.17867
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Journal reference: Astronomy & Astrophysics, 705, A229 (2026)
Related DOI:
https://doi.org/10.1051/0004-6361/202556672
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Submission history
From: Pranjal Samarth
[v1] Tue, 15 Sep 2026 21:47:38 UTC (5,130 KB)
https://arxiv.org/abs/2609.17867
Astrobiology, Astrochemistry,
