In situ characterization of volatile and refractory hydrocarbons produced by UV photolysis of interstellar C2H2 ice
Abstract
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.
Versions
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BibTeX
@misc{samarth2026situ,
title = {{In situ characterization of volatile and refractory hydrocarbons produced by UV photolysis of interstellar C$_2$H$_2$ ice}},
author = {P. Samarth and G. Fedoseev and M. Bulak and S. Ioppolo and L. Hornekær and E. F. van Dishoeck and H. Linnartz and K. -J. Chuang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.17867},
eprint = {2609.17867},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.17867},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - In situ characterization of volatile and refractory hydrocarbons produced by UV photolysis of interstellar C_2H_2 ice
AU - P. Samarth
AU - G. Fedoseev
AU - M. Bulak
AU - S. Ioppolo
AU - L. Hornekær
AU - E. F. van Dishoeck
AU - H. Linnartz
AU - K. -J. Chuang
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2609.17867
UR - https://arxiv.org/abs/2609.17867
AB - Acetylene (C_2H_2) 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 C_2H_2 on dust grains. We experimentally investigate the chemical complexity induced by UV irradiation of pure C_2H_2 ice and characterize both volatile and nonvolatile photoproducts. Experiments were performed with MATRI^2CES 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 × 10^17 photons cm^−2, corresponding to about 10^6 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 C_2H_2 ice can produce substantial molecular complexity and refractory hydrocarbons under astronomically relevant conditions, with possible implications for unidentified infrared emission bands.
ER -