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http://hdl.handle.net/20.500.12386/31348
Titolo: | Formation of complex molecules in translucent clouds: Acetaldehyde, vinyl alcohol, ketene, and ethanol via nonenergetic processing of C2H2 ice | Autori: | Chuang, K. -J. FEDOSEEV, GLEB Qasim,D. Ioppolo, S. Jäger, C. Henning, Th. PALUMBO, Maria Elisabetta Dishoeck, E. F. van Linnartz, H. |
Data pubblicazione: | 2020 | Rivista: | ASTRONOMY & ASTROPHYSICS | Numero: | 635 | Da pagina:: | A199 | Abstract: | Complex organic molecules (COMs) have been identified toward high- and low-mass protostars as well as molecular clouds, suggesting that these interstellar species originate from the early stage(s) of starformation. The reaction pathways resulting in COMs described by the formula C$_2$H$_\text{n}$O are still under debate. In this work, we investigate the laboratory possible solid-state reactions that involve simple hydrocarbons and OH-radicals along with H$_2$O ice under translucent cloud conditions (1$\leq$A$_V$$\leq$5 and \textit{n}$_\text{H}$$\sim$10$^3$ cm$^{-3}$). We focus on the interactions of C$_2$H$_2$ with H-atoms and OH-radicals, which are produced along the H$_2$O formation sequence on grain surfaces at 10 K. Ultra-high vacuum (UHV) experiments were performed to study the surface chemistry observed during C$_2$H$_2$ + O$_2$ + H codeposition, where O$_2$ was used for the in-situ generation of OH-radicals. Reflection absorption infrared spectroscopy (RAIRS) was applied to in situ monitor the initial and newly formed species. After that, a temperature-programmed desorption experiment combined with a Quadrupole mass spectrometer (TPD-QMS) was used as a complementary analytical tool. The investigated 10 K surface chemistry of C$_2$H$_2$ with H-atoms and OH-radicals not only results in semi and fully saturated hydrocarbons, such as ethylene (C$_2$H$_4$) and ethane (C$_2$H$_6$), but it also leads to the formation of COMs, such as vinyl alcohol, acetaldehyde, ketene, ethanol, and possibly acetic acid. It is concluded that OH-radical addition reactions to C$_2$H$_2$, acting as a molecular backbone, followed by isomerization (i.e., keto-enol tautomerization) via an intermolecular pathway and successive hydrogenation provides a so far experimentally unreported solid-state route for the formation of these species without the need of energetic input. The kinetics of acetaldehyde reacting with impacting H-atoms leading to ketene and ethanol is found to have a preference for the saturated product. The astronomical relevance of the reaction network introduced here is discussed. | URI: | http://hdl.handle.net/20.500.12386/31348 | URL: | https://www.aanda.org/articles/aa/full_html/2020/03/aa37302-19/aa37302-19.html http://arxiv.org/abs/2002.06971v1 |
ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201937302 | Bibcode ADS: | 2020IAUS..350...77P | Fulltext: | open |
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