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http://hdl.handle.net/20.500.12386/34340
Titolo: | Ion irradiation triggers the formation of the precursors of complex organics in space. The case of formaldehyde and acetaldehyde | Autori: | URSO, Riccardo Giovanni Hénault, E. Brunetto, R. Baklouti, D. BARATTA, Giuseppe Djouadi, Z. Elsaesser, A. SCIRE` SCAPPUZZO, Carlotta STRAZZULLA, Giovanni PALUMBO, Maria Elisabetta |
Data pubblicazione: | 2022 | Rivista: | ASTRONOMY & ASTROPHYSICS | Numero: | 668 | Da pagina:: | A169 | Abstract: | Context. Cosmic rays and solar energetic particles induce changes in the composition of compounds frozen onto dust grains in the interstellar medium (ISM), in comets, and on the surfaces of atmosphere-less small bodies in the outer Solar System. This induces the destruction of pristine compounds and triggers the formation of various species, including the precursors of complex organics. <BR /> Aims: We investigate the role of energetic ions in the formation of formaldehyde (H<SUB>2</SUB>CO) and acetaldehyde (CH<SUB>3</SUB>CHO), which are observed in the ISM and in comets, and which are thought to be the precursors of more complex compounds such as hexamethylenete-tramine (HMT), which is found in carbonaceous chondrites and in laboratory samples produced after the irradiation and warm-up of astrophysical ices. <BR /> Methods: We performed ion irradiation of water, methanol, and ammonia mixtures at 14-18 K. We bombarded frozen films with 40-200 keV H<SUP>+</SUP> that simulate solar energetic particles and low-energy cosmic rays. Samples were analysed by infrared transmission spectroscopy. <BR /> Results: Among other molecules, we observe the formation of H<SUB>2</SUB>CO and CH<SUB>3</SUB>CHO, and we find that their abundance depends on the dose and on the stoichiometry of the mixtures. We find that the H<SUB>2</SUB>CO abundance reaches the highest value after a dose of 10 eV/16u and then it decreases as the dose increases. <BR /> Conclusions: The data suggest that surfaces exposed to high doses are depleted in H<SUB>2</SUB>CO. This explains why the amount of HMT in organic residues and that formed after irradiation of ices depends on the dose deposited in the ice. Because the H<SUB>2</SUB>CO abundance decreases at doses higher than 10 eV/16u, a lower quantity of H<SUB>2</SUB>CO is available to form HMT during the subsequent warm-up. The H<SUB>2</SUB>CO abundances caused by ion bombardment are insufficient to explain the ISM abundances, but ion bombardment can account for the abundance of CH<SUB>3</SUB>CHO towards the ISM and comets. | URI: | http://hdl.handle.net/20.500.12386/34340 | URL: | https://www.aanda.org/articles/aa/full_html/2022/12/aa44522-22/aa44522-22.html https://api.elsevier.com/content/abstract/scopus_id/85145358847 |
ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/202244522 | Bibcode ADS: | 2022A&A...668A.169U | Fulltext: | open |
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