n-Alkanes formed by methyl-methylene addition as a source of meteoritic aliphatics

Merino, P. ; Martínez, L. ; Santoro, G. ; Martínez, J. I. ; Lauwaet, K. ; Accolla, M. ; Ruiz del Arbol, N. ; Sánchez-Sánchez, C. ; Martín-Jimenez, A. ; Otero, R. ; Piantek, M. ; Serrate, D. ; Lebrón-Aguilar, R. ; Quintanilla-López, J. E. ; Mendez, J. ; De Andres, P. L. ; Martín-Gago, J. A.

Resumen: Aliphatics prevail in asteroids, comets, meteorites and other bodies in our solar system. They are also found in the interstellar and circumstellar media both in gas-phase and in dust grains. Among aliphatics, linear alkanes (n-CnH2n+2) are known to survive in carbonaceous chondrites in hundreds to thousands of parts per billion, encompassing sequences from CH4 to n-C31H64. Despite being systematically detected, the mechanism responsible for their formation in meteorites has yet to be identified. Based on advanced laboratory astrochemistry simulations, we propose a gas-phase synthesis mechanism for n-alkanes starting from carbon and hydrogen under conditions of temperature and pressure that mimic those found in carbon-rich circumstellar envelopes. We characterize the analogs generated in a customized sputter gas aggregation source using a combination of atomically precise scanning tunneling microscopy, non-contact atomic force microscopy and ex-situ gas chromatography-mass spectrometry. Within the formed carbon nanostructures, we identify the presence of n-alkanes with sizes ranging from n-C8H18 to n-C32H66. Ab-initio calculations of formation free energies, kinetic barriers, and kinetic chemical network modelling lead us to propose a gas-phase growth mechanism for the formation of large n-alkanes based on methyl-methylene addition (MMA). In this process, methylene serves as both a reagent and a catalyst for carbon chain growth. Our study provides evidence of an aliphatic gas-phase synthesis mechanism around evolved stars and provides a potential explanation for its presence in interstellar dust and meteorites.

Idioma: Inglés

DOI: 10.1038/s42004-024-01248-6

Año: 2024

Publicado en: Communications Chemistry 7, 165 (2024), 10
ISSN: 2399-3669

Factor impacto JCR: 6.2 (2024)

Categ. JCR: CHEMISTRY, MULTIDISCIPLINARY rank: 50 / 239 = 0.209 (2024) - Q1 - T1

Factor impacto SCIMAGO: 1.485 - Biochemistry (Q1) - Materials Chemistry (Q1) - Chemistry (miscellaneous) (Q1) - Environmental Chemistry (Q1)

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Financiación: info:eu-repo/grantAgreement/EC/FP7/610256/EU/Gas and Dust from the Stars to the Laboratory: Exploring the NanoCosmos/NANOCOSMOS
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Financiación: info:eu-repo/grantAgreement/ES/MINECO/CEX2018-000805-M
Financiación: info:eu-repo/grantAgreement/ES/MINECO/MAT2017-85089-C2-1-R
Financiación: info:eu-repo/grantAgreement/ES/MINECO/PID2020-113142RB-C21

Tipo y forma: Article (Published version)