Astrochemistry

Acenaphthene Derivatives As Signatures Of C11H9 Reactivity With Methylated Naphthalenes

By Keith Cowing

Status Report

astro-ph.GA

June 4, 2026

Filed under astro-ph.GA, astrochemistry, Biosignatures, Interstellar, organic chemistry, PAH, PIRENEA, radiation, Spectroscopy, TMC-1

Acenaphthene Derivatives As Signatures Of C11H9 Reactivity With Methylated Naphthalenes — Top row: molecular structures of 1,4-, 1,5-, and 2,3-dimethylnaphthalene cations (1,4-, 1,5, and 2,3-diMeNp^.+). Bottom row: molecular structures of the three expected longlived isomers of C₁₁H₉⁺ cations: benzyltropylium (BzTr⁺ ), 1-, and 2-naphthylmethylium (1- and 2-NpCH₂⁺ ). — astro-ph.GA

C₁₁H⁺₉ ion is the dominant fragment cation formed from methyl-naphthalene (MeNp) and dimethyl-naphthalene (diMeNp).

Using the multiplex capabilities of PIRENEA, a setup dedicated to laboratory astrophysics, we studied the reactivity of the benzylium-like isomers of C₁₁H⁺₉ with diMeNp under isolated conditions relevant to radiative association. Two reaction products are observed, C₁₂H⁺₁₁ — also formed in the reaction with MeNp — and C₁₃H⁺₁₃, with branching ratios that depend on the specific diMeNp isomer.

The reaction products were subsequently exposed to UV-visible irradiation to gain insight into their structures. The acenaphthylene radical cation, C₁₂H^∙+₈, was identified as the most stable photofragment. We show that this experimental approach, supported by density functional theory calculations and molecular dynamics simulations, provides new constraints on the chemistry of benzylium-type species.

We highlight the role that long-lived ion-molecule complexes can have in promoting C-C coupling and the formation of a pentagonal cycle. Moreover, the chemistry uncovered here highlights new pathways for the formation of pentagonal rings during PAH growth under low-pressure and cold conditions. In particular, it can lead to efficient formation of acenaphthylene-like species, recently detected in the TMC-1 cold cloud.

Ana I. Lozano, Anthony Bonnamy, Aude Simon, Christine Joblin

Comments: 53 pages (38 pages in main and 15 pages in supplementray material)
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2606.03575 [astro-ph.GA] (or arXiv:2606.03575v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2606.03575
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Journal reference: ACS Earth Space Chem. 2026, 10, 1254-1266
Related DOI:
https://doi.org/10.1021/acsearthspacechem.5c00386
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Submission history
From: Christine Joblin
[v1] Tue, 2 Jun 2026 12:44:05 UTC (7,410 KB)
https://arxiv.org/abs/2606.03575
Astrobiology, Astrochemistry,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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