{
  "abstract": "We report the first detection of the neutral methyl radical CH$_3$ in a highly evolved C-rich object, SMP LMC 011, using JWST MIRI/MRS. CH$_3$ is well fitted by an excitation temperature of $T_{\\rm ex} \\simeq$~190\\,K and a column density of $N_{\\rm tot}(\\mathrm{CH_3}) \\simeq 5.6\\times10^{17}$ cm$^{-2}$. We also report the non-detection of ethane (C$_2$H$_6$), consistent with CH$_3$ reacting preferentially with unsaturated radicals rather than self-recombination, which may be inefficient in SMP LMC 011. Combined with the exceptionally large benzene column density of SMP LMC 011, this supports a methyl-addition route from benzene towards alkyl-substituted aromatics. We propose that the high CH$_3$ abundance is driven by the erosion of hydrogenated amorphous carbon (HAC) dust grains in the dense warm torus by UV photons from the central star and/or by shocks, which release CH$_3$ directly into the gas phase. These results establish CH$_3$ as a key reactive intermediate in the formation of complex hydrocarbons in C-rich circumstellar environments. Chemical models that incorporate methyl-addition reactions are needed for a better understanding of PAH formation pathways in evolved stars. The potential detection of alkyl-substituted aromatics such as toluene (C$_7$H$_8$) and ethylbenzene (C$_8$H$_{10}$) in C-rich evolved stars would provide direct confirmation of CH$_3$-driven aromatic growth in circumstellar environments.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.15905",
  "author_total": 20,
  "authors": [
    {
      "name": "Jialu Li"
    },
    {
      "name": "D. A. García-Hernández"
    },
    {
      "name": "A. Manchado"
    },
    {
      "name": "Debayan Das"
    },
    {
      "name": "J. Cami"
    },
    {
      "name": "Els Peeters"
    },
    {
      "name": "G. C. Sloan"
    },
    {
      "name": "B. Aringer"
    },
    {
      "name": "J. Bernard-Salas"
    },
    {
      "name": "C. Bhatt"
    },
    {
      "name": "Nicholas Clark"
    },
    {
      "name": "Harriet L. Dinerstein"
    },
    {
      "name": "M. A. Gómez-Muñoz"
    },
    {
      "name": "Kathleen E. Kraemer"
    },
    {
      "name": "M. Matsuura"
    },
    {
      "name": "R. Sahai"
    },
    {
      "name": "N. C. Sterling"
    },
    {
      "name": "Kevin Volk"
    },
    {
      "name": "G. M. Wahlgren"
    },
    {
      "name": "A. A. Zijlstra"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7av1r45zar9s7.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.15905",
  "fulltext_url": null,
  "id": "7av1r45zar9s7",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.15905",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "arxiv",
      "astro-ph.SR"
    ],
    [
      "openalex",
      "3103|Astrophysics and Star Formation Studies"
    ]
  ],
  "openalex": "W7213345490",
  "pdf_url": "https://arxiv.org/pdf/2609.15905",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-14",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/7av1r45zar9s7.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:21:25Z",
      "native_id": "2609.15905",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.15905"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.SR",
      "subfield": "stellar"
    }
  ],
  "title": "The JWST Proto-PAH Project: Detection of the methyl radical CH$_{3}$ in the highly evolved C-rich object SMP LMC 011",
  "title_text": "The JWST Proto-PAH Project: Detection of the methyl radical CH_3 in the highly evolved C-rich object SMP LMC 011",
  "type": "preprint",
  "updated_at": "2026-10-30T12:21:25Z",
  "url": "https://research.draconitic.com/paper/7av1r45zar9s7",
  "venue": "arXiv",
  "versions": []
}