{
  "abstract": "Rotational transitions of SiC$_6$ with $j=26$--$40$ have been detected in IRC+10216, but collisional rate coefficients for SiC$_6$ with He or H$_2$ were previously unavailable. We present rate coefficients for SiC$_6$ rotational excitation by He, calculated using a two-dimensional potential energy surface (PES) at the RCCSD(T)-F12 level under the rigid-rotor approximation. Close-coupling (CC) calculations were performed for low rotational levels, while the coupled-states (CS) method was used for higher levels. Convergence tests were conducted, and CC and CS scattering cross sections were compared. The CS rate coefficients cover rotational levels up to $j=40$ and temperatures of 3--60\\,K. Although CC and CS rate coefficients differ by up to a factor of $\\sim 2$ for some transitions, particularly those affected by weak coupling and resonances, they yield nearly identical excitation and brightness temperatures for the high-$j$ transitions examined, including $19\\rightarrow18$. These results support the reliability of the CS method for non-LTE modelling of the high-$j$ transitions considered, for which CC calculations are computationally impractical. We use reduced-mass scaling of the SiC$_6$--He rate coefficients to estimate those for SiC$_6$--H$_2$ and model the observed transitions. A $χ^2$ analysis of the observed line fluxes, excluding heavily blended features, yields a best-fitting of $n(\\mathrm{H_2})=4.33\\times10^5$\\,cm$^{-3}$ and $N(\\mathrm{SiC_6})=8.11\\times10^{11}$\\,cm$^{-2}$. The latter agrees excellently with the previous observational estimate of $(7.9\\pm1.5)\\times10^{11}$\\,cm$^{-2}$, supporting the consistency of our non-LTE modelling with observational constraints.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.06525",
  "author_total": 4,
  "authors": [
    {
      "name": "Liman Tian"
    },
    {
      "name": "Ziyu Xiang"
    },
    {
      "name": "Chuangang Ning"
    },
    {
      "name": "Xiaolin Chen"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/58pdhk60sr3k5.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.06525",
  "fulltext_url": null,
  "id": "58pdhk60sr3k5",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.06525",
  "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"
    ],
    [
      "openalex",
      "3103|Astrophysics and Star Formation Studies"
    ]
  ],
  "openalex": "W7220739824",
  "pdf_url": "https://arxiv.org/pdf/2610.06525",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-21",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/58pdhk60sr3k5.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:34:18Z",
      "native_id": "2610.06525",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.06525"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "Collisional excitation of SiC$_6$ by helium: cross sections, rate coefficients, and astrophysical implications",
  "title_text": "Collisional excitation of SiC_6 by helium: cross sections, rate coefficients, and astrophysical implications",
  "type": "preprint",
  "updated_at": "2026-10-30T12:34:18Z",
  "url": "https://research.draconitic.com/paper/58pdhk60sr3k5",
  "venue": "arXiv",
  "versions": []
}