{
  "abstract": "Molecular ions are crucial in initiating and regulating the formation of molecules in the interstellar medium, and are expected to be sensitive tracers of evolution in star-forming regions. Within the framework of the project `CHemical Evolution of MassIve star-forming COres' (CHEMICO), we investigate the temporal evolution of molecular ions towards three high-mass star-forming cores that represent three sequential evolutionary stages. CHEMICO is based on an unbiased spectral line survey of the bandwidth at 3, 2, and 1.2~mm carried out with the 30m telescope of the Insitut de Radioastronomie millimétrique. We detect 19 molecular ions, including isotopologues. From a local thermodynamic equilibrium analysis, we derive the following main results: (i) Overall, the physical parameters of sulphur-bearing ions are the most sensitive to evolution, whereas those of nitrogen-bearing ions are the least; (ii) The molecular abundances that exhibit the most pronounced temporal variations are those of SO+, DCO+, and N2D+; (iii) A simple analytic approach tailored for warm gas conditions provides cosmic-ray ionisation rates of H2 several orders of magnitude above the canonical values measured in the interstellar medium and with a marked increase with evolution; (iv) The abundance ratio of protonated-to-neutral species increases with the proton affinity of the neutral regardless of the evolutionary stage of the source, indicating that proton-transfer appears to proceed similarly in both cold and warm interstellar environments. Molecular ions exhibit distinct evolutionary trends in high-mass star-forming regions, with sulphur-bearing species and the abundances of N2D+, DCO+, and SO+ emerging as particularly sensitive tracers of evolution. Measured electron fractions and cosmic-ray ionisation rates are in line with an internal production of cosmic-rays that becomes increasingly efficient with time.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.08981",
  "author_total": 8,
  "authors": [
    {
      "name": "F. Fontani"
    },
    {
      "name": "E. Roueff"
    },
    {
      "name": "V. M. Rivilla"
    },
    {
      "name": "Á. López-Gallifa"
    },
    {
      "name": "L. Bizzocchi"
    },
    {
      "name": "L. Colzi"
    },
    {
      "name": "H. Martín-Caballero"
    },
    {
      "name": "P. Caselli"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/97yww8r2c7tme.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.08981",
  "fulltext_url": null,
  "id": "97yww8r2c7tme",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.08981",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.GA"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2610.08981",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-06",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/97yww8r2c7tme.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:27:37Z",
      "native_id": "2610.08981",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.08981"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "CHemical Evolution in MassIve star-forming COres (CHEMICO). II. Molecular ions, electron fraction, and cosmic-ray ionisation rate",
  "title_text": "CHemical Evolution in MassIve star-forming COres (CHEMICO). II. Molecular ions, electron fraction, and cosmic-ray ionisation rate",
  "type": "preprint",
  "updated_at": "2026-10-30T12:27:37Z",
  "url": "https://research.draconitic.com/paper/97yww8r2c7tme",
  "venue": "arXiv",
  "versions": []
}