{
  "abstract": "We report ab initio relativistic calculations on the complex Gd$^{18+}$ and Gd$^{26+}$ highly-charged ions, which are relevant to beyond-extreme-ultraviolet (BEUV) light sources based on laser-produced gadolinium plasmas. Using the particle-hole configuration-interaction with many-body perturbation theory (CI+MBPT) method, we systematically saturate the $n=4$ configuration space and determine the influence of multiply excited states on the emissivity spectrum. For Gd$^{26+}$ we find behavior analogous to that of its isoelectronic counterpart Sn$^{12+}$, with strong contributions from multiply excited states, where even the quadruply excited states become significant at certain effective temperatures. In contrast, the industry-relevant 6.7 nm emission of Pd-like Gd$^{18+}$ is dominated by the singly excited $4d^{10} {\\ }^{1}S_{0}$ -- $4d^{9}4f {\\ }^{1}P_{1}$ transition, while multiply excited states primarily contribute to out-of-band emission. The calculated spectra show good agreement with experiment and demonstrate that the importance of multiply excited states depends strongly on both charge state and plasma conditions.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2608.27097",
  "author_total": 5,
  "authors": [
    {
      "name": "M. L. Reitsma"
    },
    {
      "name": "J. Sheil"
    },
    {
      "name": "O. O. Versolato"
    },
    {
      "name": "E. V. Kahl"
    },
    {
      "name": "J. C. Berengut"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ekkvy5bg7xbhj.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2608.27097",
  "fulltext_url": null,
  "id": "ekkvy5bg7xbhj",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2608.27097",
  "language": null,
  "licence": "CC-BY-NC-ND-4.0",
  "licence_label": "CC BY-NC-ND 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "physics.atom-ph"
    ],
    [
      "openalex",
      "3107|Atomic and Molecular Physics"
    ]
  ],
  "openalex": "W7204529179",
  "pdf_url": "https://arxiv.org/pdf/2608.27097",
  "pmcid": null,
  "pmid": null,
  "published": "2026-08-31",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/ekkvy5bg7xbhj.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:41Z",
      "native_id": "2608.27097",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2608.27097"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:physics.atom-ph",
      "subfield": "amo"
    }
  ],
  "title": "Beyond-EUV spectrum of highly-charged gadolinium",
  "title_text": "Beyond-EUV spectrum of highly-charged gadolinium",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:41Z",
  "url": "https://research.draconitic.com/paper/ekkvy5bg7xbhj",
  "venue": "arXiv",
  "versions": []
}