{
  "abstract": "The aqueous bisulfite anion supports experimentally established S- and O-protonated isomers whose relative populations vary with temperature, making the pair a compact test of solution-phase electronic-structure methods. We carried out 46 independent Q-Chem 6.2 calculations spanning conformer generation, B3LYP, PBE0 and ωB97X-D, diffuse double-, triple- and quadruple-ζ basis sets, SMD and PCM water, gas-phase controls, frequency calculations and temperature-dependent thermochemistry. Four S-protonated starts collapsed to one minimum within 0.035 kcal mol-1, whereas four O-protonated starts formed a 0.412 kcal mol-1 manifold. At B3LYP/def2-SVPD/SMD, the O-protonated minimum was 12.11 kcal mol-1 lower in electronic energy, but a def2-TZVPD single-point comparison on the selected minima inverted the ordering to +0.641 kcal mol-1, favoring the S-protonated isomer. Energy decomposition localized the 12.75 kcal mol-1 basis shift almost entirely to the intrinsic electronic term; the differential SMD polarization remained near −5.46 kcal mol-1. def2-QZVPD changed the O−S gap by only 0.008 kcal mol-1 for B3LYP, 0.016 for PBE0 and −0.073 for ωB97X-D, establishing triple-ζ convergence. Combining the basis-converged B3LYP electronic energy with validated qRRHO corrections gave ΔG298 = −0.473 kcal mol-1 and Qi = 2.22, close to the experimental Qi = 2.67. However, experiment decreases from Qi = 3.31 at 278 K to 1.63 at 358 K, whereas the calculation increases from 2.03 to 2.54. The associated effective enthalpy changes sign, from −1.746 kcal mol-1 experimentally to +0.550 kcal mol-1 computationally. Continuum-solvated DFT can therefore reproduce the room-temperature equilibrium fortuitously while failing the more stringent temperature-dependent benchmark.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": null,
  "author_total": 1,
  "authors": [
    {
      "name": "Aris Tsai",
      "orcid": "0009-0004-8641-7647"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ahcn5dyw9scbe.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15008139/v1",
  "fulltext_url": null,
  "id": "ahcn5dyw9scbe",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008139/v1",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3107|Advanced Chemical Physics Studies"
    ]
  ],
  "openalex": "W7204958614",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15008139/v1",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-01",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/ahcn5dyw9scbe.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:17Z",
      "native_id": "10.26434/chemrxiv.15008139",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008139/v1"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "openalex:3107|Advanced Chemical Physics Studies",
      "subfield": "amo"
    }
  ],
  "title": "Can continuum-solvated DFT resolve the bisulfite protonation-isomer equilibrium? A quantitative benchmark of S- and O-protonated HSO3",
  "title_text": "Can continuum-solvated DFT resolve the bisulfite protonation-isomer equilibrium? A quantitative benchmark of S- and O-protonated HSO3",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:17Z",
  "url": "https://research.draconitic.com/paper/ahcn5dyw9scbe",
  "venue": "ChemRxiv",
  "versions": []
}