{
  "abstract": "Carbonic acid (H2CO3) is connected with the dissolved CO2 and bicarbonate (HCO3-) equilibria in aqueous solutions. Its two elementary reactions in water, acid dissociation and dehydration to CO2, are difficult to resolve because both are coupled to proton transfer through hydrogen-bonded networks. In this work, we combine 0.5 ns of unbiased PBE-D3 molecular dynamics of 1 molar solution of H2CO3 with metadynamics on the O - H coordination (H2CO3 = HCO3- + H+) and the C - O distance of the leaving hydroxyl (H2CO3 <=> CO2 + H2O). These unbiased trajectories show frequent cis-cis <=> cis-trans interconversion through long-lived bicarbonate (well separated from solvated proton, H3O+, and also mediated by a short-lived three-water [H2O...H3O+...H2O] ring that acts as a solvent-shared ion pair (SSIP); only 16-23% of deprotonation events reach a solvent-separated ion pair (SShIP). Resolving ion-pairs as SSIP for proper reaction leads to an improved estimate of pKa1 from 1.1 to 2.4, toward the experimental 3.45-3.59 (measured at supposedly infinite dilution). Further, metadynamics simulations provide a dehydration barrier of 17.8 (1D) and 15.3 kcal/mol (2D), suggesting that the final product CO2 + H2O is 2.8 kcal/mol below H2CO3. Our two-dimensional free energy surface also shows that C--O cleavage proceeds through the CO2 + OH- which further goes down by 9.9 kcal/mol to product CO2 + H2O.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2611.04121",
  "author_total": 4,
  "authors": [
    {
      "name": "Prabhat Prakash"
    },
    {
      "name": "Karnamohit Ranka"
    },
    {
      "name": "Frances A. Houle"
    },
    {
      "name": "William A. Goddard III"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/arkhknkncb44c.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.04121",
  "fulltext_url": null,
  "id": "arkhknkncb44c",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.04121",
  "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",
      "cond-mat.mtrl-sci"
    ],
    [
      "arxiv",
      "physics.chem-ph"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2611.04121",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/arkhknkncb44c.ris",
  "sources": [
    {
      "first_seen": "2026-11-04T15:21:25Z",
      "native_id": "2611.04121",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.04121"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "arxiv:physics.chem-ph",
      "subfield": "physical"
    },
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.mtrl-sci",
      "subfield": "condensed-matter"
    }
  ],
  "title": "Bicarbonate/carbonic acid equilibria in aqueous solutions: Conformational Dynamics, Ion-Pair Speciation, and Free Energy Landscapes from Ab Initio Molecular Dynamics and Metadynamics",
  "title_text": "Bicarbonate/carbonic acid equilibria in aqueous solutions: Conformational Dynamics, Ion-Pair Speciation, and Free Energy Landscapes from Ab Initio Molecular Dynamics and Metadynamics",
  "type": "preprint",
  "updated_at": "2026-11-05T15:20:35Z",
  "url": "https://research.draconitic.com/paper/arkhknkncb44c",
  "venue": "arXiv",
  "versions": []
}