Dynamics of Carbonic Acid in Aqueous Systems

Carbonic acid (H₂CO₃) occupies a central role in geochemical and biological processes, mediating the transfer of carbon between aqueous, gaseous and solid phases. In water, it exists in rapid equilibrium with dissolved CO₂ and its deprotonated forms, bicarbonate (HCO₃⁻) and carbonate (CO₃²⁻), with interconversion rates that are highly sensitive to pH, ionic strength and temperature. Under ambient conditions, the uncharged H₂CO₃ species is fleeting, yet its transient formation and decomposition govern buffering capacity in natural waters and physiological fluids. At elevated pressures and temperatures, neutral carbonic acid attains appreciable stability, influencing deep-Earth fluid speciation and subduction-zone carbon transport. In solution, H₂CO₃ undergoes conformational interconversion through hydrogen-bond rearrangements, and its vibrational modes are strongly perturbed by solvation dynamics. Radical-mediated pathways can accelerate its breakdown to CO₂ and H₂O or give rise to reactive intermediates that participate in complex organic transformations. A precise understanding of these dynamic processes underpins predictions of oceanic CO₂ uptake, acid–base regulation in living systems and the behaviour of carbon-bearing fluids in geological settings.

Research from Nature Portfolio

Work under high-pressure, high-temperature conditions has shown that neutral H₂CO₃ becomes a major component of CO₂–H₂O mixtures above 2.4 GPa and 110 °C. Infrared absorption and Raman spectroscopy identify significant concentrations of undissociated carbonic acid in deep-Earth fluids, suggesting a hitherto unrecognised role in fluid–rock interactions within subduction zones. Complementary single-crystal X-ray diffraction studies at pressures above 4 GPa have resolved the structure of a solid phase previously ascribed to carbonic acid, revealing triclinic lattices of hydrogen-bonded dimers. These findings redefine phase equilibria in the water–CO₂ system and extend the thermodynamic boundaries for H₂CO₃ stability in planetary interiors.

Dynamics of Carbonic Acid in Aqueous Systems publication trend

The graph below shows the total number of articles in dynamics of carbonic acid in aqueous systems across all publications each year (not limited to Nature Index journals).

Technical terms

Carbonic acid (H₂CO₃): A weak diprotic acid formed by the hydration of carbon dioxide, central to acid–base equilibria in aqueous media.

Bicarbonate (HCO₃⁻): The conjugate base of carbonic acid, predominant at physiological pH and key to buffering in biological systems.

Conformer: A distinct spatial arrangement of a molecule arising from rotation about single bonds, affecting its spectroscopic and reactive properties.

Hydration shell: The layer of solvent molecules directly interacting with a solute, influencing its dynamics and stability.

Anharmonicity: Deviation of molecular vibrations from the simple harmonic model, essential for accurate prediction of infrared spectra.

References

1. Conformer-Specific Photoelectron Spectroscopy of Carbonic Acid: H2CO3. The Journal of Physical Chemistry Letters (2024).
2. Investigation of radical-initiated carbonic acid decomposition and mediated molecule formation. iScience (2025).
3. Stable solid and aqueous H2CO3 from CO2 and H2O at high pressure and high temperature. Scientific Reports (2016).
4. Water-carbon dioxide solid phase equilibria at pressures above 4 GPa. Scientific Reports (2017).
5. Solving the Puzzle of the Carbonic Acid Vibrational Spectrum – an Anharmonic Story. ChemPhysChem (2024).