title: Stable solid and aqueous H2CO3 from CO2 and H2O at high pressure and high temperature.
abstract: Carbonic acid (H2CO3) forms in small amounts when CO2 dissolves in H2O, yet decomposes rapidly under ambient conditions of temperature and pressure. Despite its fleeting existence, H2CO3 plays an important role in the global carbon cycle and in biological carbonate-containing systems. The short lifetime in water and presumed low concentration under all terrestrial conditions has stifled study of this fundamental species. Here, we have examined CO2/H2O mixtures under conditions of high pressure and high temperature to explore the potential for reaction to H2CO3 inside celestial bodies. We present a novel method to prepare solid H2CO3 by heating CO2/H2O mixtures at high pressure with a CO2 laser. Furthermore, we found that, contrary to present understanding, neutral H2CO3 is a significant component in aqueous CO2 solutions above 2.4 GPa and 110 °C as identified by IR-absorption and Raman spectroscopy. This is highly significant for speciation of deep C-O-H fluids with potential consequences for fluid-carbonate-bearing rock interactions. As conditions inside subduction zones on Earth appear to be most favorable for production of aqueous H2CO3, a role in subduction related phenomena is inferred.
authors.affiliation: Max Planck Institute for Chemistry, Chemistry and Physics at High Pressures Group and Atmospheric Chemistry Department, PO Box 3060, 55020 Mainz, Germany.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Wang
authors.affiliation: Max Planck Institute for Chemistry, Chemistry and Physics at High Pressures Group and Atmospheric Chemistry Department, PO Box 3060, 55020 Mainz, Germany.
authors.forename: Janek
authors.initials: J
authors.lastname: Zeuschner
authors.affiliation: Max Planck Institute for Chemistry, Chemistry and Physics at High Pressures Group and Atmospheric Chemistry Department, PO Box 3060, 55020 Mainz, Germany.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Eremets
authors.affiliation: Max Planck Institute for Chemistry, Chemistry and Physics at High Pressures Group and Atmospheric Chemistry Department, PO Box 3060, 55020 Mainz, Germany.|Institute of Crystallography, Russian Academy of Sciences, Leninsky pr. 59, Moscow 119333, Russia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Troyan
authors.affiliation: Max Planck Institute for Chemistry, Chemistry and Physics at High Pressures Group and Atmospheric Chemistry Department, PO Box 3060, 55020 Mainz, Germany.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Willams
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