Stable solid and aqueous H(2)CO(3) from CO(2) and H(2)O at high pressure and high temperature

Carbonic acid (H(2)CO(3)) forms in small amounts when CO(2) dissolves in H(2)O, yet decomposes rapidly under ambient conditions of temperature and pressure. Despite its fleeting existence, H(2)CO(3) 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 CO(2)/H(2)O mixtures under conditions of high pressure and high temperature to explore the potential for reaction to H(2)CO(3) inside celestial bodies. We present a novel method to prepare solid H(2)CO(3) by heating CO(2)/H(2)O mixtures at high pressure with a CO(2) laser. Furthermore, we found that, contrary to present understanding, neutral H(2)CO(3) is a significant component in aqueous CO(2) 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 H(2)CO(3), a role in subduction related phenomena is inferred.