Synthesis and characterization of crystalline polymeric carbonic acid (H2CO3) with s p 3-hybridized carbon at elevated pressures

Abstract

Abstract The existence of polymeric carbonic acid (H2CO3) at elevated pressures has been predicted, but has not been investigated experimentally. Here, polymeric carbonic acid containing s p 3-hybridized carbon was synthesized and characterized at ≈40 GPa. H2CO3 single crystals were obtained by laser-heating a H2O + CO2 mixture in a diamond anvil cell. The orthorhombic crystal structure (C m c21 with Z = 4) was refined from synchrotron single crystal X-ray diffraction data and is in agreement with a structural model predicted earlier. The crystal structure of H2CO3-C m c21 is characterized by $${[{{\rm{CO}}}_{4}]}^{4-}$$ [ CO 4 ] 4 − building blocks which are connected via corner sharing, forming chains along the c-axis. The combination of single crystal X-ray data with experimental Raman spectroscopy and DFT-calculations confirms that the structural model of H2CO3-C m c21 is appropriate. The synthesis condition of polymeric carbonic acid points towards its potential existence in ice giants including the ones present in our solar system.