Carbon Dioxide at High Pressure and Temperature

We present a review of recent studies of carbon dioxide (CO2) at high pressures and temperatures and describe the experimental evidence for a dipole interacting bent CO2 phase IV and for a non-molecular extended phase V. Phase IV is stabilized above 12 GPa and 1000 K; the Raman activation of the internal bending mode (ν2) indicates a loss of molecular inversion symmetry in this new phase. Above 35 GPa, and 1800 K, the CO2 molecules associate to form a covalent solid (V) with a structure based on singly bonded CO4 tetrahedra, similar to that of SiO2 tridymite. We discuss the stability and properties of this polymeric form of CO2.