Carbon dioxide at high pressure and temperature

We present a review of recent studies of carbon dioxide (CO2) at high press ures and temperatures and describe the experimental evidence for a dipole i nteracting bent COL phase IV and for a nonmolecular extended phase V. Phase IV is stabilized above 12 GPa and 1000 K; the Raman activation of the inte rnal bending mode (upsilon (2)) indicates a loss of molecular inversion sym metry in this new phase. Above 35 GPa, and 1800 K, the CO2 molecules associ ate to form a covalent solid (V) with a structure based on singly bonded CO 4 tetrahedra, similar to that of SiO2 tridymite. We discuss the stability a nd properties of this polymeric form of CO2.