  We report the discovery of a new molecular phase of carbon dioxide at
high-pressure and high-temperature. Using x-ray diffraction, we identify this
phase as the theoretically predicted high-temperature Cmca phase [Bonev et al.,
Phys. Rev. Lett., 91, 065501 (2003)]. Its relation with phase III, on one hand,
and its relative stability with respect to phase IV, on the other hand, are
discussed based on spectroscopic and melting data. The existence of this
strictly molecular phase challenges the interpretation of phases IV and II as
intermediate phases between the molecular and covalent-bonded forms of CO2.
