Fig. 3.

CO₂ phase I–III transitions observed in this study. (A) XRS spectra of the O K edge of CO₂ between 2.0 and 17 GPa (circles) and their best fit (solid line) using a weighted sum of the spectra at 2.0 and 17 GPa, considered respectively as the spectrum of pure phase I and pure phase III. (B) The fraction of the CO₂ phase as a function of pressure shows a mixture of CO₂-I and -III in the 7–15-GPa range. The error bars for the fraction of phase are estimated about ±5%. The error bars for the pressure below 20 GPa are smaller than the symbols.