STRUCTURE STUDY OF SUPERCRITICAL CO2 NEAR HIGHER-ORDER PHASE-TRANSITION LINE BY X-RAY-DIFFRACTION

Wide-angle X-ray scattering experiments for supercritical CO:! near th e higher-order phase transition line on the isotherm at T = 308 K were carried out. Radial distribution functions were compared with that of the high-pressure liquid CO2. The results show that the higher-order phase transition line divides supercritical state into two phases, i.e ., liquidlike and gaslike regions, from the viewpoint of the structure . Radial distribution functions, however, indicate that this phase tra nsition is remarkably gentle even near the critical point.