Small-angle X-ray scattering study of supercritical carbon dioxide

Small-angle X-ray scattering experiments for supercritical CO2 have been carried out. In the previous study, it was pointed out that correlation lengths and density fluctuations form a ridge along the extension of the coexistence curve to the supercritical region and that singular points of various quantities are also on this curve. The present study, carried out in better experimental conditions, confirms that the preliminary results are correct and shows that the dependence of the density fluctuation on the correlation length differs across the boundary of the extension curve, which we argue to correspond to the boundary of a higher-order phase transition.