Local density enhancement in neat supercritical fluid due to attractive intermolecular interactions

Short-range structure in the neat supercritical fluid consisting of polar molecules is investigated by measuring Raman spectrum of fluoroform (CHF3) at reduced temperature Tr=T/Tc=1.02. The spectra are analyzed by the Schweizer–Chandler model, and the spectral shift is decomposed into attractive and repulsive components as a function of density varied by a factor of 50. The attractive component shows larger shift than the one anticipated from the uniform molecular distribution. A local density enhancement due to the attractive intermolecular interactions is definitely observed in the neat supercritical fluid and evaluated against bulk density.