Intermolecular interactions and local density augmentation in supercritical solvation: A survey of simulation and experimental results

Data from prior simulation and experimental studies (a total of 52 solute/s olvent pairs) an collected and analyzed in an attempt to relate the extent of local density augmentation in supercritical fluids to the strength of in termolecular interactions. For this purpose, intermolecular potential funct ions consisting of pairwise additive atom-atom potentials, with parameters either taken from literature sources or derived from quantum chemical calcu lations, are constructed and tested against experimental second-pressure vi rial coefficient data. For the solute-solvent combinations of interest in s upercritical systems near room temperature, such potentials are found to re produce experimental second-pressure virial coefficient data with reasonabl e accuracy. On the basis of these potentials, a variety of characteristics of solute-solvent and solvent-solvent interactions are computed and compare d to simulated and experimental measures of density augmentation. It is fou nd that the extent of augmentation is strongly correlated to measures of th e free energy of solute-solvent interaction. However, simulated and experim ental augmentation data apparently follow distinct correlations with these free energies, indicating the presence of a widespread error in either the measurement or the interpretation of density augmentation in supercritical solvents.