Spectroscopic study of 4-aminobenzophenone in supercritical CF3H and CO2: local density and Onsagerʹs reaction cavity radius

The measured bathochromic shifts of 4-aminobenzophenone (4ABP) in CF3H are explained by Onsagerʹs reaction field theory (ORFT) if the cavity radius is the sum of Van der Waals radii of solute and solvent, while in CO2, the cavity radius is the soluteʹs Van der Waals radius. The experimental local densities around 4ABP have been estimated and show a maximum at a reduced density of 0.5 for CF3H and 0.7 for CO2. Simulations are consistent with the high local densities found at low bulk densities and suggest possible explanations for the different radii used for CF3H and CO2.