Intermolecular solvent–solute energies for thermodynamic and spectroscopic properties of solutes in near-critical solvents

Abstract

The unusual density dependence of spectral and structural properties of naphthalene, anthracene and azulene dissolved in near-critical solvents is accounted for by theory or simulation, but the value of the solutes’ intermolecular energy (ε₂/k) is much larger than expected from the properties of the pure solutes. Two possible sources for this discrepancy are studied in this work: (i) changes in the equation of state of the fluid due to near criticality were studied calculating its thermodynamic behaviour with the hydrostatic hypernetted chain (HHNC) integral equation for inhomogeneous fluids, (ii) specific contributions to the solute–solvent interaction energies were evaluated from cross-second virial coefficients. Both have been ruled out as the origin of the observed discrepancy. The possibility that the shape of the solutes affects the local density of solvent molecules so that it cannot be described by the radial distribution functions employed by theories and simulation experiments is discussed.