HARD FLUID MODEL FOR SOLVENT-INDUCED SHIFTS IN MOLECULAR VIBRATIONAL FREQUENCIES

A model for packing forces in liquids is derived by generalization of exact results in the continuum and dense hard sphere fluid limits. The parameters of this 'hard fluid' model are fixed by the equation of state of the corresponding mixed hard sphere fluid. Results are generalized to include the very accurate Boublik-Mansoori-Carnahan-Starling-Leland (BMCSL) equation as well as the Percus-Yevick, scaled-particle-theory, and Boublik-Kolafa equations of state. Predicted hard sphere cavity distribution functions, chemical potentials, and solvation forces are compared with computer simulations and previous analytical approximations. The application to the prediction of solute vibrational frequency shifts in molecular liquids is illustrated by comparison with data obtained from high-pressure Raman spectra for iodine and pyridine in various solvents.