Modification of the Onsager Reaction Field and Its Application on Spectral Parameters.

Solvent polarity is an important solvent property. The Onsager's theory of reaction field was the most classic model to describe solvent effects and was widely used in relating dielectric constant and other solvent polarity parameters. In this study, a modified semi-empirical reaction field was presented to relate electron transition energies or hyperfine coupling constants with the dielectric constants of solvents. In previous work, this relationship was well established by traditional Onsager reaction field for nonhydrogen-bonding systems but failed for hydrogen-bonding systems. In this modified reaction field model, the radius of the field was replaced by that of the primary solvation shell or the molecular fragment rather than that of the probe. In this way, the molecular volume of the solvent which contains information of the molecular size and overall interactions is involved in the reaction field. The 154 sets of electron transition energies and 44 sets of nitrogen isotropic hyperfine coupling constants were used to verify the modified model, indicating it works far better than the traditional model for hydrogen-bonding systems.