SOLVENT EFFECTS IN INFRARED-SPECTROSCOPY - A COMPUTATIONAL APPROACH

A detailed analysis of the influence of a solvent modelled as a contin uum defined by its static and high frequency dielectric constants, eps ilon and epsilon(infinity), respectively, on the force constants of a molecule in solution is proposed. It is applied to the computation of the solvent-induced frequency shifts in the vibrational spectrum of fo rmaldehyde. The sign and the order of magnitude of the effect are corr ectly predicted at the scaled Hartree-Fock, MP2 or DFT levels. The com putations performed on conveniently distorted systems allow us to sepa rate the influence of the reaction field on the molecular vibrations f rom the influence of anharmonicity, by means of the geometry distortio n induced by the solvent. The anharmonicity contribution appears to be the major contribution to the overall effect.