Refinements on solvation continuum models: Hydrogen-bond effects on the OHstretch in liquid water and methanol

We present a study on the IR vibrational shifts of the OH stretch mode for water and methanol when passing from gas to liquid phase. Both a purely con tinuum solvation model (here the polarizable continuum model) and its semic ontinuum extensions, obtained explicitly considering small clusters of H-bo nded molecules of liquid, have been tested. The definition of such clusters as the new quantum mechanical system to be coupled to a continuum descript ion of the remainder liquid has allowed us to take into account both the "l ocal permanent specific" interaction due to the H-bond and the long-range e ffects present in all liquids. The analysis mainly focused on harmonic appr oximations and has been extended to include mechanical anharmonicities in o rder to have a more reliable comparison with the experiments. Finally, care ful attention has been paid to the analysis of the "intrinsic" parameters o f continuum models (i.e., the shape and size of the molecular cavity contai ning the QM system) and to their effects on the vibrations. (C) 2000 Americ an Institute of Physics. [S0021-9606(00)51012-5].