Solvent effect on vibrational frequencies: cryosolution experiments and density functional calculations

FTIR spectra of C2H6, COF2 and CH3F in the vapour phase and in solutions in liquefied argon, krypton and xenon were investigated. Vapour-solvent frequ ency shifts (SFS) were determined for all IR-active fundamentals of the stu died compounds. In parallel, the SFS values were calculated using the Self- Consistent Isodensity Polarizable Continuum Model (SCIPCM) at the B3LYP/6-3 11 + + G (d,p) level. Comparison of the experimental and the calculated dat a shows reasonable agreement only for three most intense IR bands under inv estigation, i.e., the C=O and the CF2 asymmetric stretching modes of COF2, and the C-F stretching mode of CH3F. For the other bands of COF2, CH3F and for all the bands of C2H6 the results of SCIPCM calculations underestimate the observed SFS significantly. It is concluded that at least for the modes with relatively small (partial derivative mu /partial derivative Q)(o) val ues, the electrostatic interactions give a minor contribution to SFS. (C) 1 999 Elsevier Science B.V. All rights reserved.