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

Abstract

FTIR spectra of C 2H 6, COF 2 and CH 3F in the vapour phase and in solutions in liquefied argon, krypton and xenon were investigated. Vapour–solvent frequency shifts (SFS) were determined for all IR-active fundamentals of the studied compounds. In parallel, the SFS values were calculated using the Self-Consistent Isodensity Polarizable Continuum Model (SCIPCM) at the B3LYP/6-311++G(d,p) level. Comparison of the experimental and the calculated data shows reasonable agreement only for three most intense IR bands under investigation, i.e., the CO and the CF 2 asymmetric stretching modes of COF 2, and the C–F stretching mode of CH 3F. For the other bands of COF 2, CH 3F and for all the bands of C 2H 6 the results of SCIPCM calculations underestimate the observed SFS significantly. It is concluded that at least for the modes with relatively small (∂μ/∂Q) o values, the electrostatic interactions give a minor contribution to SFS.