The Raman non-coincidence effect of the 12CO stretching mode of liquid acetone in chemical and in isotopic mixtures

The concentration dependences of the first moments of both the isotropic and anisotropic Raman bands of the CO stretching mode ν(12CO) of acetone in chemical mixtures of type [(CH3)2CO]x-[CCl4]1−x are compared with their dependences in isotopic mixtures of type [(CH3)212CO]x-[(CH3)213CO]1−x. The role of the intermolecular resonant vibrational coupling is discussed via the experimentally observable Raman non-coincidence effect, i.e. the difference in the frequency position between the anisotropic and isotropic first moments. The experimental results are in good agreement with (1) molecular dynamics simulations and Monte Carlo simulations and (2) analytical predictions within the framework of the mean-spherical approximation of the dipole-dipole interaction. With the help of [(CH3)213CO] occurring at natural abundance in the chemical mixture and of [(CH3)213CO] at close to infinite dilution in the isotopic mixture, we are able to separate the environmentally induced frequency shifts from the measured anisotropic and isotropic first moments, thereby isolating the frequency shifts induced just by the intermolecular resonant vibrational coupling.