Modulations of vibrational frequencies and other vibrational properties of the CO stretching mode of liquid acetone

The modulations of the vibrational frequencies and other vibrational properties are analyzed for the CO stretching band of liquid acetone, as an example of coupled-oscillators systems where the vibrational modes are delocalized. The analysis is carried out both on the basis of the vibrations of individual molecules and on the basis of the normal modes of the coupled-oscillators system, with particular interest in how the modulations appear differently in these two pictures. It is shown that, in the “molecular basis” picture, the modulations appear in the vibrational frequencies, but in the “normal-mode basis” picture, they appear mainly in the vibrational transition intensities and in the nature of the modes. The time scale of the modulations is discussed in relation to the changes in the vibrational band shapes induced by the liquid dynamics.