Solute–solvent interactions: two-dimensional ultrafast infrared vibrational echo experiments

Two-dimensional (time–frequency) ultrafast IR vibrational echo experiments were used to investigate solute–solvent interactions in solution. The experiments were performed on symmetric (S) and antisymmetric (A) CO stretching modes of (acetylacetonato) dicarbonylrhodium(I) in dibutylphthalate (DBP) at 150 K. The two-dimensional (2D) spectrum displays quantum beats at the nominal frequency difference between the S and A modes. However, as the observation wavelength is moved to higher energy, the quantum beat frequency decreases. The change in frequency is related to the nature of the solute–solvent interactions. Model calculations indicate that interactions with the solvent result in CO local mode frequencies that are strongly correlated.