The effect pf the microscopic inhomogeneity in binary liquid mixtures observed through the Raman spectroscopic noncoincidence effect

The Raman spectroscopic noncoincidence effect (NCE) describes the frequency separation between the first moments Maniso and Miso of the anisotropic and isotropic components of the Raman band associated with a vibrational mode in a molecular liquid, i.e. NCE = Maniso - Miso 1. The NCE phenomenon is closely connected with the occurrence of intermolecular resonant vibrational interactions between identical oscillators, and is particularly significant in molecular liquids structured by large dipole-dipole interactions and/or hydrogen bonding, and whenever the identical oscillators are coupled by transition dipole coupling (TDC) 2-3. After having conducted several studies on the NCE of the C=O stretching of acetone (Miso(C=O) = 1708 cm-1) in nonpolar and in polar solvents 4, we have begun to extend these measurements to hydrogen bonded solvents like water5 and methanol. In parallel, we have begun to study via NCE of the C-O stretching of methanol the disruptive effects of water on the H-bond network of methanol6. In the meantime, the influence of microscopic inhomogeneities in binary liquid mixtures on their vibrational spectra has been studied by doing calculations on a model liquid system7. This contribution will give an overview on the results obtained up to now.