RAMAN NONCOINCIDENCE EFFECT OF THE CARBONYL STRETCHING MODE IN COMPRESSED LIQUID CYCLIC CARBONATES

The Raman noncoincidence effect and line width of the symmetric C = O stretching band have been measured in liquid propylene carbonate (PC), chloroethylene carbonate (CC), and dichloroethylene carbonate (DC) as a function of pressure up to 3 kbar and over the temperature range from -20-degrees-C to 40-degrees-C. The transition dipole moments of the C = O mode for these liquids have also been determined by means of infrared spectroscopy at ambient conditions. The temperature, density, and transition dipole moment dependences of the experimental noncoincidence effect for these liquids are quantitatively interpreted in terms of Logan theory. An excellent agreement between the experimental results and theoretical predictions indicates that the observed noncoincidence effect is due to the transition dipole moment coupling and permanent dipole moment coupling. For the study of isotropic bandwidths, the band narrowing with increasing density is found for liquid CC and DC and quantitatively explained by means of intermolecular interactions, whereas band broadening is observed for PC. The latter broadening is unexpected since PC possesses the largest permanent dipole moment of these three liquids. A probable reason for difficulty in the interpretation of this result is given.