| This work is an experimental study of the Raman non-coincidence effect which is the difference between the band centers of the isotropic and the anisotropic spectra. We have studied the C=O symmetric stretching mode of N,N-dimethylacetamide (DMA) and acetone. The band shape parameters are interpreted in terms of a transition dipole-transition dipole coupling mechanism. Theories of the non-coincidence effect due to McHale and Logan have been used to quantitatively study the non-coincidence effect for both DMA and acetone. The influence of the static dielectric constant of the liquid upon the non-coincidence effect is discussed.;We have also studied the C-O symmetric stretching mode of methanol. The unusual observation of a negative non-coincidence effect for the C-O mode is discussed in terms of available theoretical models. In order to determine if the negative values for the C-O mode are typical of alcohols, we have undertaken a high pressure study of the skeletal stretching modes of ethanol. We found that the negative values of the non-coincidence effect occur in methanol and in ethanol.;Three other high pressure studies reveal the non-coincidence effect to decrease as the density is increased. This is contrary to theoretical predictions. We have reviewed these results and discuss them as being due to Fermi resonance. We have also included a preliminary study of the effects of the permanent dipole moment upon the non-coincidence effect by studying two molecules of similar structure but different dipole moment. |
