USE OF ISOTOPE EFFECTS IN STUDIES OF INTERMOLECULAR INTERACTIONS BY RAMAN-SPECTROSCOPY

A very brief introduction to vibrational spectroscopy is given with a particular emphasis on the effect of isotopic substitution. A few key references to studies of both the gaseous and the crystalline states a re cited. Intermolecular interactions in liquids are studied by (i) Re sonance Energy Transfer giving rise to a non-coincidence effect betwee n the anisotropic and the isotropic Raman components, (ii) Coalescence of Bands in Mixtures of Isotopomers, giving rise to an observation of fewer bands than expected from a simple addition of bands from the in dividual isotopomers in the mixture, and finally (iii) low-frequency R aman spectroscopy, for which the R(<(nu)over bar>) representation is u sed in order to get rid of the intense Rayleigh line appearing in the Raman spectra of liquids. Experimental data include results for isotop ically substituted liquid formamides and a solution of HCOND2 in D2O. The results show that intermolecular interactions via transfer of vibr ational energy occur for the carbonyl stretching vibration at around 1 650 cm(-1) (amide-I band). A band in the low-frequency spectrum at aro und 100 cm(-1) is assigned to a mode involving displacements of atoms in the intermolecular hydrogen bonds. Similar interactions might be of importance for the fast dynamics of biological macromolecules like pr oteins and nucleic acids.