Raman intensity calculations with the CNDO method. Part III: N,N-dimethylamide – water complexes

Abstract

Absolute differential Raman scattering coefficients of hydrogen bondedN,N-dimethylformamide (DMF) – water complexes and a N,N-dimethylacetamide (DMA) – water complex are calculated with a variational method within the CNDO approximation using an extended basis set. Changes of Raman intensities caused by intermolecular interactions are modeled in our Raman intensity calculations and the calculated intensities of the amide I (C=O stretching), OCN bending, and N—(Me)2 stretching vibration of the DMF (and DMA) – water complexes are compared with the experimental absolute Raman intensities of DMF and DMA dissolved in water. The calculated Raman intensities of characteristic normal modes of DMF and DMA and their 1:2 amide – water model are in good agreement with the experimental data. The results show that it is possible to obtain qualitative information on solute – solvent interactions from Raman intensity calculations of complex molecular systems like hydrated DMF and DMA.