DETERMINATION OF RAMAN INTENSITIES OF LATTICE-VIBRATIONS IN CRYSTALLINE UREA

Quantum-chemical methods have been used for the calculations of the intensities of Raman-active lattice vibrations in crystalline urea. In a first step, the frequencies of the external vibrations in urea are calculated by use of the concept of flexible vibrating molecules within the intermolecular atom-atom forces. The quantum-mechanical concepts are considered and finally, a semiempirical method is extended to cover the relative Raman intensities of the external modes. © 1990.