A new theory of determination of vibrational raman intensities in crystal lattices

Quantum-chemical methods have been used for the calculation of the intensities of Raman-active internal and external modes in crystalline oxamide. In a first step the frequencies and eigenvectors of the modes in oxamide are calculated by use of the concept of a flexible vibrating molecule within the intermolecular atom-atom forces. The quantum-mechanical aspects are considered and finally, a semiempirical method is extended to cover the relative Raman intensities of the external and internal modes.