Neutron Scattering and Vibrational Spectra of Molecular Crystals

Infrared and Raman spectra of a number of molecular crystals have been measured for studying molecular vibrations and the intermolecular and intramolecular force fields. The infrared absorption bands arise from interaction of the electric wave with the oscillating dipole moment of the crystal. Raman scattering covers inelastic photon scattering processes and accordingly Raman lines arise from the oscillating polarizability of the crystal. Thus, the vibrational modes observed in infrared absorption or Raman scattering spectra are k = 0 modes, for which translationally equivalent molecules vibrate in phase.