Lattice vibrations in deuterated urea

Abstract

Coherent inelastic neutron scattering was used to measure high-symmetry dispersion curves in deuterated urea. A twelve-parameter force constant model, allowing for atom-atom interactions between neighbouring molecules as well as long-range dipolar forces, is presented in the rigid molecule, harmonic approximation. The model accounts for the measured external-mode Raman frequencies, diagonal elastic constants and neutron results. On the basis of the model, LO-TO splittings for the polar external modes are calculated.