Measurement and ab initio modeling of the inelastic neutron scattering of solid melamine - Evidence of the anisotropy in the external modes spectrum

The inelastic neutron scattering spectrum of melamine has been measured and a normal coordinates analysis has been performed in order to interpret the vibrational dynamics. This study reveals the anisotropy in the external mo de spectrum and its important role in the internal modes region. Thus, the Debye-Waller factor has taken a value for the out-of-plane vibrations four times greater than that for the in-plane vibrations. A molecular force fiel d refinement has been carried out in independent symmetry coordinates (D-3h ) in order to confirm the vibrational assignments. The final force field is free of redundancies and therefore the corresponding force constants are u nambiguous. (C) 2001 Elsevier Science B.V. All rights reserved.