Structure and dynamics of maleic anhydride

We have carried out a comprehensive characterization of the structure and d ynamics of maleic anhydride using experimental (single-crystal neutron diff raction, infrared, Raman and inelastic neutron scattering (INS) spectroscop ies) and computational methods (AM1 and two levels of density functional th eory). The structure is largely in agreement with previous work, although w ith more accurate atomic positions. However, the report of an unusually sho rt C=C bond length is not supported by this work. The combination of ab ini tio results and INS spectra has confirmed the assignments of the internal m odes. In addition, the complete lattice mode region is observed and assigne d for the first time. Force fields derived by empirical means and from the ab initio data have been obtained and show differences, although both accur ately predict the INS spectrum.