Conformation moléculaire,structure cristalline, spectroscopie vibrationnelle du dibromomésitylène

Abstract

In this work we chose to study hydrogenated and deuterated dibromomésitylène DBM, this compound is very interesting because it has two types of methyl groups in the same molecule: a quasi-free methyl surrounded by two Br atoms and two very hindered methyls. The DFT calculations of the molecular conformation and vibration modes using the MPWP1W91 functional with the LanL2DZ(d,p)base,are in good agreement with the neutron diffraction and spectroscopie measurements. IR,Raman and INS spectra of deuterated DBM show a displacement of the frequency of the vibration modes towards weak energies compared to those of the hydrogenated DBM, which is due to the increased moment of inertia.We assigned almost all vibration modes. The tunnelling was studied by inelastic neutron scattering; the excitation occurs at 390 µeV in the hydrogenated DBM and at 67±2 µeV for the perdeuterated DBM. These values correspond to the same hindering potential. Second interest of this study is too complement the work done by our team on trihalogenomesitylenes (TCM,TBM and TIM); we calculated the intermolecular interactions in these crystals.