PYRIDINE ADSORPTION ONTO METAL-OXIDES - AN AB-INITIO STUDY OF MODEL SYSTEMS

In order to shed some light on the origin of the shifts of the vibrati onal frequencies of pyridine adsorbed on metal oxides, ab initio calcu lations have been performed. SCF methods may be used to assign and ide ntify the pyridine vibrations of interest, although coupling of certai n vibrational modes hamper the interpretation. The effect of the ligan ds on the vibrations of pyridine is rather complex. It appeared that t he shifts are mainly due to the direct effect of the ligand on the for ce constants and to changes in the extent of coupling with the in-plan e bending vibrations of the hydrogen atoms, and, in case of proton tra nsfer, the N-H group. Protonation, however, severely influences the ge ometry of pyridine, which may also have a considerable effect on the v ibrational frequencies.