Vibrational analysis of the inelastic neutron scattering spectrum of pyridine Original Research Article

A vibrational analysis of the pyridine molecule has been performed by combining inelastic neutron scattering (INS) data and quantum mechanical calculations at the RHF, MP2 and B3LYP levels, with the 6-31G** and 6-311G** basis sets. Firstly, in order to test which level of theory is the best in reproducing the INS profile, this was calculated from the atomic displacement matrix of the pyridine molecule. DFT proved to be the most suitable option reproducing the above-mentioned spectrum, for both wave numbers and intensities. Secondly, in order to approximate the calculated spectrum to the observed one, the initial force constants matrix calculated at the B3LYP/6-311G** level was symmetrized using a set of independent symmetry coordinates (C2v). All the diagonal and some off-diagonal force constants were fitted until the difference between observed and calculated spectra was minimized. Good agreement between both calculated and experimental INS spectra supports the validity of our ‘empirical’ (or effective) force field.