A comparative study on the vibrational spectroscopy of pyridazine, pyrimidine and pyrazine

In this work, the authors deal with the vibrational spectroscopy of the three diazine parent compounds, i.e. that of pyridazine, pyrimidine and pyrazine. Infrared spectra were recorded in vapour and condensed phases, and Raman spectra were measured in condensed phase using both parallel and perpendicular polarization of light. The vibrational fundamental frequencies were calculated applying ab initio quantum-chemical methods: Moller-Plesset perturbation and local density functional methods. The results of the calculations were applied to the assignment of the vibrational fundamentals and the measured fundamental frequencies were used to refine the vibrational force constants. The main deviations between the recalculated and the measured frequencies are about 2.5% or smaller. (C) 1998 Elsevier Science B.V.