Vibrational spectral assignments of paraldehyde by ab initio and density functional methods.

The FTIR and Laser-Raman spectra of paraldehyde have been recorded in the regions 4000-400 cm(-1) and 3500-250 cm(-1) respectively. Molecular electronic energy, geometrical structure, harmonic vibrational spectra, infrared intensities and Raman scattering activities have been computed at the HF/6-31G(d,p) and B3LYP/6-31G(d,p) levels of theory. The results were compared with experimental values with the help of scaling procedures. The observed wave numbers in FTIR and Laser-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wave numbers in the expected range and are in good agreement with computed values.