Theoretical synthesis of vibrational spectra of polycyclic aromatic hydrocarbons. Infrared spectra of coronene

Abstract

Vibrational frequencies and infrared (IR) intensities were calculated for coronene C 24H 12 as an example to test various methods for theoretical syntheses of the vibrational spectra of polycyclic aromatic hydrocarbons. The average frequency errors for the E 1u modes were 202 cm −1 (AM1), 151 cm −1 (PM3), 137 cm −1 (scaled RHF/STO-3G), 66 cm −1 (scaled RHF/4-31G), 51 cm −1 (five-parameter model), 29 cm −1 (Kekulé model), and 13 cm −1 (MO/8 model). IR intensities calculated by a combined approach utilizing MO/8 normal coordinates with AM1 or PM3 electron distributions were in good agreement with experimental values. IR intensities calculated by the RHF/4-31G method were also satisfactory. The computation time for the combined method of MO/8 + PM3 (114s) was approximately 2500 times shorter than that for the RHF/4-31G approach (28 1674s).