THEORETICAL SYNTHESIS OF VIBRATIONAL-SPECTRA OF POLYCYCLIC AROMATIC-HYDROCARBONS - INFRARED-SPECTRA OF CORONENE

Vibrational frequencies and infrared (IR) intensities were calculated for coronene C24H12 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(lu) 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) (Kekule model), and 13 cm(-1) (MO/8 model). IR intensities calculated by a combined approach utilizing MO/8 normal coordinates with AMI 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 (114 s) was approximately 2500 times shorter than that for the RHF/4-31G approach (28 1674 s).