THE INFRARED AND UV-VISIBLE SPECTRA OF POLYCYCLIC AROMATIC HYDROCARBONS CONTAINING (5,7)-MEMBER RING DEFECTS: A THEORETICAL STUDY

We report a theoretical investigation of the infrared (IR) spectra of polycyclic aromatic hydrocarbons (PAHs) containing (5, 7)-member ring defects based on a C48H18 model. Calculations are mostly performed using the hybrid B3LYP density functional theory (DFT) with a 6-31G(d) or 4-31G basis set. The results show that the Stone-Wales defect in PAHs can yield a strong IR band at 1448 cm(-1) and a weak band at 611 cm(-1), which may contribute to the UIR (unidentified infrared) bands at 6.9 mu m and 16.4 mu m observed in the interstellar medium. The charge effect on the IR spectra is discussed. The stability of the ring defected PAHs is also addressed by exploring the minimum energy pathway on the potential energy surface and through their UV-visible spectra, which are computed using a TDDFT method.