Electronic spectra and ionization potentials of a stable class of closed shell polycyclic aromatic hydrocarbon cations

Due to their stability, closed shell polycyclic aromatic hydrocarbon (PAH) cations are possible candidates as carriers for some of the diffuse interst ellar bands (DIBs). The electronic absorption spectra and ionization potent ials of several closed shell PAH cations are determined in this study. We u se density functional theory (DFT) at the BLYP/6-31G* level to determine th e ionization potentials and thus confirm the stability of the PAH cations o f interest. We use time-dependent density functional theory (TDDFT), again at the BLYP/6-31G* level, to calculate the vertical excitation energies and oscillator strengths of the PAH cations. We observe dominant single absorp tions within the DIB spectral region of interest in all of the PAH cation s pectra except for the smallest member of the series. (C) 2001 Elsevier Scie nce B.V. All rights reserved.