Rotational, vibrational and electronic properties of neutral polycyclic aromatic hydrocarbons and their positive ions via density functional calculations

Polyciclic Aromatic Hydrocarbons (PAHs) are thought to be abundant in the interstellar medium and to play a crucial role for the chemistry and global energy balance in space. We present rotational costants and harmonic vibrational frequencies and intensities for a total of 20 PAHs and their respective cations, ranging in size from naphthalene (C$_{10}$H$_{8}$) to dicoronylene (C$_{48}$H$_{20}$), obtained in the framework of Density Functional Theory (DFT). Using Time-Dependent DFT we obtained the low-lying electronic excited states below the ionization potential of the species under study. Calculations were also carried out for a few PAH anions. Our theoretical results are in reasonable agreement with the available experimental data. This work shows that an ab initio approach is reliable enough to obtain some key parameters which can be used to model the behavior of these molecules in astrophysical environments.