Optical absorption spectra of polycyclic aromatic hydrocarbons of astrophysical interest

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 our preliminary results of the photoabsorption cross-section of anthracene (C14H10), pyrene (C16H10), coronene (C24H12) and ovalene (C32H14) in the framework of Time Depen- dent Density Functional Theory (TDDFT). Results obtained using two very dierent TDDFT implementations, namely Octopus and NWChem, are compared with available experimental re- sults. The computed spectra are in reasonable agreement with the experimental data, especially for the low-lying excited states below the ionization potential of the species under study. Our work shows that computer codes commonly available to the community of condensed matter physicists are reliable enough for the theoretical study of the optical properties of this class of astrophysically relevant molecules. This makes them particularly precious when direct experi- mental data are not easily obtainable, as is often the case for the highly reactive radicals and ions of such species.