2011MNRAS.416.1509B

We study hydrogenated cations of two polycyclic hydrocarbon molecules as models of hydrogenated organic species that form in the interstellar medium. Optical spectra of the hydrogenated naphthalene cation H_n–C₁₀H⁺₈ for n= 1, 2 and 10, as well as the astrobiologically interesting hydrogenated proflavine cation H_n–C₁₃H₁₁N⁺₃ for n= 1 and 14, are calculated. The pseudopotential time-dependent density functional theory is used. It is found that the fully hydrogenated proflavine cation H₁₄–C₁₃H₁₁N⁺₃ shows a broad spectrum in which the positions of individual lines are almost lost. The positions, shapes and intensities of lines change in hydronaphthalene and hydroproflavine cations, showing that hydrogen additions induce substantially different optical spectra in comparison with base polycyclic hydrocarbon cations. One calculated line in the visible spectrum of H₁₀–C₁₀H⁺₈ and one in the visible spectrum of H–C₁₃H₁₁N⁺₃ are close to the measured diffuse interstellar bands. We also present the positions of near-ultraviolet lines.