Theoretical studies on the vibrationally-resolved absorption and fluorescence spectra of H-Pyrene+ and H-Coronene+

Abstract H-Pyrene + and H-Coronene + are important carrier candidates for the diffuse interstellar band. In order to understand the observed absorption and fluorescence emission spectra of H-Pyrene + and H-Coronene + , time-dependent density functional theory (TD-DFT) method and Franck–Condon approximation have been employed to simulate the corresponding vibrationally-resolved optical spectra. For H-Pyrene + , the calculated absorption, emission and 0-0 band energies are in good agreement with the experimental values. The strong absorption and emission vibrational peaks near the 0-0 band match well with the experiment peaks. A noticeable deviation for several weak peaks far away from the origin band is observed, as a result of the vibronic coupling with other excited states. For H-Coronene + , the predicted vibrationally resolved electronic absorption and emission spectra resemble very well their experimental counterparts spectra, allowing to fully assign the observed vibronic peaks.