The exploitation of the recent observations (in particular by ISO) of the near infrared emission bands (UIBs) requires a good knowledge of the spectroscopic properties of the main proposed carriers, i.e. the Polycyclic Aromatic Hydrocarbons, which are expected to act as efficient UV/visible to infrared free-flying light converters.
The charge state of the interstellar PAHs strongly affects their spectroscopy. The laboratory study of the electronic transitions of PAH cations in the gas phase enables to address important questions, like their possible contribution to the Diffuse Interstellar Bands (visible and near-IR absorption), and the mechanism responsible for electronic to vibrational intramolecular energy conversion.
Microcanonical simulations based on hybrid quantum/classical theoretical methods reveal how strongly affected are the infrared intensities by both the charge state and the vibrational temperature.