Laboratory Spectroscopy of Protonated PAH Molecules Relevant For Interstellar Chemistry

In this contribution, we summarize the recent progress made in recording laboratory infrared (IR) spectra of protonated polycyclic aromatic hydrocarbon molecules (H+PAH) in the gas phase. The IR spectra of a large variety of H+PAH species ranging from benzene to coronene have been obtained by various variants of photodissociation spectroscopy. The employed techniques include single-photon IR photodissociation (IRPD) of tagged H+PAH ions and IR multiple-photon dissociation (IRMPD) of bare H+PAH ions. The comparison of the laboratory IR spectra with astronomical spectra supports the hypothesis that H+PAH ions are possible carriers of the unidentified IR emission (UIR) bands. Moreover, the spectra provide detailed information about the geometric and electronic structure as well as the chemical reactivity and stability of these fundamental hydrocarbon ions