GENERAL PHYSICS COLLOQUIUM _____ Title: Excited states of protonated aromatic molecules Speaker: Christophe Jouvet, Université Paris-Sud Time: Wednesday, 25 May, 2011 at 3:15 p.m. Place: Physics Auditorium, 3rd floor, Department of Physics Abstract Protonated aromatic molecules constitute a fundamental class of organic molecules which intervene in various environments, from organic chemistry (s complexes as reaction intermediates of) to astrochemistry, plasmas and biochemistry. These protonated molecules can be easily detected by mass spectrometry when we can produce them in situ or to obtain samples. On the other hand, we do not know how to detect them by optical methods in inaccessible environments because the data on their spectroscopy is very scarce. Even for molecules as simple as benzene and its derivatives or polycyclic aromatic hydrocarbons (PAHs), there is almost no information on the geometrical and electronic structure, the reactivity or the dynamics. However, protonated PAHs could be present in the interstellar medium and could be of good candidates as carriers of the interstellar diffuse bands (DIBs) observed in the visible and near IR. Different examples will be presented and compared with electronic excited states ab initio calculations. _____ Coffee/tea and cake will be served at 3 p.m. David Field