Physics Colloquium, Paul Scheier, Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Austria

Abstract:

Diffuse interstellar clouds are penetrated by both, visible and ultraviolet light. The latter will photo ionize large molecules that are expected to be carriers of about 600 absorption lines discovered so far.

However, until now, only five lines could be assigned to C₆₀ ⁺. One reason is a lack of data from laboratories. The low density of ions in laboratory plasmas makes the assignment of absorption lines of specific molecular ions very challenging and thus alternative methods such as cavity ring down, matrix isolation or action spectroscopy have been developed. Tagging ions with helium turns out to be most suitable due to its minimal matrix shift and a dissociation event following the absorption of a single photon even in the far infrared. Several groups recently achieved physisorption of a few He atoms to ions in cryogenic traps.

In Innsbruck, we use a different approach that enables us to solvate basically any ion with up to several 100 He atoms via electron ionization of doped helium nanodroplets. Besides the most accurate assignment of the electronic transitions of the bare ions, we obtain detailed information about micro solvation of these ions with helium but also other solvents. Recent results for C₆₀ ⁺ and the corannulene cation will be presented.