Speaker
Description
The discovery of molecular anions in the interstellar medium nearly 20 years ago has profoundly changed our understanding of astrochemical networks. The radio-astronomical identification of carbon-chain and nitrile anions such as C$_8$H$^⁻$ and C$_3$N$^-$ has revealed that anions can reach appreciable abundances in cold interstellar environments. In addition to interstellar and circumstellar sources, molecular anions have also been detected in the atmosphere of Titan. These discoveries have triggered extensive experimental and theoretical studies in the last decades on their spectroscopy, formation pathways, reactivity, and destruction mechanisms, significantly advancing our understanding of their role in an astrochemical and astrophysical context.
Laboratory rotational spectroscopy has in the past been essential in providing the precise transition frequencies required for astronomical detection. More recently, infrared action spectroscopy of mass-selected anions has emerged as a powerful complementary approach, with the potential to provide laboratory reference data for their infrared detection, e.g., with the James Webb Space Telescope. The focus of this talk will be on experiments at the FELion cryogenic ion trap beamline at HFML-FELIX which enables broadband, high-sensitivity vibrational spectroscopy of cold ions using the intense and widely tunable FELIX free-electron lasers. They provide detailed structural fingerprints and allow the characterization of transient or weakly bound species inaccessible to conventional methods. Applications extend to a wide range of astrochemically relevant anions, including hydrocarbons, nitriles, halogen-containing species, and polycyclic aromatic hydrocarbon (PAH) anions. These experiments, employing infrared-predissociation spectroscopy at cryogenic temperatures, yield vibrational spectra that can be directly compared with quantum-chemicalcalculations and astronomical infrared signatures.