CANCELLED
DQC Seminar Series: Probing the Frontiers of Interstellar Chemistry Through Cold and Controlled Ion Experiments

Ion-molecule reactions are fundamental to the chemistry that drives processes in the interstellar medium, but experimental measurements of these reactions are scarce due to significant technical challenges. We apply techniques from the cold atom field to examine ion-molecule reactions under well-controlled conditions that replicate the environment of space. Benzene, a key precursor to larger polycyclic aromatic hydrocarbons (PAHs), has long been proposed to form in space through a sequence initiated by acetylene protonation. We present the first experimental study of this pathway under single-collision conditions and find that, contrary to predictions, it terminates at the formation of C₆H₅⁺-a species unreactive to both acetylene and hydrogen, which disproves a widely cited mechanism for interstellar benzene formation. Building on this approach, we extend our investigation to related ion-molecule systems and find a consistent trend: reactions of small carbocations and neutral molecules proceed through successive additions until an aromatic molecule is formed, at which point the ion is unreactive. This behavior suggests that aromatic stabilization acts as a natural endpoint for many interstellar ion-molecule growth processes, which has important implications for understanding the origins and abundance of PAHs in space. --- Heather Lewandowski is a professor of physics and Fellow of JILA at the University of Colorado Boulder. She also serves as the Faculty Director of the CUbit Quantum Initiative focused on Education and Workforce. She leads two research programs, one in experimental molecular physics, and the other in physics education research. Her molecular physics research efforts focus on studying interactions and reactions of cold, chemically important molecules and ions. Her physics education research program studies ways to increase students' proficiency in experimental scientific practices, as well as research in the area of quantum science education and workforce development. --- Upcoming seminars: 16 Oct: Senrui Chen 30 Oct: Aziza Suleymanzade 20 Nov: Jeff Thompson 04 Dec: Felix Knollman