Reactions of Coronene^•+ Photodissociation Fragment Ions with Water in a Room-Temperature Quadrupole Ion Trap

Polycyclic aromatic hydrocarbons (PAHs) are present in a wide variety of interstellar environments. Only large PAHs can survive in the harsh radiation fields in photon-dominated regions, and small PAHs photodissociate. Although the (photo)dissociation mechanisms of PAHs are quite well understood, the formed reaction products’ structures and their further reaction with closed-shell species remain to be investigated. In this work, we study the reactivity of room-temperature coronene•+ photodissociation fragments by mass-selectively isolating the C11•+, C10•+, C9H+, C9•+, C7H+, C7•+, and C5H+ fragment ions and subsequently reacting them with gas-phase water. Furthermore, a resonant ejection technique is applied to elucidate the chemical link between the C9H+, C9•+, C7H+, and C7•+ reactants and reaction products. Several fragments are found to react with water and some of the formed reaction products stabilize by the loss of atomic hydrogen or CO. Some differences in fragment reactivity are observed, and we argue that these may be explained by the (cyclic vs linear) geometry of the coronene•+ dissociation fragments. Reaction mechanisms for the cyclic and linear C7•+ isomers reacting with water, based on potential energy surface (PES) calculations, are presented to rationalize the experimental findings. Lastly, the role that dissociation fragments of small interstellar PAHs play in the chemical evolution of carbonaceous material in the interstellar medium (ISM) is discussed.