Gas-Phase Study of Coronene Cation Reactivity of Interstellar Relevance

Abstract

Recent research suggests that cations of polycyclic aromatic hydrocarbons (PAHs) may be responsible for the observed diffuse interstellar bands. Determining the reaction rate constants and reactivity trends of these ions with species relevant to the interstellar medium will help lead the search for specific diffuse interstellar band carriers and develop pathways for their transformation. This Letter presents the gas-phase ion-neutral reaction rate constants of a specific PAH cation, the parent molecular cation of coronene (C24H), with H atom, N atom, O atom, and H2, and discusses the reactivity trends of PAH cations of increasing size with these small interstellar species. This study examines the kinetics of the largest PAH cation to date. These experiments were carried out using a flowing afterglow-selected ion flow tube coupled to a quadrupole mass spectrometer. The reaction rate constants of the coronene cation with H atom, O atom, N atom, and H2 have been measured to be 1.4 × 10-10, 1.3 × 10-10, <1 × 10-12, and <5 × 10-13 cm3 s-1, respectively.