2024MNRAS.531..682W

In interstellar environment, fullerene species readily react with large molecules (e.g. polycyclic aromatic hydrocarbons, PAHs and their derivatives) in the gas phase, which may be the formation route of carbon dust grains in space. In this work, the gas-phase ion-molecule collision reaction between fullerene cations (${\rm C}_{n}\, ^+$, n = 32, 34,…, 60) and functionalized PAH molecules (9-hydroxyfluorene, C₁₃H₁₀O) are investigated both experimentally and theoretically. The experimental results show that fullerene/9-hydroxyfluorene cluster cations are efficiently formed, leading to a series of large fullerene/9-hydroxyfluorene cluster cations (e.g. [(C₁₃H₁₀O)C₆₀]⁺, [(C₁₃H₁₀O)₃C₅₈]⁺, and [(C₂₆H₁₈O)(C₁₃H₁₀O)₂C₄₈]⁺). The binding energies and optimized structures of typical fullerene/9-hydroxyfluorene cluster cations were calculated. The bonding ability plays a decisive role in the cluster formation processes. The reaction surfaces, modes, and combination reaction sites can result in different binding energies, which represent the relative chemical reactivity. Therefore, the geometry and composition of fullerene/9-hydroxyfluorene cluster cations are complicated. In addition, there is an enhanced chemical reactivity for smaller fullerene cations, which is mainly attributed to the newly formed deformed carbon rings (e.g. 7 C-ring). As part of the co-evolution network of interstellar fullerene chemistry, our results suggest that ion-molecule collision reactions contribute to the formation of various fullerene/9-hydroxyfluorene cluster cations in the interstellar medium, providing insights into different chemical reactivity caused by oxygenated functional groups (e.g. hydroxyl, OH, or ether, C-O-C) on the cluster formations.