  In interstellar environment, fullerene species readily react with large
molecules (e.g., 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 (Cn+, 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 coevolution 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 ISM,
providing insights into different chemical reactivity caused by oxygenated
functional groups (e.g., hydroxyl, OH, or ether, C-O-C) on the cluster
formations.
