Coevolution of the interstellar chemistry: gas-phase laboratory formation of hydrogenated fullerene-PAH clusters

Abstract

ABSTRACT Fullerene molecules are affected and constrained by different interstellar environmental factors, such as UV radiation, atoms, and other coexisting molecules. To understand the coevolution of the interstellar fullerene chemistry, by tracking the accretion processes on fullerene cations, we present an investigation of the chemical reactivity of fullerene (C60) cations and smaller fullerene (C54/56/58) cations with hydrogen and C14H10 in the gas phase. Experiments are performed using a quadrupole ion trap in combination with time-of-flight mass spectrometry. The experimental results show hydrogenated fullerene-C14H10 cluster cations (i.e. [Hn C60(C14H10)m ]+ and [Hn C54/56/58(C14H10)m ]+) are efficiently formed through ion-molecule collision reaction. H-atoms are more likely to accumulate on the surface of fullerenes than C14H10; not only does hydrogen more easily form a covalent bond, the later accreted hydrogen will also expel the already accreted C14H10. Through theoretical calculations, we obtain the structure of newly formed clusters (e.g. [HC60(C14H10)]+ and [HC58(C14H10)]+) and the binding energies of their reaction pathways, together with IR spectra. The bonding ability plays a decisive role in the ternary cluster formation processes, and the existence of occupation and expulsion competitive reaction channels in the accretion processes on fullerene surfaces is confirmed. As part of the coevolution of the interstellar chemistry, the occupation and expulsion reaction modes should be considered when fullerenes further react with H-atoms and PAHs. As a result, the molecular structures of hydrogen/fullerene/PAH clusters are diverse, and hydrogenated-fullerene-related clusters (e.g. hydrogenated fullerenes or hydrogenated fullerenes-PAHs) have a higher distribution than non-hydrogenated-fullerene-related clusters (e.g. fullerenes or fullerenes-PAHs) in the interstellar environment.