SIMBAD references

To understand the chemical evolution processes of nitrogen-containing polyaromatic species in interstellar environments, the formation of large amino (NH$_2$)-containing polycyclic aromatic hydrocarbon (PAH) clusters and their photochemical behavior are studied here. Large amino-containing PAH cluster cations are efficiently formed through an ion-molecule reaction between large PAH cations [e.g. dicoronylene (DC, C$_{48}$H$_{20}$)] and small amino-substituted PAH molecules [e.g. 9-aminoanthracene (C$_{14}$H$_{11}$N) and 1-pyrenamine (C$_{16}$H$_{11}$N)]. Two types of large cluster cations are observed: [PAH-PAH]$^+$ (e.g. [(C$_{14}$H$_{11}$N)$_{2}$C$_{48}$H$_{(1-20)}]^+$ and [(C$_{16}$H$_{11}$N)$_{2}$C$_{48}$H$_{(1-20)}]^+$) and [carbon clusters-PAH]$^+$ (e.g. [(C$_{14}$H$_{11}$N)$_{2}$C$_{n}]^+$ and [(C$_{16}$H$_{11}$N)$_{2}$C$_{n}]^+$, with n = [34, 48]). Upon irradiation, the newly formed cluster cations undergo a complex photofragmentation process; both dehydrogenation and NH$_2$ unit loss channels are identified. Through theoretical calculations, the structure and bonding energy for the formation reactions, as well as the photodissociation pathways for the newly formed PAH cluster cations, are obtained. The adduct processes and the newly formed molecular structure depend on the carbon reaction sites and connection pathways. Gas-phase reactions between PAH species easily occur, resulting in many reactions and very complex molecular clusters. The NH$_2$ unit plays an important role in the formation and photochemistry processes, in which two molecular connection pathways are considered (C-C and C-N bonding types). We infer that small aminosubstituted PAHs (e.g. 9-aminoanthracene and 1-pyrenamine) can effectively aggregate on large PAH species (e.g. (dehydrogenated) DC cations or carbon clusters), which provides a general molecular evolution route for the formation of nitrogen-containing nanometre-sized dust grains through a bottom-up process in the interstellar medium.