Growth mechanism of aromatic prebiotic molecules: insights from different processes of ion–molecule reactions in benzonitrile–ammonia and benzonitrile–methylamine clusters

Abstract

Benzonitrile (BN, C₆H₅CN) has been detected in the cold molecular cloud Taurus molecular cloud-1 (TMC-1) in 2018, which is suggested to be a precursor in the formation of more complex nitrogen-containing aromatic interstellar compounds. In this study, we utilized mass-selected infrared (IR) photodissociation spectroscopy and quantum chemical calculations to investigate the structures and gaseous ion–molecule reactions of benzonitrile–ammonia (BN–NH₃) and benzonitrile–methylamine (BN–MA) clusters. The spectral observations indicate that the cyclic hydrogen bonding structure predominates in both neutral clusters. After VUV (118 nm) single-photon ionization, a new C–N covalent bond formed between BN and NH₃ in the (BN–NH₃)⁺ cluster. However, proton sharing constitutes the primary structure of the (BN–MA)⁺ cluster. The two nitrogen-containing interstellar molecules react with BN to yield distinct products due to difference in charge distribution and molecular polarity in the ionized clusters. The reactions of BN with other molecules contribute to our understanding of the growth mechanisms of complex interstellar molecules.