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Description
Nitrogen-bearing polycyclic aromatic hydrocarbons (N-PAHs) are key precursors to complex organic molecules in both the interstellar medium and nitrogen-rich planetary atmospheres. Despite the recent detections of nitrogen functionalized astromolecules [1], their formation pathways remain an open question. The discrepancies between their predicted and observed abundances point to unknown mechanisms such as ion-molecule reaction that govern their evolution in the astrophysical environments. Here we employed a newly built 22-pole radio-frequency ion trap [2] to probe cosmically relevant ion-molecule reaction. Since, the nitrogen atom in the aromatic ring gives rise to exotic interactions that enable their molecular growth [3], we choose pyrimidine (C$_4$H$_4$N$_2$), an aromatic heterocycle containing two N-atoms. Our kinetic study augmented by quantum chemistry calculations reveal a spontaneous formation of hitherto unreported endocyclic N-PAHs, revealing pathways which could be active in space.
References: [1]. G. Wenzel, et al., Discovery of the Seven-ring Polycyclic Aromatic Hydrocarbon Cyanocoronene (C24H11CN) in GOTHAM Observations of TMC-1. The Astrophysical Journal Letters 984 (1), L36 (2025).
[2]. N. R. Behera, S. Dutta, R. Chacko, S. Barik, G. Aravind, A 22-pole radiofrequency ion trap setup for laboratory astrophysical studies. Review of Scientific Instruments 95 (1) (2024).
[3]. D. B. Rap, J. G. Schrauwen, A. N. Marimuthu, B. Redlich, S. Brunken, Low-temperature nitrogen-bearing polycyclic aromatic hydrocarbon formation routes validated by infrared spectroscopy. Nature Astronomy 6 (9), 1059–1067 (2022).