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Researchers used an ion trap technique combined with electronic structure calculations to observe barrier-less gas-phase reactions between pyrimidine cations (C4H4N2+) and acetylene (C2H2), resulting in the formation of a previously unreported endocyclic nitrogen-bearing polycyclic aromatic hydrocarbon (N-PAH) with the formula C8H7N2+. These reactions proceed spontaneously without an energy barrier, providing a plausible mechanism for the formation of N-PAHs in environments such as Titan's atmosphere and the interstellar medium. The findings help address the discrepancy between theoretically predicted and observationally detected abundances of nitrogen-functionalized molecules in astrophysical settings.
Why it matters
Understanding how complex nitrogen-bearing organic molecules form in space has direct implications for astrochemistry and the study of prebiotic chemistry, as N-PAHs are considered key precursors to biologically relevant molecules. This work may also improve atmospheric models of nitrogen-rich planetary bodies such as Saturn's moon Titan.
arXiv:2605.14424v1 Announce Type: cross
Abstract: Nitrogen-bearing polycyclic aromatic hydrocarbons (N-PAHs) are key precursors to complex organic molecules in both the interstellar medium and the nitrogen-rich planetary atmospheres. Despite the recent detections of nitrogen-functionalized astromolecules, their formation pathways remain an open question. The discrepancies between their predicted and observed abundances point to unknown mechanism that govern their evolution in the astrophysical environments. Employing an ion trap technique and electronic structure calculations, we unravel multiple barrier-less reactions between gas-phase pyrimidine cations (C$_4$H$_4$N$_2^+$) and acetylene (C$_2$H$_2$) which form an hitherto unreported endocyclic- N-PAHs (C$_8$H$_7$N$_2^+$). The present measurements on reactions involving a double-nitrogen subsituted aromatic heterocycle have implications to the astrochemistry of both the Titan’s atmosphere and interstellar medium.