Observation of spontaneous N-bearing PAH formation using ion trap: a new formation pathway in the interstellar medium

TL;DR

This study uncovers a new, barrier-less pathway for forming nitrogen-bearing polycyclic aromatic hydrocarbons in space, using ion trap experiments and calculations, with implications for astrochemistry.

Contribution

It reveals a previously unknown formation mechanism for N-PAHs involving barrier-less reactions between pyrimidine cations and acetylene.

Findings

Identified barrier-less reactions forming N-PAHs in interstellar conditions.

Demonstrated formation of endocyclic N-PAHs via ion trap experiments.

Implications for nitrogen-rich planetary atmospheres and interstellar chemistry.

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.