Polycyclic aromatic hydrocarbons (PAHs) are among the most ubiquitous compounds in the universe, accounting for up to ~25% of all interstellar carbon. Since most unsubstituted PAHs do not possess permanent dipole moments, they are invisible to radio astronomy. Constraining their abundances relies on the detection of polar chemical proxies, such as aromatic nitriles. We report the detection of 2- and 4-cyanopyrene, isomers of the recently detected 1-cyanopyrene. We find that these isomers are present in an abundance ratio of ~2:1:2, which mirrors the number of equivalent sites available for CN addition. We conclude that there is evidence that the cyanopyrene isomers formed by direct CN addition to pyrene under kinetic control in hydrogen-rich gas at 10 K and discuss constraints on the H/CN ratio for PAHs in TMC-1.
@article{arxiv.2410.00670,
title = {Detections of interstellar 2-cyanopyrene and 4-cyanopyrene in TMC-1},
author = {Gabi Wenzel and Thomas H. Speak and P. Bryan Changala and Reace H. J. Willis and Andrew M. Burkhardt and Shuo Zhang and Edwin A. Bergin and Alex N. Byrne and Steven B. Charnley and Zachary T. P. Fried and Harshal Gupta and Eric Herbst and Martin S. Holdren and Andrew Lipnicky and Ryan A. Loomis and Christopher N. Shingledecker and Ci Xue and Anthony J. Remijan and Alison E. Wendlandt and Michael C. McCarthy and Ilsa R. Cooke and Brett A. McGuire},
journal= {arXiv preprint arXiv:2410.00670},
year = {2024}
}
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