Volume 251, 2024

Exploring the chemical dynamics of phenanthrene (C14H10) formation via the bimolecular gas-phase reaction of the phenylethynyl radical (C6H5CC) with benzene (C6H6)

Abstract

The exploration of the fundamental formation mechanisms of polycyclic aromatic hydrocarbons (PAHs) is crucial for the understanding of molecular mass growth processes leading to two- and three-dimensional carbonaceous nanostructures (nanosheets, graphenes, nanotubes, buckyballs) in extraterrestrial environments (circumstellar envelopes, planetary nebulae, molecular clouds) and combustion systems. While key studies have been conducted exploiting traditional, high-temperature mechanisms such as the hydrogen abstraction–acetylene addition (HACA) and phenyl addition–dehydrocyclization (PAC) pathways, the complexity of extreme environments highlights the necessity of investigating chemically diverse mass growth reaction mechanisms leading to PAHs. Employing the crossed molecular beams technique coupled with electronic structure calculations, we report on the gas-phase synthesis of phenanthrene (C14H10)—a three-ring, 14π benzenoid PAH—via a phenylethynyl addition–cyclization–aromatization mechanism, featuring bimolecular reactions of the phenylethynyl radical (C6H5CC, X2A1) with benzene (C6H6) under single collision conditions. The dynamics involve a phenylethynyl radical addition to benzene without entrance barrier leading eventually to phenanthrene via indirect scattering dynamics through C14H11 intermediates. The barrierless nature of reaction allows rapid access to phenanthrene in low-temperature environments such as cold molecular clouds which can reach temperatures as low as 10 K. This mechanism constitutes a unique, low-temperature framework for the formation of PAHs as building blocks in molecular mass growth processes to carbonaceous nanostructures in extraterrestrial environments thus affording critical insight into the low-temperature hydrocarbon chemistry in our universe.

Graphical abstract: Exploring the chemical dynamics of phenanthrene (C14H10) formation via the bimolecular gas-phase reaction of the phenylethynyl radical (C6H5CC) with benzene (C6H6)

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
06 Dec 2023
Accepted
12 Jan 2024
First published
20 May 2024

Faraday Discuss., 2024,251, 509-522

Exploring the chemical dynamics of phenanthrene (C14H10) formation via the bimolecular gas-phase reaction of the phenylethynyl radical (C6H5CC) with benzene (C6H6)

S. J. Goettl, Z. Yang, C. He, A. Somani, A. Portela-Gonzalez, W. Sander, A. M. Mebel and R. I. Kaiser, Faraday Discuss., 2024, 251, 509 DOI: 10.1039/D3FD00159H

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