Unraveling reaction mechanisms of aromatic and resonance-stabilized radicals is critical to understanding molecular mass growth processes to polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanoparticles in distinct astrophysical environments (molecular clouds, circumstellar envelopes) and combustion systems. Using photoelectron photoion coincidence spectroscopy (PEPICO), we explored the gas-phase reaction of the methyl radical (CH3•) with the aromatic and resonance-stabilized fluorenyl radical (C13H9•) under high-temperature conditions in a chemical microreactor. Anthracene and phenanthrene were detected isomer-selectively using photoionization efficiency (PIE) curves and mass-selected threshold photoelectron (ms-TPE) spectra. While phenanthrene is produced through a radical-radical recombination of the carbon-centered radicals, anthracene may plausibly be formed through an unconventional radical addition to a low spin-density fluorenyl carbon. These pathways result in five-membered ring expansion—a critical mechanism crucial to PAH mass growth converting bent PAHs into planar nanostructures.
Goettl, Shane J., Turner, Andrew M., Krasnoukhov, Vladislav S., Azyazov, Valeriy N., Kanayama, Keisuke, Hemberger, Patrick, Mebel, Alexander M., & Kaiser, Ralf I. (2025). Gas-phase synthesis of anthracene and phenanthrene via radical-radical reaction induced ring expansions. Science Advances, 11(23). https://doi.org/10.1126/sciadv.adv0692
Goettl, Shane J., Turner, Andrew M., Krasnoukhov, Vladislav S., et al., "Gas-phase synthesis of anthracene and phenanthrene via radical-radical reaction induced ring expansions," Science Advances 11, no. 23 (2025), https://doi.org/10.1126/sciadv.adv0692
@article{osti_2584220,
author = {Goettl, Shane J. and Turner, Andrew M. and Krasnoukhov, Vladislav S. and Azyazov, Valeriy N. and Kanayama, Keisuke and Hemberger, Patrick and Mebel, Alexander M. and Kaiser, Ralf I.},
title = {Gas-phase synthesis of anthracene and phenanthrene via radical-radical reaction induced ring expansions},
annote = {Unraveling reaction mechanisms of aromatic and resonance-stabilized radicals is critical to understanding molecular mass growth processes to polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanoparticles in distinct astrophysical environments (molecular clouds, circumstellar envelopes) and combustion systems. Using photoelectron photoion coincidence spectroscopy (PEPICO), we explored the gas-phase reaction of the methyl radical (CH3•) with the aromatic and resonance-stabilized fluorenyl radical (C13H9•) under high-temperature conditions in a chemical microreactor. Anthracene and phenanthrene were detected isomer-selectively using photoionization efficiency (PIE) curves and mass-selected threshold photoelectron (ms-TPE) spectra. While phenanthrene is produced through a radical-radical recombination of the carbon-centered radicals, anthracene may plausibly be formed through an unconventional radical addition to a low spin-density fluorenyl carbon. These pathways result in five-membered ring expansion—a critical mechanism crucial to PAH mass growth converting bent PAHs into planar nanostructures.},
doi = {10.1126/sciadv.adv0692},
url = {https://www.osti.gov/biblio/2584220},
journal = {Science Advances},
issn = {ISSN 2375-2548},
number = {23},
volume = {11},
place = {United States},
publisher = {AAAS},
year = {2025},
month = {06}}
Florida International University, Miami, FL (United States); Paul Scherrer Institute, Villigen PSI (Switzerland); Samara National Research University (Russian Federation); University of Hawai‘i at Mānoa, Honolulu, HI (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 610, Issue 2https://doi.org/10.1016/j.nima.2009.08.069