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  4. Competitive Dehydrogenation and Backbone Fragmentation of Superhydrogenated PAHs: A Laboratory Study
 
research article

Competitive Dehydrogenation and Backbone Fragmentation of Superhydrogenated PAHs: A Laboratory Study

Stockett, Mark H.
•
Avaldi, Lorenzo
•
Bolognesi, Paola
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May 1, 2021
The Astrophysical Journal

Superhydrogenated polycyclic aromatic hydrocarbons (PAHs) have been suggested to catalyze the formation of H-2 in certain regions of space, but it remains unclear under which circumstances this mechanism is viable given the reduced carbon backbone stability of superhydrogenated PAHs. We report a laboratory study on the stability of the smallest pericondensed PAH, pyrene (C16H10+N, with N = 4, 6, and 16 additional H atoms), against photodestruction by single vacuum ultraviolet photons using the photoelectron-photoion coincidence technique. For N = 4, we observe a protective effect of hydrogenation against the loss of native hydrogens, in the form of an increase in the appearance energies of the C16H9+ and C16H8+ daughter ions compared to those reported for pristine pyrene (C16H10). No such effect is seen for N = 6 or 16, where the weakening effect of replacing aromatic bonds with aliphatic ones outweighs the buffering effect of the additional hydrogen atoms. The onset of fragmentation occurs at similar internal energies for N = 4 and 6, but is significantly lower for N = 16. In all three cases, H-loss and CmHn-loss (m >= 1, carbon backbone fragmentation) channels open at approximately the same energy. The branching fractions of the primary channels favor H-loss for N = 4, CmHn-loss for N = 16, and are roughly equal for the intermediate N = 6. We conclude that superhydrogenated pyrene is probably too small to support catalytic H-2-formation, while trends in the current and previously reported data suggest that larger PAHs may serve as catalysts up to a certain level of hydrogenation.

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Type
research article
DOI
10.3847/1538-4357/abf354
Web of Science ID

WOS:000655287700001

Author(s)
Stockett, Mark H.
Avaldi, Lorenzo
Bolognesi, Paola
Bull, James N.
Carlini, Laura
Carrascosa, Eduardo  
Chiarinelli, Jacopo
Richter, Robert
Zettergren, Henning
Date Issued

2021-05-01

Published in
The Astrophysical Journal
Volume

913

Issue

1

Start page

46

Subjects

Astronomy & Astrophysics

•

polycyclic aromatic-hydrocarbons

•

molecular-hydrogen formation

•

mass-spectrometry

•

cations

•

dissociation

•

emission

•

ultraviolet

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anthracene

•

dynamics

•

spectra

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LCPM  
Available on Infoscience
June 5, 2021
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/178628
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