![Panels a and c display the C3H + 3 ion signal from the dissociative photoionization of allene and propyne, respectively. Panels b and d show the reaction cross sections (left axis) and rate coefficients (right axis) with C2H4 , as a function of photon energy. The secondary x-axes indicate the maximum internal energy deposited in the system for the cyclic (top axis) and the linear (bottom axis) of C3H + 3 . -- [physics.chem-ph]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/11/Gasphase.png?fit=1200%2C674&ssl=1)
[physics.chem-ph] The gas-phase chemistry of C3H+3 plays a central role in the growth of carbonaceous species across a wide range of environments, from combustion systems to interstellar media.
However, the presence of multiple isomers, primarily the linear propargyl cation and the cyclic cyclopropenyl cation, has so far prevented the determination of reliable isomer-specific reaction kinetics. In this work, we combine tunable vacuum-ultraviolet (VUV) photoionization with controlled ion–molecule reaction measurements to selectively produce and probe the reactivity of C3H+3 isomers.
By employing a titration approach, we extract isomer-specific reaction rate coefficients and branching ratios for reactions of C3H+3 with C2H4, C3H4, and C3H6. Our results demonstrate a strong contrast in reactivity: the most stable cyclic isomer is found to be essentially unreactive under the investigated conditions, whereas the linear isomer exhibits efficient and diverse chemistry leading to the formation of larger hydrocarbon ions.
In particular, the formation of C6H+5 is observed, providing an important intermediate in pathways toward aromatic species. These findings help resolve long-standing ambiguities in previously reported rate coefficients and provide new quantitative constraints for kinetic and astrochemical models.
More broadly, this work highlights the importance of isomer-specific chemistry in carbon growth processes and demonstrates the effectiveness of VUV-based photoionization methods for disentangling complex reaction networks in the gas phase.
Corentin Rossi, Jean-Christophe Loison, Anne P. Rasmussen, Roland Thissen, Nandana Pattathadathil, Christian Alcaraz, Ugo Jacovella
Subjects: Chemical Physics (physics.chem-ph); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2610.11985 [physics.chem-ph] (or arXiv:2610.11985v1 [physics.chem-ph] for this version)
https://doi.org/10.48550/arXiv.2610.11985
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Submission history
From: Corentin Rossi
[v1] Thu, 8 Oct 2026 13:57:17 UTC (211 KB)
https://arxiv.org/abs/2610.11985
Astrobiology, Astronomy, Astrochemistry,
