Astrochemistry

Rate Constants and Product Yields for the C + CH3CHO Reaction at Low Temperatures

By Keith Cowing
Status Report
astro-ph.GA
June 6, 2025
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Rate Constants and Product Yields for the C + CH3CHO Reaction at Low Temperatures
Triplet potential energy surface for the reaction of C with CH3CHO with geometries and energies calculated at the M06-2X/aug-cc-pVTZ level (energy values in black). Certain structures close in energy to the reactant asymptote at the M06-2X/aug-cc-pVTZ level were calculated with the more accurate DLPNO-CCSD(T)/ aug-cc-pVTZ method (energy values in red). All energies were corrected for zero-point energy differences. — astro-ph.GA

Reactions involving atomic carbon in its ground electronic state, C(3P), play an important role in astrochemistry due to high C-atom abundance levels.

Here we performed a kinetic investigation of the reaction between C(3P) and acetaldehyde, CH3CHO, determining rate constants for this process over the 50-296 K range. Measurements of the formation of atomic hydrogen, H(2S), were also performed to provide insight into product formation.

Experiments were conducted using a supersonic flow reactor coupled with pulsed laser photolysis for C-atom generation and pulsed laser induced fluorescence in the vacuum ultraviolet range for the detection of both C(3P) and H(2S) atoms. Quantum chemical calculations of the ground triplet state potential energy surface of C3H4O were also performed to provide theoretical support for the measurements.

The rate constants were large and temperature independent with an average value of 4.0 x 10-10 cm3 s-1. This result is consistent with the theoretical results which predict either very low barriers or none at all on the underlying potential energy surface. Although experimental difficulties prevented the quantitative determination of H-atom formation, qualitatively, H-atom yields were very low with CH3CH/C2H4 + CO as the major products based on the calculations.

The influence of this reaction on interstellar chemistry was tested using a gas-grain model of dense interstellar clouds. These simulations predict that the C(3P) + CH3CHO reaction decreases gas-phase CH3CHO abundances by more than an order of magnitude at early and intermediate cloud ages, with a lower influence at typical dense cloud ages.

Kevin M. Hickson, Jean-Christophe Loison, Valentine Wakelam

Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2506.04794 [astro-ph.GA] (or arXiv:2506.04794v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2506.04794
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Related DOI:
https://doi.org/10.1021/acsearthspacechem.5c00111
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Submission history
From: Kevin Hickson
[v1] Thu, 5 Jun 2025 09:22:50 UTC (1,694 KB)
https://arxiv.org/abs/2506.04794
Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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