Formation of Acetaldehyde on Grain Surfaces

Complex Organic Molecules (COMs) have been detected in the interstellar medium (ISM). However, it is not clear whether their synthesis occurs on the icy surfaces of interstellar grains or via a series of gas-phase reactions.

As a test case of the COMs synthesis in the ISM, we present new quantum chemical calculations on the formation of acetaldehyde (CH3CHO) from the coupling of the HCO and CH3 radicals, both in gas phase and on water ice surfaces. The binding energies of HCO and CH3 on the amorphous water ice were also computed (2333 and 734 K, respectively). Results indicate that, in gas phase, the products could be either CH3CHO, CH4 + CO, or CH3OCH, depending on the relative orientation of the two radicals.

However, on the amorphous water ice, only the CH4 + CO product is possible due to the geometrical constraints imposed by the water ice surface. Therefore, acetaldehyde cannot be synthesized by the CH3 + HCO coupling on the icy grains. We discuss the implications of these results and other cases, such as ethylene glycol and dimethyl ether, in which similar situations can occur, suggesting that formation of these molecules on the grain surfaces might be unlikely.

The (impossible?) formation of acetaldehyde on the grain surfaces: insights from quantum chemical calculations

Joan Enrique-Romero, Albert Rimola, Cecilia Ceccarelli, Nadia Balucani
(Submitted on 30 Mar 2016)

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference: Monthly Notices of the Royal Astronomical Society Letters, 2016, Volume 459, Issue 1, L6-L10
DOI: 10.1093/mnrasl/slw031
Cite as: arXiv:1603.09096 [astro-ph.EP] (or arXiv:1603.09096v1 [astro-ph.EP] for this version)
Submission history
From: Albert Rimola
[v1] Wed, 30 Mar 2016 09:31:07 GMT (652kb)
http://arxiv.org/abs/1603.09096

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