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. 2021 Nov 11;12(44):10854-10860.
doi: 10.1021/acs.jpclett.1c02760. Epub 2021 Nov 2.

Carbon Atom Reactivity with Amorphous Solid Water: H2O-Catalyzed Formation of H2CO

Germán Molpeceres  1 , Johannes Kästner  1 , Gleb Fedoseev  2   3 , Danna Qasim  2 , Richard Schömig  1 , Harold Linnartz  2 , Thanja Lamberts  2   4
Affiliations

Carbon Atom Reactivity with Amorphous Solid Water: H2O-Catalyzed Formation of H2CO

Germán Molpeceres et al. J Phys Chem Lett. .

Abstract

We report new computational and experimental evidence of an efficient and astrochemically relevant formation route to formaldehyde (H2CO). This simplest carbonylic compound is central to the formation of complex organics in cold interstellar clouds and is generally regarded to be formed by the hydrogenation of solid-state carbon monoxide. We demonstrate H2CO formation via the reaction of carbon atoms with amorphous solid water. Crucial to our proposed mechanism is a concerted proton transfer catalyzed by the water hydrogen bonding network. Consequently, the reactions 3C + H2O → 3HCOH and 1HCOH → 1H2CO can take place with low or without barriers, contrary to the high-barrier traditional internal hydrogen migration. These low barriers (or the absence thereof) explain the very small kinetic isotope effect in our experiments when comparing the formation of H2CO to D2CO. Our results reconcile the disagreement found in the literature on the reaction route C + H2O → H2CO.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Transition-state geometries for reaction 2 (upper row) and reaction 6 (lower row) in the gas phase (left column) and for both the traditional internal isomerization mechanism 1 (middle column) and the concerted water-assisted mechanism 2 (right column). Atoms directly involved in the reaction mechanism are depicted in full color; water molecules not participating in the reaction are transparent in the background. Color code: teal, carbon; red, oxygen; white, hydrogen.
Figure 2
Figure 2
Schematic reaction profiles for reactions 2 and 6 within the internal isomerization mechanism (mechanism 1, red) and the water-assisted mechanism (mechanism 2, green). Note that green dashed lines here represent paths with a small barrier and barrierless paths. The minima are taken as the average binding energies listed in Table 1, and the saddle points as the highest activation energies in Table 2. For 1H2CO, the binding energy is taken as the average of the end points of intrinsic reaction coordinate calculations. The reader is referred to the text for an extensive discussion of the energetics of the reaction.
Figure 3
Figure 3
RAIR spectra of the four experiments outlined in Table 4. The vertical lines indicate peak positions of the formaldehyde and water isotopologues.
See this image and copyright information in PMC

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