Carbon Atom Reactivity with Amorphous Solid Water: H${}_2$O Catalyzed Formation of H${}_2$CO

Abstract

We report new computational and experimental evidence of an efficient and astrochemically relevant formation route to formaldehyde (H${}_2$CO). 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 H${}_2$CO 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 ${}^3$C + H${}_2$O -> ${}^3$HCOH and ${}^1$HCOH -> ${}^1$H${}_2$CO can take place with low or without barriers, contrary to the high-barrier traditional internal hydrogen migration. These low barriers or absence thereof explain the very small kinetic isotope effect in our experiments when comparing the formation of H${}_2$CO to D${}_2$CO. Our results reconcile the disagreement found in the literature on the reaction route: C + H${}_2$O -> H${}_2$CO.

arXiv commentAccepted for publication in JPCL

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