Photochemical pathways in astronomical ices: A computational study of singlet oxygen reactions with hydrocarbons

Amit Daniely, Alon Zamir, Helen R. Eisenberg, Ester Livshits, Elettra Piacentino, Jennifer B. Bergner, Karin I. Öberg, Tamar Stein*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Complex organic molecules are widespread in different areas of the interstellar medium, including cold areas, such as molecular clouds, where chemical reactions occur in ice. Among the observed molecules are oxygen-bearing organic molecules, which are of high interest given their significant role in astrobiology. Despite the observed rich chemistry, the underlying molecular mechanisms responsible for molecular formation in such cold dilute areas are still not fully understood. In this paper, we study the unique chemistry taking place in astronomically relevant ices, where UV radiation is a central driving force for chemical reactions. Photofragmentation of ice components gives rise to highly reactive species, such as the O(1D) atom. These species provide a pathway for chemical complexity even in cold areas. Using quantum chemistry calculations, we demonstrate that O(1D) reacts barrierlessly with hydrocarbons. Moreover, photoprocessing of the reaction products (and other components of the ice), followed by radical recombination, is found to be an essential part of the overall mechanism. In ice containing O(1D) and hydrocarbons, the formation of formaldehyde in methane ice, acetaldehyde in ethane ice, and carbon monoxide in acetylene ice, and the consumption of alcohol in all systems, was predicted in agreement with experimental results.

Original languageEnglish
Article number014303
JournalJournal of Chemical Physics
Volume162
Issue number1
DOIs
StatePublished - 7 Jan 2025

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