Formation of interstellar aldehydes and enols - tracers of a cosmic-ray driven non-equilibrium synthesis of complex organic molecules

M.J. Abplanalp, S. Gozem, A.I. Krylov, C.N. Shingledecker, E. Herbst, and R.I. Kaiser
PNAS 113, 7727 – 7732 (2016)

Complex organic molecules such as sugars and amides are ubiquitous in star- and planet-forming regions, but their formation mechanisms have remained largely elusive until now. Here we show in a combined experimental, computational, and astrochemical modeling study that two prototype representatives of interstellar aldehydes and enols, acetaldehyde (CH3CHO) and vinyl alcohol (C2H3OH), act as key tracers revealing that organics can be synthesized via a vigorous cosmic ray driven non-equilibrium chemistry within low temperature interstellar ices. These mechanisms operate even at temperatures as low as 10 K, against conventional wisdom, and define a hitherto poorly explored key reaction class resulting in a facile synthesis of complex organic molecules via exotic non-equilibrium reaction pathways. Interstellar aldehydes and their enol isomers exemplify prototype systems representing a whole set of complex organic molecules, which are first synthesized via non-equilibrium chemistry inside interstellar ices and then released by sublimation into star forming star-forming regions, of vital importance in initiating a chain of chemical reactions leading eventually to the molecular precursors of biorelevant molecules as planets form in their interstellar nurseries.

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