On the Formation of the Popcorn Flavorant 2,3-Butanedione (CH3COCOCH3) in Acetaldehyde-Containing Interstellar Ices |
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Authors: | Dr N Fabian Kleimeier Dr Andrew M Turner Prof?Dr Ryan C Fortenberry Prof?Dr Ralf I Kaiser |
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Institution: | 1. Department of Chemistry and W. M. Keck Research Laboratory in Astrochemistry, University of Hawai'i at Manoa 2545 McCarthy Mall, Honolulu, HI, 96822 USA;2. Department of Chemistry & Biochemistry, University of Mississippi, 322 Coulter Hall, University, MS, 38677-1848 USA |
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Abstract: | Acetaldehyde (CH3CHO) is ubiquitous throughout the interstellar medium and has been observed in cold molecular clouds, star forming regions, and in meteorites such as Murchison. As the simplest methyl-bearing aldehyde, acetaldehyde constitutes a critical precursor to prebiotic molecules such as the sugar deoxyribose and amino acids via the Strecker synthesis. In this study, we reveal the first laboratory detection of 2,3-butanedione (diacetyl, CH3COCOCH3) – a butter and popcorn flavorant – synthesized within acetaldehyde-based interstellar analog ices exposed to ionizing radiation at 5 K. Detailed isotopic substitution experiments combined with tunable vacuum ultraviolet (VUV) photoionization of the subliming molecules demonstrate that 2,3-butanedione is formed predominantly via the barrier-less radical–radical reaction of two acetyl radicals (CH3?O). These processes are of fundamental importance for a detailed understanding of how complex organic molecules (COMs) are synthesized in deep space thus constraining the molecular structures and complexity of molecules forming in extraterrestrial ices containing acetaldehyde through a vigorous galactic cosmic ray driven non-equilibrium chemistry. |
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Keywords: | complex organic molecules interstellar synthesis IR spectroscopy mass spectroscopy non-equilibrium processes |
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