Constraining the formation of interstellar methanol using isotopologues

Abstract

The formation of so-called complex mols. in the early stages of star formation has implications not only for how we decipher the evolution of planetary systems but also how we understand the evolution of mols. themselves. Interstellar complex mols., which are simple by terrestrial stds. with only six or more atoms, are key precursors to the rich chem. diversity found in comets and meteorites and on planetary bodies. Isotopologues have proven useful in other areas of chem., for instance in pinning down formation mechanisms of mols. in synthetic org. chem., but there has been relatively little work done using isotopologues to understand how interstellar mols. form. Isotopologues have been used, however, in constraining the formation of compds. such as Me cyanide (CH_3CN) and methanol (CH_3OH) in the Orion Kleinmann-Low nebula (Orion KL). Previous low-spatial-resoln. studies of methanol in Orion KL have been inconclusive, and thus we have obtained high-resoln. imaging data of deuterated methanol (CH_2DOH, CH_3OD) toward Orion KL with the Atacama Large Millimeter/submillimeter Array (ALMA). These data show the distribution of deuterated methanol on spatial scales commensurate with local star formation. Comparing ratios of CH_2DOH and CH_3OD with ^(13)CH_3OH, we aim to assess how methanol chem. varies across the nebula and det. observationally whether the compd. is formed predominantly on the surfaces of icy dust grains as predicted by lab. expts. and computational models. Moreover, mol. clouds also contain relatively acidic compds., such as water, that can prompt spontaneous hydrogen/deuterium exchange on the oxygen atom in methanol. Thus, we will also explore the persistence of deuterium in methanol across the nebula by assessing how the relative abundances of CH_2DOH and CHOD change. Using these results, we can better constrain both the formation and reactivity of methanol in star-forming regions, a first step in understanding how even more complex chem.-perhaps even prebiotic chem.-evolved over the history of the universe.

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