The formation of so-called complex molecules 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 molecules themselves. Interstellar complex molecules, which are simple by terrestrial standards with only six or more atoms, are key precursors to the rich chemical diversity found in comets and meteorites and on planetary bodies. Isotopologues have proven useful in other areas of chemistry, for instance in pinning down formation mechanisms of molecules in synthetic organic chemistry, but there has been relatively little work done using isotopologues to understand how interstellar molecules form. Isotopologues have been used, however, in constraining the formation of compounds such as methyl cyanide (CH3CN) and methanol (CH3OH) in the Orion Kleinmann-Low nebula (Orion KL). Previous low-spatial-resolution studies of methanol in Orion KL have been inconclusive, and thus we have obtained high-resolution imaging data of deuterated methanol (CH2DOH, CH3OD) 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 CH2DOH and CH3OD with 13CH3OH, we aim to assess how methanol chemistry varies across the nebula and determine observationally whether the compound is formed predominantly on the surfaces of icy dust grains as predicted by laboratory experiments and computational models. Moreover, molecular clouds also contain relatively acidic compounds, 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 CH2DOH 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 chemistry—perhaps even prebiotic chemistry—evolved over the history of the universe.

Constraining the formation of interstellar methanol using isotopologues

2019 Fall National Meeting

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