ABSTRACT Determining the level of chemical complexity within dense starless and gravitationally bound pre-stellar cores is crucial for constructing chemical models, which subsequently constrain the initial chemical conditions of star formation. We have searched for complex organic molecules (COMs) in the young starless core L1521E, and report the first clear detection of dimethyl ether (CH3OCH3), methyl formate (HCOOCH3), and vinyl cyanide (CH2CHCN). Eight transitions of acetaldehyde (CH3CHO) were also detected, five of which (A states) were used to determine an excitation temperature to then calculate column densities for the other oxygen-bearing COMs. If source size was not taken into account (i.e. if filling fraction was assumed to be one), column density was underestimated, and thus we stress the need for higher resolution mapping data. We calculated L1521E COM abundances and compared them to other stages of low-mass star formation, also finding similarities to other starless/pre-stellar cores, suggesting related chemical evolution. The scenario that assumes formation of COMs in gas-phase reactions between precursors formed on grains and then ejected to the cold gas via reactive desorption was tested and was unable to reproduce observed COM abundances, with the exception of CH3CHO. These results suggest that COMs observed in cold gas are formed not by gas-phase reactions alone, but also through surface reactions on interstellar grains. Our observations present a new, unique challenge for existing theoretical astrochemical models.
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Radiative Association between Neutral Radicals in the Interstellar Medium: CH3 + CH3O
Uncertainties in the production mechanisms of interstellar complex organic molecules call for a precise
investigation of gas-phase synthetic routes for these molecules, especially at low temperatures. Here, we report a
study of the gas-phase formation of dimethyl ether from the neutral radicals methyl and methoxy via the process of
radiative association. This process may be important to synthesize dimethyl ether and species such as methyl
formate, for which dimethyl ether is a precursor. The reaction is found to be rapid by the standards of radiative
association, especially at 10 K, where its rate coefficient is calculated by two different methods to be 3 × 10−11 or
2 × 10−10 cm3 s−1; the lower rate is calculated with a more precise theory and is likely more accurate. Insertion of
this reaction into the Nautilus network is found not to explain fully the abundance of dimethyl ether in cold and
prestellar cores, especially in those cores with the highest dimethyl ether abundances.
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- Award ID(s):
- 1906489
- NSF-PAR ID:
- 10339092
- Date Published:
- Journal Name:
- The astrophysical journal
- Volume:
- 922
- Issue:
- 2
- ISSN:
- 2041-8213
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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