Abstract
Abstract Despite the harsh conditions of the interstellar medium, chemistry thrives in it, especially in star-forming regions where several interstellar complex organic molecules (iCOMs) have been detected. Yet, how these species are synthesized is a mystery. The majority of current models claim that this happens on interstellar grain surfaces. Nevertheless, evidence is mounting that neutral gas-phase chemistry plays an important role. In this paper, we propose a new scheme for the gas-phase synthesis of glycolaldehyde, a species with a prebiotic potential and for which no gas-phase formation route was previously known. In the proposed scheme, the ancestor is ethanol and the glycolaldehyde sister species are acetic acid (another iCOM with unknown gas-phase formation routes) and formic acid. For the reactions of the new scheme with no available data, we have performed electronic structure and kinetics calculations deriving rate coefficients and branching ratios. Furthermore, after a careful review of the chemistry literature, we revised the available chemical networks, adding and correcting several reactions related to glycolaldehyde, acetic acid, and formic acid. The new chemical network has been used in an astrochemical model to predict the abundance of glycolaldehyde, acetic acid, and formic acid. The predicted abundance of glycolaldehyde depends on the ethanol abundance in the gas phase and is in excellent agreement with the measured one in hot corinos and shock sites. Our new model overpredicts the abundance of acetic acid and formic acid by about a factor of 10, which might imply a yet incomplete reaction network.
Highlights
About one-third of the ∼200 molecules detected in the interstellar medium (ISM) are constituted by six or more atoms.6 All of these molecules contain at least one carbon atom
Following the suggestion provided by this possible correlation, in this work we propose a series of gas-phase reactions that start from ethanol (CH3CH2OH) and that lead to the synthesis of glycolaldehyde in a sequence of gas-phase reactions that is similar to that connecting dimethyl ether and methyl formate, two other common interstellar complex organic molecules (iCOMs) (Balucani et al 2015)
We have presented a new scheme for the synthesis of glycolaldehyde, acetic acid, and formic acid from reactions involving ethanol as an ancestor species
Summary
About one-third of the ∼200 molecules detected in the interstellar medium (ISM) are constituted by six or more atoms. All of these molecules contain at least one carbon atom. About one-third of the ∼200 molecules detected in the interstellar medium (ISM) are constituted by six or more atoms.. About one-third of the ∼200 molecules detected in the interstellar medium (ISM) are constituted by six or more atoms.6 All of these molecules contain at least one carbon atom. We will call molecules with at least six atoms and containing at least one carbon atom interstellar complex organic molecules (iCOMs7). In the majority of iCOMs, hydrogen and oxygen are the additional elements. Slightly more than 40 iCOMs that contain elements other than C and H have been detected. They represent about 20% of detected ISM molecules
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