Computational Study of the Reaction between Ethylene Glycol and the CH Radical: Competition between Carbon Addition and Dehydrogenation

The gas-phase reaction between ethylene glycol ((CH₂OH)₂) and the methylidyne radical (CH) has been investigated with the aim of understanding the competition between carbon addition and dehydrogenation processes under interstellar conditions. The former type of reaction increases the molecular complexity and leads to the formation of members of the C₃H₆O₂ family (with the hydrogen atom as coproduct), while the latter somewhat decreases the chemical complexity but opens the way toward the gas-phase production of C₂H₄O₂ isomers (together with the CH₃ radical as coproduct). An accurate investigation of the reactive potential energy surface indicates the formation of five isomers belonging to the C₂H₄O₂ family and six species belonging to the C₃H₆O₂ one. From a thermochemical point of view, the most stable product is acetic acid + CH₃, while 2-methoxyacetaldehyde + H is the least stable. However, because of the low temperatures of the interstellar medium, reactivity is ruled by kinetics. Kinetic simulations turn the tide, with the formation of 2-methoxyacetaldehyde becoming the fastest process. The title reaction also produces glycolaldehyde + CH₃, followed by the formation of methyl formate + CH₃ and methyl acetate + H to a lesser extent.