Competition between Abstraction and Addition Channels for the Reaction between the OH Radical and Vinyl Alcohol in the Interstellar Medium

Vinyl alcohol (Vy)and hydroxyl radical (OH) are involved in severalprocesses, which take place in environments characterized by verydifferent physical-chemical conditions, ranging from the lowpressures and temperatures typical of the interstellar medium (ISM)up to the high temperatures of interest for combustion processes.A gas-phase reaction mechanism involving Vy and OH has been proposedas a possible path for the formation of (Z)-1,2-ethenediol (Et), a molecule recently identified in the ISM. Et, the enolic formof glycolaldehyde, is considered a key precursor for the formationof sugars in both interstellar and prebiotic chemistry. We have thereforeundertaken a detailed quantum chemical study of possible reactionchannels starting from the interaction between the OH radical andboth conformers of Vy (syn and anti). The formation of a prereactive complex always represents the firststep of the reaction, which can then proceed through the attack tothe C=C double bond (leading in turn to the formation of differentdissociation products) or through hydrogen abstraction, which eventuallyproduces a radical species and water. Then, a master equation approachbased on ab initio transition state theory has been employed to calculatethe reaction rate constants of different products for temperaturesup to 500 K. A comparison of the kinetic results for the differentreaction channels shows that hydrogen abstraction is strongly favoredfor both Vy conformers and leads to the formation of water and CH2CHO radical. As a matter of fact, formation of Et is stronglydisfavored under the harsh conditions of the ISM from both kineticand thermodynamic points of view because of the high activation energyand strong endothermicity of the corresponding reaction path.

Automated summary

Vinyl alcohol (Vy) and hydroxyl radical (OH) participate in various processes under different physical-chemical conditions. A detailed quantum chemical study was conducted to investigate the possible reaction paths between OH and both conformers of Vy. The formation of (Z)-1,2-ethenediol (Et) is strongly disfavored under the harsh conditions of the ISM.