Hydrogenated Polycyclic Aromatic Hydrocarbons (HnPAHs) as Catalysts for Hydrogenation Reactions in the Interstellar Medium: a Quantum Chemical Model

FERRULO RICARDO M; ZUBIETA C.; PATRICIA G. BELELLI

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2019

1463-9076

The sticking of H atoms onto dust grains and large hydrocarbon molecules has received considerableattention because it is thought to govern the formation of H2 and other H-containing molecules in theinterstellar medium. Using the density functional theory (DFT) approximation, we have investigated thecapacity of neutral hydrogenated polycyclic aromatic hydrocarbons (HnPAH) to catalyze simplehydrogenation reactions by acting as a source of atomic hydrogen. In particular, the interaction of OHand CO with H1-anthracene (singly hydrogenated) and H14-anthracene (fully hydrogenated) to form H2Oand HCO was modeled following the Eley?Rideal mechanism. In this process, a hydrogen atom isabstracted from the HnPAH molecule forming the corresponding hydrogenated compound. The resultswere compared to the most known case of the HnPAH-catalyzed formation of H2. It was observed thatwhereas H2 is formed by overcoming activation barriers of approximately 0.02 and 0.10 eV withH1-anthracene and H14-anthracene, respectively, H2O is produced in a barrierless fashion with bothhydrocarbon molecules. The production of HCO was found to be a highly unfavorable process(with activation barriers of 0.73 eV and 3.13 eV for H1- and H14-anthracene, respectively). Complementarycalculations performed using the rest of the Hn-anthracene molecules (from 2 to 13 extra H atoms) showedthat in all the cases the reaction with OH is barrierless as well. This efficient mechanism could therefore be apossible route for water formation in the cold interstellar medium.