Ferullo Ricardo M, Zubieta Carolina E, Belelli Patricia G
Departamento de Química, Universidad Nacional del Sur - INQUISUR (UNS, CONICET), Av. Alem 1253, 8000 Bahía Blanca, Argentina.
Phys Chem Chem Phys. 2019 Jun 5;21(22):12012-12020. doi: 10.1039/c9cp02329a.
The sticking of H atoms onto dust grains and large hydrocarbon molecules has received considerable attention because it is thought to govern the formation of H2 and other H-containing molecules in the interstellar medium. Using the density functional theory (DFT) approximation, we have investigated the capacity of neutral hydrogenated polycyclic aromatic hydrocarbons (HnPAH) to catalyze simple hydrogenation reactions by acting as a source of atomic hydrogen. In particular, the interaction of OH and CO with H1-anthracene (singly hydrogenated) and H14-anthracene (fully hydrogenated) to form H2O and HCO was modeled following the Eley-Rideal mechanism. In this process, a hydrogen atom is abstracted from the HnPAH molecule forming the corresponding hydrogenated compound. The results were compared to the most known case of the HnPAH-catalyzed formation of H2. It was observed that whereas H2 is formed by overcoming activation barriers of approximately 0.02 and 0.10 eV with H1-anthracene and H14-anthracene, respectively, H2O is produced in a barrierless fashion with both hydrocarbon 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). Complementary calculations performed using the rest of the Hn-anthracene molecules (from 2 to 13 extra H atoms) showed that in all the cases the reaction with OH is barrierless as well. This efficient mechanism could therefore be a possible route for water formation in the cold interstellar medium.
氢原子附着于尘埃颗粒和大型碳氢化合物分子上的现象已受到广泛关注，因为人们认为这一过程控制着星际介质中氢气及其他含氢分子的形成。我们采用密度泛函理论（DFT）近似方法，研究了中性氢化多环芳烃（HnPAH）作为原子氢源催化简单氢化反应的能力。具体而言，按照埃利-里德机理对OH和CO与H1-蒽（单氢化）和H14-蒽（完全氢化）相互作用形成H2O和HCO的过程进行了建模。在此过程中，一个氢原子从HnPAH分子中被提取出来，形成相应的氢化化合物。将结果与HnPAH催化形成H2的最知名案例进行了比较。结果发现，H1-蒽和H14-蒽形成H2时分别克服了约0.02 eV和0.10 eV的活化能垒，而两种碳氢化合物分子与OH反应生成H2O时均无活化能垒。发现生成HCO是一个极不利的过程（H1-蒽和H14-蒽的活化能垒分别为0.73 eV和3.13 eV）。使用其余Hn-蒽分子（额外含有2至13个氢原子）进行的补充计算表明，在所有情况下与OH的反应也都没有活化能垒。因此，这种高效的机理可能是寒冷星际介质中形成水的一条途径。
