Interstellar catalysis: Formation of small molecules on a graphitic flake

Abstract

The formation of organic molecules of the type X H n , where X is H, C, N and O and n = 1 − 4 , on the hydrogenated surface of a polycyclic aromatic hydrocarbon flake (coronene) has been examined in detail with the CATIVIC parametric quantum chemical code. Hydrogen chemisorption on different sites, surface–adsorbate bonding properties and layer formation are studied. The interactions of H, O, N and C on one-center sites of the H-saturated monolayer give rise to the formation of free H 2, OH and NH while the CH molecule remains attached to the surface. Reactions on two-center sites lead to the formation of the free triatomic molecules H 2O, NH 2 and CH 2. One-center interactions of OH, NH, NH 2, CH 2 and CH 3 also result in the respective formation of H 2O, NH 2, NH 3, CH 3 and CH 4. We find that the reactions of atoms and small molecules with the hydrogenated coronene surface in most cases must overcome relatively high energy barriers in order to lead to reaction products.