Effects of a Nonrigid Graphene Surface on the LH Associative Desorption of H Atoms and on the Deexcitation of Nascent H2 Molecules Colliding with Model Walls of Carbonaceous Porous Material

A planar slab of 200 C atoms bound by the Brenner potential is used to study the Langmuir−Hinshelwood (LH) recombination of two physisorbed H atoms on a graphene sheet and to simulate afterward successive collisions of the nascent H2 molecule with pore walls of a carbonaceous dust grain of the interstellar medium. The study is based on successive propagations of classical trajectories for the 200 C + 2 H atoms. The characteristics of H2 molecules formed by the LH reaction on the flexible surface are found to differ but negligibly from those formed on a rigid one. Collisions of those H2 molecules with graphitic pore walls are studied next. Reflection from and “trapping” onto the surface is observed and discussed. The most important energy transfer is from the molecule vibration to its rotation. This conversion mediates the transfer of the molecule internal energy to its translation or to surface heating. It is found that a single H2−surface impact has little effect on the internal energy of the molecules. ...