Polymerization via cluster-solid surface impacts: Molecular dynamics simulations

Molecular dynamics simulations of collisions between simple organic molecular clusters and a nonrigid, hydrogen-terminated diamond (111) surface have been performed to study the chemical reactions that occur within the clusters and between the cluster and the surface as a result of impact. A second-generation version of the reactive empirical bond order potential for hydrocarbons developed by Brenner, which has been modified to include long-range van der Waals interactions, is used in the simulations. The velocities considered are in the hyperthermal region and are comparable to those that result in shock-induced chemistry in energetic materials and that occur between particles and solid surfaces in interstellar space. The outcome of the scattering event is monitored as the reactivity of the molecular cluster is varied, and the dependence of the chemistry on the incident cluster velocity and the position of the reacting molecules within the cluster is examined. We find that polymerization reactions occur when the incident cluster velocity corresponds to an external kinetic energy that is within 3 eV/molecule of the binding energy of an individual cluster molecule. Following impact, some of the chemical products chemisorb to the surface in the initial stages of thin film growth, but the exact nature of the thin film is not clear.