Effect of cluster size on the reactivity of organic molecular clusters: Atomistic simulations

Abstract

The effect of cluster size on the impact of ethyne molecular clusters with a non-rigid, hydrogen-terminated diamond (1 1 1) surface was examined using classical molecular dynamics. Specifically, the outcome of the scattering event was monitored as the size of the clusters was varied from 1 to 216 molecules. A second-generation version of the reactive empirical bond order potential for hydrocarbons, that has been modified to include long-range van der Waals interactions, was used in the simulations. The clusters were given hyperthermal incident velocities that are comparable to those that result in shock-induced chemistry in energetic materials. At sufficiently high velocities, chemical addition reactions occurred among cluster molecules and between the cluster and the surface. These reactions resulted in the formation of short polymer chains (oligomers), some of which remained chemisorbed to the surface in a hydrocarbon thin film. The simulations showed that as the cluster size increased, the reactivity of the cluster increased but the percentage of atoms from the cluster that chemisorbed to the surface following impact decreased. The composition of the hydrocarbon films that resulted from the collision also varied with cluster size.