Molecular dynamics simulation study of molecular ejection mechanisms: KeV particle bombardment of C6H6/Ag{111}

Molecular dynamics simulations have been performed to gain microscopic insi ght into the factors that lead to molecular ejection after ion bombardment of an organic overlayer on a metal surface. The specific system modeled is benzene (C6H6) adsorbed on Ag{111}. The kinetic energy and angular distribu tions of C6H6 molecules obtained from the simulations match well with the e xperimentally measured distributions. The angular distributions of C6H6 mol ecules show both normal and off-normal components. Analysis of individual t rajectories reveal that the off-normal ejection arises from single collisio ns between substrate Ag atoms and C6H6 molecules, while multiple collisions result in low-energy ejection along the surface normal. To separate issues of rotational and vibrational excitation from translational motion, calcul ations are also performed on an atomic adsorbate with a mass similar to tha t of C6H6.