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

Molecular dynamics simulations have been performed to gain microscopic insight 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 distributions of C6H6 molecules obtained from the simulations match well with the experimentally measured distributions. The angular distributions of C6H6 molecules show both normal and off-normal components. Analysis of individual trajectories reveal that the off-normal ejection arises from single collisions 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, calculations are also performed on an atomic adsorbate with a mass similar to that of C6H6.