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.