A molecular dynamics study of ion bombardment induced ejection of C2H4 from Ni(111): Relationships of the angle distributions of the translational and rotational angular momentum of ejected C2H4 to surface structure

Abstract

The angular distributions of the translational and rotational angular momentum of C2H4 molecules ejected from a Ni(111) surface by ion bombardment have been calculated from molecular dynamics simulations of the ion–surface collision process. Both the translational and rotational momentum of ejected C2H4 tend to orient in preferred directions which are dependent on the C2H4 bonding site geometry. Most C2H4 molecules are ejected by a collision with a single energetic Ni atom. It is shown that the translational angle distribution is governed primarily by the distribution of Ni–C2H4 collision geometries. A preference for Ni atoms to eject in the directions between surrounding nearest neighbor Ni atoms gives rise to preferred Ni–C2H4 collision geometries that cause C2H4 to eject in preferred directions. The preferred orientations of the rotational angular momentum of ejected C2H4 are shown to be governed directly by the orientation of the C–C bond axis of the original chemisorbed C2H4 molecules, independent of the Ni–C2H4 collision geometry.