A molecular dynamics study of collisional excitation/deexcitation at ion-bombarded surfaces
On the basis of ab initio potentials, a three-dimensional classical trajectory model of the dynamics of energetic collision events for ion-bombarded alkali halide surfaces is introduced. In this model, a distance-of-closest-approach method is used to determine the occurrence of core excitation and electron capture. The results show that an excited sodium ion may be formed when a sodium 2p electron is promoted into thet 3s state during a hard Ar^+-N^a+ collision. This inner-shell electron excitation is shown to be an initiating process, which can result in the subsequent neutralization and Auger electron emission from Na in the solid. We give numerical estimates of the probability for both the excitation and neutralization events that produce an excited sodium atom with a 2p vacancy which undergoes Auger electron emission. In addition, the lifetime of the promoted electron in sodium is calculated by applying quantum perturbation theory. Our results may be useful in interpreting the data from a recent experiment, in which three interesting spectral features due to the Auger decay of the core excitation appear in the autoionization spectrum.
© 1996 Elsevier Science B.V. Received 3 March 1995; revised form received 17 July 1995. Supported in part by the National Science Foundation [Grant DMR93-18931 at Caltech and DMR93-12468 at CSUF]. One of us (KOS) is grateful to Professor Tien T. Tsong and the Institute of Physics at Academia Sinica in Taiwan for generous support of this work. We also acknowledge Caltech's support of one of us (JC) by its Ph 11 undergraduate research program.