Ion Scattering The Collision Process

Ef is the energy of the scattered ion Mion is the atomic mass of the incoming ion 

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In ISS, ions such as H, He and Ar are scattered off a surface and their energy distribution is observed. During the scattering process, the ions lose energy to the surface atoms. The collision process is usually so rapid (with kinetic energies of the order of 1 keV to 1 MeV) that a binary collision model is a good description of the situation. 

Differential scattering experiments with Ne and other beams state selected with a tuneable dye laser are near realization. Differences in the potential-energy curves and reaction probabilities for the iP2 and iP0 states will provide valuable insight into the role of the core ion on the collision dynamics and electronic structure as well as clarify the relative importance of the two states in macroscopic processes. Experiments using a metal-atom crossed beam, also currently in progress at Freiburg, promise a revealing contrast to the weak van der Waals interactions thus far studied. 

There are two basic physical phenomena which govern atomic collisions in the keV range. First, repulsive interatomic interactions, described by the laws of classical mechanics, control the scattering and recoiling trajectories. Second, electronic transition probabilities, described by the laws of quantum mechanics, control the ion-surface charge exchange process. 

This review illustrates the complementary nature of recoil-ion momentum spectroscopy, projectile scattering measurements, and conventional electron emission spectroscopy in ion-atom ionizing collisions. We have examined recent applications of both the CDW and CDW-EIS approximations from this perspective. We have shown that both models provide a flexible and quite accurate theory of ionization in ion-atom collisions at intermediate and high energies and also allows simple physical analysis of the ionization process from the perspective of these different experimental techniques. 

Figure 6. Schematic illustration of scattering dynamics seen as slow electron-collision process. Sodium ion core, N2 molecule, and the 3p electron orbit are displayed in realistic dimensions.

Fig. 4.6. The two double-binary collision processes resulting in positronium formation following positron impact at high energies. The positron collides with an atomic electron on the left the electron then scatters off the residual ion into the same direction as the positron, whilst on the right the process is shown in which the positron scatters off the residual ion.

The theoretical foundation upon which backscattering stands is extremely straight-forward. The primary mechanism is the elastic collision process. The conservation of energy and momentum provide nonrelativistically that the ratio of the energy of the scattered ion, E, to that of the incident ion,... 

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