Relation between distances of negative and positive ion formation in molecule–surface scattering

Abstract

In this letter we address the issue of the relation between critical distances of negative and positive ion formation during a collisional charge exchange between a large polyatomic projectile and a metallic surface. Based on the ‘freezing distance’ approximation, we have derived a simple expression relating the distances of negative and positive ion formation with the corresponding ionization potential and electron affinity of the neutral molecule. We test this expression by a comparison with experimental values measured for C₆₀–surface scattering, the only system for which distances of formation of both molecular ionic states have been measured. A good agreement with experiment is found.

Keywords:

• molecule–surface scattering
• fullerene ion beam
• charge exchange

Acknowledgements

This research was supported by grants from the Israeli Science Foundation (ISF) and the German–Israeli Binational James Franck Program.