Electron swaps and the stopping of protons by hydrogen

The relevance of the electronic swap in the stopping process of proton by hydrogen is investigated. To this end, the Classical Trajectory Monte-Carlo method is used to calculate the k-stopping cross-section, i.e. the stopping cross-section given the occurrence of k-swaps during the collision. It is found that electron swaps can be used to label electron trajectories, as it seems to describe fairly well the extent of the electron-ion interaction during the collision. Depending on the ion energy, the number of swaps entering the stopping cross section may vary. In the keV range the number of swaps can be as large as five or more, whereas, at larger energies, only three or less electron swaps may take place in collisions of relevance to stopping.