Excitation of highly charged hydrogenlike ions by the impact of equivelocity electrons and protons: A comparative study

We consider excitation of highly charged, hydrogenlike ions by the impact of equivelocity electrons and protons. The kinetic energy of the protons is more than 3 orders of magnitude larger than that of the equivelocity electrons. It is shown, however, that despite this fact, the electrons can be much more effective in inducing excitation at collision velocities (slightly) above the threshold for electron-impact excitation. The basic reason for this is the strong distortion of the motion of the electron by the attractive field of the nucleus of the highly charged ion.