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

Abstract We consider excitation of highly charged hydrogen-like ions by the impact of equivelocity electrons and protons. The kineticenergy of the protons is more than three 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 thetheshold for electron impact excitation. The basic reason for this is the strong distortion of the motion of the electron by theattractive field of the nucleus of the highly charged ion. PACS numbers: PACS:34.10.+x, 34.50.Fa I. INTRODUCTION Excitation of highly charged ions by the impact ofcharged particles (projectiles) is an interesting physi-cal process which may also have many applications. Inparticular, in case of electron projectiles the studies ofthis process are of importance for the physics of high-temperature plasmas produced in laboratories and exist-ing in astrophysical sources.Collisions of energetic highly charged ions with atomsrepresent an important field of research at modern accel-erators of heavy ions. In collisions of a highly chargedion with neutral atoms the ion can also be excited. Ifthe momentum transferred to the atom in the collision ismuch larger than the typical momenta of the electrons inthe atom the excitation process can be regarded as oc-curring due to the incoherent interactions of the electronof the ion with the nucleus and the electrons of the atomwhich behave with respect to each other as (quasi-) freeparticles [1]. In the rest frame of the ion the excitationthen can be viewed as induced by the incoherent impactsof the “independent” beams of the atomic nucleus andatomic electrons.If the collision velocity is much larger than the Bohrvelocity in the K-shell of the atom, the contribution σ