Bonn 2000 – scientific programme

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A: Atomphysik

A 4: Atom–/Ionenstöße II

A 4.6: Talk

Monday, April 3, 2000, 17:45–18:00, HS II

Impact parameter dependence of projectile-electron excitation and loss in relativistic collisions with atomic targets — •A.B. Voitkiv, M. Gail und N. Grün — Institut für Theoretische Physik, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 16, D-35392 Giessen

The semi-classical approximation is extended to relativistic collisions of two composite atomic particles. Electron excitation and loss of relativistic ion-projectiles colliding with atomic targets are studied. A general expression is derived for the semi-classical transition amplitude. In the limit of non-relativistic collision velocities this expression goes over into the known non-relativistic formula. The main focus of the present study is on the projectile-electron excitation, for which numerical calculations have been performed. Our calculations for ultrarelativistic collisions between a heavy single-electron projectile and light atomic targets show the importance of the shielding effects, which reduce transition probabilities at larger impact parameters, and a considerable contribution from the antiscreening mode in collisions with few-electron atoms. An enhancement in probabilities for the dipole-allowed transitions and a reduction of the probabilities for transitions to the 2s-state are found compared to relativistic collisions at low γ.

For electronic cross sections the semi-classical treatment is shown to be equivalent to the plane-wave Born approximation.