Post-collision effects in the beam direction in fast ion-atom collisions

Auger line shifts induced by post-collision interaction are studied for pro ton-atom (argon, neon) collisions. The energy shift is determined for Auger electrons emitted in the beam direction, in the Auger electron-projectile matching velocity region, for several acceptance angles for electron detect ion. For projectile velocities above the matching velocity, the Auger line energy shifts determined by the experiment agree with the values calculated by the existing theories, while for projectile velocities below the matchi ng velocity, the measured and the calculated energy shifts show unambiguous disagreement. The advantage of the present work is the achievement of very small acceptance angles for electron detection (+/-0.2 degrees, +/-0.3 deg rees). For these acceptance angles, in the case when the projectile is slow er than the Auger electron, the determined energy shift is negative, which is reported for the first time for fast-ion-atom collision processes.