Bremsstrahlung during electron capture to continuum

Theoretical approaches for radiative ionization (RI) in energetic collisions of highly stripped projectiles with target atoms are reviewed and set into context with related processes. The interrelation between RI and electron-nucleus bremsstrahlung is displayed with the help of inverse kinematics. Particular emphasis is laid on the forward-peak region of the electron spectrum resulting from target electrons which are slowed down to approximately zero velocity in the projectile frame of reference. The forward-peak intensity and shape for RI is contrasted to the one obtained from nonradiative capture to continuum. The ridge in the photon spectrum related to forward-peak electrons can unambiguously be identified in measured doubly differential photon emission cross sections resulting from ion-atom collisions at relativistic impact energies.