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Electrons ejected in collisions with neutral hydrogen and helium projectiles (200 keV/u) into the forward direction are measured in coincidence with the charge-state-analyzed outgoing projectile (H, H+; He, He+, He'+). A11 electron spectra, including those recorded in coincidence with H and He atoms, where the long-range Coulomb field is screened, show a cusplike structure. The data are compared with available theories for electron capture to the continuum.PACS number(s): 34.10.+x, 34.50.Fa, 34.70.+e

The projectile energy dependence of the cross sections for electron capture and for electron loss to the continuum states of the projectiles (ECC and ELC) in 50-150 keV amu-1 He+-He,Ar collisions has been studied measuring the spectra of forward ejected 'cusp' electrons in coincidence with the scattered He+ and He2+ projectiles at five different impact energies. The contribution of the ECC to the forward electron cusp has been found to increase with decreasing projectile energy dominating the forward electron cusp production at 50 keV amu-1 collision energies.

Abstract. A systematic study of the doubly differential cross sections for the electron emission occurring in fast strongly asymmetric collisions is presented. Protons and atomic hydrogen (0.5 MeV) were collided with the heavy targets krypton and xenon under single collision conditions. The ejected electrons were observed at laboratory angles in the range 0'<8,5180"and with energies E,from 25 to 1400eV.In addition to the familiar strong ejection in the forward direction (0,%0') arising from capture and loss to continuum states there is pronounced emission in the backward hemisphere for the case of atomic hydrogen projectiles. This.is accompanied by large variations in the angular dependent singly differential cross section and in the energy and width of the electron loss peak as measured at particular angles These Rudtuations in the ability of a heavy target to ionize the structured projectile are a manifestation of a RamsauerTownsend efect and can be understood within the framework of quasi-free electron scattering by the target potential. We give a relativistic quantum mechanical model based on the electron impact approximation which shows good agreement with experiment for these strongly asymmetric collision systems.

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