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The history of the Ramsauer–Townsend effect and its influence on electrons emitted during ion-atom collisions is reviewed. Experimental methods as well as theoretical approaches are presented. Particular emphasis is laid on similarities between the angular variation of the elastic electron scattering cross sections and that of the singly differential electron loss cross sections or, using inverse kinematics, that of the target ionization cross sections.

We present an analysis of electron loss to the continuum (ELC) for 1.6-2.8 MeV He+ colliding with He, Ne and Ar using the first six terms of the multipole expansion method. We give absolute values for E,, and discuss the way in which the method of analysis influences the values of the dipole and quadrupole parameters. Our dipole parameter is slightly positive for the He target and becomes progressively more negative for Ne and Ar. Our quadrupole parameter is slightly positive for He and Ne and nearly zero for Ar. For HeC+ He the magnitude of E,, and its velocity dependence are in reasonable quantitative agreement with a recent theoretical calculation based on the second Born approximation. However our dipole and quadrupole parameters are both more positive than predicted.

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.