  The concept of dominant interaction hamiltonians is introduced and applied to
classical planar electron-atom scattering. Each trajectory is governed in
different time intervals by two variants of a separable approximate
hamiltonian. Switching between them results in exchange of energy between the
two electrons. A second mechanism condenses the electron-electron interaction
to instants in time and leads to an exchange of energy and angular momentum
among the two electrons in form of kicks. We calculate the approximate and full
classical deflection functions and show that the latter can be interpreted in
terms of the switching sequences of the approximate one. Finally, we
demonstrate that the quantum results agree better with the approximate
classical dynamical results than with the full ones.
