Experimental and theoretical velocity distributions of electrons ejected in l -6 keV ionizing H"-H collisions are presented. Both the experimental velocity distributions and the relative total ionization cross sections can be explained by the theory in a fully consistent~ay. Strong evidence is found for the existence of a saddle-point ionization mechanism at collision energies of 4 keV and higher.A very fundamental problem in atomic collision physics is ionization in ion-atom systems. The continuum distribution of electrons ejected in such collision systems is still not completely understood, neither theoretically nor experimentally, particularly at low (keV) impact energies,~here the collision dynamics possesses a molecular character. Recently, one of the most surprising theoretical predictions was the existence of a so-called "saddle-point ionization mechanism. " Saddle-point electrons were revealed in classical trajectory Monte Carlo
An approximate, analytic expression is derived for the distribution of saddle-point electrons emitted in ionizing one-electron atomic collision systems. The electron distributions of two other relevant ionization mechanisms, the direct S and the radial decoupling mechanisms, are also taken into account. The electron velocity distributions of 1-6 keV amu-1 collisions of H+ and He2+ with atomic hydrogen are presented.
Approximate analytic expressions for the total ionization CIWS section for H+-H and H&-H collisions M obtained within the framework of the theory of non-adiabatic transitions in slow atomic collisions. Theoretical predictions for the cross section of the saddle point mechanism are presented. It is shown that this ionization channel contributes significantly to the total ionization. For both collision system the calculated total ionization emss section a -well with experimental dataobtained by Shah et d.
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