Mutual ionization in $200\text{−}\mathrm{keV}$ ${\mathrm{H}}^{-}+\mathrm{He}$ collisions

We studied mutual ionization in $200\text{−}\mathrm{keV}$ ${\mathrm{H}}^{-}+\mathrm{He}$ collisions in a kinematically complete experiment by measuring the fully momentum-analyzed recoil ions and both active electrons in coincidence. Comparison of the data to our calculations, based on various theoretical models, show that mutual ionization proceeds predominantly through the interaction between both electrons. The post-collision interaction between the outgoing ejected electrons as well as higher order processes involving the interaction between the core of both collision partners are also important.

Figure 1

Longitudinal electron momentum spectra for the target electrons (open symbols) and projectile electrons (closed symbols). The arrow indicates the projectile speed $v_p$. Triangle-dashed curves, FBA for mutual ionization with Yukawa potential for ${\mathrm{H}}^{-}$; solid curve, CDW-EIS for pure target ionization by antiproton impact; cross-dashed curve, FBA for pure target ionization by proton impact; dashed curve, CDW-EIS for pure target ionization by proton impact.

Figure 2

Energy spectrum of the ejected projectile electrons in the projectile rest frame calculated with the FBA for H-like ion impact (solid curve) and with the FBA describing ${\mathrm{H}}^{-}$ by a Yukawa potential (dashed curve).

Figure 3

Schematic sketch of the collision geometry. The rectangle indicates the azimuthal plane, which is the plane perpendicular to the initial ${\mathrm{H}}^{-}$ projectile momentum $p_{p_0}$. The other arrows indicate the momentum vectors of the various collision fragments projected into the azimuthal plane. Some of the angles plotted in Figs. 4, 5, 6 are shown.

Figure 4

The angle between both ejected electrons ${\varphi }_{e\text{−}e}$ versus the angle between the target electron and the $H^0$ core of the projectile ${\varphi }_{e_t\text{−}H}$ in the azimuthal plane.

Figure 5

The angle between both ejected electrons ${\varphi }_{e\text{−}e}$ versus the angle between the target electron and the ${\mathrm{He}}^{+}$ recoil ion ${\varphi }_{e_t\text{−}\mathrm{rec}}$ [panel (a)] and versus the angle between the projectile electron and the projectile core ${\varphi }_{e_p\text{−}H}$ [panel (b)] in the azimuthal plane. Panels (c) and (d) show the corresponding theoretical spectra calculated with the FBA using the Yukawa potential for ${\mathrm{H}}^{-}$.

Figure 6

The angle between the target electron and the ${\mathrm{He}}^{+}$ recoil ion ${\varphi }_{e_t\text{−}\mathrm{rec}}$ versus the angle between the recoil ion and the $H^0$ core ${\varphi }_{H\text{−}\mathrm{rec}}$ in the azimuthal plane.