State-selective differential cross sections for single and double electron capture in ${\text{He}}^{+,2+}\text{-He}$ and $p\text{-He}$ collisions

Using the cold target recoil ion momentum spectroscopy technique, we have measured state-selective projectile scattering angles for single and double electron captures in collisions of protons and ${\text{He}}^{1,2+}$ projectiles with a helium target for incident energies of 60–630 keV/u. We also report theoretical results obtained by means of four-body one-channel distorted-wave models (continuum distorted-wave Born final state, continuum distorted-wave Born initial state, and Born distorted wave) and find mixed agreement with the measured data.

Figure 1

(Color online) Longitudinal recoil ion momenta $\left(p_{\parallel }\right)$ for the single capture in the collision system ${\text{He}}^{2+}$ (He) at 60 keV/u. The subscript letters P (T) indicate the particle corresponding to the final electronic state in the bracket. The final states “nl” include all states for $n\ge 3$. The numbers shown present the $Q$ value of the reaction. For the two peaks around $p_{\parallel }\simeq 1\text{a}\text{.u}\text{.}$ one cannot distinguish whether the projectile (p) or the target (t) is excited, only that one of both is.

Figure 2

The differential cross sections $d{\sigma }_{if}/d\Omega \left({\text{cm}}^2/\mathrm{sr}\right)$ as a function of scattering angle $\theta \left(\text{rad}\right)$ for single-electron capture to the ground state in ${\text{H}}^{+}\text{-He}$ collisions at 60, 100, 150, and 300 keV/u in the laboratory system. ◼: experiment; solid line CDW BFS model (present computation).

Figure 3

Differential cross sections $d{\sigma }_{if}/d\Omega \left({\text{cm}}^2/\text{sr}\right)$ as a function of scattering angle $\theta \left(\text{rad}\right)$ for single-electron capture to the ground state in ${\text{He}}^{2+}\text{-He}$ collisions at 60, 150, 300, 450, and 630 keV/u in the laboratory system. ◼: experiment; solid line CDW BIS model (present computation).

Figure 4

The differential cross sections $d{\sigma }_{if}/d\Omega \left({\text{cm}}^2/\text{sr}\right)$ as a function of scattering angle $\theta \left(\text{rad}\right)$ for single-electron capture to the ground state in ${\text{He}}^{+}\text{-He}$ collisions at 60, 150, 300, and 630 keV/u in the laboratory system. ◼: experiment; solid line CDW BIS model (present computation).

Figure 5

The differential cross sections $d{\sigma }_{if}/d\Omega \left({\text{cm}}^2/\text{sr}\right)$ as a function of scattering angle $\theta \left(\text{rad}\right)$ for double-electron capture to the ground state in ${\text{He}}^{2+}\text{-He}$ collisions at 60, 150, 200, and 300 keV/u in the laboratory system. ◼: experiment; solid line BDW model (present computation).