Role of the recoil ion in single-electron capture and single-ionization processes for collisions of protons with He and Ar atoms

In this work the single-electron capture and single-ionization processes are studied for proton collisions with He and Ar atoms at impact energies in the range 25–100 keV. Classical trajectory Monte Carlo simulations are benchmarked against experimental data obtained at the reaction microscope in Bariloche, Argentina, which employs the cold target recoil-ion momentum spectroscopy technique. Special emphasis is placed on describing the momentum transfer to the recoil ion for these collision systems.

Figure 1

Transverse momentum distributions for ${\mathrm{H}}^{+}+\mathrm{He}$ collisions at 80 keV: (a) adiabatic expansion cooling only, (b) with additional precooling stage, (c) projected distributions along the transverse directions $(x$ and $y$ axes), (d) transverse momentum distribution.

Figure 2

Recoil-ion transverse momentum distributions of the single-electron capture process for ${\mathrm{H}}^{+}+\mathrm{He}$ collisions at 50, 80, and 100 keV.

Figure 3

Theoretical $d^2\sigma /\left(d{p}_{\mathrm{elec}}d{p}_{\mathrm{rec}}\right)$ and $d^2\sigma /\left(d{p}_{\mathrm{rec}\text{−}z}d{p}_{\mathrm{rec}\text{−}t}\right)$ of the single-ionization process for 50, 80, and $100\mathrm{keV}{\mathrm{H}}^{+}$ collisions on He. The dashed lines indicate the recoil-ion longitudinal momentum values associated to the electron capture to the continuum (ECC) and electron capture to the target (ECT) mechanisms. Predictions within the IEV and IEL models are indistinguishable in this plot.

Figure 4

CTMC-IEV longitudinal and transverse momentum distributions of the single-ionization process for 50, 80, and $100\mathrm{keV}{\mathrm{H}}^{+}$ collisions on He. The experimental longitudinal recoil-ion momentum distribution of Weber et al. [24] for 100 keV/amu $d^{+}$ collisions on He is included for comparison.

Figure 5

$\mathrm{A}{\mathrm{r}}^{\mathrm{q}+}$ ion spectra obtained in coincidence with ${\mathrm{H}}^0$ at a proton impact energy of 25 keV.

Figure 6

Recoil-ion transverse momentum distributions of the single-electron capture process for ${\mathrm{H}}^{+}+\mathrm{Ar}$ collisions at 25, 50, and 80 keV.

Figure 7

Theoretical impact parameter distributions for single-electron capture at $80\mathrm{keV}{\mathrm{H}}^{+}$ impact collisions on He and Ar.

Figure 8

CTMC events plot of $p_{\mathrm{rec}\text{−}t}$ as a function of $b$ for $80\mathrm{keV}{\mathrm{H}}^{+}+\mathrm{Ar}$ collisions leading to electron capture. The dashed lines indicates the region 0.2–0.8 a.u. at which the maximum of the $p_{\mathrm{rec}\text{−}t}$ distribution shown in Fig. 6 is predicted. Predictions within the IEV and IEL models are indistinguishable in this plot.

Figure 9

Theoretical $d^2\sigma /\left(d{p}_{\mathrm{elec}}d{p}_{\mathrm{rec}}\right)$ and $d^2\sigma /\left(d{p}_{\mathrm{rec}\text{−}z}d{p}_{\mathrm{rec}\text{−}t}\right)$ of the single-ionization process for 25, 50, and $80\mathrm{keV}{\mathrm{H}}^{+}$ collisions on Ar. The dashed lines indicate the recoil-ion longitudinal momentum values associated with the electron capture to the continuum (ECC) and electron capture to the target (ECT) mechanisms. The dotted line indicates the linear momentum conservation equation for electron emission in the $z$ direction. Predictions within the IEV and IEL models are indistinguishable in this plot.

Figure 10

CTMC-IEV longitudinal and transverse momentum distributions of the single-ionization process for 25, 50, and $80\mathrm{keV}{\mathrm{H}}^{+}$ collisions on Ar.