Single- and double-electron capture cross sections for slow ${\mathrm{He}}^{2+}$ impact on ${\mathrm{O}}_2$, ${\mathrm{H}}_2$, and ${\mathrm{D}}_2$

Single- and double-electron capture cross sections have been measured for ${\mathrm{He}}^{2+}$ impact on ${\mathrm{O}}_2$, ${\mathrm{H}}_2$, and ${\mathrm{D}}_2$ at impact energies smaller than $2\mathrm{keV}∕\mathrm{amu}$. The method applied combines the collection of slow product ions and electrons with primary ion-beam attenuation and stopping in a differentially pumped target gas chamber. Comparison with previous experimental and theoretical results is made. For ${\mathrm{He}}^{2+}$ collisions with ${\mathrm{H}}_2$ we find that double-electron capture is more important than single-electron capture below $0.2\mathrm{keV}∕\mathrm{amu}$. This result is also confirmed by cross-section measurements for ${\mathrm{He}}^{2+}$ on ${\mathrm{D}}_2$.

Figure 1

Schematic view of the charge-exchange experiment. First aperture $\left(A_1\right)$ with $2.5\mathrm{mm}$ diameter opening, Faraday cup for incoming current normalization $\left({\mathrm{FC}}_1\right)$ with $1.0\mathrm{mm}$ aperture, insulated second aperture $\left(A_2\right)$ for final ion selection with $10\mathrm{mm}$ diameter aperture. ${\mathrm{FC}}_2$ serves for attenuated ion current measurement.

Figure 2

Single-electron capture cross section for ${}^4\mathrm{He}^{2+}$ and ${}^3\mathrm{He}^{2+}$ on ${\mathrm{O}}_2$ collisions as a function of impact energy. Full circles—this work (${}^4\mathrm{He}^2$ projectile), full squares—this work (${}^3\mathrm{He}^2$ projectile), full triangles—Kusakabe et al. [6], open diamonds—Kamber et al. [8], open triangles—Ishii et al. [4], open circles—Rudd et al. [19], inverted open triangles—Shah and Gilbody [24].

Figure 3

Double electron capture cross section for ${}^4\mathrm{He}^{2+}$ and ${}^3\mathrm{He}^{2+}$ on ${\mathrm{O}}_2$ collisions as a function of impact energy. Full circles—this work (${}^4\mathrm{He}^2$ projectile), full squares—this work (${}^3\mathrm{He}^2$ projectile), full triangles—Kusakabe et al. [6], open triangles—Ishii et al. [4], open diamonds—Rudd et al. [19], inverted open triangles—Shah and Gilbody [24].

Figure 4

Single-electron capture cross section for ${}^3\mathrm{He}^{2+}$ on ${\mathrm{H}}_2$ collisions as function of impact energy. Experimental results: full circles—this work, full squares—Kusakabe et al. [6], open diamonds—Kusakabe et al. [16], open inverted triangles—Okuno et al. [18], open squares—Rudd et al. [19], open triangles—Shah and Gilbody [24]. Theoretical results: full lines—Errea et al. [20], dashed line—Shimakura and Kimura [22], dotted line—Kusakabe et al. [6].

Figure 5

Double-electron capture cross section for ${}^3\mathrm{He}^{2+}$ on ${\mathrm{H}}_2$ collisions as function of impact energy. Experimental results: full circles—this work, full squares—Kusakabe et al. [6], open diamonds—Kusakabe et al. [16], open inverted triangles—Okuno et al. [18], open squares—Rudd et al. [19], full diamonds—Afrosimov et al. [27], open triangles—Shah and Gilbody [24]. Theoretical results: full lines—Errea et al. [20], dashed line—Shimakura and Kimura [22], dotted line—Kusakabe et al. [6].

Figure 6

Transfer ionization cross section [process (16)] for ${}^3\mathrm{He}^{2+}$ on ${\mathrm{H}}_2$ collisions as function of impact energy. Full circles—present work, full squares—Rudd et al. [19].

Figure 7

SEC and DEC cross sections for ${}^3\mathrm{He}^{2+}$ on ${\mathrm{D}}_2$ compared to ${}^3\mathrm{He}^{2+}$ on ${\mathrm{H}}_2$ collisions as function of impact energy in center-of-mass system. SEC: open circles—${\mathrm{H}}_2$ target, open squares—${\mathrm{D}}_2$ target. DEC: full circles—${\mathrm{H}}_2$ target, full squares—${\mathrm{D}}_2$ target.