Charge transfer in slow collisions of ${\mathrm{O}}^{8+}$ and ${\mathrm{Ar}}^{8+}$ ions with $\mathrm{H}\left(1s\right)$ below $2\mathrm{keV}∕\mathrm{amu}$

We calculated the charge-transfer cross sections for ${\mathrm{O}}^{8+}+\mathrm{H}$ collisions for energies from $1\mathrm{eV}∕\mathrm{amu}$ to $2\mathrm{keV}∕\mathrm{amu}$, using the recently developed hyperspherical close-coupling method. In particular, the discrepancy for electron capture to the $n=6$ states of ${\mathrm{O}}^{7+}$ from the previous theoretical calculations is further analyzed. Our results indicate that at low energies (below $100\mathrm{eV}∕\mathrm{amu}$) electron capture to the $n=6$ manifold of ${\mathrm{O}}^{7+}$ becomes dominant. The present results are used to resolve the long-standing discrepancies from the different elaborate semiclassical calculations near $100\mathrm{eV}∕\mathrm{amu}$. We have also performed the semiclassical atomic orbital close-coupling calculations with straight-line trajectories. We found the semiclassical calculations agree with the quantal approach at energy above $100\mathrm{eV}∕\mathrm{amu}$, where the collision occurs at large impact parameters. Calculations for ${\mathrm{Ar}}^{8+}+\mathrm{H}$ collisions in the same energy range have also been carried out to analyze the effect of the ionic core on the subshell cross sections. By using diabatic molecular basis functions, we show that converged results can be obtained with small numbers of channels.

Figure 1

(a) Hyperspherical adiabatic potential curves for ${\mathrm{OH}}^{8+}$ that dissociate to ${\mathrm{O}}^{7+}$ $\left(n=5,6\right)$ manifolds. For clarity, only $I=0$ (solid) and $I=1$ (dashed) curves are shown. (b) Dominant seven diabatic potential curves.

Figure 2

(a) Partial charge-transfer cross sections for ${\mathrm{O}}^{8+}+\mathrm{H}\left(1s\right)$ collision as functions of collision energy. Note that the solid symbols are for $n=5$ and the open symbols are for $n=6$. $\mathrm{HSCC}7$, present seven-channel results; $\mathrm{HSCC}33$, present 33-channel results; $\mathrm{MO}\text{−}\mathrm{SGB}$, $\mathrm{MO}$ results by Shipsey et al. [5]; $\mathrm{AO}$, present $\mathrm{AO}$ results; $\mathrm{AO}\text{−}\mathrm{FL}$, $\mathrm{AO}$ results by Fritsch and Lin [4]. (b) Similar to (a) except for lower range of collision energy. The inset in (b) shows $n=6$ charge-transfer cross section times velocity vs the collision energy.

Figure 3

Total electron-capture cross sections for ${\mathrm{O}}^{8+}+\mathrm{H}\left(1s\right)$ collision. Theoretical results: $(—)$ denotes the present results of $\mathrm{HSCC}$; $(\cdots )$ the results of Kimura and Lane (Ref. 6); $\left(---\right)$ the results of Shipsey et al. (Ref. 5); $(◇)$ the results of $\mathrm{AO}$ expansion with curved-line trajectory by Fritsch and Lin (Ref. 4); $\left(\Delta \right)$ the present $\mathrm{AO}$ expansion with straight-line trajectory. Experimental results are from Meyer et al. (Ref. 1).

Figure 4

The evolution of the $b{P}_{cap}\left(b\right)$ vs $b$ with respect to the collision energies. $\left(---\right)$ and $(\cdots )$ denote the first two $I=0$ channels in the $n=6$ manifold and $(—)$ represents the lowest $I=1$ channel in the $n=6$ manifold for ${\mathrm{O}}^{8+}+\mathrm{H}\left(1s\right)$ collisions. Note that the 5 and 100 scaling factors only apply to the first panel.

Figure 5

Comparison of the quantal $\mathrm{HSCC}$ and present semiclassical straight-line trajectory $\mathrm{AO}$ results for $b{P}_{cap}$ for the $n=5$ manifold for ${\mathrm{O}}^{8+}+\mathrm{H}\left(1s\right)$ collisions at a collision energy of $E=400\mathrm{eV}∕\mathrm{amu}$ (top) and $2\mathrm{keV}∕\mathrm{amu}$ (bottom).

Figure 6

(a) Hyperspherical adiabatic potential curves for ${\mathrm{ArH}}^{8+}$, which dissociate into ${\mathrm{Ar}}^{7+}\left(n=5,6\right)$. Only $I=0$ (solid) and $I=1$ (dashed) channels are shown. The inset gives a zoom in of $n=6$ curves near a series of avoided crossings in the range of $R=10–20\text{a.u.}$ (b) Hyperspherical diabatic potential curves. For clarity, only $I=0$ curves are shown.

Figure 7

Partial charge-transfer cross sections for the ${\mathrm{Ar}}^{8+}+\mathrm{H}\left(1s\right)$ collision system as functions of collision energy. $\mathrm{HSCC}21$, present 21-channel results; $\mathrm{HSCC}33$, present 33-channel results. Note that the solid and open symbols denote the $n=5$ and $n=6$, respectively. The inset shows the $n=6$ charge-transfer cross section times velocity vs the collision energy.

Figure 8

State selective charge-transfer cross sections for the ${\mathrm{Ar}}^{8+}+\mathrm{H}\left(1s\right)$ collision system as functions of collision velocity.