Coincidence Measurements of Large-AngleAr+-on-Ar Collisions

Large-angle single collisions of keV-energy ${\mathrm{Ar}}^{+}$ ions with Ar atoms are studied wherein both particles scattered from the same encounter are detected in coincidence. The scattered incident particle appears $m$-times ionized at angle $\theta$ and the recoiling target particle appears $n$-times ionized at angle $\phi$. Values of $m$ and $n$ range from zero to eight. It is found that $m$ and $n$ are independent and uncorrelated, i.e., the distribution among charge states $m$ is the same regardless of the charge state $n$ seen in coincidence. An exception to this rule is seen in one region where the inelastic energy has multiple values. Relative probabilities for the ($m, n$) reaction are given for many data sets, with incident energies $T_0$ from 3 to 400 keV and for angles $\theta$ between 8° and 40°. The inelastic energy ${\overline{Q}}_{\mathrm{mn}}$ associated with the ($m, n$) reaction is also measured for a number of values of $m$ and $n$ in each data set. It is found that a particular reaction does not have a fixed characteristic energy. Thus, for example, ${\overline{Q}}_{55}$ increases from 877 to 1473 eV depending on the violence of the collision. Average values of inelastic energy loss $\overline{Q}$ are plotted versus incident energy at various scattering angles, versus the average number of electrons lost in the collision, and versus the distance of closest approach. Values of $\overline{Q}$ range from 26 eV at $T_0=3\mathrm{}$ keV, $\theta =8\mathrm{}°$, to 2430 eV at $T_0=300\mathrm{}$ keV, $\theta =40\mathrm{}°$. The effects of thermal motion of the target atom, of finite instrumental resolution, and of a possible distribution in values of inelastic energy all combine to give "linewidth" effects. These are measured and discussed.