Collision Spectroscopy. I. Analysis of the Scattering ofHe+by Ne and Ar

Experimental data on the differential scattering of ${\mathrm{He}}^{+}$ by Ne and Ar in the energy range from 10 eV to 100 keV are plotted in a reduced coordinate system suggested by a scaling law for the forward scattering. The resulting curves are used to determine the interaction potential. The repulsive interaction dominating at higher energies shows pronounced shell-structure effects, leading to the deduction of the screening constants for the $L$ and $M$ shells of Ar and for the $K$ and $L$ shells of Ne. At lower energies a polarization attraction appears, allowing deduction of the polarizabilities of Ne and Ar. A simple analytic potential is constructed, including a polarizability term appropriately damped inside the outer shell, which fits the data over the entire range. In addition to the pure elastic scattering, effects of inelastic interactions are diagnosed. A prominent curve crossing is located and the scattering pattern arising from it is interpreted by a semiclassical theory. In collisions with closer encounters, a different type of inelastic process appears which apparently involves a more intense coupling than the curve crossing and which appears to open up a number of competing inelastic channels.