Analysis of theHe+on He Collision

Abstract

This paper is the second of two consecutive papers dealing with resonant electron capture in ${\mathrm{He}}^{+}$ on He collisions. The first of these, by Lockwood, Helbig, and Everhart, describes differential measurements of electron capture probability ${P}_{0}$ made over a wide range of incident energy and scattering angle. The present paper treats these data within the framework of an improved theory for charge transfer due to Bates and McCarroll. The theory requires a knowledge of the energy levels of the ${\mathrm{He}}_{2}^{+}$ molecular ion at all internuclear distances. Using values of these energy levels given by Lichten, the present paper computes the location of the maxima and minima of ${P}_{0}$ at all impact parameters and velocities. The repulsive potential energy of the ${\mathrm{He}}_{2}^{+}$ system is also calculated here so that these impact parameters can be related to the scattering angle. These results allow the values of ${P}_{0}$ to be predicted over a wide range of impact parameters (0.05 to 1.4 \AA{}), scattering angles (\textonehalf{} to 4\ifmmode^\circ\else\textdegree\fi{}), and energies (0.4 to 1000 keV). There is fair quantitative agreement with the data curves. However, a detailed comparison of theory and data shows discrepancies. At high velocities and low impact parameters there is rather good agreement and there is again fair agreement at low velocities and large impact parameters. In between, however, at intermediate impact parameters the data curves are such that the interaction appears to be different depending on whether the velocity is above or below a critical value of about 6\ifmmode\times\else\texttimes\fi{}${10}^{7}$ cm/sec. This behavior of the data is not predicted by the present theory.