Orbiting charge-transfer cross sections between He+ ions and cesium atoms at near-thermal ion-atom energies

The energy dependence of the total charge-transfer cross section for the collision of helium ions with cesium atoms at epithermal energies (0.1 to 1 eV) has been measured. It was observed that the cross section increases with ${E}^{\ensuremath{-}\frac{1}{2}}$. This can be attributed to orbiting collisions. The charge-transfer cross section is expressed as the product of the classical orbiting cross section and a quantum-mechanical charge-transfer probability which is shown to be energy independent.