Ionisation of He+ions by electron impact

The classical three-body theory of Abrines and Pervical (1966) has been extended to describe collisions between electrons and hydrogenic ions. The new theory has been applied to the case of electron impact ionisation of He + ions initially in an arbitrary uniformly populated level n. The theory yields the same scaled cross sections for ionisation from all initial levels n. For high n the results should be accurate to within the stated statistical errors. The results are compared with those of the binary-encounter (classical-impulse) model of Thomas and Garcia (1969). Ionisation of the hydrogenic isoelectronic sequence is discussed.