Excitation functions in low-energy He+-He collisions

In order to study the relations between the profile of excitation function and excitation mechanism, the equations of rotational coupling and radial coupling have been solved with various forms of transition moment and potential energy curve in the two-level model. The excitation functions populated by the rotational coupling through potential curve crossings at small internuclear distance increase gradually with increasing of ion energy and hardly show clear threshold. On the other hand, the excitation functions of the radial coupling increase rapidly near threshold energy and take their maximum values at low colliding energy compared with those of rotational coupling. These characteristics originating from the excitation mechanisms have been recognized on the profiles of the observed emission cross sections. (author)