INTERMEDIATE-STATE DYNAMIC CORRELATION IN THE IONIZATION OF HELIUM

Forced impulse method (FIM) calculations of cross sections for the ion ization of helium by energetic ions of various charge are analysed by studying intermediate-state dynamic correlation as it reveals the role of the interelectron interaction, V-ee during the collision. In the F IM, the collision time is cut into sub-intervals, or segments. If thes e are short enough, it is supposed that the time development of the sy stem for the segment can be described in terms of an independent parti cle model U-matrix in which V-ee is turned off. However, knowledge of fully correlated eigenstates at the beginning and end of each segment is required to implement the method. If the collision time is sufficie ntly short, dynamic correlation in just the initial and final states i s all that is needed. For slower collisions multiple cuts may be requi red; this introduces intermediate-state dynamic correlation. In this p aper we discuss the placements of the cuts in relation to a correlatio n length. We introduce a useful new concept, pliability, an action tha t allows the prediction of the cut placements needed and characterizes the collision. We present results with the sign of V-ee reversed to i nvestigate the role of the mean field.