Coordinate system for projectile-helium atom system

Figure 1. Coordinate system for projectile-helium atom system.

Abstract

The frozen core approximation has been successfully used for many years to model 4-body collisions as 3-body collisions. We present a comprehensive comparison of 3-body and 4-body models for the process of single ionization of helium by electron impact using our 4-body distorted wave model. Differences between the two models are observed in both magnitude and peak locations. We identify four possible sources for the discrepancies between the models, and isolate the specific physical causes of the discrepancies.