Dichroism in the electron-impact ionization of excited and oriented sodiumatoms - art. no. 012706

Measurements are reported for kinematically complete electron-impact ioniza tion collisions with oriented 3 P sodium atoms excited from the ground stat e by right- and left-hand circularly polarized light. The measurements reve al a strong dependence of the ionization cross section on the helicity inve rsion of the exciting photon. This dichroic effect and the magnetic state r esolved cross sections are described using the distorted-wave Born approxim ation and the dynamically screened Coulomb wave method. Within the context of these methods we investigate the role of different short- and long-range interactions involved in the process. For moderate values of incident ener gy we conclude that the shape and magnitude of the dichroism is predominant ly determined by the Coulomb interactions of the outgoing electrons with th e residual ion. For slow escaping electrons the dichroism is also influence d by the interelectronic correlations.