Anisotropy of excited He+ formed in the photoionization of helium

Semianalytic methods are developed to predict the alignment and orientation of excited helium ions produced in the photoionization of neutral helium in the low-energy limit. The ionic electron probability distribution is shown to align itself orthogonal to the direction of the incident light polarization axis in the same manner as the photoelectron angular distribution [C.H. Greene, Phys. Rev. Lett. 44, 869 (1980)]. In certain instances, propensity rules for the alignment and orientation of the ionic electron are violated. Coherent contributions from different degenerate orbital angular momenta are seen to be partially responsible for these ''unfavored'' trends. Explicit predictions of the time-unresolved fluorescence polarization are presented, including the effects of fine-structure depolarization