Final-State Symmetry for then=2States in Photoionized Helium Determined by Theory and Experiment

Experiment and theory have been used to determine the final-state symmetry for the $n=2$ state in photoionized helium. The angular asymmetry parameter β has been measured as a function of photon energy by means of angle-resolved photoelectron spectroscopy. From these measured β values, which are a weighted average of β₂ₛ and β₂ₚ, together with the theoretical values of β₂ₚ and β₂ₛ, the ratio, R, of the partial $2p$ photoionization cross section to the partial $2s$ photoionization cross section has been obtained.