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

Abstract

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