Dirac-Fock calculations of the photoionization of the outer $\mathrm{ns}$ electrons in Na, K, Rb, and Cs have been performed. The resulting photoelectron angular distribution asymmetry parameters $\beta$ show strong variations with energy, in contrast to the nonrelativistic prediction of $\beta =2\mathrm{}$, independent of energy, for $s$ electrons. This deviation is due to the spin-orbit interaction of the continuum electron which gives rise to two final states $\epsilon p_{\frac{1}{2}}$ and $\epsilon p_{\frac{3}{2}}$, in place of the single $\epsilon p$ nonrelativistically. The transitions to the $\epsilon p_{\frac{1}{2}}$ and $\epsilon p_{\frac{3}{2}}$ have matrix elements and phase shifts which differ and interfere, thereby resulting in an energy-dependent $\beta$. The effects are particularly dramatic between the Cooper minima in the two channels, and they persist even for $Z$ as low as that for Na.

• Received 6 July 1979

DOI:https://doi.org/10.1103/PhysRevA.20.2364