Angular Distribution ofXe 5s→εpPhotoelectrons: Direct Evidence for Anisotropic Final-State Interaction

The angular distribution of Xe $\mathrm{Xe} 5s\to \epsilon p$ photoelectrons has been measured yielding an asymmetry parameter $\beta =1.4\mathrm{}\pm 0.1$ at 304 Ă. This deviation from the intuitively expected result $\beta =2\mathrm{}$ (for a pure ${cos}^2\theta$ distribution) for photoionization of an $s$ subshell of a ${}_{}{}^1{}_{}{}^{}s_0^{}{}_{}{}^{}$ target is a direct manifestation of anisotropic interactions experienced by the electron during the ejection process. The combined effect of interchannel and spin-orbit coupling is proposed as the likely interaction mechanism.