Energy dependence of the photoelectron branching ratio in the5pshell of xenon

The technique of photoelectron spectrometry has been used to measure the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}:{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ branching ratio in the photoionization of the $5p$ shell of xenon, using discrete UV lines and synchrotron radiation, in the entire energy range between 21 and 107 eV. A strong energy dependence is observed, with a minimum around 30 eV and a maximum, slightly higher than the statistical ratio, between 60 and 70 eV. Between 21 and 40 eV, the present data confirm the earlier calculations of Walker and Waber, using the Dirac-Slater model, which predicted a minimum in the branching ratio around 30 eV, in contrast to the conclusions of a previous experimental analysis which were that this branching ratio be constant in this energy range. The discrepancy between our data and these previous measurements might be attributed to pressure effects that are found to play a major role below 40-eV photon energy. New Dirac-Slater calculations by Desclaux reproduce the experimental behavior qualitatively between 40 and 100 eV.