Measurements of relative subshell photoionization cross sections in the noble gases by ultraviolet photoelectron spectroscopy

A method is described for the measurement of relative subshell photoionization cross sections (SPCS) in the noble gases by the technique of ultraviolet photoelectron spectroscopy. Values are reported for the photoionization cross sections of the neon $2p$, krypton $4p$, xenon $5p$, and xenon $5s$ levels relative to that of the argon $3p$ level. The photon energies used for these measurements were 21.22, 40.81, and 48.37 eV. Approximate absolute subshell photoionization cross sections deduced from these relative cross sections are compared to other absolute SPCS obtained from total photoabsorption measurements and also from theory. Results of some relative photoionization cross-section measurements for the outer $p$ bands associated with the halide ions in solid alkali halides and the outer $d$ bands of metallic gold and silver are also presented. Close similarities in variation with photon energy and atomic number are found between the relative photoionization cross sections of the outer $p$ bands of the alkali halides and the outer $p$ levels of the noble gases, but the photoionization cross sections of the $d$ bands of both gold and silver exhibit quite different properties from those found for the outer $p$ bands and levels of both alkali halides and noble gases. A general conclusion is drawn concerning cross sections for photoionization from electron energy bands in solids.