Experimental techniques in the study of absolute photoionization cross-sections

Abstract The ionization chamber of a photoelectron spectrometer has been modified to permit ready measurement of ionization cross-sections. Essentially, monochromatic ultraviolet light from an electric discharge passes above three flat electrodes in sequence and the flux of ions from the gas just above each electrode is collected on it. From the ratios of collected currents on successive electrodes at various gas pressures the cross-section for ionization is calculated. By integrating the conventional photoelectron spectrum electronically and taking the ratio of the height of the step corresponding to any state to the total height, along with the total cross-section, the partial cross-section for that state is calculated. The method is illustrated by measurements on argon, krypton and hydrogen.