Studies of Ar photoion charge-state distributions near the K-shell threshold

Abstract

An ion time-of-flight (TOF) spectrometer was used to measure Ar photoion charge-state distributions near the K-shell threshold ( hν=3206.3 eV). When photons interact with argon atoms producing 1s holes, the atoms typically decay by KLL Auger-electron emission so that two holes in the L-shell are created; the atoms can further decay by LMM Auger electron emission. The result is a cascade-like decay process. When cascade decays take place, the final photoion charge-state depends on the decay path. Previous measurements performed by our group and others showed large discrepancies in the lowest and highest charge fractions measured. The measured charge-state fractions, however, are sensitive to several experimental parameters that can adversely affect the values of the charge-state fractions. We therefore performed a quantitative study of the variation of the measured charge-state fractions with the experimental parameters. Branching ratios for several decay processes were obtained from measurements of the photoion charge-state fractions as a function of the photon energy as well as the fluorescence yield, which is now in much better agreement with other determinations than was the case heretofore.