THRESHOLD BEHAVIOR OF THE MULTIPLY-CHARGED PHOTOION YIELDS NEAR THE AR K EDGE

We have measured yield curves of the multiply-charged ions produced by the photoexcitation in the vicinity of the Ar K-shell ionization threshold using monochromatized undulator radiation and a time-of-flight mass spectrometer. The charge distribution of the multiply-charged Ar ions produced by the K-shell excitation suggests that both the electron in the outer shell and the excited Rydberg electron are shaken off with high probability during successive electronic relaxation processes. Post-collision interaction effects are also seen at the photon energies just above the K threshold. The fluorescence yield for the K hole is estimated to be 0.135 +/- 0.03 from the charge distribution above the K threshold.