PcL A threshold photoelectron specmm and its component spectra of Auger cascades aRer AI K-shell photoionization have been measxed by wincidenoes between threshold photoelectrons and residual ions of Lhe cascades. These spectra exhibit remarkable profiles of postcollision interaction effects due to the Auger cascades. The peak shift increases gradually according to the tims of interactions. but the peak broadening is almost indepndent of the times of interactions. Tbese p m 6 k a~ analysed in terms of a simple model expressing the pmbability of A u p eleftmu emissions by statistical w e i g hIn near-threshold inner-shell photoionization of atoms, the subsequent Auger decay might be influenced by the presence of a slowly receding photoelectron. This influence is called post-collision interaction ( F a ) .Close to the threshold, the slower photoelectron shields the doubly charged atomic ion so that the faster Auger electron gains energy and, as its counter

A threshold photoelectron spectrum and its component spectra of Auger cascades following Kr -shell photoionization have been measured by a threshold photoelectron-ion coincidence technique. These spectra exhibit characteristic profiles of post-collision interaction effects induced by the Auger cascades. Peak shifts of the profiles increase gradually according to the times of the interactions, but peak widths of the profiles are almost independent of the times of interactions. These characteristics are analysed in terms of a simple model based on the assumption that double-Auger (Auger shake-off) decays reduce the effective number of steps of the Auger cascades.

Yield spectra of multiply charged ions in coincidence with threshold electrons (Ekin⩽0.03 eV) have been measured near the 4p-shell ionization region of Xe. The coincidence spectra of Xe3+ and Xe4+ ions as a function of photon energy exhibit characteristic profiles induced by post-collision interactions in Auger cascades following 4p-shell threshold ionization of Xe. Peaks of the profiles shift from the nominal 4p-shell threshold, and those shapes are asymmetric and broadened. The profiles have the same peak-shifts and the same peak-widths in both Xe3+ and Xe4+ coincidence spectra. Based on the properties of the profiles, it is concluded that both of these ions result from two-step Auger cascades. Furthermore, it is found that Auger shake-off (i.e. double Auger) decays play a significant role in the cascades following 4p-shell ionization of Xe.

Multiple photoionization cross sections of Kr have been measured in the photon energy region of 90-260 eV. Partial cross sections for valence ionization, 3d ionization and 3d shake (shake-up and shake-off) have been derived from these multiple photoionization cross sections. The experimental results are compared with a recent theoretical calculation.

The yield spectra of Xe" and Xe3+ ions near the 4d ionization limits have been measured by a threshold electron-photoion coincidence method. These spectra consist of some prominent peaks corresponding to the 4d-'np Rydberg states and two dominant peaks corresponding to 4d threshold ionization. It is proposed that threshold-electron emission from the inner-shell resonance states is due to not only shake-off (e.g. Xe 4d-'6p-+ Xe2' Sp-') but also two-step autoionization (e.g. Xe 4d-'6p+ Xei 5s-'5p-'7p+ XeZL SsCISp-'). The two-step autoionization process plays an important role in decays from the lower n Rydberg states. Two dominant peaks somewhat above the 4d ionization limits show the effect of post-collision interaction, namely, shifts of peak positions and asymmetric profiles. The shifts are almost the same in the Xe'+ and Xe'+ spectra

Multiple photoionization of Xe near the 3d 5/2 -shell threshold photoionization region is studied by threshold electron-ion coincidence spectroscopy. The coincidence spectra of Xe 3+ to Xe 7+ ions exhibit characteristic profiles associated with multi-step post-collision interactions in Auger cascades following 3d 5/2 -shell threshold photoionization. The Auger cascade decay channels leading to the formation of multiply charged ions are deduced from the energies of the profile peaks, which increase gradually with increasing charge state. The formation of Xe 3+ to Xe 5+ ions is found to arise from cascades of normal Auger decays, whereas the formation of Xe 6+ and Xe 7+ ions involves double Auger decays. The branching ratio of double to normal Auger decays is estimated to be 0.25 (±0.1) for the decays following the creation of 3d 5/2 -hole states in Xe.

The yield spectra of Ar2+ and Ar3+ ions in coincidence with threshold electrons near the 2p ionisation limits have been measured using a time-of-flight mass spectrometer and synchrotron radiation. Below the 2p ionisation limits, the Ar2+ yield spectrum exhibits a prominent peak corresponding to the 2p-'4d, 5d and 6d resonance states. It is proposed that these resonance states can decay by emitting threshold electrons through two-step autoionisation, such as Ar 2p-'5d+ Ar+ 3p-'('D)6d+ Ar" ~P -~( ~P ) .Above the 2p ionisation limits, the Ar2+ and Ar3+ yield spectra exhibit two dominant peaks. These peaks show the effect of post-collision interaction, namely shifts of peak positions and asymmetric profiles. The shifts are almost the same in the Ar2+ and Ar3+ yield spectra.

Yield spectra of multiply charged ions have been measured in coincidence with threshold electrons near the Xe L 3 -shell ionization region. The ion-yield spectra exhibit characteristic profiles of postcollision interaction effects induced by Auger cascades following Xe L 3 -shell ionization. The peak shifts of the spectral profiles increase gradually along with the increase of the charge states, but the peak widths are almost independent of the charge states. The spectral profiles are reproduced by a simple model based on the assumption that Coster-Kronig and Auger shake-off decays play a major role in the Auger cascades following the Xe L 3 -shell vacancy creation.