CORRELATION EFFECTS IN PHOTOELECTRON SPECTROMETRY OF ATOMS

As intense, continuously-tunable photon sources become available throughout the vacuum-ultraviolet and soft-X-ray energy range, it is useful to survey the effects that can be studied using photoelectron spectrometry. Such a survey is presented, and examples are cited to illustrate the current state of our knowledge in this area. Photoelectron spectrometry differs from absorption studies in that kinetic energy analysis of electrons yields information about each channel in a photoionization event, rather than yielding only the total cross-section. Electron angular distribution measurements can also provide further information about spins and multipolarities. Probably the most intriguing feature of electron spectrometry is the direct insight that it can give into electron correlation effects. In a general description of electron correlation effects there is no necessity to consider one-electron orbitals. However, as a heuristic device it is convenient to do so, and to consider at least four different manifestations of electron correlation in electron spectrometry : Initial-State Configuration Interaction (ISCI), Final-Ionic-State Configuration Interaction (FISCI), Continuum-State Configuration Interaction (CSCI), and autoionization. There now exist rather well-understood examples of CI satellites, which will be cited and reviewed. Future directions that further studies of these and related phenomena might take to better understand electron correlation in atoms will be discussed