LOW-ENERGY AUGER ELECTRONS - A PROBE OF ELECTRON CORRELATIONS IN ATOMS AND MOLECULES

Until very recently Auger decay was exclusively regarded as an inner-shell phenomenon. However, recent studies of the decay of certain valence states in atoms and molecules excited by electron correlation accompanying photoionization have shown the importance of non-radiative decay processes, so-called participator Auger transitions. The fact that such states decay non-radiatively was previously ignored, and is of critical importance for the interpretation of double-photoionization data, for both, photoion yield measurements, particularly near threshold, and photoelectron spectra, especially at low kinetic energies. Hence the spectroscopy of these participator Auger transitions is of considerable interest for our understanding of electron correlations. Two modes of such transitions were identified; the inner-valence type in which the inner vs hole is filled in the decay process, and the valence-multiplet type in which the valence shell remains unchanged in occupancy during the transition, but experiences a change of LS multiplet symmetry. The analysis of these processes shows that in the sudden limit up to 30-40% of the double-ionization rate in neon and argon is due to participator Auger decay, which was previously attributed to simultaneous double ionization.