A practical theoretical formalism for atomic multielectron processes: direct multiple ionization by a single auger decay or by impact of a single electron or photon

Abstract

Multiple electron processes occur widely in atoms, molecules, clusters, and condensed matters when they are interacting with energetic particles or intense laser fields. Direct multielectron processes are the most involved among the general multiple electron processes and are the most difficult to describe theoretically. In this work, a unified and accurate theoretical formalism is proposed on the direct multielectron processes of atoms including the multiple Auger decay and multiple ionization by an impact of an energetic electron or a photon based on the atomic collision theory described by a correlated manybody Green's function. Such a practical treatment is made possible due to different coherence features of the particles (matter waves) in the initial and final states. We first explain how the coherence characteristics of the ejected continuum electrons is largely destructed, by taking the electron impact direct double ionization process as an example. This process is completely different from the single ionization where the complete interference can be maintained. The detailed expressions are obtained for the energy correlations among the continuum electrons and energy resolved differential and integral cross sections according to the separation of knock-out and shake-off mechanisms for the electron impact direct double ionization, direct double and triple Auger decay, and double and triple photoionization processes. Extension to higherorder direct multielectron processes than triple ionization is straight forward by adding contributions of following knock-out and shake-off processes. The approach is applied to investigate the electron impact double ionization processes of C + , N + , and O + , the direct double and triple Auger decay of the K-shell excited states of C + 1s2s 2 2p 2 2 D and 2 P , and the double and triple photoionization of lithium. Comparisons with available experimental and theoretical results show that our proposed theoretical formalism is accurate and effective in treating the atomic multielectron processes.

Relative extent of triple Auger decay in CO and CO2

“…5,14,15 Only in a negligible fraction of TA events do two of the electrons share their total kinetic energy equally. This is in agreement with the theoretical work on direct triple Auger decay in atoms by Liu et al, 27 who conclude that the probability density for equal energy sharing between the three Auger electrons is very small, while one fast and two slower electrons are favoured. No clear asymmetric energy sharing with the third electron and any of the other two electrons can be seen in the coincidence maps, which may be explained by the third electron mainly having a low (2-10 eV) kinetic energy.…”

“…At the present time, theoretical investigations on TA decay are limited to one study by Liu et al, 27 which is based on calculations with many-body Green's functions for triple Auger decay in the C atom after 1s ionization. They predict that the dominating mechanism for direct triple Auger decay is double knock-out (KO), which is more than one order of magnitude larger than knock-out plus shake-off (SO) or SO + KO, and more than two magnitudes larger than double SO.…”

“…Studies of triple Auger decay are still very limited, with just a few experimental 7,16,17 and theoretical 26,27 investigations on atoms. The relative abundance of triple Auger decay in atoms can be estimated from previous studies on ion mass 11 and multi-electron spectroscopy.…”

Transient space localization of electrons ejected from continuum atomic processes in hot dense plasma

“…Finally, electron localization modifies the laser-matter interactions, particularly in laser interactions with solids and dense plasma. An enhancement should be more pronounced for direct multi-electron processes, where several continuum electrons are ejected simultaneously 45 .…”

Strong enhancement of electron-impact-ionization processes in hot dense plasma by transient spatial localization

“…Looking more into detail, we find that, surprisingly, the differential cross section is modified by electron localization in a dense plasma and thus exhibits new features. The isolated-ion model predicts a "U-shaped" energy dependence for the energy differential cross section that is steeper at high residual electron energies [30][31][32][33][34][35]. The screened-ion model does not significantly modify this energy dependence, although the differential cross section exhibits some notable differences.…”