Inner shell photoionization

Figure 1.3 Illustration of the two classes of two-electron processes caused by photoionization using magnesium as an example, using, on the left the model-picture of Fig. 1.1 and on the right an energy-level diagram (not to scale) (a) direct double photoionization in the outer 3s shell (b) 2p inner-shell photoionization with subsequent Auger decay where one 3s electron jumps down to fill the 2p hole and the other 3s electron is ejected into the continuum (Auger electron). The wavy line represents the incident photon (which is often omitted in such representations) electrons and holes are shown as filled and open circles, respectively arrows indicate the movements of electrons continuum electrons are classified according to their kinetic energy e.

In the shakeup process accompanying the inner-shell photoionization, the electrons are excited from occupied orbitals to unoccupied orbitals. In the case of a one-electron shakeup, there are three open shells in the final state. We represent their orbitals as a, b, c, and denote the up-spin electron by -i-, the down-spin electron by -. We can write the determinantal wave function of the final state with open shell structure in the following form (6) ... 

The absorption can also be measured by recording core-hole decay products in the case of diluted systems. The inner shell photoionization process can be described as a two-step process. In the first step the photon excites a core hole-electron pair, and in the second step the recombination process of the core hole takes place. There are many channels for the core hole recombination. These channels can produce the emission of photons, electrons or ions, which can be collected with special detectors. The recombination channel that is normally used to record bulk x-ray absorption spectra of dilute systems is the direct radiative core-hole decay producing x-ray fluorescence lines. In Fig. 3 a beam line with an apparatus to record absorption spectra in the fluorescence mode is represented schematically. 

These unique properties of core level excitation spectroscopies are briefly reviewed. The fundamentals of core level spectroscopies, such as X-ray absorption, X-ray absorption fine structure, inner-shell photoionization, electronic and radiative relaxation, and fragmentation in the regime of core level excitation, are outlined along with their characteristics to size effects... 

Inner-shell photoionization of atoms, molecules, clusters, and the condensed phase cannot be simply described by one electron photoemission, assuming frozen orbital energies. This simple approach, which corresponds to Koopmans theorem, is often successfully applied to describe valence-shell photoionization. However, this approach completely fails for inner-sheU photoionization, where deviations of the order of 10-20 eV relative to the experimental results are found. 

Inner-shell photoionization leaves a core hole that is stabilized via relaxation processes (cf. Sec. 2.3). The core hole is filled by an outer-shell electron leading either to the emission of an Auger electron or an X-ray photon (cf. Fig. 4). The branching ratio between both relaxation processes depends on the nuclear charge... 

W.T. Silfvast, J.J. Macklin, O.R. Wood II High-gain inner-shell photoionization laser in Cd vapor pumped by soft X-ray radiation from a laser produced plasma source. Opt. Lett. 8, 551 (1983)... 

Consider the following inner-shell photoionization process... 

In the case of inner-shell photoionization Niehaus has predicted within a semiclassical framework the PCI shifts Ae and shapes of Auger lines. Both, the shift and the shape depend - apart from the life time x (or width F) of inner-shell vacancy -only on the excess energy Ej. Also quantum mechanical treatments have been formulated but to date neither shifts nor line shapes have been calculated quantitatively. As example, in Fig. 18 the experimental Xenon 4d-y -Sp Auger peak following the... 

Collective effects near threshold in inner shell photoionization include along with RPAE corrections also relaxation processes. They are a consequence of the fact that near inner shell threshold the photoelectron leaves the atom slowly and all other electrons have sufficiently time to feel the field of the vacancy created as well as its decay-Auger or radiative. It is very essential that because the field variation takes place after vacancy creation, the photoelectron wave function must be ortogonalized to all other electron states of the atom - otherwise it includes the interaction with the final state of the ion before its formation. 

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