Auger decay/electrons energy

Figure 3.25 The probability Q, to create a core hole in a level with binding energy E, with a primary electron of energy Ev maximizes for EfE, 2-3 (left). Auger decay is the preferred mode of dcexcitation in light elements, while X-ray fluorescence becomes more important for heavier elements... 

In kinetic emission, at higher kinetic energy above a certain threshold energy the impact of an ion can cause the emission of an electron from an inner shell. The core-ionized atom may subsequently decay by an Auger decay, which leads to the emission of another electron. 

Interatomic Coulombic decay (ICD) is an electronic decay process that is particularly important for those inner-shell or inner-subshell vacancies that are not energetic enough to give rise to Auger decay. Typical examples include inner-valence-ionized states of rare gas atoms. In isolated systems, such vacancy states are bound to decay radiatively on the nanosecond timescale. A rather different scenario is realized whenever such a low-energy inner-shell-ionized species is let to interact with an environment, for example, in a cluster. In such a case, the existence of the doubly ionized states with positive charges residing on two different cluster units leads to an interatomic (or intermolecular) decay process in which the recombination part of the two-electron transition takes part on one unit, whereas the ionization occurs on another one. ICD [73-75] is mediated by electronic correlation between two atoms (or molecules). In clusters of various sizes and compositions, ICD occurs on the timescale from hundreds of femtoseconds [18] down to several femtoseconds [76-79]. 

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.

Within the two-step model for photoionization and subsequent Auger decay, the kinetic energy of Auger electrons for normal (diagram) transitions comes from the energy difference of the ion states before (subscript i) and after (subscript f) the Auger decay, i.e.,... 

In Part A the aims and the potential of electron spectrometry of free atoms have been discussed for the example of photoionization and subsequent Auger decay in neon. Now the apparatus details and the basic features of the technique of electron spectrometry will be considered. The discussion is restricted to electrostatic deflection analysers. However, the properties discussed can easily be adapted and transferred to other kinds of electron energy analysers. 

A PCI is the energy gain for the Auger electron, but the energy loss for the photoelectron.) It should be pointed out that this situation differs considerably from the case of electron impact ionization with subsequent Auger decay. Following electron impact, there are three free particles present in the final state... 

Figure 4.46 Energy- and angle-resolved patterns for two-electron emission in the two-step process of 2p3/2 photoionization of magnesium with subsequent L3-M, M, Auger decay induced by 80 eV photons with linear polarization (electric field vector along the x-axis). Both electrons are detected in a plane perpendicular to the photon beam direction the direction of the photoelectron (ea) is fixed at ( ) a = 180° and (b) = 150°, while the...

After this schematic discussion of possible processes around the 4d ionization shell in xenon, Fig. 5.2(h) can be compared with the experimental results shown in Fig. 5.1. The main structures can be related to 4d, photoexcitation/ionization, and autoionization/Auger decay to 5s25p4fa electron configurations can be identified in the energy regions of overlap. 

In Fig. 5.26(a) and for Ecxe < E% one can see that PCI effects also exist for the 4d5/2 photoline, because towards the ionization threshold hv — kin(4d5/2) increases, i.e., ki (4d5/2) decreases. A quantitative interpretation of these data, however, will be omitted for two reasons. First, the study requires quantitative electron spectrometry at low kinetic energies which is difficult due to the cutoff problem in the spectrometer transmission (see Fig. 4.15). Second, the cumulative effects of all possible Auger decays following 4d5/2 photoionization, not just a single chosen one, contribute to the photoline. 

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