Coster—Kronig electrons

A particularly interesting Auger process is the xenon L2-L3N4 Coster-Kronig decay excited by photons close to threshold. The emitted L2-L3N4 Coster-Kronig electron has a low electron energy of 228.4 eV, which makes it sensitive to electron-electron interactions. Close to threshold the photoelectron recedes only slowly from the atom and is still in the vicinity of the... 

Figure 34. Energies of xenon L2-L3N4 Coster-Kronig electrons as a function of the exciting x-ray energy. The solid curve for the diagram line indicates the prediction of the semiclassical Niehaus theory above threshold. (From Ref. 103.)...

Fig. 24a-i. One-electron level pictures and self-energy diagrams for dynamic relaxation of 4 s and 4p holes, (a)—(c) and (f, g) describe giant Coster-Kronig fluctuation (full plus dashed arrows) and decay processes (full arrows) while (d, e) and (f,) (h, i) correspondingly describe Coster-Kronig fluctuations and decay processes... 

Since the energy of the electron in the Coster-Kronig decay is high up in the continuum (cf. Fig. 2) one can argue that the choice of basis set is not very critical and that neglecting the attraction of the extra hole is compensated for by neglecting the repulsion from coupling the electron-hole excitation to P. 

Finally, Figs. 32 b, c demonstrate that in La and Ce metal, the shift of the 5 s level is at least as large as in Xe, indicating that the giant Coster-Kronig fluctuation process (Eq. (81)) is very strong and atomic-like. However, since the 5 d/6 s electrons now form rather broad bands, one can understand that the satellite structure appears to be washed out in the metal. These types of problems will be further discussed in Section 8. 

When an ion is created with a core vacancy, relaxation can occur by the emission of an X-ray photon, by the emission of an Auger electron, or by the emission of an electron in a Coster-Kronig process (19). The probability of each of these processes depends on several factors and the resulting particle emission may be detected by well-known methods. 

Fluorescence yield (tUx) of an atomic shell/subshell is defined as the probability that a vacancy in that shell/subshell is filled through radiative transitions. Since the vacancy can also be filled by nonradiative processes (Auger electrons and Coster-Kronig transitions), the fluorescence yield (cuk or cul) = Radiative yield/Total yield. The fluorescence yield values have been given by Bambynek et al. (1972) and Krause (1979). 

Coster-Kronig decay Tliis decay process is a special Auger decay in which the original vacancy is transferred to a higher subshell of the same shell. Auger and Coster-Kronig transitions are (essentially) two-electron processes and cause the emission of electrons with characteristic energies. 

An accurate knowledge of the individual rates of vacancy decay is interesting in several fields. Firstly, transition rates present a sensitive tool to investigate details of atomic structure since they probe static properties (atomic wave functions) as well as dynamic properties (electron correlation and relaxation). Secondly, an accurate knowledge of relative decay rates is important in practical applications In experimental studies of ion-atom collisions either fluorescence or electron emission is detected and the ionization cross sections are derived. In the L-shell case uncertainties of fluorescence and Coster-Kronig yields are a limiting factor upon deriving ionization cross sections. ... 

Comprehensive theoretical calculations of radiative transition rates as well as Auger and Coster-Kronig transition rates are available. However, uncertainties are large for Coster-Kronig transitions with small excess energy due to the strong influence of several effects (i) many-body interactions in the initial and final atomic systems, (ii) relaxation in the final ionic state, and (iii) exchange interaction between the continuum electron and the final bound-state electrons. For an experimental determination of decay rates, various techniques have been employed, e.g., the use of radioactive sources or coincidence techniques. Most techniques... 

In contrast to 3d and 4d levels 4p and 4s core levels have received less attention up to now either from EELS or from other core level spectroscopies. The case of 4p excitation is complicated by breakdown of the one-electron approximation for 4p core holes, which in this part of the Periodic Table may decay by 4p <—>4d f giant Coster-Kronig coupling, leading to broad ill-defined peaks in photoemission (Wendin 1981). In the rare earths (except Yb) such processes are allowed for 4pi/2 holes but not for 4p3/2- In electron loss the unstable 4p /2 excitations lead to ill-defined structure in the corresponding energy region, but sharp peaks are observed near the 4p3/2 ionisation threshold (Strasser et al. 1984). 

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