Coster-Kronig

A.G. Kochur, D. Petrini, E.P. da Silva, 2s-photoionisation of atomic magnesium Shake processes and Coster-Kronig radiationless decay, A A 365 (2001) 248. 

Lower-energy multiplets result from super Coster-Kronig and Coster-Kronig decay channels and thus their spectrum is less sensitive to the chemistry of the environment [24]. 

So far, we have said nothing about the 4s XPS spectrum. Judging from the experimental spectra in Fig. 1 one might think that the 4 s levels look rather normal. However, there is again a giant Coster-Kronig fluctuation and decay process involving the 4 s hole... 

I. Giant Coster-Kronig (gCK)-intra-main shell fluctuations... 

II. Super Coster-Kronig (sCK) fluctuations - all hole levels in the same main shell ... 

Figure 17 illustrates a less spectacular but quite common situation, namely degeneracies leading to super Coster-Kronig fluctuation and decay of hole levels, in the present... 

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... 

As seen in Table 2, for those solutions which occur outside the gCK continuum the width is quite small, being determined by the much weaker Coster-Kronig and Auger processes. For a number of elements we have included the dipole parts of the following Coster-Kronig fluctuation 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. 

As already mentioned in Section 4, the 5 s and 5 p core level spectra of the 5f-series and a number of the preceding elements should show pronounced effects of giant Coster-Kronig fluctuation and decay processes much in the same way as happens in the 4.S, 4 p spectra in the range 48 Z < 70. In the case of the 5 p spectrum, the gCK interaction process becomes... 

The experimental 5s XPS spectrum in Xe7,8 (Fig. 32a) looks quite similar to the 4p spectrum in Ba, suggesting that the 5 s level lies just below the 5 1 level structure, forming a well-defined 5 s1/2 quasi-particle excitation and giving considerable strength to a prominent satellite spectrum, mainly 5 p25 d94, 95. The basic process is again giant Coster-Kronig fluctuation of the core hole... 

Coster-Kronig fluctuations increases the 5si/2 shift by 0.6 eV to 3.1 eV, showing that there is an appreciable amount of 4d-screening charge that moves along with the 5si/2 hole. 

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. 

Fig. 58a-e. Comparison of giant Coster-Kronig (intra- valence band) fluctuation and decay processes in atoms (a), molecules (b, c) and metals (d, e)... 

We shall conclude this review by a comment on open-shell systems, in particular on the development of the 4p-hole spectrum in the rare-earth series, where the 4f shell gradually becomes filled. In this region, the problem reduces to very strong interactions between basically two configurations, 4p 4fN and 4 d24fN+1 which, in the spirit of this article, can be expressed as a giant Coster-Kronig (gCK) fluctuation process... 

---