FISCI final ionic state configuration

As demonstrated in the previous section, satellites are due to electron correlation effects, and, in principle, all types which are classified in a configurational picture as initial state configuration interaction (ISCI), final ionic state configuration interactions (FISCI) and final state configuration interactions (FSO which includes interchannel interactions in the continuum) have to be taken into account. In certain cases, however, one type of correlation is more important than the others, and in the present case of 3s and 3p photoionization in argon this is FISO. This property allows a rather transparent analysis of the implications which these correlations have on the corresponding satellites. 

Electron correlation, conventionally treated by configuration interaction (Cl), can enter through the initial and/or the final state of the transition. Cl may be divided into initial state configuration interaction (ISCI) and final state configuration interaction (FSCI). The latter is usually subdivided into final ionic state Cl (FISCI) and final continuum state Cl (FCSCI). Since the final state of the photoionization is the initial state of the Auger transition it follows that FSCI studied by means of PES is identical to ISCI studied by means of AES. 

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