Postcollision interaction

In addition, the observed width of an Auger line is also affected by the spectrometer resolution. However, the bandpass of the incident radiation which produces the initial state for the Auger decay does not play a role, unlike in the case of the width of an observed photoline. (This statement only holds for the two-step model of inner-shell ionization and subsequent Auger decay. In the vicinity of the inner-shell ionization threshold it significantly fails due to postcollision interaction (Section 5.5) and the resonant Raman Auger effect (Section 5.1.2.1).) Hence, Auger transitions often appear in the spectra of ejected electrons as lines much sharper than the corresponding photolines. 

Figure 6. (a) Schematic potential energy diagram for the explanation of postcollision interaction. Autoionization processes at intermediate intemuclear distances yield electrons at energies lower than the nominal energy, (b) Resulting line shape (schematically). 

F we 8. Schematic potential curve diagram for the explanation of postcollision interaction in electron-atom collision. Decay at a distance R between scattered electron and excited atom will yield an electron energy e > s,. Subsequently the system follows the Coulomb curve, yielding a kinetic energy -D for the scattered electron. Decay at smaller R will eventually lead to a trapping of the scattered electron. 

The situation is more complicated if several autoionizing states in He are excited by low-energy ion impact such that postcollision interaction leads to interferences between transitions from these states. As an example Figure 20 shows coincident electron energy spectra from Li" + He collisions. 

Up to now we have mainly considered the autoionization of atoms which can be regarded as more or less isolated particles. Only for the case of a charged collision partner at low velocities was the influence of the charge on the final state potential curve taken into account in the description of postcollision interaction. A first step in describing the autoionization process as starting from quasimolecular levels is the treatment by Stolterfoht... 

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