Transition, radiative atomic, inner shell

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]. 

The different emission products which are possible after photoionization with free atoms lead to different experimental methods being used for example, electron spectrometry, fluorescence spectrometry, ion spectrometry and combinations of these methods are used in coincidence measurements. Here only electron spectrometry will be considered. (See Section 6.2 for some reference data relevant to electron spectrometry.) Its importance stems from the rich structure of electron spectra observed for photoprocesses in the outermost shells of atoms which is due to strong electron correlation effects, including the dominance of non-radiative decay paths. (For deep inner-shell ionizations, radiative decay dominates (see Section 2.3).) In addition, the kinetic energy of the emitted electrons allows the selection of a specific photoprocess or subsequent Auger or autoionizing transition for study. 

A possibility to extend this set comes from the use of an Electron-Cyclotron-Resonance-Ion-Trap (ECRIT), which will be realized using the cyclotron trap itself [22]. Here, hydrogen-like electronic atoms will be produced to obtain narrow calibration lines independent of an accelerator s pion beam. The radiative widths of light elements with Z k. 15 are of the order of a few 10 meV because of the absence of non-radiative inner-shell transitions. 

Emission. Generally, the emission hnes are emitted after an ionization in an inner atomic shell an electronic reorganisation follows immediately after the creation of the irmer hole and radiative transitions are observed at lower energies than the absorption discontinuity. 

Fig. 2 shows a diagram summarizing the various transitions which can be observed in the Mjjj and My spectra of a metal as well as in the 3 d Auger spectra. The Mjjj and My absorption transitions are shown in Fig. 2a and b the energy of the Mjjj discontinuity corresponds to the transfer of an inner 3p i2 electron to the Fermi level and its shape involves the 6d unoccupied distribution the energy of the My absorption line is exactly that of the 5/" -> SJjyj excitation transition. The My emission is shown in Fig. 2e an inner 3 d i2 hole is created and a 5/electron transits to this hole with the emission of a photon. In the corresponding non-radiative transition, there is simultaneously the 5/ electron transition, and the excitation or ionization of a 5/electron (or 6p or 6 s) (Fig. 2f). The My resonance line is represented in 2c the excited 5/electron drops back to the inner hole the corresponding emission line then coincides with an absorption line. The competing non-radiative transition is shown in 2d this is an Auger transition in the excited atom the final state has only one hole in an outer shell and the configuration is the same as in a photoemission process.

The same problem of controlled spontaneous radiative decay is connected with perspectives creation of short wave (X I A) laboratory X-Ray laser on radiative transitions between inner electron shells in heavy atoms. In such systems, timelife of excited electron state is very short r I fs) that lead to necessity of use fantastic and nonreal... 

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