Auger widths

Let us now consider the effect of a spectator vacancy on the Auger rate of the C, N, and O core hole in CH4, NH3, and H20 molecules, respectively. These molecules are isoelectronic with Ne however, the degeneracy of the outer valence orbitals is preserved only in the tetrahedral CH4. The Fano-ADC Auger widths of the singly core-ionized molecules [44] are presented in Table 6.4 alongside the available literature data. The calculated total Auger... 

Argon-37 Analysis. The II counter has been calibrated for analysis of the 2.62-k.e.v. x-rays and Auger electrons emitted in the decay of argon-37. Figure 14a and b show the argon-37 spectra measured in 9 1 Ar CH4 gas mixture at pressures of 400 and 760 cm. Hg, respectively. The resolution full width at half maximum (FWHM) in both cases is 27% or 0.82 k.e.v. In both cases the spectra were measured in the center... 

These features of lines of various spectra (X-ray, emission, photoelectron, Auger) are determined by the same reason, therefore they are discussed together. Let us briefly consider various factors of line broadening, as well as the dependence of natural line width and fluorescence yield, characterizing the relative role of radiative and Auger decay of a state with vacancy, on nuclear charge, and on one- and many-electron quantum numbers. 

The lifetime of a separate atom in its ground state is infinite, therefore the natural width of the ground level equals zero. Typical lifetimes of excited states with an inner vacancy are of the order 10-14 — 10 16 s, giving a natural width 0.1 — 10 eV. The closer the vacancy is to the nucleus, the more possibilities there are to occupy this vacancy and then the broader the level becomes. That is why T > Tl > Tm- Generally, the total linewidth T is the sum of radiative (Tr) and Auger (T ) widths, i.e. 

Effective nuclear charge grows with increase of ionization and excitation of an atom, therefore, the fluorescence yield in ions and, to a less extent, in excited atoms, tends to increase. Radiative and Auger linewidths, as well as fluorescence yields, depend on relativistic and correlation effects to less extent in comparison with the probabilities of separate transitions, because in sums the individual corrections partly compensate each other. Therefore, calculations of radiative widths in the Hartree-Fock-Pauli approach lead to reasonably accurate results. 

Figure 6.2 Auger decay width of (2p n) Mg+-H+ as a function of the Mg-proton distance, R.z is Mg-proton axis. Diamonds and solid line Fano-ADC(2)x calculation with atomic orbital basis centered both on Mg and on the proton circles and long-dashed line Fano-ADC(2)x calculation with atomic orbital basis centered only on Mg stars and short-dashed line Fano-ADC(2)x calculation for (2p 1) Mg+ alone, with atomic orbital basis centered both on Mg and at the distance R along the z-axis, showing the so-called basis set superposition error (BSSE) triangles and dashed-dotted line Fano-ADC(2)x calculation with atomic orbital basis centered on Mg only, with the 3s orbital of Mg being frozen at its shape at R = 6.5A. The inset shows the low-r part of the plot on logarithmic scale. See Ref. [35] for the details of the computation.

Table 6.3 Fano-ADC total and partial Auger decay widths (in meV) for doubly ionized Ne atom...

Table 6.4 Comparison of the Fano-ADC results with the available theoretical and experimental values for the K-LL Auger decay widths in CH4, NH3, and H2O molecules...

The decay widths are in meV, citations are given in square brackets. Experimental value for ammonia is lacking because of the vibrational broadening in the Auger electron spectrum of ammonia [65], See Ref. [44] for the details of the Fano-ADC computation. 

With rn( only the total decay rate or, equivalently, the total level width of an inner-shell hole-state has been considered so far. In general, the system has different decay branches. In many cases these branches can be classified as radiative (fluorescence) or non-radiative (Auger or autoionizing) transitions, and even further, by specifying within each group individual decay branches to different final ionic states. (Combinations of radiative and non-radiative transitions are also possible in which a photon is emitted and simultaneously an electron is excited/ ejected. These processes are termed radiative Auger decay (see [Abe75]).) As a result, the total transition rate Pnr and, hence, the total level width is composed of sums over partial values ... 

Before these partial quantities are discussed further, an important comment has to be made unlike the partial transition rates, the partial level widths have no direct physical meaning, because even for a selected decay branch it is always the total level width which determines the natural energy broadening. The partial level width is only a measure of the partial transition rate. Both aspects can be inferred from the Lorentzian distribution attached to a selected decay branch, e.g., Auger decay, which is given by... 

Figure 2.7 Theoretical level widths for K-shell ionization as a function of the atomic number. The total level width T is the sum of two contributions that come from radiative (fluorescence) decay, TR, and non-radiative (Auger) decay, TA. From [Kra79].

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