Autoionization decay

Figure 14 Interaction potential and autoionization decay width employed and determined in the...

Penning ionization, as has been noted earlier, occurs due to energy exchange between electrons. This means that the initial state of the colliding atoms A 4- B is autoionized and, consequently, is characterized not only by the interatomic potential, but also by a definite lifetime as related to decay with electron emission this time t(R) depends on the distance R between atoms. The parameter T(J ) = 1/t(jR) represents the width of autoionization decay. 

A similar process selection is possible for inner-shell excitation or double excitation and subsequent autoionization decay (described in the first case by a cross section of the first step, cr, and in the latter case by o ). These processes occur only at specific photon energies hvr (subscript r for resonance), and the kinetic energy of electrons from the autoionization decay is then fixed by... 

Hitherto the discussion of Fig. 5.2 has neglected the possibility of non-radiative decay following 4d shell excitation/ionization. These processes are explained with the help of Fig. 5.2(h) which also reproduces the photoelectron emission discussed above, because both photo- and autoionization/Auger electrons will finally yield the observed pattern of electron emission. (In this context it should be noted that in general such direct photoionization and non-radiative decay processes will interfere (see below).) As can be inferred from Fig. 5.2(h), two distinct features arise from non-radiative decay of 4d excitation/ionization. First, 4d -> n/ resonance excitation, indicated on the photon energy scale on the left-hand side, populates certain outer-shell satellites, the so-called resonance Auger transitions (see below), via autoionization decay. An example of special interest in the present context is given by... 

Many features typical of atomic inner-shell photoexcitation with its autoionization decay have been explored for the case of 4d - np excitation in xenon. Though the 4d5/2 -> 6p resonance at 65.11 eV photon energy is just outside the energy range shown in Fig. 5.1, it will be considered here because it can be treated as an isolated resonance, and is the best-studied case the 4d5/2 - 7p resonance seen in Fig. 5.1 at 66.37 eV photon energy shows rather similar features. The notation 4d5/2 -> 6p is an abbreviation for... 

Ekin(electron from autoionization decay) = hv, — Ef(one-hole state), (1.29c)... 

Further, let us also underline that a tedious procedure of the phase convention in calculating the matrix elements of different operators is avoided in the energy approach, although certainly the final formulae must coincide with the formulae obtained using the traditional amplitude method. Therefore, the energy approach simplifies an analysis of complex atomic processes including processes with the interference of different kinds of channels (i.e., radiation and autoionization decay channels, etc.). 

Cerium. For cerium films crystallized as the y-phase (fee), L.I. Johansson et al. (1978) report a giant enhancement of the valence-band photoemission intensity. The photoemission peak is located at 120 eV The effect is interpreted as being due to autoionization decay following the 4d —> 4f transitions. 

The results were rationalized on the basis of the increasing number of autoionization decay channels that become available to the high-w Rydberg states as each ionization threshold is reached. An analysis of the decay-dependence of the ZEKE spectra via the E IA2 state provided evidence for a non-exponential decay of the high-n Rydberg states. 

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