Auger deexcitation

PI, PIS Penning ionization [116, 118] Auger deexcitation of metastable noble-gas atoms 4. ... 

Fluorescence was indeed observed for CI2 interacting with K surfaces, but with much lower yield than exoelectron emission, while in the reaction with O2 the light intensity was below the detection limit [16]. This is in agreement with general experience whereafter at metal surfaces, fluorescence is strongly suppressed by Auger deexcitation for energies up to 500 eV [17]. 

Figure 11.28 The two primary mechanisms for electron emission from a surface. Left thermionic emission in which heat is used to emit electrons from a surface. Right Auger deexcitation of the incoming ion can release enough energy to kick another electron out of the solid.

Figure 1 Schematic of inner sheil ionization and subsequent deexcitation by the Auger...

When an excited state is converted by ejection of an atomic electron, a high positive charge can be produced through subsequent Auger electron emission. Within the period of molecular vibration this charge is spread throughout the molecule to all atoms, and a Coulomb explosion results. This primary phenomenon occurs, of course, not only as a result of [ decay, but must be taken into account in all cases of nuclear reaction when deexcitation by inner electron conversion occurs... 

Let us turn our attention to the dominant recombination or deexcitation processes that follow the excitation of electrons from the inner shell or from the valence shell (Fig. 13). The first mode of deexcitation is the Auger process, which leads to further electron emission. The second mode of deexcitation may result in the emission of electromagnetic radiation and is commonly called X-ray fluorescence. In the Auger transition, the electron vacancy in an inner shell is filled by an electron from an outer band. The energy released by this transition is transferred to another electron in any... 

Exotic atoms are produced by stopping a beam of negatively charged particles like muons, pions, or antiprotons in a target, where they are captured in the Coulomb potential of the atoms at high principal quantum numbers n. These systems deexcite mainly by fast Auger emission of electrons in the upper part of the atomic cascade and more and more by X-radiation for lower-lying states. 

Fig. 1. Energy levels of the antiproton in pHe+. The p is captured by replacing one of the Is electrons, which corresponds for the p to a state with principal quantum number no JW /m, where M is the reduced mass of the atomcule, and m the electron mass. About 3% of antiprotons are captured in metastable states (black lines) at high angular momenta L n — 1, for which deexcitation by Auger transitions is much slower than radiative transitions. The lifetimes of these states is in the order of /is. The antiprotons follow predominantly cascades with constant vibration quantum number v = n — L — 1 (black arrows) until they reach an auger-dominated short-lived state. The atomcule then ionizes within < 10 ns and the pHe++ is immediately destroyed in the surrounding helium medium. The overall average lifetime of atomcules is about 3 — 4 ps...

After the emission of a photoelectron in XPS, the atom is left behind as an ion with a hole in one of its core levels. This is an unstable state. Deexcitation of the excited ion occurs via X-ray fluorescence or via an Auger transition (Fig. 10.6). Therefore, XPS spectra contain peaks due to Auger electrons, which have the characteristic property that they occur at fixed kinetic energies, characteristic of the element from which they are emitted. 

The energy scheme of Fig. 4.4 suggests that apart from Auger decay deexcitation might also occur via light emission. 

Figure 2 Schematic mechanism of X-ray fiuorescence. (A) interaction of primary X-ray photon with eiectronic orbitai of an atom causing ionization of a K-sheii eiectron. (B) Deexcitation invoiving an eiectron transition from the L sheii to the K sheii accompanied by the emission of a K-La.s (Ka) fiuorescence X-ray. (C) Competitive mode of deexcitation invoiving an eiectron transition from the M sheii to the K sheii accompanied by the emission of a K-Ma.s (K 8) fiuorescence X-ray. (D) internai capture of a fiuorescence X-ray ieading to the emission of an Auger eiectron.

The photoelectric effect is followed by the deexcitation of the atom via X-ray transitions or by the emission of a secondary electron (Auger effect, see later in Sect. 8.5.2). As above the K edge absorption dominates, one can collect a complete X-ray spectrum from the subsequent electron transitions. The energy and intensity of the X-rays are characteristic of the composition of the emitter. Thus, y sources can be used to induce photoelectric effect and subsequent X-ray transitions in order to make qualitative and quantitative analyses of samples, which is called the X-ray fluorescence method. 

The deexcitation will start via Auger processes, while the level spacing is small (as its rate weakly depends on the AE transition energy) and there are electrons to be ejected, and then via radiative transitions as the probability of the latter is roughly proportional to (AE). The initial population of the atomic states will be related (though not exactly proportional) to the available density of states, so for any given principal quantum number n the higher orbital momenta will be more populated. 

In media of not too low densities the deexcitation process is dominated by collisions. Collisions can cause external Auger effect when the exotic atom loses excitation energy by ejecting an... 

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