Shake-off processes

Fig 7 a-f. Shake-up and shake-off processes in photoionization (a) Real space picture illustrating contraction of the atomic charge density in response to the creation of a core hole (b, d) Shake-up (c, f) Conjugate shake-up and (e) inelastic scattering... 

Fig. 4. Schematic illustrating photoionization, shake up and shake off processes.

The Si(k) term takes into account amplitude reduction due to many-body effects and includes losses in the photoelectron energy due to electron shake-up (excitation of other electrons in the absorber) or shake-off (ionization of low-binding-energy electrons in the absorber) processes. 

At 2000 K there is sufficient energy to make the H2 molecules dissociate, breaking the chemical bond the core density is of order 1026 m-3 and the total diameter of the star is of order 200 AU or about the size of the entire solar system. The temperature rise increases the molecular dissociation, promoting electrons within the hydrogen atoms until ionisation occurs. Finally, at 106 K the bare protons are colliding with sufficient energy to induce nuclear fusion processes and the protostar develops a solar wind. The solar wind constitutes outbursts of material that shake off the dust jacket and the star begins to shine. 

We have tacitly assumed that the photoemission event occurs sufficiently slowly to ensure that the escaping electron feels the relaxation of the core-ionized atom. This is what we call the adiabatic limit. All relaxation effects on the energetic ground state of the core-ionized atom are accounted for in the kinetic energy of the photoelectron (but not the decay via Auger or fluorescence processes to a ground state ion, which occurs on a slower time scale). At the other extreme, the sudden limit , the photoelectron is emitted immediately after the absorption of the photon before the core-ionized atom relaxes. This is often accompanied by shake-up, shake-off and plasmon loss processes, which give additional peaks in the spectrum. 

The term S0 k) in (6-9) is a correction for relaxation or final state effects in the emitting atom, such as the shake-up, shake-off and plasmon excitations discussed in Chapter 3. The result of these processes is that some absorbed X-ray quanta of energy hv are converted not into photoelectrons of kinetic energy hv-Eb, but into electrons with lower kinetic energy as well. 

The paper 6.5 [63] is particularly interesting historically, because the writer mentions explicitly that the esters involved in the propagation may be (or need to be) activated or deactivated. As we have seen, this idea was not developed to fruition until some 30 years later Other useful features in that paper are the examination of the evidence for the ionic nature of the propagators in the cationic polymerisations, and explanations of how difficult it was for polymer chemists to shake off the ideas taken over from the familiar radical polymerisations and to adapt their thinking to ionic processes. 

In the present example a change of 6p to np with different principal quantum numbers n is possible. Hence, shake-modified spectator transitions or resonance shake transitions can occur, and if) and (g) are examples of shake-up and shake-off resonance double Auger processes, respectively. (If there is a lower unoccupied orbital, shake-down is also possible). 

---