Correlation effects in triple photoionization processes
(with J. Burgdörfer)
Recently, an increasing number of studies, both experimentally and theoretically,
have focussed on triple ionization by photon impact. A point of particular
interest is the modelling of the electron-electron correlations and their
influence on the break-up dynamics and the cross section. Recently, we have been
interested in the description of these correlation effects in the special
case of lithium, which plays a dominant role in recent efforts to understand
triple ionization mechanisms. First of all, Li is a three electron system, so
triple ionization is only possible by simultaneous ejection of all electrons
and no indirect processes are possible. Therefore, Li is
the most 'pure' system where three-electron processes can be studied.
For our current work, however, the more interesting aspect is the extremely
asymmetric electron configuration in the ground state, with two highly
correlated and tightly bound inner electrons and one weakly correlated,
loosely bound outer electron. Starting from this picture, it has been
suggested that the triple ionization process in Li should - at least in the
high energy limit - be envisioned as a photo double ionization of the
inner electrons, while the outer electron is promoted to the continuum by a
simple shakeoff. While this model in its most rudimentary form is
too simple to describe the triple ionization cross section, we showed that
it can be reasonably generalized by taking into account the energy dependent
impact of the inner (photoionized) electrons on the outer electron as a
perturbation. Calculations within this 'Half Collision Model' show
surprisingly good agreement with available experimental data [2,3].
[1] The Near-Threshold Triple Photoionization Cross Section of
Lithium; R. Wehlitz, T. Pattard, M.-T. Huang, I.A. Sellin, J. Burgdörfer
and Y. Azuma, Phys. Rev. A 61 (2000) 030704(R)
[Abstract]
[2] Half-collision model for triple photoionization of lithium;
T. Pattard and J. Burgdörfer, Phys. Rev. A 63 (2001) 020701(R)
[Abstract]
[3]Half-collision model for multiple ionization by photon impact;
T. Pattard and J. Burgdörfer, Phys. Rev. A 64 (2001) 042720
[Abstract]
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last change: 11/30/01