Photon Factory Activity Report 2005 #23 Part B (2006)
Atomic and Molecular Science

1C,16B/2001G202, 2003G152

Electron correlation in Xe 4d Auger decay,
studied by photoelectron – Auger electron coincidence spectroscopy
S SHEINERMAN1.2, P LABLANQUIE1, F PENENT1, J PALAUDOUX1, J H D ELAND3,T AOTO4, Y HIKOSAKA5 and K ITO*4
1LCP-MR, Université Pierre et Marie Curie, 11, rue P et M Curie, 75231 Paris, France
Department of Physics, State Maritime Technical University, 198262 St. Petersburg, Russia
3PTCL, Oxford University, Oxford OX1 3QZ, UK4Photon Factory, Institute of Materials Structure Science, Oho 1-1, Tsukuba 305-0801, Japan
4
Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan2

Innershell ionisation creates highly excited states thatdecay generally by emission of secondary Auger
electrons. This schematic two step description fails whenelectron correlation is important as it is the case nearthreshold when the photoelectron escapes with a low
velocity. Post Collision Interaction then plays a crucialrole: it involves interaction between the 2 released
electrons in the presence of the changing ion field.
Emission of 0 eV or threshold electrons is a very sensitive
tool to observe PCI properties, but has been only partially
understood. We demonstrate, on the Xe 4d case [1], thatan experiment where the Auger electron and thephotoelectron are detected in coincidence enables one todefine precisely the system and to clarify the process.
Threshold electrons

The experiment was performed at undulator beamline
BL16B, on our set up combining a threshold electron
selector and a hemispherical electrostatic analyzer [2].
Figure 1 demonstrates that the coincidence method allows
the decomposition of the threshold electron yield into2+-2
partial channels associated to well defined Xe 5p finalstates. Strong PCI distortion of electron spectra areobserved in all channels, and differ strongly from one
another. Comparison with calculations carried out in theframework of a quantum mechanical PCI model allows us
to clarify the dynamics of threshold electron production.
For instance, in the 5p-2 (1S) channel, the main
contribution comes from the PCI retardation of slow
photoelectrons -see Figure 2- while for the 5p-2 (1D) final
state, an additional contribution is observed on 4dnp
resonances, that comes from the recapture of thephotoelectron into discrete states of the 5p4 (1S) channel
followed by valence multiplet decay.
1S

1.0
0.8
0.6
0.4
0.2

Coincidences

38

3
3

P2

32

P1,0

130

D

128

S

64

26
65

66
67
68
Photon Energy (eV)69

70

Figure 1. Top: yield of threshold electrons in thevicinity of the Xe 4d threshold. Bottom: two-dimensional
map of the coincidence between threshold electrons andfast electrons whose energies are reported on the y axis.

Cross Section (Mb/Ryd)

34

Fast electron Energy (eV)

36

0.0

2.0

1D

1.5
1.0
0.5
0.0
67

68

69
Photon Energy (eV)70

Figure 2. Comparison between partial thresholdelectron yields from figure 1 (dots) and theoretical
calculations, thin lines show only retardation of thephotoelectron, thick lines include also capture processes.
References[1] S.Sheinerman et al., J. Phys. B 39, 1017 (2006).
[2] Y.Hikosaka et al., Meas. Sci. Technol. 11, 1697 (2000).
* kenji.ito@kek.jp

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