Mechanisms of

1
Mechanisms of Photo Double Ionization of Helium
by 529 eV Photons
Alexandra Knapp Group of R. Dörner and H.
Schmidt-Böcking University of Frankfurt, Germany
2
Single ionization
Energy
0
25 eV 79 eV only single ionization
3
Shake off
4
Shake off
First electron absorbs photon and removes from
the nucleus
5
Shake off
6
Shake off
Change of the effektiv nuclear charge
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Shake off
Second electron is in its eigenstate ? Only
single ionization occurs
8
Shake off
Second electron is NOT in its eigenstate ? Shake
off
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Electron-electron scattering (TS1)
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Electron-electron scattering (TS1)
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Electron-electron scattering (TS1)
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Electron-electron scattering (TS1)
13
Electron-electron scattering (TS1)
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Electron-electron scattering (TS1)
15
Electron-electron scattering (TS1)
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Electron-electron scattering (TS1)
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Electron-electron scattering (TS1)
90
(e,2e) like collision between the two electrons
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Ratio of double to single ionization (theory)
Shake off TS1
Shake off
TS1
Photon energy above the threshold eV
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COLTRIMS
with electric field
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COLTRIMS
Collecting electrons up to 60 eV with 4 ? solid
angle with a combination of an electric and a
magnetic field
with electric magnetic field
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Questions

• Is the assumption of a two-step model valid?
• Energy sharing
• Asymmetry parameter
• Mechanisms of photo double ionization
• Angular distributions

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Energy sharing
CCC-Calculation A. Kheifets, I. Bray
Extreme asymmetric energy sharing
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Asymmetry parameter
Fast electron absorbs photon energy and its
angular momentum
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Asymmetry parameter
Two-step model is valid
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Angular distributions
Very slow electrons 2 eV
Faster electrons 30 eV
Shake off
TS1
CCC-Calculation
CCC-Calculation
The fast electron (indicated by the red arrow) is
fixed into the direction of the polarization
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TDCS for Eslow 2 eV and 30 eV
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Shake off and TS1 can be seen for all angles
??fast- ?slow? 180
??fast- ?slow? 90
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Comparison between experiment and theory
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Conclusion

• TDCS of the DPI of Helium were measured at 450 eV
  above the threshold
• electrons are distinguishable because of the
  asymmetric energy sharing
• ?2 for very fast and ?0 for very slow electrons
  
• very slow (? 2 eV) electrons Shake off
• slightly faster (? 30 eV) electrons TS1

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Reinhard Dörner Horst Schmidt-Böcking Alexandra
Knapp Thorsten Weber Sven Schößler Till
Jahnke Jürgen Nickles Susanne Kammer Ottmar
Jagutzki Lothar Schmidt C. Lewis Cocke Timur
Osipov Michael H. Prior Jürgen Rösch Allen
Landers Anatoli Kheifets Igor Bray
University Frankfurt Kansas State
University LBNL Western Michigan
University Australian National University
Canberra Murdock University Perth





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