Mechanisms of
Photo Double Ionization of Helium
by 529 eV Photons
Alexandra Knapp
Group of R. Dörner and H. Schmidt-BöckingUniversity of Frankfurt, Germany
0
Ene
rgy
Single ionization
25 eV … 79 eV: only single ionization
0
Ene
rgy
Double ionization
79 eV and higher: single + double ionization
Shake off
Shake off
First electron absorbs photon and removes from the nucleus
Shake off
Shake off
Change of the effektiv nuclear charge
Shake off
Second electron is in its eigenstate Only single ionization occurs
Shake off
Second electron is NOT in its eigenstate Shake off
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
90°
(e,2e) like collision between the two electrons
Photon energy above the threshold [eV]
TS1
Shake off
Shake off + TS1
Ratio of double to single ionization (theory)
%
with electric field
COLTRIMS
with electric + magnetic field
COLTRIMS
Collecting electrons up to 60 eV with 4 solid angle with a combination
of an electric and a magnetic field
Questions
• Is the assumption of a two-step model
valid?
• Energy sharing
• Asymmetry parameter
• Mechanisms of photo double ionization
• Angular distributions
Energy sharing
Extreme asymmetric energy sharing
CCC-Calculation A. Kheifets, I. Bray
Asymmetry parameter
Fast electron absorbs photon energy and its angular momentum
Polynomial fit
Asymmetry parameter
Two-step model is valid
Polynomial fit
Shake off TS1
CCC-Calculation CCC-Calculation
Very slow electrons: 2 eV
Angular distributions
Faster electrons: 30 eV
The fast electron (indicated by the red arrow) is fixed into the direction of the polarization
fast electron (420 eV)
fast electron (448 eV)
s
low
er e
lect
ron
(2 e
V)
s
low
er e
lect
ron
(30
eV)
TDCS for Eslow = 2 eV and 30 eV
fast- slow =180
fast- slow =90
fast electron (420 eV)
fast electron (448 eV)
s
low
er e
lect
ron
(2 e
V)
s
low
er e
lect
ron
(30
eV)
Shake off and TS1 can be seen for all angles
fast electron (420 eV)
fast electron (448 eV)
s
low
er e
lect
ron
(2 e
V)
s
low
er e
lect
ron
(30
eV)
Comparison between experiment and theory
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
Reinhard Dörner Horst Schmidt-BöckingAlexandra KnappThorsten WeberSven SchößlerTill JahnkeJürgen Nickles Susanne KammerOttmar JagutzkiLothar Schmidt
C. Lewis CockeTimur Osipov
Michael H. PriorJürgen Rösch
Allen Landers
Anatoli Kheifets
Igor Bray
University Frankfurt:
Kansas State University:
LBNL:
Western Michigan University:
Australian National University Canberra:
Murdock University Perth:
Supported by BMBF, DFG and DOE