1. Non-local autoionisation processes in homo- and heterogeneous systems
Marko Förstel
Max-Planck-Institute for Plasmaphysics

2. Non-local autoionisation processes in homo- and heterogeneous systems
Introduction
Non-local autoionisation processes in homo- and heterogeneous systems
Interatomic /-molecular Coulombic Decay (ICD)
Electron Transfer Mediated Decay (ETMD)
First transparency:
Before I start I would like to thank the organizers for the invitation. I am very grateful for the possibility to present our research.
11/10/2018

3. Introduction Atom Surrounding Eb (eV) Vacancy
Atom
Surrounding
Eb (eV)
Imagine a vacancy in an atom or molecule. Now we ask how its relaxation modes are changed by the presence of other atoms or molecules. Here we will not consider covalent or ionic bonding. Only weak bonding is considered. We can thus still speak of isolated states.
Vacancy
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4. Intermolecular Coulombic Decay
Introduction
atom e-
Eb (eV)
surrounding e-
energy transfer
We found experimentally that decay channels become possible which involve an energy transfer between two diferent sites
vacancy
Intermolecular Coulombic Decay
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5. Electron transfer mediated decay
Introduction e-
atom
surrounding
Eb (eV) e-
energy transfer
charge transfer
And we even found decay channels which involve a charge transfer.
vacancy
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Electron transfer mediated decay

6. Overview Introduction ETMD vs. ICD The Experiment
ETMD in Ar – Kr clusters
ICD and ETMD in Ar – Xe clusters
ICD after Auger decay in water clusters
Summary, Outlook and Acknowledgements
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7. ETMD vs. ICD
ETMD depends on orbital overlap: exponential distance dependence
ICD benefits from orbital overlap, but does not depend on it: polynomial distance dependence
First calculated results (Ne Ar)
Estimated electronic decay widths and lifetime of the Ne(2s21)Ar inner-valence state as a function of the interatomic distance.
The individual contributions of the two principal decay processes ICD and ETMD to the total decay width are displayed on a logarithmic scale.
Note that the lifetime is inversely proportional to the total decay width.
-> ETMD seems so much more unlikely than ICD. When can it be observed anyway?
Zobeley, Cederbaum et al., JCP 115, 5076 (2001).
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8. ETMD vs. ICD
Decay via charge transfer (ETMD) can compete with decay via energy transfer (ICD) if
Decay via energy transfer is forbidden by selection rules
Sakai, Ueda et al., PRL 106, (2011)
Jahnke et al., PRL 99, (2007).
Charge transfer is needed because at vacancy site there are no electrons
prediction: Müller & Cederbaum, JCP 122, (2005).
Decay via energy transfer is energetically not allowed
Eb (eV) IP e-
IP*
Li+
H2O
There are some cases where etmd is possible while icd is not.
the last example is the one we will discuss in more detail later in this talk…
Li+
H2O
Eb (eV) IP e-
IP*
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9. Experiment Electron – electron coincidence spectroscopy
“Magnetic Bottle“ electron time of flight analyser
Free cluster jet
Supersonic expansion through cooled nozzle
Synchrotron radiation
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10. Experiment “Magnetic Bottle“ electron time of flight analyser
interaction
region
gradient of magnetic
field lines
magnetic tip
solenoid
simulated
electron
trajectories
entrance
aperture
drifttube
vacuum
chamber
MCP -
detector
The important point is that a magnetic guiding field is used to collect the electrons.
Two advantages:
1. Very efficient. We have a good chance to detect both electrons, primary from ionization and secondary from autoionization. (Note: synchrotron radiation is a thin, pulsed high rep rate source. Event rate is much smaller than one/pulse, but rep. rate is over 1 MHz.)
2. Good transmission even for very slow electrons.
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11. Overview Introduction ETMD vs. ICD The Experiment ETMD in Ar – Kr
ICD and ETMD in Ar – Xe cluster
ICD after Auger decay of water clusters
Summary, Outlook and Acknowledgements
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12. ETMD(3) - scheme e- = 2.7 eV hν = 32 eV 15.7 Eb (eV) fluorescence e-3 / 2
15.7
Eb (eV)
Argon 3p 1 / 2 e-
fluorescence
Create valence hole
decay only possible via fluorescence..
DIP (Ar) = 43.4 eV[1]
29.3
Argon 3s
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[1] Holland et al J.Phys.B 12

13. ETMD(3) - scheme e- ~ 3 - 4 eV DIP (Ar2) = 34.5 eV[1]*
hν = 32 eV
DIP (Ar2) = 34.5 eV[1]*
(Ar3) = 36 eV[2] :
(Ar101) = 32 eV[3]
* theoretical 3 /
Argon 3p 3 / 2 1
Argon 3s 2
15.7 e-
fluorescence
Eb (eV)
Argon 3p 1 / 2
Argon bänder mit actual spektren versehen (hergenhahn et al prb 2009)
29.3
Argon 3s
[1] Pernpointer et al J.Chem.Phys. 129
[2] Rühl et al Chem.Phys.Lett. 191
[3] Scheier et al Phys.Rev.Lett. 59
Spectra from:
[1] Hergenhahn et al Phys.Rev.B 79
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14. ETMD(3) - scheme e-1 ~ 3 - 4 eV e-2 DIP (ArKr2) = 29 eV[1]* 14.0 15.7
hν = 32 eV
DIP (ArKr2) = 29 eV[1]*
* theoretical +
D∞h - symmetrie
14.0 3 / 2 3 / 2
e- transfer 3 / 1 / 2 2 1 / 2
15.7
Krypton 4p
Krypton 4p
Eb (eV) 1 / 2
Argon 3p
etmd(3) erwähnen
gleichzeitigkeit der autoionisation erwähnen
notwendigkeit der elektronenkorrelation zwischen den drei partizipienten erwähnen!
27.5
Krypton 4s
Krypton 4s
29.3
Argon 3s
[1] Pernpointer et al J.Chem.Phys. 129
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15. ETMD in mixed Ar-Kr cluster
1.5 bar
118 K
Ar + Kr
20 / 1
Nozzle
100 µm
Skimmer
1 mm
Our target are mixed Argon – Krypton clusters
this is how we make them…!
Supersonic expansion
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16. ETMD in mixed Ar-Kr cluster
Coexpansion:
Krypton core
Argon surface[1]
Size uncertain,
similar expansion
conditions lead to a mean
size of the homogeneous system of [2,3]:
<N>Ar = 1700
Clarke et al. J.chem.phys. Zitieren
wach (pick up)
vorstellung, cluster
[1] Lundwall et al Phys. Rev. A. 74
[2] Hagena et al Z. Phys. D 4
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[3] Karnbach et al Rev. Sci. Instr. 64

17. ETMD in mixed Ar-Kr cluster
this geometry allows for many possibilities that a DinfH symmetry is possible…
black arrows -> distance to close (but maybe even here possible due to shielding effects)
green arrows -> distance long enough…
D∞h – symmetrie !
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18. ETMD in mixed Ar-Kr clusters
Ar 3s monomer
Ar 3s cluster
Ar 3p + Kr 4p cluster + monomer
primary photoionization spectrum
red: electrons which leave a hole that can be filled via ETMD
many very slow electrons where ETMD signal should lie as well. So we cannot identify the etmd signal
 coincident analysis
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19. ETMD produces two electrons:
Coincident analyses
ETMD produces two electrons:
take all two electron events and make map
draw energy of electron one vs energy electron two:
electron pair
-> every time we detect two electrons we record both their kinetic energies and plot these on a map -> ekin (e1) vs. ekin (e2)
->
energy electron two
energy electron one
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20. Results – coincident electron spectrum Ar-Kr cluster
hv = 32 eV
Results – coincident electron spectrum Ar-Kr cluster
energy electron two
say: We have pairs of electrons where one electron is very slow and the second has a binding energy equivalent to the Ar3s cluster band!
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energy electron one

21. Results – coincident electron spectrum Ar cluster and Kr cluster
hv = 32 eV
Results – coincident electron spectrum Ar cluster and Kr cluster
Krypton cluster
Argon cluster
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22. Results – coincident electron spectrum Ar-Kr cluster
hv = 32 eV
Results – coincident electron spectrum Ar-Kr cluster
energy electron two
So we can say that we could show here that etmd occurs…!
ETMD
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energy electron one

23. Overview Introduction ETMD vs. ICD The Experiment ETMD in Ar – Kr
ICD and ETMD in Ar – Xe cluster
ICD after Auger decay in water clusters
Summary, Outlook and Acknowledgements
11/10/2018

24. ETMD vs ICD in mixed Ar-Xe cluster
Argon
Xenon
Eb (eV)
Xe – Ar –Xe
ETMD(3) as in Ar-Kr-Kr [1]
In Ar Xe the case is completely different!
etmd is still possible for the trimer!
but
Vacancy
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[1] Faßhauer et al J. Chem. Phys. 133

25. from 3rd coordination shell on: ICD becomes energetically possible [1]
ETMD vs ICD in mixed Ar-Xe cluster
Ar-Xe Cluster
Xe – Xe – Xe – Xe -Ar
But!
!!!but!!!
with increasing size, ICD may become energetically possible!
both processes compete and may be distinguished or can be used to distinguish the clusters
from 3rd coordination shell on:
ICD becomes energetically possible [1]
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[1] Faßhauer et al J. Chem. Phys. 133

26. ETMD vs ICD in mixed Ar-Xe cluster
.3 – 1.5 bar K
Ar + Xe
20 /
Nozzle
Skimmer
Our target are mixed Argon – Krypton clusters
Supersonic expansion
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27. Results – coincident electron spectrum Ar-Xe cluster
hv = 32 eV
Ar + 3% Xe
0.3 bar
Our target are mixed Argon – Krypton clusters
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28. Results – coincident electron spectrum Ar-Xe cluster
hv = 32 eV
Our target are mixed Argon – Krypton clusters
Ar + 3% Xe 0.3 bar
Ar + 3% Xe 0.5 bar
Ar + 3% Xe 0.7 bar

29. ETMD vs ICD in mixed Ar-Xe cluster
hv = 32 eV
secondary
we always see a signal even for very small clusters -> ETMD
If ICD is starting to happen, its signal should appear at very low energies
we observe a small change at energies of around 1eV
conclusions will follow after a more thorough study of the inner valence spectra of the cluster……..
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30. Overview Introduction ETMD vs. ICD The Experiment ETMD in Ar – Kr
ICD and ETMD in Ar – Xe cluster
ICD after Auger decay in water clusters
Summary, Outlook and Acknowledgements
11/10/2018

31. ICD after Auger decay in water clusters
Initial Auger decay
Eb (eV)
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32. ICD after Auger decay in water clusters
Initial Auger decay
Followed by ICD
Eb (eV)
So far only in rare gas clusters. Appearance in water clusters?
Santra & Cederbaum, PRL 90, (2003)
Morishita, Ueda et al., PRL 96, (2006)
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33. ICD after Auger decay in water clusters
Ionization of water clusters leads to formation of ion cores ('Eigen form' H3O+ or 'Zundel form' H5O2+)
Ion yield always shows protonated clusters
(H2O)N + hn  (H2O)N-1 H+ + OH + eph-
or  (H2O)N-x-1 H+ + (H2O) x + OH + eph-
Water post-ionization dynamics: Formation of ion cores (Zundel or Eigen)
Only protonated fragments observeable
Simulated dynamics
No experimental dynamics so far
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34. site of ionization Furuhama et al.,JCP 124, 164310 (2006).
Water post-ionization dynamics: Formation of ion cores (Zundel or Eigen)
Only protonated fragments observeable
Simulated dynamics
No experimental dynamics so far
(komplexer mechanismus führt zu..:
-> abspaltung von neutralem OH
-> aus diesem grund sieht man in ionisationsspektron von wasserclustern immer das fragment: (H2O)nH+
Furuhama et al.,JCP 124, (2006).
Tachikawa, JPC A 108, 7853 (2004).
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35. Intact H2O+ fragments due to ultrafast dynamics
Inner valence ICD of H2O dimer:
(H2O)2 + hn  H2O H2O+ (2a1-1) + eph-
 H2O + (ov-1) + H2O+ (ov-1) + eICD- + eph-
time (fs) / O-O distance (Å)
Intact water cations due to ultrafast dynamics, e.g. inner valence ICD of water
Observation: Jahnke, Dörner same time as our paper
Simulation: Cederbaum group, see figure (note rotation)
-> bei ICD nachgewiesen: h2o+ wird gebildet.!weil icd schneller ist als die molekulare dynamik! Coulombkräfte nach icd stark -> auseinanderfliegen bevor moleküldynamik
-> also ist H2O+ indikator für ICD in wasserdimer -> auch in clustern?
Vendrell, Cederbaum, ChemPhysChem 11, 1006 (2010).
Jahnke, Dörner, Nature Phys. 6, 139 (2010).
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36. Measure excitation - energy dependent ion yield
! New Experiment
Measure excitation - energy dependent ion yield
of water clusters
DIFFERENT EXPERIMENT!
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37. Water cluster partial ion yield
!!! New experiment:
Water cluster partial ion yield
In this experiment very small clusters
monomer data: Piancastelli,Becker, et al. PRA 59, 300

38. Water cluster partial ion yield
Appearance of intact water cations in ion yield only in cluster spectra  Ultrafast decay mechanism
Interpretation: 1. Auger decay, 2. ICD
Alternative: ¿ Non-local Auger decay ?
Experiment on partial ion yield of water clusters below O K edge
Below K edge level of intact water cations from valence ionization
Water cation signal above K edge higher for clusters
Ion-ion coincidence spectra: Only (H2O)1H+ in coincidence with H2O+ (cannot detect H2O+ + H2O+ though)

39. Summary Non-local autoionization mediated by electran transfer ETMD(3)
Indication of cooccurence of ICD and ETMD in Ar-Xe clusters
Ion yield spectra show evidence for ICD after Auger decay of water clusters
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40. Outlook ICD / ETMD in solvent systems time domain experiments
relevance for radiation damage
Reviews on ICD:
U. Hergenhahn, J. Electron Spectrosc. Relat. Phenom. 184, 78 (2011).
V. Averbukh et al., J. Electron Spectrosc. Relat. Phenom. 183, 36 (2011).
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41. Acknowledgements Our current group: Former group members:
Tiberiu Arion, Hans-Peter Rust, Martin Stier, Alex Bradshaw
Uwe Hergenhahn
Former group members:
Melanie Mucke, Silko Barth, Toralf Lischke, Volker Ulrich, Sanjeev Joshi, Simon Marburger
Collaboration
Lenz Cederbaum and his group (theory), Axel Reinköster & Uwe Becker (ion yield)
Funding
ASG of the Max-Planck-Society, Euratom Association
- ASG paid for me… -