1. A double time-of-flight multi-electron-ion coincidence spectroscopy technique
Raimund Feifel
Uppsala University/Stockholm University

2. In memory of Fabian Österdahl

3. Historical overview

4. Historical overview

5. Photoionisation Photoelectric law, A. Einstein 1905: h = Ekin+ EB =IP

6. Photoelectron spectroscopy
Before
After
Ekin = h - EB
Kai Siegbahn et al., Uppsala University

7. Photoelectron spectroscopy today
Bl MAX-lab, Lund, Sweden

8. Photoelectron spectrum of Argon
Intensity ratio 2 : 4
2P1/2
2P3/2
Spin-orbit components
Intensity 18 17 16 15 14 13
Electron binding energy (eV)
Dept. of Physics, course laboratory spectrometer

9. Ar+ - one electron less Electron configuration
1s2 2s2 2p6 3s2 3p5 (2P3/2, 2P1/2) Ar+
MJ = - J, -J+1, …, J-1, J

10. Photoexcitation and ionisation processes

11. Deexcitation processes

12. Single photon - multiple ionisation
EB1 + EB2 (+ …) = h - Ekin1 - Ekin2 (- …)
Double (multiple) ionisation energy (DIP, …)

13. TOF-PEPECO spectroscopy
several m
J.H.D. Eland et al., Phys. Rev. Lett. 90, , 2003

14. TOF-PEPECO instrument…
World’s longest electron time-of-flight spectrometer

15. … now operational at AlbaNova…

16. … and it’s ‘little brother’

17. Timing principle

18. Single photon - double ionisation of Argon (h = 48.372 eV)
deadtime ~ 50 ns

19. Double ionisation spectrum of Ar
Electron configuration:
1s2 2s2 2p6 3s2 3p4 (3P2,1,0, 1D2, 1S0) Ar2+

20. Ar2+, Kr2+ and Xe2+

21. Rule-of-thumb empirically Lowest DIP (eV) IP (eV)* Ratio DIP/IP Ar
43.39
15.76
2.75 Kr
38.36
14.00
2.74 Xe
33.11
12.13
2.73
*Physics
Handbook
To appear in
Kosmos 2007
empirically

22. Rule-of-thumb for molecules
empirically
R.D. Molloy et al., Chem. Phys. 335, 49 (2007)
P. Linusson et al., in manuscript 2008

23. Possible double ionisation processes
A + h  A2+ + 2e-
(direct double ionisation; continuous energy sharing)
A + h  A+* + 1e-  A2+ + 1e- (indirect double ionisation involving discrete intermediate states)

24. Formation of Xe2+ states

25. Xe+ intermediate states

26. A polyatomic example: SF6

27. Electron distribution of SF62+

28. Differently selected SF62+ spectra
Slice of 2 38 eV; “direct” SF62+
E1: eV; akin “TPEsCO”
E1: eV
‘complete’ e- e- spectrum
R. Feifel, J.H.D. Eland, L. Storchi and F. Tarantelli, J. Chem. Phys. 122, , 2005

30. Core valence double ionisation of O2
560
570
580
590
600
Double ionisation energy (eV)
E. Andersson, M. Stenrup et al. , in preparation

31. TOF-PEPEPIPICO spectroscopy
2 m
Simultaneously possible to conduct:
1) Electron-ion coincidence (PEPICO)
2) Electron-ion-ion coincidence (PEPIPICO)
3) Electron-electron coincidence (PEPECO)
4) Electron-electron-ion coincidence (PEPEPICO)
5) Electron-electron-ion-ion coincidence (PEPEPIPICO)
… “PE(n)PI(m)CO experiment”; n, m = 0, 1, 2…
fe ~ 40%
fi ~ 10%
J.H.D Eland and R. Feifel Chem. Phys (2006)
R. Feifel et al., J. Chem. Phys. 125, (2006)

32. Mass selected TOF-PEPECO spectra of CS2
Collection efficiencies for ions
taken into account
Threshold for CS+ + S+ formation ~ 29.3 eV

33. Breakdown diagrams

34. Two-dimensional mass spectra, e.g. CS+ + S+
KER as function of dication internal energy

35. Summary: Time-Of-Flight PhotoElectron-PhotoElectron
COincidence spectroscopy reveals electronic states of doubly-ionised systems in direct analogy to PES
Rules-of-thumb for double ionisation
Direct vs. indirect double ionisation mechanisms
TOF-PEnPImCO spectroscopy

36. Acknowledgments Uppsala: Stockholm: Oxford: Leif Karlsson Mats Larsson
Tony Hansson
Fabian Österdahl
Tomasz Kloda
Isak Bakken
Mohamed Elsakre
Kjell Schmidt & workshops
Meryll Colombet
Uppsala:
Leif Karlsson
Jan-Erik Rubensson
Egil Andersson
Lage Hedin
Martin Berglund
Pelle Linusson
Aila Gengelbach
Pernilla Andersson
Tommy Karlsson
Benedikt Pfeiffer
Oxford:
John H.D. Eland
Swedish Research Council (VR), Göran Gustafsson (UU/KTH),
Knut & Alice Wallenberg and Wenner Gren Foundations