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Raimund Feifel Uppsala University/Stockholm University (raimund.feifel@fysik.uu.se) PowerPoint Presentation
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Raimund Feifel Uppsala University/Stockholm University (raimund.feifel@fysik.uu.se) - PowerPoint PPT Presentation

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  1. A double time-of-flight multi-electron-ion coincidence spectroscopy technique Raimund Feifel Uppsala University/Stockholm University (raimund.feifel@fysik.uu.se) http://usxs.fysik.uu.se/projectweb/portalproject/MEICSAM.html

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

  7. Photoelectron spectroscopy today Bl I411 @ MAX-lab, Lund, Sweden

  8. Photoelectron spectrum of Argon 3p Ar Intensity ratio 2 : 4 2P1/2 2P3/2 Spin-orbit components Intensity 15 14 16 13 17 18 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. e- e- e- e- TOF-PEPECO spectroscopy several m J.H.D. Eland et al., Phys. Rev. Lett. 90, 053003, 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 *Physics Handbook To appear in Kosmos 2007 empirically

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

  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 eV @ 38 eV; “direct” SF62+ E1: 0 - 0.1 eV @ 38 eV; akin “TPEsCO” E1: 0 - 1 eV @ 38 eV ‘complete’ e- e- spectrum R. Feifel, J.H.D. Eland, L. Storchi and F. Tarantelli, J. Chem. Phys. 122, 144309, 2005

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

  30. e- e- i+ i++ i++ i+ e- e- 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. 327 85 (2006) R. Feifel et al., J. Chem. Phys. 125, 194318 (2006)

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

  32. Breakdown diagrams

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

  34. 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

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