Transcript PowerPoint-presentation

A double time-of-flight multi-electron-ion
coincidence spectroscopy technique
Raimund Feifel
Uppsala University/Stockholm University
([email protected])
http://usxs.fysik.uu.se/projectweb/portalproject/MEICSAM.html
In memory of Fabian Österdahl
Historical overview
Historical overview
Photoionisation
Photoelectric law, A. Einstein 1905: h = Ekin+ EB
IP
Photoelectron spectroscopy
h
After
EFTER
Before
FÖRE
A
A+
e - (E k in )
h -+EEBA  EA+ + Ekin
Ekin = h
+
Kai Siegbahn et al., Uppsala University
Photoelectron spectroscopy today
Bl I411 @ MAX-lab, Lund, Sweden
Photoelectron spectrum of Argon
3p
Ar
Intensity ratio 2 : 4
2P
3/2
Spin-orbit
components
Intensity
2P
1/2
18 17 16 15 14 13
Electron binding energy (eV)
Dept. of Physics, course laboratory spectrometer
Ar+ - one electron less
Electron configuration
1s2 2s2 2p6 3s2 3p5 (2P3/2, 2P1/2) Ar+
MJ = - J, -J+1, …, J-1, J
Photoexcitation and ionisation
processes
Deexcitation processes
Single photon - multiple ionisation
EB1 + EB2 (+ …) = h - Ekin1 - Ekin2 (- …)
Double (multiple) ionisation energy (DIP, …)
TOF-PEPECO spectroscopy
e- ee- e-
several m
t
D
E Kin

J.H.D. Eland et al., Phys. Rev. Lett.
90, 053003, 2003
TOF-PEPECO instrument…
World’s longest electron time-of-flight spectrometer
… now operational at AlbaNova…
… and it’s ‘little brother’
Timing principle
Single photon - double ionisation
of Argon (h = 48.372 eV)
deadtime ~ 50 ns
Double ionisation spectrum of Ar
Electron configuration:
1s2 2s2 2p6 3s2 3p4 (3P2,1,0, 1D2, 1S0) Ar2+
Ar2+, Kr2+ and Xe2+
Rule-of-thumb
Lowest
DIP
(eV)
Lowest
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
empirically
DIPlow  2.7  IPlow
To appear in
Kosmos 2007
Rule-of-thumb for molecules
empirically
DIPlow  2.0  IPlow  11.5 
1
r12
R.D. Molloy et al., Chem. Phys. 335, 49 (2007)
P. Linusson et al., in manuscript 2008
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)
Formation of
2+
Xe
states
+
Xe
intermediate states
A polyatomic example: SF6
Electron distribution of SF62+
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
Core valence double ionisation of O2
560
570
580
590
Double ionisation energy (eV)
600
E. Andersson, M. Stenrup et al. , in preparation
TOF-PEPEPIPICO spectroscopy
i+
i++
i++
i+
e- ee- e-
2m
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)
Mass selected TOF-PEPECO spectra of CS2
Collection efficiencies for ions
taken into account
Threshold for CS+ + S+ formation ~ 29.3
eV
Breakdown diagrams
Two-dimensional mass spectra, e.g. CS+ + S+
KER as function of dication internal energy
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
Acknowledgments
Stockholm:
•Mats Larsson
•Tony Hansson
•Fabian Österdahl
•Tomasz Kloda
•Isak Bakken
•Mohamed Elsakre
•Kjell Schmidt & workshops
•Meryll Colombet
Oxford:
Uppsala:
•Leif Karlsson
•Jan-Erik Rubensson
•Egil Andersson
•Lage Hedin
•Martin Berglund
•Pelle Linusson
•Aila Gengelbach
•Pernilla Andersson
•Tommy Karlsson
•Benedikt Pfeiffer
•John H.D. Eland
Swedish Research Council (VR), Göran Gustafsson (UU/KTH),
Knut & Alice Wallenberg and Wenner Gren Foundations