Embed Size (px)
Citation preview
Raimund FeifelUppsala University/Stockholm University
http://usxs.fysik.uu.se/projectweb/portalproject/MEICSAM.html
A double time-of-flight multi-electron-ion coincidence spectroscopy technique
In memory of Fabian Österdahl
Historical overview
Historical overview
Photoionisation
Photoelectric law, A. Einstein 1905: h = Ekin+ EB
IP
=
Photoelectron spectroscopy
+
-
h
A
e - (E kin )
FÖRE EFTER
A+
h + EA → EA+ + EkinEkin = h - EB
Before
After
Kai Siegbahn et al., Uppsala University
Photoelectron spectroscopy today
Bl I411 @ MAX-lab, Lund, Sweden
Photoelectron spectrum of Argon
Electron binding energy (eV)18 17 16 15 14 13
Inte
nsity
Ar
3p
2P3/22P1/2 Spin-orbit
components
Dept. of Physics, course laboratory spectrometer
Intensity ratio 2 : 4
Ar+ - one electron lessElectron 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
Double (multiple) ionisation energy (DIP, …)
EB1 + EB2 (+ …) = h - Ekin1 - Ekin2 (- …)
TOF-PEPECO spectroscopy
J.H.D. Eland et al., Phys. Rev. Lett. 90, 053003, 2003
e-
e-
e-
e-
several m
€
t =D
EKin
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-thumbLowest
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
€
DIPlow ≈ 2.7 ⋅ IPlow
*PhysicsHandbook
empirically To appear in Kosmos 2007
Rule-of-thumb for molecules
€
DIPlow ≈ 2.0 ⋅ IPlow +11.5 ⋅1
r12empirically 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 Xe2+ states
Xe+ intermediate states
A polyatomic example: SF6
Electron distribution of SF6
2+
Differently selected SF62+
spectra
‘complete’ e- e- spectrum
E1: 0 - 1 eV @ 38 eV
E1: 0 - 0.1 eV @ 38 eV; akin “TPEsCO”
Slice of 2 eV @ 38 eV; “direct” SF62+
R. Feifel, J.H.D. Eland, L. Storchi and F. Tarantelli, J. Chem. Phys. 122, 144309, 2005
Double ionisation energy (eV)
560 570 580 590 600
Core valence double ionisation of O2
E. Andersson, M. Stenrup et al. , in preparation
TOF-PEPEPIPICO spectroscopy
e-
e-
e-
e-
i++
i++
i+
i+
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%
2 m
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
AcknowledgmentsStockholm:•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 PfeifferOxford:
•John H.D. Eland
Swedish Research Council (VR), Göran Gustafsson (UU/KTH),
Knut & Alice Wallenberg and Wenner Gren Foundations
