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Photo double ionization of H 2 resp. of D 2 or the correlated motion of electrons in a two center coulomb potential Fragmentation of molecules: Franck-Condon.

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Presentation on theme: "Photo double ionization of H 2 resp. of D 2 or the correlated motion of electrons in a two center coulomb potential Fragmentation of molecules: Franck-Condon."— Presentation transcript:

1 Photo double ionization of H 2 resp. of D 2 or the correlated motion of electrons in a two center coulomb potential Fragmentation of molecules: Franck-Condon model Experimental technique: Imaging of the momentum space Dynamics of the electrons in a single and a two center potential  …if time permits: One more goody at the end ;-)

2 Co-workers & friends: FRANKFURT: Th. Weber R. Dörner V. Mergel A. Czasch O. Jagutzki M. Weckenbrock M. Hattaß H. Schmidt-Böcking KANSAS: L. Cocke T. Ossipov BERKELEY: M. Prior FREIBURG: M. Walter J. Briggs MICHIGAN: A. Landers

3 ... motivation - problem - principal task... e1e1 H+H+ H+H+ e2e2 80 eV h + H 2 2 e H + Interaction / correlation

4 Emission of two electrons from a single- and a double center - coulomb potential HELIUMHYDROGEN MOLECULE Fixed in space molecular axis breaks symmetry >> ALIGNMENT <<   

5 Franck-Condon model: … the energy levels in the molecule (static) photon energy binding energy excess ion energy fragmentationkin. energy of the nuclei

6 how to describe a simple molecule ?... the pro’s and contra’s and the limitations... Heitler - London solution of SE with sym. wave functions (including the spin) consideration of all exchanges/interactions establishment of a stabile H 2 possible (error in binding energy = 1.4 eV) description of wave function only very roughly Linear Combination of Atomic Orbitals (LCAO) description of two electrons in the field of a H 2 + ion molecular orbital: Linear combination of atomic wave functions good prediction of the electronic probability distribution in the molecule error in binding energy is bigger than in H - L model Born - Oppenheimer separation of the electronic motion and the motion of the nuclei adiabatic modulation of the electrons simplified calculations; nuclei momenta set up along molecular axis open question: How do these systems interact or couple...?

7 The “strange” nature of the molecule/atom … which effects play an important role ? Electron emission for “equal energy-sharing” Coulomb repulsion favorites “back-to-back emission” selection rules:...electrons are fermions...  complete wave function is antisymmetric rule of Hundt: Spin is antisym.  r-/k-space has to be sym. e1e1 e2e2 e1e1 e2e2

8 …more effects (interactions): coupling of the electrons to the binding system HELIUM Atom: The electronic two body systems vibrates with respect to the nucleus HYDROGEN MOELCULE Born-Oppenheimer: The electrons move in respect to the CM- system of the nuclei Reality: A complex 4 body system vibrates in a correlated state CM

9 The COLTRIMS - setup … an imaging-system also for molecular fragmentation ?! recoil-ion detector electron-detector electric fieldmagnetic field

10 ...more features: pulsed extraction for the recoil-ions: electron double hit recoil-ion double hit 60 V/cm 3 V/cm 4  solid angle Magnetic field to guide the electrons electrons up to 100 eV (for 10 Gauss) Time of Flight and 2dim position 3dim momentum vector High resolution for 0 eV < 10 meV electronic energy

11 Characteristics of the experiment … more facts : Target = Deuterium (instead of Hydrogen) eV ( eV for D 2 ) dissociation energy eV = 18.8 eV energy of the Coulomb explosion  24.5 eV kin. sum energy of the electrons Projectiles = Photons 75 eV energy of the photons linear polarized (99.5 %) Imaging system multi hit pulsed recoil-ion extraction data acquisition in “list mode” two 80 mm MCP-detectors with delay line anode experiment at the ALS powered by :

12 The new detector: … multihit rulez …!? HITEC powered by AOC & ROENTDEK  t < 5ns  t < 8ns  t < 100ns  t < 10ns Hexanode: DL80anode: 5200 lines computer code

13 Coordinates/systems of reference … where does the action takes place ? laboratory frame internal scattering plane 2 1 2

14 Energy distribution: … the kin. energy of the fragments after the photon absorption balance:

15 Detection of the molecular fragments: … An image of the Coulomb explosion The pulsed recoil-ion spectrometer …. and its consequences: 50.4 a.u.

16 Kin. energy of the electrons in the final state: … which role does the molecule play …? H2H2 e1e1 e2e2 Interference effect: First maximum ? e1e1 

17 Momentum distribution of the electrons : A comparison... HELIUM HYDROGEN MOLECULE

18 Helium Hydrogen molecule  He/H 2

19 H2H2 e1e1 Hydrogen molecule more details

20 Azimuthal angle of the electrons:... the  - parameter P.S.: valid near photo double ionization threshold  as a function of the alignment of the molecule ?! HeliumHydrogen molecule

21 And how about the recoil ions…? H. Kossmann & V. Schmidt PRL (1989), 63, p  = Let’s compare with the literature:

22 Distribution of the polar angles... do we see correlated electron emission ? 1. The Helium-atom equal energy sharing E 1 = E 2

23 unequal energy sharing e 1 fast e1e1 sl ow

24 … let’s switch to the hydrogen-molecule equal energy sharing  H2H2 all orientations

25 … just to get an overview : animated Triple Differential Cross Sections (TDCS) Hydrogen molecule equal energy sharing

26 Helium atom and hydrogen molecule … a comparison of both systems:  H2H2 equal energy sharing Helium Hydrogen molecule all orientations

27 … more movies : How does the distribution depend on the molecular orientation ? Hydrogen molecule equal energy sharing

28 unequal energy sharing e 1 = fast Hydrogen molecule :  H2H2 all orientations

29 … let’s get a more detailed insight Influence of the molecular orientation: H2H2 e1e1 equal energy sharing

30 unequal energy sharing H2H2 e 1 fast e 1 slow

31 TRANSFER OF ANGULAR MOMENTUM: Coupling of the electrons to the molecule ?!...which orientation is relevant ? H2H2 e1e1 H2H2 e2e2 e 1+2 No angular mo- mentum transfer e1e1 equal energy sharing

32 Let’s probe the molecule: …molecules illuminated from within... equal energy sharing Hydrogen molecule electron-electron interaction

33 … go even deeper : let’s scan the coulomb explosion ! Hydrogen molecule equal energy sharing

34 … summary and future prospect What is still to do ? What comes next...? …goody …Future: more D 2 : What’s going on with circular polarized light ? new experiment with HD (angular momentum transfer)/ ALS (Berkeley) simple molecules in strong laser-fields/ Roskos (FFM)/ Corkum (Canada) COLTRIMS: An imaging-system for molecules pulsed extraction multi hit capable detectors 4  solid angle snapshots of Experimental results Energy-sharing depends on the orientation of the molecule !? Final state of the electrons in momentum space Highly differential cross sections as a function of the molecular orientation finish line

35 ...goody…: “Alignment” even in atoms ?! linear polarized circular polarized Helium  


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