vuv photofragmentation pathways of cooled heh … · ion source experimental station at fel focus...

Ion source

Experimental stationat FEL focus

Ion trap

FLASHmonochromatorbeamline

Fragmentdetectors

VUV PHOTOFRAGMENTATION PATHWAYS OF COOLED HeH+ STUDIED AT FLASH

The TIFF experiment [3,4] – Trapped Ion Fragmentation at FLASH [1,2]

H. B. Pedersen1, L. Lammich1, B. Jordon-Thaden2, C. Domesle2, O. Heber3, J. Ullrich2, R. Treusch4, N. Guerassimova4, and A. Wolf2

HeH+ XUV photodissociation

1Department of Physics and Astronomy, Aarhus University, Denmark, 2Max-Planck-Institut für Kernphysik, Heidelberg, Germany , 3Dept. of Particle Physics, Weizmann Institute of Science, Rehovot, Israel, 4HASYLAB, DESY at Hamburg, Germany.

Ionsource

Quadrupole deflector

Separatormagnet

Focusing& steering

Ion beam preparation

4.2 kV

Diagnostics & collimation

DET 1

DET 2

FLASH beam

FLASH dump

Trapping and pulsing

Ion dumpFragmentdetection

Interactionregions

Key features

Photofragmentation of fast mass-selected, gas-phase molecular ions

Fast ion beam

• target preparation

• universal acces to all fragments, including neutrals

Ion trapping

• preparation/characterization of initial state

Momentum imaging

• Kinematically complete analysis of fragments -determining m/q, energy and emission angle

• Identification of electron proceses - electron spectrometry under development.

• Reaction microscope

Ion pulses

He

DET 2

DET 1

H+

Ion dump

FLASH pulses

Interaction regionElectrodes for biasing,deflection, trapping

Detection systemTime- and position sensitive,coincidence detection

HeH+ is a fundamental system

• Non-adiabatic interactions

• Astrophysics

• Neutrino mass measurements

• Ionic analog of H2

– e.g. dissociation in strong laser fields

XUV photodissociation of HeH+

• Dominating reaction channels ?He + H+ or He+ + H

• Dominating absorption states ?- versus -

• Dominating fragment states ?H(nl), He(1snl) – which n ?

• Importance of vibrational excitation ?

HeH+ + 32 nm

He+(1s) + H(nl)

[HeH+(/)]*

He(1snl) + H+

p

p

References

[1] W. Ackermann et al., Nature Photonics 1, 336 (2007)

[2] K. Tiedtke et al., New J. Phys. 11, 023029 (2009)

[3] H. B. Pedersen et al. , Phys. Rev. Lett. 98, 223202 (2007)

[4] H. B. Pedersen et al., Phys. Rev. A 80, 012707 (2009)

[5] H. B. Pedersen et al., Phys. Rev A 82, 023415 (2010)

[6] I. Dumitriu and A. Saenz, J. Phys. B 42, 165101 (2009)

[7] K. Sodoga et al., Phys. Rev. A 80, 033417 (2009)

Absorption states Angular distributions

HOT ions COLD ions (v=0) Theory [6]

He + H+ : - 30 2 % - 24 6 % ~ 30 %

- 70 2 % - 76 6 % ~ 70 %

He+ + H : - 38 3 % - 50 3 % ~ 15 %

- 62 1 % - 50 5 % ~ 85 %

Summary of results on HeH+ + 32 nm [5]

Reactions channels Imaging with biased interaction region

HOT ions COLD ions (v=0) Theory [6]

0.96 0.11 1.70 0.48 ~ 1.6

Final states - fragment excitation Final kinetic energy

HOT ions COLD ions (v=0) Theory

He(1snl) + H+ : n > 3 - 4 n > 3 - 4 ?

He+ + H(nl) : n > 3 - 4 n > 3 - 4 ?

He+ + H----------He + H+

Experimental results [5]

Imaging with a biased interaction region

He+ + H(nl)

Imaging with coincidence detection

He(1snl) + H+

Vibrationally hot and cold ions [5]