Electron Rearrangement Dynamics in Dissociating I 2 n Molecules Accessed by Extreme Ultraviolet Pump Probe Experiments

The charge rearrangement in dissociating In 2 molecules is measured as a function of the internuclear distance R using extreme ultraviolet pulses delivered by the free electron laser in Hamburg. Within an extreme ultraviolet pump probe scheme, the first pulse initiates dissociation by multiply ionizing I2, and the delayed probe pulse further ionizes one of the two fragments at a given time, thus triggering charge rearrangement at a well defined R. The electron transfer between the fragments is monitored by analyzing the delay dependent ion kinetic energies and charge states. The experimental results are in very good agreement with predictions of the classical over the barrier model demonstrating its validity in a thus far unexplored quasimolecular regime relevant for free electron laser, plasma, and chemistry application

Recoil-free relativistic (e,2e) collisions

We report here on (e,2e) measurements at relativistic electron energies (up to 500 keV) under 'boundelectron Bethe ridge' conditions. Absolute triple differential cross sections for K-shell ionization of silver (Ebind=25.5 keV) have been measured. Appreciable discrepancies are found with calculations in the relativistic distorted-wave Born approximation whereas results of the Coulomb-Born approximation give better accord with the experimental data. At the highest incident energy (500 keV) the Coulomb-Born approximation is in perfect agreement with the experimental results

Fragmentation of molecules studied with laser-induced Coulomb explosion imaging and femtosecond pump-probe experiments

We report on the experimental realisation of time-resolved coincident Coulomb explosion imaging of H2-fragmentation in 1014 W/cm2 laser fields. Combining a high-resolution 'reaction microscope' and a fs pump-probe setup, we map the motion of wave packets dissociating via one- or two-photon channels, respectively, and observe two region of enhanced ionization in accordance with earlier theoretical predictions. The long-term interferometric stability of our system allows us to extend pump-probe experiments into the region of overlapping pulses, which offers new possibilities for the manipulation of ultrafast molecular fragmentation dynamics

Double Ionization of Helium by Electron-Impact: Complete Pictures of the Four-Body Break-Up Dynamics

The dynamics of He double ionization by 2 keV electron impact is studied experimentally for a momentum transfer of 0.6 a.u. at excess energies of 10 and 40 eV. Complete sets of fivefold differential cross sections are presented for all electron emission angles in coplanar geometry. Contributions beyond the first Born approximation are identified comparing experimental data with first order convergent close-coupling calculations which are in considerably better agreement with the present experiment than with the earlier measurement of Kheifets et al. [J. Phys. B 32, 5047 (1999)]

Double ionization of helium by fast electron impact

We report on a kinematically complete investigation of He double ionization by 3 keV electron impact. A new experimental approach for experiments on electron impact ionization is applied : in a multi-electron recoil-ion coincidence the momentum vectors of the recoiling ion and of two slowly ejected electrons (Eb,c < 20 eV) are determined. The momentum of the fast scattered electron follows from momentum conservation. By examining the double ionization process as a function of the momentum transferred to the target by the scattered projectile different kinematical regimes are separated. For small values of the momentum transfer the angular correlation and the energy partitioning of the slowly ejected electrons exhibit the characteristics of double photoionization. For Bethe ridge kinematics signatures of the TS 1 ionization mechanism are observed