W. Schmitt

Cold Target Recoil Ion Momentum Spectroscopy

The experimental technique of Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) is described. It allows a three dimensional imaging of momentum space of the recoiling ion for all ionizing atomic reaction with 4π solid angle for momentum measurement. The resolution presently achieved is ±0.035 a.u.. Depending on the collision system this corresponds to a resolution in projectile energy loss of down to ΔE/E=10−9 and a scattering angle resolution of down to 10−9 rad for fast heavy ion collisions. We discuss the experimental technique and some recent results on dynamics of recoil ion production for electron capture, target ionization and projectile electron loss.

DIFFERENTIAL PROJECTILE ENERGY LOSS IN MULTIPLY IONIZING COLLISIONS

The momentum vectors of the recoil ion and up to three electrons were measured in coincidence with the projectiles which did not change charge state for 3.6 MeV amu-1 Au53+ Ne collisions. New techniques were applied to obtain differential energy-loss spectra for multiple-target ionization as a function of the recoil-ion charge state. A resolution unprecedented for this energy regime was achieved. The data are in good agreement with a classical trajectory Monte Carlo calculation. Our studies represent a first step for a method of modelling stopping powers on a microscopic level and are relevant for plasma applications.

Double ionization of helium in fast ion collisions: the role of momentum transfer

Double ionization of helium in the perturbative regime has been explored in a kinematically complete collision experiment using 100 MeV/u C 6+ ions. Different ionization mechanisms are identified by inspecting the angular distribution of the electrons as a function of the momentum transfer q to the target by the projectile. For q 1 :2 au, the faster electron resulting from a binary encounter with the projectile is emitted along the direction of momentum transfer, while the other electron is distributed uniformly. Experimental data are compared with various model calculations based on the Bethe-Born approximation with shake-off. Surprisingly, the effect of the final state interaction is found to depend decisively on the choice of the initial state wavefunction.

Recoil Ion Momentum Spectroscopy Momentum Space Images of Atomic Reactions

Recoil-ion momentum spectroscopy is a powerful tool for investigating the dynamics of ion, electron or photon impact reactions with atoms or molecules. It allows to measure the three-dimensional momentum vector of the ion from those reactions with high resolution and 4 π solid angle. In many cases already the recoil-ion momentum distribution alone unveils directly the physical processes dominating the reaction. The most detailed information, however is gained by combining the recoil-ion momentum measurement with the coincident detection of momentum vector of one or more emitted electrons or a measurement of the momentum exchange of the projectile. By such many particle momentum imaging one obtains a fully differential cross section of the reaction, i.e. for each registered event one measures the momenta of all particles and the full final state momentum space is covered in one experiment. Thus the experiment yields the square of the final state wave function of the reaction in momentum space. Such multidimensional data arrays can be sorted in many different ways after the actual experiment. Examples for ion impact ionization are discussed.

Recoil-ion momentum spectroscopy: Ionization in ion-atom collisions

The rapid development in the field of recoil-ion momentum spectroscopy now allows one to perform complete momentum experiments of all the reaction products for single target ionization. This experimental technique can address distinct features characterizing ionization processes in ion-atom collisions and can serve as a most stringent test for theory. The quantum mechanical models used most commonly in the description of ion-atom ionization will be discussed. In particular we will survey some new theoretical results which will illustrate the suitability of the continuum-distorted-wave (CDW) and continuum-distorted-wave eikonal-initial-state (CDW-EIS) models for both high and low Z projectiles in fast ion-atom collisions. The influence of the post collision interaction (PCI) effects in these collisions will also examined.