Electron transfer in fast ion-atom collisions

Electron transfer is defined as the transfer of electrons from the target to the colliding projectile. If the projectile speed is low compared to the speed of the bound electrons in the target, the electrons have sufficient time to arrange themselves according to the changing positions of the nuclei. We study fast collisions, where the speed of the projectile is much higher than the speed of the elecrons. In these collisions the probability to transfer an electron from the target to the projectile is extremely low, as the active electron has to undergo a large momentum and energy change within the short collision time. The cross section can be as small as 10-27cm². That makes the investigation of these processes extremely difficult.

The CRYRING facility at MSL (left figure) and the gas-jet target (right fig.)

With the CRYRING facility at the Manne Siegbahn Laboratory we have access to unique experimental conditions where the high beam currents make the study of these processes feasible. In combination with a COLTRIMS setup at the internal gas-jet target we can study fast electron transfer collisions with high luminosity and with high resolution.

The investigation of the final momentum space and the projectile scattering angle provides a fundamental and detailed insight into the dynamics of these collisions, and even different electron transfer mechanisms can be separated. In addition, these experiments provide a sensitive test of different theoretical modells.

The reactions, we are focussing on, are:

Single electron capture in ion-atom collisions
Transfer-ionization in proton-helium collisions, i.e. one target electron is transfered to the projectile whereas another one is ejected to the continuum
Young-slit type of experiment in fast proton-H2 collisions where the two nuclei of the H2-molecules serve as the double slit


How COLTRIMS works:

COLTRIMS (COLd Target Recoil Ion Momentum Spectroscopy) is an imaging technique to measure the fragmentation of a few body system. The ionized target fragments from an atomic or molecular collision are projected by an electric field onto a position sensitive detector. From the measured time-of-flight of the particles and their position of impact on the detector the three dimensional momentum vector is obtained. Cooling of the the target atoms before the fragmentation by supersonic expansion makes a high momentum resolution achievable.



PhD-Thesis, Kristian Støchkel (2005):

    Electron-transfer processes in fast ion-atom collisions
Postal Address: AlbaNova University Center, 106 91 Stockholm, Sweden
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