F. Melchert

Crossed‐beams arrangement for the investigation of charge‐changing collisions between multiply charged ions

A crossed‐beams experiment designed to study charge‐changing collisions between singly charged ions has been modified to extend its applicability to collisions between multiply charged ions in a broader range of collision energies. Computer simulations of the beam transport system and the new electrostatic analyzing units are presented. The ion‐optical predictions are tested experimentally. A data acquisition system that allows measurements of angular differential cross sections in ion–ion collisions is described.

Single- and double-electron detachment in collisions of two negative hydrogen ions

Employing the crossed-beams technique in conjunction with a beam-pulsing method, we have measured absolute cross sections sigma tot for the process H-+H- to H0+... for CM energies between 2.5 and 100 keV. Combining the present results with our previously measured cross sections for double-electron detachment ( sigma 00) and triple-electron detachment ( sigma 0+). We obtain cross sections sigma 0- for the single-electron detachment process from the relation sigma 0-= sigma tot- sigma 00- sigma 0+ The experimental data of singleand double-electron detachment are well described by theoretical results based on the non-stationary tunnelling approach. Both cross sections are calculated for CM energies between 0.15 and 300 keV. A new two-electron simultaneous transition mechanism is introduced. The importance of this process for the theoretical assessment of the experimental results is discussed.

Charge transfer in collisions

By means of a crossed-beams technique we have measured absolute cross sections for the charge-transfer reaction by coincident detection of the product ions and for CM energies between 4 and 200 keV. Estimates of angular differential cross sections are made from measured scattering distributions of reaction products at CM energies of 5.15 and 15.86 keV. The total cross sections for charge transfer are calculated by close coupling of a two-centre atomic basis.

Measurements of resonant charge transfer in He2+-He+ collisions

An intersecting beam technique has been used to measure total cross sections for resonant charge transfer in 3He2+-4He+ collisions at barycentric energies between 4 and 200 keV. Our measurements, obtained using coincident detection of the reaction products, are in good agreement with theoretical predictions. Furthermore, they confirm a scaling law by Reinhold and Falcon (1988) for symmetric resonant charge transfer in one-electron systems at intermediate energies.

Total and differential charge transfer cross sections in He2+ N4+ collisions

Charge transfer in the collision system He2+ + N4+ has been investigated both theoretically and experimentally for centre-of-mass energies between 8 and 200 keV. The theoretical calculations of the collision process have been carried out in the semi-classical impact parameter eikonal approach expanding the electronic wavefunction in a multi-state molecular-orbital basis with translation factors. The measurements of the charge-transfer cross sections were performed at an ion-ion crossed-beams experiment. Good agreement between the calculations and the experimental results for both total and differential cross sections is obtained.

Quasi-resonant charge exchange between carbon and boron ions

Quasi-resonant charge-exchange reaction C2++B+ to C++B2+ by coincident detection of the product ions C+ and B2+ for CM-energies between 1.3 and 160 keV. The reverse reaction was also investigated in the energy range between 2.5 and 80 keV: B2++C+ to B++C2+. The theoretical treatment is based on the correlation diagrams for the system (CB)3+ and shows that distinct channels are responsible for the direct and inverse reactions. The results of calculations are in good agreement with me experimental data.