S. Szucs

Experimental-study of the Mutual Neutralization of H+ and H- Between 5-ev and 2000-ev

The cross section for the mutual neutralisation process: H++H- to H+H has been measured over the energy range 5-2000 eV, using merged beams and coincident detection of the products. The results obtained differ significantly from those published by other investigators. In particular, the energy dependence is free of structures and similar to that predicted by theory. The cross section is also in excellent agreement with recent calculations.

Merged-beams study of the charge exchange between He/sup 2+/ ions and highly excited hydrogen atoms

Measurements are reported of the cross section for the non-symmetric charge transfer /sup 3/He/sup 2+/+H* rarr /sup 3 /He/sup +/+H/sup +/ in the relative energy range 0.25 to 478 eV for excited hydrogen atoms with principal quantum numbers /b n/ ranging from 8 to 24. The experimental method involves merged beams and time-correlation analysis of the reaction products. Field ionisation is used to modify and specify the population of the excited states. The results are presented as cross sections sigma (/b n//sub 1/, /b n//sub 2/) averaged over consecutive values of /b n/ ranging from /b n//sub 1/ to /b n //sub 2/, namely sigma (8, 9), sigma (10, 14), sigma (15, 19) and sigma (20, 24). The cross sections are large, up to 10/sup -10/ cm/sup 2/, and appear to be roughly independent of energy below 50 eV.

One-electron charge exchange between and positive multiply charged ions. 1. Collisions

The cross section for one-electron transfer is calculated in this paper. The collisional system is treated as a three-electron one and matrix elements for the formation of excited helium in both singlet and triplet states (1S, , P and , P, D) are obtained. Close-coupling calculations were done for the 27 (1S, , P and , P, D) final states covering the range 1 - of the relative collision velocity. An approximation is used for the effective potential of and Coulomb Greens functions are used to describe the weakly bound electron of . A satisfactory agreement is obtained with the experimental cross section.

Charge exchange in low energy He+-He2+ collisions

Measurements of the absolute cross section for the resonant charge transfer: He++He2+ to He2++He+, over the range 10-1700 eV, using merged beams are reported. The data are presented together with a calculation which takes into account the experimental limits in scattering angle.

Transfer ionization in slow H++H- collisions

The transfer ionization reaction H-a(-) + H-b(+) = H-a(+) + H-b(1s) + e, on which we had previously carried out experiments and calculations, is reconsidered here at higher collision energies and interpreted as ionization of weakly bound electron of the H- ion, accompanied by a simultaneous resonant exchange of the 1s core electron. The ionization of H- is treated as being strongly coupled to the dominant mutual neutralization channels H-a(-) + H-b(+) = H-a (1s) + H-b (nlm), and the cross sections for all relevant reaction channels are calculated by using the molecular-orbital close-coupling scheme.

Improvement of the merged-beam method and its application to the study of the reaction: H-+He+->H+He

It is shown that two parallel ion beams react at a rate that is independent of their density profiles when made to oscillate against each other in a two-dimensional scanning motion. An experimental set-up that makes use of this principle is described. Absolute cross sections obtained in this way are in good agreement with those obtained with the beams merging in the usual (static) mode. Cross sections for single-charge transfer between H-(D-) and He+ in the energy range 5-4000 eV are presented and compared to other existing data.

Transfer ionization in He2+-H- collisions: measurement of the exothermicity and theoretical interpretation

The energy imparted to the ions in the transfer ionization reaction He2+ + H- --> He+ + H+ + e has been measured in a merged beam experiment using two different techniques (magnetic analysis and time of flight). The result obtained in both cases is of the order of 6 eV and confirms that the transfer ionization proceeds in two steps: a single electron transfer at large internuclear separation followed by a resonant Penning ionization at small distances. With this view, a simple calculation of the cross section is presented, with results that are in good agreement with the available experimental data.

Associative ionization in collisions of , with and

Absolute cross sections of the associative ionization in the collision of with or have been measured in a merged beam experiment over a relative velocity interval ranging from 0.4 to . At a given relative velocity, the two cross sections significantly differ at low velocities where the cross section for formation exceeds that of by as much as 35%. The difference, however, decreases with the velocity and falls in the experimental error above . In both cases the energy dependence becomes compatible at low energy with an law.

Transfer ionization in He2+-H- collisions: cross section measurements in the energy range 0.2-1300 eV

This paper reports on measurements of the cross section for transfer ionization in He2+-H- collisions over the barycentric energy range 0.16-1300 eV. The experimental method involves merged beams and coincident detection of the reaction products. The dependence of the cross section on the energy is rather similar to that of the one-electron exchange, suggesting that a two-step mechanism dominates the process.

Associative ionization in collisions of C+ with D−

The absolute cross section of associative ionization in the collision of C+ with D− has been measured in a merged beam experiment for collision energies ranging from 0.01 to 2 eV. The measured cross section is found to be compatible with an E−1 law at low energies and presents a relative maximum between 0.8 and 1 eV.