Electron capture and ionisation in collisions of slow H⁺and He²⁺ions with helium

Abstract

A crossed-beam technique previously developed and used in this laboratory for studies of ionisation and electron capture in H+-He and He2+-He collisions down to 64 keV amu-' and 50 keV amu-l has been adapted to extend measurements down to 9 keV amu-' and 6 keV amu-' respectively. The method, which incorporates time-of-flight spectroscopy together with electron-ion and ion-ion coincidence counting of the collision products, provides high precision cross sections for individual collision channels. Some serious discrepancies are obtained with previous cross sections for single ionisation measured by Afrosimov er a2 and the important role of transfer ionisation at low energies is confirmed. The need for better theoretical descriptions of low-energy ionisation is demonstrated.

Transfer excitation reactions in fast proton-helium collisions

“…Experimentally we can no distinguish between the different excited states; e.g., we sum over all n ≥ 2. The integral of the electron transfer (with and without excitation) has been normalized to that in [58,59]. TE contributes 4%-5% to the total electron transfer cross section, while the CT without any additional excitation amounts to 75%-80% [33].…”

“…Experimental data have been normalized to published total electron transfer cross sections [58,59]. experiment [33].…”

Ab initiocalculation ofH+He+charge-transfer cross sections for plasma physics

“…This process is dominated by the capture into the H(1s) state but later on, the charge transfer excitation and the direct excitation processes have been studied in detail both theoretically and experimentally [7][8][9][10][11][12][13][14][15]. All these reactions require intermediate collision energy which suits perfectly the semi-empirical description of the collision.…”

Superelastic and inelasticHe2++He state-selective electron capture

“…tained in this manner were then put on an absolute scale by normalizing to the total single-capture and transfer ionization data of Shah, McCallion, and Gilbody [8] and Dubois [9]. The results are given in Table I.…”

“…Experimental data from the work of Shah, McCallion, and Gilbody [8], and the work of Dubois [9], exhibit a maximum value of 8 X cm2 at an incident projectile energy near 30 keV/u. Another important process that can occur in collisions of H e nuclei with He is "transfer ionization" (TI):…”