Ionisation and electron capture in collisions of slow H⁺and He²⁺ions with hydrogen

Abstract

A crossed-beam technique previously used in the authors' laboratory for studies of ionisation of H2 by H+ and He2+ impact in the ranges 38-1500 and 31-550 keV amu-1, respectively, has been adapted to permit measurements to be extended down to 10 keV amu-1. Both ionisation and electron capture have been studied using time-of-flight mass spectroscopy together with electron-slow-ion and slow-ion-fast-ion coincidence counting of the collision products. Separate cross sections for non-dissociative and dissociative electron capture and ionisation channels have been determined. Some significant discrepancies between the authors' results and previous measurements due to Afrosimov et al. (1969) are noted. At their lowest impact energies electron capture substantially exceeds ionisation. In addition, for He2+ impact, unlike protons, dissociative ionisation and transfer ionisation cross sections substantially exceed those for non-dissociative ionisation.

Single and double ionization of He by slow protons and antiprotons

“…The qualitative agreement between the two sets of results is good. The agreement of the present doubleand singleionization cross sections for p impact with the measured results of Hvelplund et al [6] is reasonable (within 45%%uo at energies of 20 and 50 keV), while the consistency between results for p impact is somewhat unclear because Shah, McCallion, and Gilbody [15] did not directly measure double ionization. However, the trend of the increase and decrease in the ratios for p and p impact is unambiguous.…”

“…Several comparative tests were performed to examine coupling schemes and collision dynamics by including or not including in the calculations states such as (i) charge-transfer channels, (ii) some continuum channels, and (iii) single-single, single-double, and double-double continuum-continuum couplings in p and p impact. the measurements for p impact of Hvelplund et al [6] and for p impact of Shah, McCallion, and Gilbody [15]. The qualitative agreement between the two sets of results is good.…”

Nonperturbative treatment of multielectron processes in ion-molecule scattering: Application to He2+-H2collisions

“…(7) for a set of initial conditions, and (v) evaluation of total cross sections using Eqs. (11) and (12).…”

“…(11) and (12) has been proven to give good estimates of the total cross sections [5,20]. At this level, the cross sections depend upon the value of the molecular target internuclear distance R AB .…”

“…In more recent years double-electron processes, (e.g., double transfer or transfer ionisation) were addressed by several groups [11][12][13][14][15][16][17]. One of the important problems to elucidate was the dominance of single-versus double-transfer processes at low (keV) impact energies (cf.…”