A study of the mean kinetic energy of recoil ions from ion-charge-resolved electron spectra produced in 3.5 keV electron-argon collisions

New experimental results for the dependence of mean kinetic energy (MKE) of argon recoil ions of charge state 1+ to 4+ on energy selected correlated Auger electrons produced in 3.5 keV electron impact with thermal argon atoms using TOF mass spectrometry and electron spectroscopy techniques are presented. Values of the MKE of recoil ions are deduced from the width of the TOF peaks. The measured average values of MKE of Ar+, Ar2+, Ar3+ and Ar4+ recoil ions are found to be respectively 216 meV +/- 5 meV, 247 meV +/- 6 meV, 290 meV +/- 7 meV, and 324 meV +/- 8 meV in the electron energy range of 125-210 eV. The average charge state ratios (Sigma n sigma(n)/Sigma sigma(n)) of recoil ions have been determined to be 1.8, 2.4 and 2.0 in the electron energy range of 125-145 eV, 150-200 eV, and 200-210 eV respectively. For the investigated electron energy range 120-210 eV, the considered Auger transitions are found to dominate the direct ionization: for low electron energies (<100 eV), the direct multiple ionization dominates which has not been considered in this work. Survey of results obtained from the present measurements suggests that the MKE depends not only on the charge state of the recoil ions but also weakly on the specific energy range of ejected electrons in the considered collision reaction. Presently we are not aware of any theoretical calculations that can be compared with our results. (C) 2018 Elsevier B.V. All rights reserved.