B N Roy

Electron impact double ionization of Ba and Ba

Electron impact double ionization cross-sections for Ba and Ba+ have been calculated in the binary encounter approximation. Hartree-Fock velocity distribution has been used for the first ejected electron and a hydrogenic velocity distribution for the second. For Ba+ the focusing effects of the target ion on the incident electron have been incorporated in the calculations. Contributions from ionization-autoionization to the ionization cross-sections, as observed in experiments, have been included in the present work. The calculated results show structures as observed in recent experiments.

Modified BEA calculations of He2+ impact double electron capture cross sections of atoms

The recent BEA model developed by Chatterjee et al. (1984) for the calculations of double electron capture cross sections by multi-charged ions incident on heavy targets has been suitably modified. The concept of partial rearrangement of the target after the capture of the first electron has been incorporated. The method has been used for the computation of cross sections for double electron capture by He2+ ions up to an impact energy of 1 MeV from He, Li, Ar and Kr. Hartree-Fock velocity distributions for the target electrons have been used in the calculations. The present calculations show improvement over the previous method and reasonably good agreement is observed with the available experiments and other theoretical results.

Electron impact double ionisation of Ca and Sr

Electron impact double ionisation cross sections for Ca and Sr have been calculated in the modified binary encounter model. Contributions of inner-shell ionisation and Auger emission have been included in the calculations. The calculated cross sections are in good agreement with the experimental observations of McFarland (1968) and Okudaira (1970). The probable reasons behind the discrepancies observed between the experiments and the calculated cross sections have been discussed.

Electron impact double ionisation of Ar2+, Ar3+ and Xe+

Electron impact double ionisation cross sections for Ar2+, Ar3+ and Xe+ have been calculated in the modified binary-encounter model incorporating the effects of the Coulombic field of the target. Contributions of inner-shell ionisation and Auger emission have been included in the calculations. The calculated cross sections are in good agreement with the available experimental and theoretical results. The probable reasons behind the discrepancies observed between the experimental and present cross sections have been discussed.

Single and double ionization of magnesium by H + and He 2+ impact

Theoretical investigations of H+ and He2+ impact single and double ionization of magnesium atoms have been performed in the binary encounter approximation. Direct double ionization cross sections have been calculated in the modified binary encounter model. Accurate expressions of σ ΔE (cross section for energy transfer ΔE) and Hartree–Fock velocity distributions for the target electrons have been used throughout the calculations. Contributions to double ionization from the Auger effect following a vacancy in the 2p shell have been considered in the present work. Our H+ impact single and double ionization cross sections are in good agreement with experimental observations. The calculated He2+ impact single ionization cross sections show satisfactory agreement with experiment but in the case of double ionization, success is limited in the experimentally investigated region (42.5–438 keV amu−1).

2s-ns (n = 3–6) and 2s–3p excitation of hydrogen atom by electron impact

Excitation of hydrogen atom from its metastable 2s-state to ns (n = 3, 4, 5, 6) and np (n = 3) states has been investigated by employing a distorted wave method in the frame work of the two potential formulation. Effect of exchange is included by antisymmetrizing the total wave function of the system. The angle integrated cross sections are reported at medium energies. The present 2s-3s excitation integrated cross sections are found to be in very good agreement with the most elaborate recent calculation of Odgers et al at medium energies. 2s-6s results are being reported for the first time.

Features of the differential cross section in the 2s-3s excitation of the hydrogen atom by electron and positron impact

Differential cross sections for the 2s-3s excitation of hydrogen atoms by electron and positron impact are reported at two incident energies, 10 eV and 50 eV, using a distorted wave method based on the two potential model. Dramatic differences between the electron and positron results are noticed at both energies.

Electron impact ionization of Zn+ and Ga+

We have investigated the contribution of excitation-autoionization to the electron impact ionization of Zn+ and Ga+ using the binary encounter approximation. Hartree-Fock velocity distributions for the bound electrons have been used throughout the calculations of direct and indirect ionization cross-sections. The calculated cross-sections are in good agreement with recent experiments. We have also compared our results with other theoretical calculations.

Ionisation of Mg+, Ca+ and Sr+ due to electron impact

Electron impact ionisation cross sections for Mg+, Ca+ and Sr+ have been calculated in the binary encounter approximation. The contributions of the excitation-autoionisation process have been included in the present work. Hartree-Fock velocity distributions for the bound electrons have been used throughout the calculations. The present calculations give a good account of the experimental observations.

Binary encounter calculations for electron capture from noble gases by He2

Single electron capture cross sections for rare gases (He, Ar and Kr) due to alpha -particle impact have been calculated in the binary encounter approximation for incident energies 200-2500 keV. Both Hartree-Fock and delta -function velocity distributions have been used in the calculations. The present calculations which include the Hartree-Fock velocity distribution for the target electron show good agreement with experimental observations.