Single-Electron Capture Processes in Slow Collisions of He^2+ Ions with Molecular Targets

Author

Osama Abu-Haija, Western Michigan University

Date of Award

6-2005

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Dr. Emanuel Karaber

Second Advisor

Dr. Thomas Gorozyca

Third Advisor

Dr. Nora Berrah

Fourth Advisor

Dr. Song Cheng

Abstract

Translational energy-gain spectroscopy (TES) has been used to investigate state-selective dissociative and non-dissociative single-electron capture processes in low-energy collisions of He²⁺ ions with O₂ , H₂ O, CO₂ , N₂ , and NH3 at impact energies between 100 eV and 1600 eV. The measured energy spectra for theHe²⁺ -O₂ and H₂ O collision systems show that the dominant exit channel is due to dissociative transfer ionization (DTI), single-electron captureaccompanied by ionization of the molecular target-ion, at the lowest collision energies. As the impact energy is increased non-dissociative single-electron capture (SEC) into the He + (n = 2) states is found to populate at collision energies in excess of 1000 eV. For N₂ and CO₂ targets, the dominant reaction is due to DTI. In the case of the He²⁺ -NH₃ collisions, it is the SEC that is predominantly populated. The dominant reaction channels observed for collisions of He²⁺ with N₂ , CO₂ , and NH₃ remain dominant over the entire impact energy region studied and at laboratory scattering angles between 0° and 8°. The energy-gain spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the Landau-Zener model and the extended version of the classical-over-barrier model. The energy dependence of total cross sections for single-electron capture was also measured and found to be weakly dependent on the projectile energy. The present cross sections are also compared with the available data and are interpreted in terms of theoretical formulations based on Landau-Zener and Demkov models. These calculations show that the He + (n = 2) formation (i.e., SEC) proceeds through a single-electron process governed by nucleus-electron interactions. In contrast, the He+ (n = 1) formation (i.e., DTI) mechanisms involves an exothermic two-electron process driven by electron-electron interactions.

Access Setting

Dissertation-Open Access

Recommended Citation

Abu-Haija, Osama, "Single-Electron Capture Processes in Slow Collisions of He^2+ Ions with Molecular Targets" (2005). Dissertations. 1011.
https://scholarworks.wmich.edu/dissertations/1011