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P: Fachverband Plasmaphysik
P 17: Poster Session - Helmholtz Graduate School for Plasma Physics
P 17.12: Poster
Wednesday, March 19, 2014, 16:30–18:30, SPA Foyer
Negative ion formation in Ion-Molecule collisions — •Angelin Ebanezar John and Rainer Hippler — Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, 17489 Greifswald
Positively charged H+, H2+, He+, and Ar+ ions, with impact energies of 50 – 350 keV, were employed to bombard O2 and SF6 molecules. The collision cross sections of positive and negative ionic fragments were determined and their dependence on impact energy will be presented. Besides positively charged ion fragments, negatively charged secondary ions are an important contibution for various applications especially in atmospheric chemistry and plasma physics.
One of the exciting observation is superoxide anion O2− belong to the reactive oxygen species(ROS). We propose formation of superoxide anion to proceed via a charge-transfer reaction with the positively charged incident ion,
X+ + O2 —→ X2+ + O2−
where an electron transferred to the oxygen molecule originates from the incident ion, (X=H2+or He+ or Ar+) having atleast one electron for the reaction. Measured cross sections for O2− formation are about 2 orders of magnitude smaller compared to O2+ formation, which is attributed to the larger energy transfer required.