Metastable atomic ion production in electron-O2 collisions

• A novel method is used to detect metastable O+.
• O+ kinetic energies range from 2 to 20 eV.
• Peak metastable ion production occurs at an electron energy of ∼130 eV.
• Metastable ions are identified as being in the 2P ground state.

Pulsed electron impact ionization, time-of-flight (TOF) spectroscopy and a novel detector are used to study the production of metastable O+ in e-O2 collisions in the electron energy range from threshold to 450 eV. Measured fragment ion kinetic energies are in the range 2–20 eV. The ions are identified as being in the 2P state within the ground 2p3 configuration. Peak metastable ion production occurs at an electron energy of ∼130 eV in agreement with the energy for maximum production of all O+ ions but the fall off in ionization efficiency toward higher incident electron energies is faster in the metastable case.

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